/src/ntp-dev/ntpd/ntp_proto.c

Source
/*
 * ntp_proto.c - NTP version 4 protocol machinery
 *
 * ATTENTION: Get approval from Harlan on all changes to this file!
 *      (Harlan will be discussing these changes with Dave Mills.)
 *
 */
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include "ntpd.h"
#include "ntp_stdlib.h"
#include "ntp_unixtime.h"
#include "ntp_control.h"
#include "ntp_string.h"
#include "ntp_leapsec.h"
#include "ntp_psl.h"
#include "refidsmear.h"

#include <stdio.h>
#ifdef HAVE_LIBSCF_H
#include <libscf.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

/* [Bug 3031] define automatic broadcastdelay cutoff preset */
#ifndef BDELAY_DEFAULT
# define BDELAY_DEFAULT (-0.050)
#endif

#define SRVFUZ_SHIFT  6  /* 64 seconds */
#define SRVRSP_FUZZ(x)          \
  do {           \
    x.l_uf = 0;       \
    x.l_ui &= ~((1 << SRVFUZ_SHIFT) - 1U);  \
  } while (FALSE)

/*
 * This macro defines the authentication state. If x is 1 authentication
 * is required; otherwise it is optional.
 */
#define AUTH(x, y)  ((x) ? (y) == AUTH_OK \
           : (y) == AUTH_OK || (y) == AUTH_NONE)

typedef enum
auth_state {
  AUTH_UNKNOWN = -1,  /* Unknown */
  AUTH_NONE,    /* authentication not required */
  AUTH_OK,    /* authentication OK */
  AUTH_ERROR,   /* authentication error */
  AUTH_CRYPTO   /* crypto_NAK */
} auth_code;

/*
 * Set up Kiss Code values
 */

typedef enum
kiss_codes {
  NOKISS,       /* No Kiss Code */
  RATEKISS,     /* Rate limit Kiss Code */
  DENYKISS,     /* Deny Kiss */
  RSTRKISS,     /* Restricted Kiss */
  XKISS       /* Experimental Kiss */
} kiss_code;

typedef enum
nak_error_codes {
  NONAK,        /* No NAK seen */
  INVALIDNAK,     /* NAK cannot be used */
  VALIDNAK      /* NAK is valid */
} nak_code;

/*
 * traffic shaping parameters
 */
#define NTP_IBURST  6  /* packets in iburst */
#define RESP_DELAY  1  /* refclock burst delay (s) */

/*
 * pool soliciting restriction duration (s)
 */
#define POOL_SOLICIT_WINDOW 8

/*
 * flag bits propagated from pool/manycast to individual peers
 */
#define POOL_FLAG_PMASK   (FLAG_IBURST | FLAG_NOSELECT)

/*
 * peer_select groups statistics for a peer used by clock_select() and
 * clock_cluster().
 */
typedef struct peer_select_tag {
  struct peer * peer;
  double    synch;  /* sync distance */
  double    error;  /* jitter */
  double    seljit; /* selection jitter */
} peer_select;

/*
 * System variables are declared here. Unless specified otherwise, all
 * times are in seconds.
 */
u_char  sys_leap;   /* system leap indicator, use set_sys_leap() to change this */
u_char  xmt_leap;   /* leap indicator sent in client requests, set up by set_sys_leap() */
u_char  sys_stratum;    /* system stratum */
s_char  sys_precision;    /* local clock precision (log2 s) */
double  sys_rootdelay;    /* roundtrip delay to root (primary source) */
double  sys_rootdisp;   /* dispersion to root (primary source) */
double  prev_rootdisp;    /* previous root dispersion */
double  p2_rootdisp;    /* previous previous root dispersion */
u_int32 sys_refid;    /* reference id (network byte order) */
l_fp  sys_reftime;    /* last update time */
l_fp  prev_reftime;   /* previous sys_reftime */
l_fp  p2_reftime;   /* previous previous sys_reftime */
u_long  prev_time;    /* "current_time" when saved prev_time */
u_long  p2_time;    /* previous prev_time */
struct  peer *sys_peer;   /* current peer */

#ifdef LEAP_SMEAR
struct leap_smear_info leap_smear;
#endif
int leap_sec_in_progress;

/*
 * Rate controls. Leaky buckets are used to throttle the packet
 * transmission rates in order to protect busy servers such as at NIST
 * and USNO. There is a counter for each association and another for KoD
 * packets. The association counter decrements each second, but not
 * below zero. Each time a packet is sent the counter is incremented by
 * a configurable value representing the average interval between
 * packets. A packet is delayed as long as the counter is greater than
 * zero. Note this does not affect the time value computations.
 */
/*
 * Nonspecified system state variables
 */
int sys_bclient;    /* broadcast client enable */
int sys_mclient;    /* multicast client enable */
double  sys_bdelay;   /* broadcast client default delay */
int sys_authenticate; /* requre authentication for config */
l_fp  sys_authdelay;    /* authentication delay */
double  sys_offset; /* current local clock offset */
double  sys_mindisp = MINDISPERSE; /* minimum distance (s) */
double  sys_maxdist = MAXDISTANCE; /* selection threshold */
double  sys_jitter;   /* system jitter */
u_long  sys_epoch;    /* last clock update time */
static  double sys_clockhop;  /* clockhop threshold */
static int leap_vote_ins; /* leap consensus for insert */
static int leap_vote_del; /* leap consensus for delete */
keyid_t sys_private;    /* private value for session seed */
int sys_manycastserver; /* respond to manycast client pkts */
int ntp_mode7;    /* respond to ntpdc (mode7) */
int peer_ntpdate;   /* active peers in ntpdate mode */
int sys_survivors;    /* truest of the truechimers */
char  *sys_ident = NULL;  /* identity scheme */

/*
 * TOS and multicast mapping stuff
 */
int sys_floor = 0;    /* cluster stratum floor */
u_char  sys_bcpollbstep = 0;  /* Broadcast Poll backstep gate */
int sys_ceiling = STRATUM_UNSPEC - 1; /* cluster stratum ceiling */
int sys_minsane = 1;  /* minimum candidates */
int sys_minclock = NTP_MINCLOCK; /* minimum candidates */
int sys_maxclock = NTP_MAXCLOCK; /* maximum candidates */
int sys_cohort = 0;   /* cohort switch */
int sys_orphan = STRATUM_UNSPEC + 1; /* orphan stratum */
int sys_orphwait = NTP_ORPHWAIT; /* orphan wait */
int sys_beacon = BEACON;  /* manycast beacon interval */
u_int sys_ttlmax;   /* max ttl mapping vector index */
u_char  sys_ttl[MAX_TTL]; /* ttl mapping vector */

/*
 * Statistics counters - first the good, then the bad
 */
u_long  sys_stattime;   /* elapsed time */
u_long  sys_received;   /* packets received */
u_long  sys_processed;    /* packets for this host */
u_long  sys_newversion;   /* current version */
u_long  sys_oldversion;   /* old version */
u_long  sys_restricted;   /* access denied */
u_long  sys_badlength;    /* bad length or format */
u_long  sys_badauth;    /* bad authentication */
u_long  sys_declined;   /* declined */
u_long  sys_limitrejected;  /* rate exceeded */
u_long  sys_kodsent;    /* KoD sent */

/*
 * Mechanism knobs: how soon do we peer_clear() or unpeer()?
 *
 * The default way is "on-receipt".  If this was a packet from a
 * well-behaved source, on-receipt will offer the fastest recovery.
 * If this was from a DoS attack, the default way makes it easier
 * for a bad-guy to DoS us.  So look and see what bites you harder
 * and choose according to your environment.
 */
int peer_clear_digest_early = 1;  /* bad digest (TEST5) and Autokey */
int unpeer_crypto_early   = 1;  /* bad crypto (TEST9) */
int unpeer_crypto_nak_early = 1;  /* crypto_NAK (TEST5) */
int unpeer_digest_early   = 1;  /* bad digest (TEST5) */

int dynamic_interleave = DYNAMIC_INTERLEAVE;  /* Bug 2978 mitigation */

int kiss_code_check(u_char hisleap, u_char hisstratum, u_char hismode, u_int32 refid);
nak_code  valid_NAK (struct peer *peer, struct recvbuf *rbufp, u_char hismode);
static  double  root_distance (struct peer *);
static  void  clock_combine (peer_select *, int, int);
static  void  peer_xmit (struct peer *);
static  void  fast_xmit (struct recvbuf *, int, keyid_t, int);
static  void  pool_xmit (struct peer *);
static  void  clock_update  (struct peer *);
static  void  measure_precision(void);
static  double  measure_tick_fuzz(void);
static  int local_refid (struct peer *);
static  int peer_unfit  (struct peer *);
#ifdef AUTOKEY
static  int group_test  (char *, char *);
#endif /* AUTOKEY */
#ifdef WORKER
void  pool_name_resolved  (int, int, void *, const char *,
         const char *, const struct addrinfo *,
         const struct addrinfo *);
#endif /* WORKER */

const char *  amtoa   (int am);


void
set_sys_leap(
  u_char new_sys_leap
  )
{
  sys_leap = new_sys_leap;
  xmt_leap = sys_leap;

  /*
   * Under certain conditions we send faked leap bits to clients, so
   * eventually change xmt_leap below, but never change LEAP_NOTINSYNC.
   */
  if (xmt_leap != LEAP_NOTINSYNC) {
    if (leap_sec_in_progress) {
      /* always send "not sync" */
      xmt_leap = LEAP_NOTINSYNC;
    }
#ifdef LEAP_SMEAR
    else {
      /*
       * If leap smear is enabled in general we must
       * never send a leap second warning to clients,
       * so make sure we only send "in sync".
       */
      if (leap_smear.enabled)
        xmt_leap = LEAP_NOWARNING;
    }
#endif  /* LEAP_SMEAR */
  }
}


/*
 * Kiss Code check
 */
int
kiss_code_check(
  u_char hisleap,
  u_char hisstratum,
  u_char hismode,
  u_int32 refid
  )
{

  if (   hismode == MODE_SERVER
      && hisleap == LEAP_NOTINSYNC
      && hisstratum == STRATUM_UNSPEC) {
    if(memcmp(&refid,"RATE", 4) == 0) {
      return (RATEKISS);
    } else if(memcmp(&refid,"DENY", 4) == 0) {
      return (DENYKISS);
    } else if(memcmp(&refid,"RSTR", 4) == 0) {
      return (RSTRKISS);
    } else if(memcmp(&refid,"X", 1) == 0) {
      return (XKISS);
    }
  }
  return (NOKISS);
}


/*
 * Check that NAK is valid
 */
nak_code
valid_NAK(
    struct peer *peer,
    struct recvbuf *rbufp,
    u_char hismode
    )
{
  int   base_packet_length = MIN_V4_PKT_LEN;
  int   remainder_size;
  struct pkt *  rpkt;
  int   keyid;
  l_fp    p_org;  /* origin timestamp */
  const l_fp *  myorg;  /* selected peer origin */

  /*
   * Check to see if there is something beyond the basic packet
   */
  if (rbufp->recv_length == base_packet_length) {
    return NONAK;
  }

  remainder_size = rbufp->recv_length - base_packet_length;
  /*
   * Is this a potential NAK?
   */
  if (remainder_size != 4) {
    return NONAK;
  }

  /*
   * Only server responses can contain NAK's
   */

  if (   hismode != MODE_SERVER
      && hismode != MODE_ACTIVE
      && hismode != MODE_PASSIVE
     ) {
    return INVALIDNAK;
  }

  /*
   * Make sure that the extra field in the packet is all zeros
   */
  rpkt = &rbufp->recv_pkt;
  keyid = ntohl(((u_int32 *)rpkt)[base_packet_length / 4]);
  if (keyid != 0) {
    return INVALIDNAK;
  }

  /*
   * During the first few packets of the autokey dance there will
   * not (yet) be a keyid, but in this case FLAG_SKEY is set.
   * So the NAK is invalid if either there's no peer, or
   * if the keyid is 0 and FLAG_SKEY is not set.
   */
  if (!peer || (!peer->keyid && !(peer->flags & FLAG_SKEY))) {
    return INVALIDNAK;
  }

  /*
   * The ORIGIN must match, or this cannot be a valid NAK, either.
   */

  if (FLAG_LOOPNONCE & peer->flags) {
    myorg = &peer->nonce;
  } else {
    if (peer->flip > 0) {
      myorg = &peer->borg;
    } else {
      myorg = &peer->aorg;
    }
  }

  NTOHL_FP(&rpkt->org, &p_org);

  if (L_ISZERO(&p_org) ||
      L_ISZERO( myorg) ||
      !L_ISEQU(&p_org, myorg)) {
    return INVALIDNAK;
  }

  /* If we ever passed all that checks, we should be safe. Well,
   * as safe as we can ever be with an unauthenticated crypto-nak.
   */
  return VALIDNAK;
}


/*
 * transmit - transmit procedure called by poll timeout
 */
void
transmit(
  struct peer *peer /* peer structure pointer */
  )
{
  u_char  hpoll;

  /*
   * The polling state machine. There are two kinds of machines,
   * those that never expect a reply (broadcast and manycast
   * server modes) and those that do (all other modes). The dance
   * is intricate...
   */
  hpoll = peer->hpoll;

  /*
   * If we haven't received anything (even if unsync) since last
   * send, reset ppoll.
   */
  if (peer->outdate > peer->timelastrec && !peer->reach)
    peer->ppoll = peer->maxpoll;

  /*
   * In broadcast mode the poll interval is never changed from
   * minpoll.
   */
  if (peer->cast_flags & (MDF_BCAST | MDF_MCAST)) {
    peer->outdate = current_time;
    poll_update(peer, hpoll, 0);
    if (sys_leap != LEAP_NOTINSYNC)
      peer_xmit(peer);
    return;
  }

  /*
   * In manycast mode we start with unity ttl. The ttl is
   * increased by one for each poll until either sys_maxclock
   * servers have been found or the maximum ttl is reached. When
   * sys_maxclock servers are found we stop polling until one or
   * more servers have timed out or until less than sys_minclock
   * associations turn up. In this case additional better servers
   * are dragged in and preempt the existing ones.  Once every
   * sys_beacon seconds we are to transmit unconditionally, but
   * this code is not quite right -- peer->unreach counts polls
   * and is being compared with sys_beacon, so the beacons happen
   * every sys_beacon polls.
   */
  if (peer->cast_flags & MDF_ACAST) {
    peer->outdate = current_time;
    poll_update(peer, hpoll, 0);
    if (peer->unreach > sys_beacon) {
      peer->unreach = 0;
      peer->ttl = 0;
      peer_xmit(peer);
    } else if (   sys_survivors < sys_minclock
         || peer_associations < sys_maxclock) {
      if (peer->ttl < sys_ttlmax)
        peer->ttl++;
      peer_xmit(peer);
    }
    peer->unreach++;
    return;
  }

  /*
   * Pool associations transmit unicast solicitations when there
   * are less than a hard limit of 2 * sys_maxclock associations,
   * and either less than sys_minclock survivors or less than
   * sys_maxclock associations.  The hard limit prevents unbounded
   * growth in associations if the system clock or network quality
   * result in survivor count dipping below sys_minclock often.
   * This was observed testing with pool, where sys_maxclock == 12
   * resulted in 60 associations without the hard limit.  A
   * similar hard limit on manycastclient ephemeral associations
   * may be appropriate.
   */
  if (peer->cast_flags & MDF_POOL) {
    peer->outdate = current_time;
    poll_update(peer, hpoll, 0);
    if (   (peer_associations <= 2 * sys_maxclock)
        && (   peer_associations < sys_maxclock
      || sys_survivors < sys_minclock))
      pool_xmit(peer);
    return;
  }

  /* [Bug 3851] drop pool servers which can no longer be reached. */
  if (MDF_PCLNT & peer->cast_flags) {
    if (   (IS_IPV6(&peer->srcadr) && !nonlocal_v6_addr_up)
        || (IS_IPV4(&peer->srcadr) && !nonlocal_v4_addr_up)) {
      unpeer(peer);
      return;
    }
  }

   /*
   * In unicast modes the dance is much more intricate. It is
   * designed to back off whenever possible to minimize network
   * traffic.
   */
  if (peer->burst == 0) {
    u_char oreach;

    /*
     * Update the reachability status. If not heard for
     * three consecutive polls, stuff infinity in the clock
     * filter.
     */
    oreach = peer->reach;
    peer->outdate = current_time;
    peer->unreach++;
    peer->reach <<= 1;
    if (!peer->reach) {

      /*
       * Here the peer is unreachable. If it was
       * previously reachable raise a trap. Send a
       * burst if enabled.
       */
      clock_filter(peer, 0., 0., MAXDISPERSE);
      if (oreach) {
        peer_unfit(peer);
        report_event(PEVNT_UNREACH, peer, NULL);
      }
      if (   (peer->flags & FLAG_IBURST)
          && peer->retry == 0)
        peer->retry = NTP_RETRY;
    } else {

      /*
       * Here the peer is reachable. Send a burst if
       * enabled and the peer is fit.  Reset unreach
       * for persistent and ephemeral associations.
       * Unreach is also reset for survivors in
       * clock_select().
       */
      hpoll = sys_poll;
      if (!(peer->flags & FLAG_PREEMPT))
        peer->unreach = 0;
      if (   (peer->flags & FLAG_BURST)
          && peer->retry == 0
          && !peer_unfit(peer))
        peer->retry = NTP_RETRY;
    }

    /*
     * Watch for timeout.  If ephemeral, toss the rascal;
     * otherwise, bump the poll interval. Note the
     * poll_update() routine will clamp it to maxpoll.
     * If preemptible and we have more peers than maxclock,
     * and this peer has the minimum score of preemptibles,
     * demobilize.
     */
    if (peer->unreach >= NTP_UNREACH) {
      hpoll++;
      /* ephemeral: no FLAG_CONFIG nor FLAG_PREEMPT */
      if (!(peer->flags & (FLAG_CONFIG | FLAG_PREEMPT))) {
        report_event(PEVNT_RESTART, peer, "timeout");
        peer_clear(peer, "TIME");
        unpeer(peer);
        return;
      }
      if (   (peer->flags & FLAG_PREEMPT)
          && (peer_associations > sys_maxclock)
          && score_all(peer)) {
        report_event(PEVNT_RESTART, peer, "timeout");
        peer_clear(peer, "TIME");
        unpeer(peer);
        return;
      }
    }
  } else {
    peer->burst--;
    if (peer->burst == 0) {

      /*
       * If ntpdate mode and the clock has not been
       * set and all peers have completed the burst,
       * we declare a successful failure.
       */
      if (mode_ntpdate) {
        peer_ntpdate--;
        if (peer_ntpdate == 0) {
          msyslog(LOG_NOTICE,
              "ntpd: no servers found");
          if (!msyslog_term)
            printf(
                "ntpd: no servers found\n");
          exit (0);
        }
      }
    }
  }
  if (peer->retry > 0)
    peer->retry--;

  /*
   * Do not transmit if in broadcast client mode.
   */
  poll_update(peer, hpoll, (peer->hmode == MODE_CLIENT));
  if (peer->hmode != MODE_BCLIENT)
    peer_xmit(peer);

  return;
}


#ifdef DEBUG
const char *
amtoa(
  int am
  )
{
  char *bp;

  switch(am) {
      case AM_ERR: return "AM_ERR";
      case AM_NOMATCH: return "AM_NOMATCH";
      case AM_PROCPKT: return "AM_PROCPKT";
      case AM_BCST: return "AM_BCST";
      case AM_FXMIT: return "AM_FXMIT";
      case AM_MANYCAST: return "AM_MANYCAST";
      case AM_NEWPASS: return "AM_NEWPASS";
      case AM_NEWBCL: return "AM_NEWBCL";
      case AM_POSSBCL: return "AM_POSSBCL";
      default:
    LIB_GETBUF(bp);
    snprintf(bp, LIB_BUFLENGTH, "AM_#%d", am);
    return bp;
  }
}
#endif  /* DEBUG */


/*
 * receive - receive procedure called for each packet received
 */
void
receive(
  struct recvbuf *rbufp
  )
{
  register struct peer *peer; /* peer structure pointer */
  register struct pkt *pkt; /* receive packet pointer */
  u_char  hisversion;   /* packet version */
  u_char  hisleap;    /* packet leap indicator */
  u_char  hismode;    /* packet mode */
  u_char  hisstratum;   /* packet stratum */
  r4addr  r4a;      /* address restrictions */
  u_short restrict_mask;    /* restrict bits */
  const char *hm_str;   /* hismode string */
  int kissCode = NOKISS;  /* Kiss Code */
  int has_mac;    /* length of MAC field */
  int authlen;    /* offset of MAC field */
  auth_code is_authentic = AUTH_UNKNOWN;  /* Was AUTH_NONE */
  nak_code crypto_nak_test; /* result of crypto-NAK check */
  int retcode = AM_NOMATCH; /* match code */
  keyid_t skeyid = 0;   /* key IDs */
  u_int32 opcode = 0;   /* extension field opcode */
  sockaddr_u *dstadr_sin;   /* active runway */
  u_char  cast_flags;   /* MDF_* flags for newpeer() */
  struct peer *peer2;   /* aux peer structure pointer */
  endpt *match_ep;    /* newpeer() local address */
  l_fp  p_org;      /* origin timestamp */
  l_fp  p_rec;      /* receive timestamp */
  l_fp  p_xmt;      /* transmit timestamp */
#ifdef DEBUG
  const char *am_str;   /* association match string */
#endif
#ifdef AUTOKEY
  char  hostname[NTP_MAXSTRLEN + 1];
  char  *groupname = NULL;
  struct autokey *ap;   /* autokey structure pointer */
  int rval;     /* cookie snatcher */
  keyid_t pkeyid = 0, tkeyid = 0; /* key IDs */
#endif  /* AUTOKEY */
#ifdef HAVE_NTP_SIGND
  static unsigned char zero_key[16];
#endif /* HAVE_NTP_SIGND */

  /*
   * Note that there are many places we do not call record_raw_stats().
   *
   * We only want to call it *after* we've sent a response, or perhaps
   * when we've decided to drop a packet.
   */

  /*
   * Monitor the packet and get restrictions. Note that the packet
   * length for control and private mode packets must be checked
   * by the service routines. Some restrictions have to be handled
   * later in order to generate a kiss-o'-death packet.
   */
  /*
   * Bogus port check is before anything, since it probably
   * reveals a clogging attack. Likewise the mimimum packet size
   * of 2 bytes (for mode 6/7) must be checked first.
   */
  sys_received++;
  if (0 == SRCPORT(&rbufp->recv_srcadr) || rbufp->recv_length < 2) {
    sys_badlength++;
    return;       /* bogus port / length */
  }
  restrictions(&rbufp->recv_srcadr, &r4a);
  restrict_mask = r4a.rflags;

  pkt = &rbufp->recv_pkt;
  hisversion = PKT_VERSION(pkt->li_vn_mode);
  hismode = (int)PKT_MODE(pkt->li_vn_mode);

  if (restrict_mask & RES_IGNORE) {
    DPRINTF(2, ("receive: drop: RES_IGNORE\n"));
    sys_restricted++;
    return;       /* ignore everything */
  }
  if (hismode == MODE_PRIVATE) {
    if (!ntp_mode7 || (restrict_mask & RES_NOQUERY)) {
      DPRINTF(2, ("receive: drop: !mode7 or RES_NOQUERY\n"));
      sys_restricted++;
      return;     /* no query private */
    }
    process_private(rbufp, !(RES_NOMODIFY & restrict_mask));
    return;
  }
  if (hismode == MODE_CONTROL) {
    if (restrict_mask & RES_NOQUERY) {
      DPRINTF(2, ("receive: drop: RES_NOQUERY\n"));
      sys_restricted++;
      return;     /* no query control */
    }
    process_control(rbufp, restrict_mask);
    return;
  }
  if (restrict_mask & RES_DONTSERVE) {
    DPRINTF(2, ("receive: drop: RES_DONTSERVE\n"));
    sys_restricted++;
    return;       /* no time serve */
  }


  /* If we arrive here, we should have a standard NTP packet. We
   * check that the minimum size is available and fetch some more
   * items from the packet once we can be sure they are indeed
   * there.
   */
  if (rbufp->recv_length < LEN_PKT_NOMAC) {
    sys_badlength++;
    return;       /* bogus length */
  }
  
  hisleap = PKT_LEAP(pkt->li_vn_mode);
  hisstratum = PKT_TO_STRATUM(pkt->stratum);
  DEBUG_INSIST(0 != hisstratum);  /* paranoia check PKT_TO_STRATUM result */
          /* TODO: this should be in a unit test */
  DPRINTF(1, ("receive: at %ld %s<-%s ippeerlimit %d mode %d iflags %s "
        "restrict %s org 0x%x.%08x xmt 0x%x.%08x\n",
        current_time, stoa(&rbufp->dstadr->sin),
        stoa(&rbufp->recv_srcadr), r4a.ippeerlimit, hismode,
        iflags_str(rbufp->dstadr->flags),
        rflags_str(restrict_mask),
        ntohl(pkt->org.l_ui), ntohl(pkt->org.l_uf),
        ntohl(pkt->xmt.l_ui), ntohl(pkt->xmt.l_uf)));

  /*
   * This is for testing. If restricted drop ten percent of
   * surviving packets.
   */
  if (restrict_mask & RES_FLAKE) {
    if (ntp_uurandom() < .1) {
      DPRINTF(2, ("receive: drop: RES_FLAKE\n"));
      sys_restricted++;
      return;     /* no flakeway */
    }
  }

  /*
  ** Format Layer Checks
  **
  ** Validate the packet format.  The packet size, packet header,
  ** and any extension field lengths are checked.  We identify
  ** the beginning of the MAC, to identify the upper limit of
  ** of the hash computation.
  **
  ** In case of a format layer check violation, the packet is
  ** discarded with no further processing.
  */

  /*
   * Version check must be after the query packets, since they
   * intentionally use an early version.
   */
  if (hisversion == NTP_VERSION) {
    sys_newversion++;   /* new version */
  } else if (   !(restrict_mask & RES_VERSION)
       && hisversion >= NTP_OLDVERSION) {
    sys_oldversion++;   /* previous version */
  } else {
    DPRINTF(2, ("receive: drop: RES_VERSION\n"));
    sys_badlength++;
    return;       /* old version */
  }

  /*
   * Figure out his mode and validate the packet. This has some
   * legacy raunch that probably should be removed. In very early
   * NTP versions mode 0 was equivalent to what later versions
   * would interpret as client mode.
   */
  if (hismode == MODE_UNSPEC) {
    if (hisversion == NTP_OLDVERSION) {
      hismode = MODE_CLIENT;
    } else {
      DPRINTF(2, ("receive: drop: MODE_UNSPEC\n"));
      sys_badlength++;
      return;     /* invalid mode */
    }
  }

  /*
   * Validate the poll interval in the packet.
   * 0 can indicate a data-minimized packet.
   * A valid poll interval is required for RATEKISS, where
   * a value of 0 is not allowed.  We check for this below.
   * 
   * There might be arguments against this check.  If you have
   * any of these arguments, please let us know.
   *
   * At this point, the packet cannot be a mode[67] packet.
   */
  if (   pkt->ppoll
      && (   (NTP_MINPOLL > pkt->ppoll)
          || (NTP_MAXPOLL < pkt->ppoll)
         )
     ) {
#ifdef BUG3870
    DPRINTF(2, ("receive: drop: Invalid ppoll (%d) from %s\n",
        pkt->ppoll, stoa(&rbufp->recv_srcadr)));
    sys_badlength++;
    return;     /* invalid packet poll */
#else
    DPRINTF(2, ("receive: info: Invalid ppoll (%d) from %s\n",
        pkt->ppoll, stoa(&rbufp->recv_srcadr)));
#endif
  }

  /*
   * Parse the extension field if present. We figure out whether
   * an extension field is present by measuring the MAC size. If
   * the number of words following the packet header is 0, no MAC
   * is present and the packet is not authenticated. If 1, the
   * packet is a crypto-NAK; if 3, the packet is authenticated
   * with DES; if 5, the packet is authenticated with MD5; if 6,
   * the packet is authenticated with SHA. If 2 or * 4, the packet
   * is a runt and discarded forthwith. If greater than 6, an
   * extension field is present, so we subtract the length of the
   * field and go around again.
   *
   * Note the above description is lame.  We should/could also check
   * the two bytes that make up the EF type and subtype, and then
   * check the two bytes that tell us the EF length.  A legacy MAC
   * has a 4 byte keyID, and for conforming symmetric keys its value
   * must be <= 64k, meaning the top two bytes will always be zero.
   * Since the EF Type of 0 is reserved/unused, there's no way a
   * conforming legacy MAC could ever be misinterpreted as an EF.
   *
   * There is more, but this isn't the place to document it.
   */

  authlen = LEN_PKT_NOMAC;
  has_mac = rbufp->recv_length - authlen;
  while (has_mac > 0) {
    u_int32 len;
#ifdef AUTOKEY
    u_int32 hostlen;
    struct exten *ep;
#endif /*AUTOKEY */

    if (has_mac % 4 != 0 || has_mac < (int)MIN_MAC_LEN) {
      DPRINTF(2, ("receive: drop: bad post-packet length\n"));
      sys_badlength++;
      return;     /* bad length */
    }
    /*
     * This next test is clearly wrong - it needlessly
     * prohibits short EFs (which don't yet exist)
     */
    if (has_mac <= (int)MAX_MAC_LEN) {
      skeyid = ntohl(((u_int32 *)pkt)[authlen / 4]);
      break;

    } else {
      opcode = ntohl(((u_int32 *)pkt)[authlen / 4]);
      len = opcode & 0xffff;
      if (   len % 4 != 0
          || len < 4
          || (int)len + authlen > rbufp->recv_length) {
        DPRINTF(2, ("receive: drop: bad EF length\n"));
        sys_badlength++;
        return;   /* bad length */
      }
#ifdef AUTOKEY
      /*
       * Extract calling group name for later.  If
       * sys_groupname is non-NULL, there must be
       * a group name provided to elicit a response.
       */
      if (   (opcode & 0x3fff0000) == CRYPTO_ASSOC
          && sys_groupname != NULL) {
        ep = (struct exten *)&((u_int32 *)pkt)[authlen / 4];
        hostlen = ntohl(ep->vallen);
        if (   hostlen >= sizeof(hostname)
            || hostlen > len -
            offsetof(struct exten, pkt)) {
          DPRINTF(2, ("receive: drop: bad autokey hostname length\n"));
          sys_badlength++;
          return;   /* bad length */
        }
        memcpy(hostname, &ep->pkt, hostlen);
        hostname[hostlen] = '\0';
        groupname = strchr(hostname, '@');
        if (groupname == NULL) {
          DPRINTF(2, ("receive: drop: empty autokey groupname\n"));
          sys_declined++;
          return;
        }
        groupname++;
      }
#endif /* AUTOKEY */
      authlen += len;
      has_mac -= len;
    }
  }

  /*
   * If has_mac is < 0 we had a malformed packet.
   */
  if (has_mac < 0) {
    DPRINTF(2, ("receive: drop: post-packet under-read\n"));
    sys_badlength++;
    return;   /* bad length */
  }

  /*
  ** Packet Data Verification Layer
  **
  ** This layer verifies the packet data content.  If
  ** authentication is required, a MAC must be present.
  ** If a MAC is present, it must validate.
  ** Crypto-NAK?  Look - a shiny thing!
  **
  ** If authentication fails, we're done.
  */

  /*
   * If authentication is explicitly required, a MAC must be present.
   */
  if (restrict_mask & RES_DONTTRUST && has_mac == 0) {
    DPRINTF(2, ("receive: drop: RES_DONTTRUST\n"));
    sys_restricted++;
    return;       /* access denied */
  }

  /*
   * Update the MRU list and finger the cloggers. It can be a
   * little expensive, so turn it off for production use.
   * RES_LIMITED and RES_KOD will be cleared in the returned
   * restrict_mask unless one or both actions are warranted.
   */
  restrict_mask = ntp_monitor(rbufp, restrict_mask);
  if (restrict_mask & RES_LIMITED) {
    sys_limitrejected++;
    if (   !(restrict_mask & RES_KOD)
        || MODE_BROADCAST == hismode
        || MODE_SERVER == hismode) {
      if (MODE_SERVER == hismode) {
        DPRINTF(1, ("Possibly self-induced rate limiting of MODE_SERVER from %s\n",
          stoa(&rbufp->recv_srcadr)));
      } else {
        DPRINTF(2, ("receive: drop: RES_KOD\n"));
      }
      return;     /* rate exceeded */
    }
    if (hismode == MODE_CLIENT) {
      fast_xmit(rbufp, MODE_SERVER, skeyid,
          restrict_mask);
    } else {
      fast_xmit(rbufp, MODE_ACTIVE, skeyid,
          restrict_mask);
    }
    return;       /* rate exceeded */
  }
  restrict_mask &= ~RES_KOD;

  /*
   * We have tossed out as many buggy packets as possible early in
   * the game to reduce the exposure to a clogging attack. Now we
   * have to burn some cycles to find the association and
   * authenticate the packet if required. Note that we burn only
   * digest cycles, again to reduce exposure. There may be no
   * matching association and that's okay.
   *
   * More on the autokey mambo. Normally the local interface is
   * found when the association was mobilized with respect to a
   * designated remote address. We assume packets arriving from
   * the remote address arrive via this interface and the local
   * address used to construct the autokey is the unicast address
   * of the interface. However, if the sender is a broadcaster,
   * the interface broadcast address is used instead.
   * Notwithstanding this technobabble, if the sender is a
   * multicaster, the broadcast address is null, so we use the
   * unicast address anyway. Don't ask.
   */

  peer = findpeer(rbufp,  hismode, &retcode);
  dstadr_sin = &rbufp->dstadr->sin;
  NTOHL_FP(&pkt->org, &p_org);
  NTOHL_FP(&pkt->rec, &p_rec);
  NTOHL_FP(&pkt->xmt, &p_xmt);
  hm_str = modetoa(hismode);
#ifdef DEBUG
  am_str = amtoa(retcode);
#endif

  /*
   * Authentication is conditioned by three switches:
   *
   * NOPEER  (RES_NOPEER) do not mobilize an association unless
   *         authenticated
   * NOTRUST (RES_DONTTRUST) do not allow access unless
   *         authenticated (implies NOPEER)
   * enable  (sys_authenticate) master NOPEER switch, by default
   *         on
   *
   * The NOPEER and NOTRUST can be specified on a per-client basis
   * using the restrict command. The enable switch if on implies
   * NOPEER for all clients. There are four outcomes:
   *
   * NONE    The packet has no MAC.
   * OK      the packet has a MAC and authentication succeeds
   * ERROR   the packet has a MAC and authentication fails
   * CRYPTO  crypto-NAK. The MAC has four octets only.
   *
   * Note: The AUTH(x, y) macro is used to filter outcomes. If x
   * is zero, acceptable outcomes of y are NONE and OK. If x is
   * one, the only acceptable outcome of y is OK.
   */
  crypto_nak_test = valid_NAK(peer, rbufp, hismode);

  /*
   * Drop any invalid crypto-NAKs
   */
  if (crypto_nak_test == INVALIDNAK) {
    report_event(PEVNT_AUTH, peer, "Invalid_NAK");
    if (0 != peer) {
      peer->badNAK++;
    }
    msyslog(LOG_ERR, "Invalid-NAK error at %ld %s<-%s",
      current_time, stoa(dstadr_sin), stoa(&rbufp->recv_srcadr));
    return;
  }

  if (has_mac == 0) {
    restrict_mask &= ~RES_MSSNTP;
    is_authentic = AUTH_NONE; /* not required */
    DPRINTF(1, ("receive: at %ld %s<-%s mode %d/%s:%s len %d org 0x%x.%08x xmt 0x%x.%08x NOMAC\n",
          current_time, stoa(dstadr_sin),
          stoa(&rbufp->recv_srcadr), hismode, hm_str, am_str,
          authlen,
          ntohl(pkt->org.l_ui), ntohl(pkt->org.l_uf),
          ntohl(pkt->xmt.l_ui), ntohl(pkt->xmt.l_uf)));
  } else if (crypto_nak_test == VALIDNAK) {
    restrict_mask &= ~RES_MSSNTP;
    is_authentic = AUTH_CRYPTO; /* crypto-NAK */
    DPRINTF(1, ("receive: at %ld %s<-%s mode %d/%s:%s keyid %08x len %d auth %d org 0x%x.%08x xmt 0x%x.%08x CRYPTONAK\n",
          current_time, stoa(dstadr_sin),
          stoa(&rbufp->recv_srcadr), hismode, hm_str, am_str,
          skeyid, authlen + has_mac, is_authentic,
          ntohl(pkt->org.l_ui), ntohl(pkt->org.l_uf),
          ntohl(pkt->xmt.l_ui), ntohl(pkt->xmt.l_uf)));

#ifdef HAVE_NTP_SIGND
    /*
     * If the signature is 20 bytes long, the last 16 of
     * which are zero, then this is a Microsoft client
     * wanting AD-style authentication of the server's
     * reply.
     *
     * This is described in Microsoft's WSPP docs, in MS-SNTP:
     * http://msdn.microsoft.com/en-us/library/cc212930.aspx
     */
  } else if (   has_mac == MAX_MD5_LEN
       && (restrict_mask & RES_MSSNTP)
       && (retcode == AM_FXMIT || retcode == AM_NEWPASS)
       && (memcmp(zero_key, (char *)pkt + authlen + 4,
            MAX_MD5_LEN - 4) == 0)) {
    is_authentic = AUTH_NONE;
    DPRINTF(1, ("receive: at %ld %s<-%s mode %d/%s:%s len %d org %x.%08x xmt %x.%08x SIGND\n",
          current_time, stoa(dstadr_sin),
          stoa(&rbufp->recv_srcadr), hismode, hm_str, am_str,
          authlen,
          ntohl(pkt->org.l_ui), ntohl(pkt->org.l_uf),
          ntohl(pkt->xmt.l_ui), ntohl(pkt->xmt.l_uf)));
#endif /* HAVE_NTP_SIGND */

  } else {
    /*
     * has_mac is not 0
     * Not a VALID_NAK
     * Not an MS-SNTP SIGND packet
     *
     * So there is a MAC here.
     */

    restrict_mask &= ~RES_MSSNTP;
#ifdef AUTOKEY
    /*
     * For autokey modes, generate the session key
     * and install in the key cache. Use the socket
     * broadcast or unicast address as appropriate.
     */
    if (crypto_flags && skeyid > NTP_MAXKEY) {

      /*
       * More on the autokey dance (AKD). A cookie is
       * constructed from public and private values.
       * For broadcast packets, the cookie is public
       * (zero). For packets that match no
       * association, the cookie is hashed from the
       * addresses and private value. For server
       * packets, the cookie was previously obtained
       * from the server. For symmetric modes, the
       * cookie was previously constructed using an
       * agreement protocol; however, should PKI be
       * unavailable, we construct a fake agreement as
       * the EXOR of the peer and host cookies.
       *
       * hismode  ephemeral persistent
       * =======================================
       * active 0   cookie#
       * passive  0%    cookie#
       * client sys cookie  0%
       * server 0%    sys cookie
       * broadcast  0   0
       *
       * # if unsync, 0
       * % can't happen
       */
      if (has_mac < (int)MAX_MD5_LEN) {
        DPRINTF(2, ("receive: drop: MD5 digest too short\n"));
        sys_badauth++;
        return;
      }
      if (hismode == MODE_BROADCAST) {

        /*
         * For broadcaster, use the interface
         * broadcast address when available;
         * otherwise, use the unicast address
         * found when the association was
         * mobilized. However, if this is from
         * the wildcard interface, game over.
         */
        if (   crypto_flags
            && rbufp->dstadr ==
               ANY_INTERFACE_CHOOSE(&rbufp->recv_srcadr)) {
          DPRINTF(2, ("receive: drop: BCAST from wildcard\n"));
          sys_restricted++;
          return;   /* no wildcard */
        }
        pkeyid = 0;
        if (!SOCK_UNSPEC(&rbufp->dstadr->bcast))
          dstadr_sin =
              &rbufp->dstadr->bcast;
      } else if (peer == NULL) {
        pkeyid = session_key(
            &rbufp->recv_srcadr, dstadr_sin, 0,
            sys_private, 0);
      } else {
        pkeyid = peer->pcookie;
      }

      /*
       * The session key includes both the public
       * values and cookie. In case of an extension
       * field, the cookie used for authentication
       * purposes is zero. Note the hash is saved for
       * use later in the autokey mambo.
       */
      if (authlen > (int)LEN_PKT_NOMAC && pkeyid != 0) {
        session_key(&rbufp->recv_srcadr,
            dstadr_sin, skeyid, 0, 2);
        tkeyid = session_key(
            &rbufp->recv_srcadr, dstadr_sin,
            skeyid, pkeyid, 0);
      } else {
        tkeyid = session_key(
            &rbufp->recv_srcadr, dstadr_sin,
            skeyid, pkeyid, 2);
      }

    }
#endif  /* AUTOKEY */

    /*
     * Compute the cryptosum. Note a clogging attack may
     * succeed in bloating the key cache. If an autokey,
     * purge it immediately, since we won't be needing it
     * again. If the packet is authentic, it can mobilize an
     * association. Note that there is no key zero.
     */
    if (!authdecrypt(skeyid, (u_int32 *)pkt, authlen,
        has_mac))
      is_authentic = AUTH_ERROR;
    else
      is_authentic = AUTH_OK;
#ifdef AUTOKEY
    if (crypto_flags && skeyid > NTP_MAXKEY)
      authtrust(skeyid, 0);
#endif  /* AUTOKEY */
    DPRINTF(1, ("receive: at %ld %s<-%s mode %d/%s:%s keyid %08x len %d auth %d org 0x%x.%08x xmt 0x%x.%08x MAC\n",
          current_time, stoa(dstadr_sin),
          stoa(&rbufp->recv_srcadr), hismode, hm_str, am_str,
          skeyid, authlen + has_mac, is_authentic,
          ntohl(pkt->org.l_ui), ntohl(pkt->org.l_uf),
          ntohl(pkt->xmt.l_ui), ntohl(pkt->xmt.l_uf)));
  }


  /*
   * Bug 3454:
   *
   * Now come at this from a different perspective:
   * - If we expect a MAC and it's not there, we drop it.
   * - If we expect one keyID and get another, we drop it.
   * - If we have a MAC and it hasn't been validated yet, try.
   * - if the provided MAC doesn't validate, we drop it.
   *
   * There might be more to this.
   */
  if (0 != peer && 0 != peer->keyid) {
    /* Should we msyslog() any of these? */

    /*
     * This should catch:
     * - no keyID where one is expected,
     * - different keyID than what we expect.
     */
    if (peer->keyid != skeyid) {
      DPRINTF(2, ("receive: drop: Wanted keyID %d, got %d from %s\n",
            peer->keyid, skeyid,
            stoa(&rbufp->recv_srcadr)));
      sys_restricted++;
      return;     /* drop: access denied */
    }

    /*
     * if has_mac != 0 ...
     * - If it has not yet been validated, do so.
     *   (under what circumstances might that happen?)
     * - if missing or bad MAC, log and drop.
     */
    if (0 != has_mac) {
      if (is_authentic == AUTH_UNKNOWN) {
        /* How can this happen? */
        DPRINTF(2, ("receive: 3454 check: AUTH_UNKNOWN from %s\n",
            stoa(&rbufp->recv_srcadr)));
        if (!authdecrypt(skeyid, (u_int32 *)pkt, authlen,
            has_mac)) {
          /* MAC invalid or not found */
          is_authentic = AUTH_ERROR;
        } else {
          is_authentic = AUTH_OK;
        }
      }
      if (is_authentic != AUTH_OK) {
        DPRINTF(2, ("receive: drop: missing or bad MAC from %s\n",
              stoa(&rbufp->recv_srcadr)));
        sys_restricted++;
        return;   /* drop: access denied */
      }
    }
  }
  /**/

  /*
  ** On-Wire Protocol Layer
  **
  ** Verify protocol operations consistent with the on-wire protocol.
  ** The protocol discards bogus and duplicate packets as well as
  ** minimizes disruptions due to protocol restarts and dropped
  ** packets.  The operations are controlled by two timestamps:
  ** the transmit timestamp saved in the client state variables,
  ** and the origin timestamp in the server packet header.  The
  ** comparison of these two timestamps is called the loopback test.
  ** The transmit timestamp functions as a nonce to verify that the
  ** response corresponds to the original request.  The transmit
  ** timestamp also serves to discard replays of the most recent
  ** packet.  Upon failure of either test, the packet is discarded
  ** with no further action.
  */

  /*
   * The association matching rules are implemented by a set of
   * routines and an association table. A packet matching an
   * association is processed by the peer process for that
   * association. If there are no errors, an ephemeral association
   * is mobilized: a broadcast packet mobilizes a broadcast client
   * aassociation; a manycast server packet mobilizes a manycast
   * client association; a symmetric active packet mobilizes a
   * symmetric passive association.
   */
  DPRINTF(1, ("receive: MATCH_ASSOC dispatch: mode %d/%s:%s \n",
    hismode, hm_str, am_str));
  switch (retcode) {

  /*
   * This is a client mode packet not matching any association. If
   * an ordinary client, simply toss a server mode packet back
   * over the fence. If a manycast client, we have to work a
   * little harder.
   *
   * There are cases here where we do not call record_raw_stats().
   */
  case AM_FXMIT:

    /*
     * If authentication OK, send a server reply; otherwise,
     * send a crypto-NAK.
     */
    if (!(rbufp->dstadr->flags & INT_MCASTOPEN)) {
      /* HMS: would be nice to log FAST_XMIT|BADAUTH|RESTRICTED */
      record_raw_stats(&rbufp->recv_srcadr,
          &rbufp->dstadr->sin,
          &p_org, &p_rec, &p_xmt, &rbufp->recv_time,
          PKT_LEAP(pkt->li_vn_mode),
          PKT_VERSION(pkt->li_vn_mode),
          PKT_MODE(pkt->li_vn_mode),
          PKT_TO_STRATUM(pkt->stratum),
          pkt->ppoll,
          pkt->precision,
          FPTOD(NTOHS_FP(pkt->rootdelay)),
          FPTOD(NTOHS_FP(pkt->rootdisp)),
          pkt->refid,
          rbufp->recv_length - MIN_V4_PKT_LEN, (u_char *)&pkt->exten);

      if (AUTH(restrict_mask & RES_DONTTRUST,
         is_authentic)) {
        /* Bug 3596: Do we want to fuzz the reftime? */
        fast_xmit(rbufp, MODE_SERVER, skeyid,
            restrict_mask);
      } else if (is_authentic == AUTH_ERROR) {
        /* Bug 3596: Do we want to fuzz the reftime? */
        fast_xmit(rbufp, MODE_SERVER, 0,
            restrict_mask);
        sys_badauth++;
      } else {
        DPRINTF(2, ("receive: AM_FXMIT drop: !mcast restricted\n"));
        sys_restricted++;
      }

      return;     /* hooray */
    }

    /*
     * This must be manycast. Do not respond if not
     * configured as a manycast server.
     */
    if (!sys_manycastserver) {
      DPRINTF(2, ("receive: AM_FXMIT drop: Not manycastserver\n"));
      sys_restricted++;
      return;     /* not enabled */
    }

#ifdef AUTOKEY
    /*
     * Do not respond if not the same group.
     */
    if (group_test(groupname, NULL)) {
      DPRINTF(2, ("receive: AM_FXMIT drop: empty groupname\n"));
      sys_declined++;
      return;
    }
#endif /* AUTOKEY */

    /*
     * Do not respond if we are not synchronized or our
     * stratum is greater than the manycaster or the
     * manycaster has already synchronized to us.
     */
    if (   sys_leap == LEAP_NOTINSYNC
        || sys_stratum >= hisstratum
        || (!sys_cohort && sys_stratum == hisstratum + 1)
        || rbufp->dstadr->addr_refid == pkt->refid
#     ifdef WORDS_BIGENDIAN /* see local_refid() comment */
        || (   IS_IPV6(&rbufp->dstadr->sin)
      && rbufp->dstadr->old_refid ==  pkt->refid)
#     endif
                  ) {
      DPRINTF(2, ("receive: sys leap: %0x, sys_stratum %d > hisstratum+1 %d, !sys_cohort %d && sys_stratum == hisstratum+1, loop refid %#x == pkt refid %#x\n", sys_leap, sys_stratum, hisstratum + 1, !sys_cohort, rbufp->dstadr->addr_refid, pkt->refid));
      DPRINTF(2, ("receive: AM_FXMIT drop: LEAP_NOTINSYNC || stratum || loop\n"));
      sys_declined++;
      return;     /* no help */
    }

    /*
     * Do not respond if the packet came into an IPv6 link-local
     * address on an interface where we also have a usable
     * global address, to avoid duplicate associations.
     */
    if (INT_LL_OF_GLOB & rbufp->dstadr->flags) {
      DPRINTF(2, ("receive: declining manycast solicitation on link-local IPv6\n"));
      sys_declined++;
      return;
    }

    /*
     * Respond only if authentication succeeds. Don't do a
     * crypto-NAK, as that would not be useful.
     */
    if (AUTH(restrict_mask & RES_DONTTRUST, is_authentic)) {
      record_raw_stats(&rbufp->recv_srcadr,
          &rbufp->dstadr->sin,
          &p_org, &p_rec, &p_xmt, &rbufp->recv_time,
          PKT_LEAP(pkt->li_vn_mode),
          PKT_VERSION(pkt->li_vn_mode),
          PKT_MODE(pkt->li_vn_mode),
          PKT_TO_STRATUM(pkt->stratum),
          pkt->ppoll,
          pkt->precision,
          FPTOD(NTOHS_FP(pkt->rootdelay)),
          FPTOD(NTOHS_FP(pkt->rootdisp)),
          pkt->refid,
          rbufp->recv_length - MIN_V4_PKT_LEN, (u_char *)&pkt->exten);

      /* Bug 3596: Do we want to fuzz the reftime? */
      fast_xmit(rbufp, MODE_SERVER, skeyid, restrict_mask);
    }
    return;       /* hooray */

  /*
   * This is a server mode packet returned in response to a client
   * mode packet sent to a multicast group address (for
   * manycastclient) or to a unicast address (for pool). The
   * origin timestamp is a good nonce to reliably associate the
   * reply with what was sent. If there is no match, that's
   * curious and could be an intruder attempting to clog, so we
   * just ignore it.
   *
   * If the packet is authentic and the manycastclient or pool
   * association is found, we mobilize a client association and
   * copy pertinent variables from the manycastclient or pool
   * association to the new client association. If not, just
   * ignore the packet.
   *
   * There is an implosion hazard at the manycast client, since
   * the manycast servers send the server packet immediately. If
   * the guy is already here, don't fire up a duplicate.
   *
   * There are cases here where we do not call record_raw_stats().
   */
  case AM_MANYCAST:

#ifdef AUTOKEY
    /*
     * Do not respond if not the same group.
     */
    if (group_test(groupname, NULL)) {
      DPRINTF(2, ("receive: AM_MANYCAST drop: empty groupname\n"));
      sys_declined++;
      return;
    }
#endif /* AUTOKEY */
    /* Do not spin up duplicate manycast associations */
    if (INT_LL_OF_GLOB & rbufp->dstadr->flags) {
      DPRINTF(2, ("receive: AM_MANYCAST drop: link-local server\n"));
      sys_declined++;
      return;
    }
    if ((peer2 = findmanycastpeer(rbufp)) == NULL) {
      DPRINTF(2, ("receive: AM_MANYCAST drop: No manycast peer\n"));
      sys_restricted++;
      return;     /* not enabled */
    }
    if (!AUTH(  (!(peer2->cast_flags & MDF_POOL)
           && sys_authenticate)
        || (restrict_mask & (RES_NOPEER |
            RES_DONTTRUST)), is_authentic)
        /* MC: RES_NOEPEER? */
       ) {
      DPRINTF(2, ("receive: AM_MANYCAST drop: bad auth || (NOPEER|DONTTRUST)\n"));
      sys_restricted++;
      return;     /* access denied */
    }

    /*
     * Do not respond if unsynchronized or stratum is below
     * the floor or at or above the ceiling.
     */
    if (   hisleap == LEAP_NOTINSYNC
        || hisstratum < sys_floor
        || hisstratum >= sys_ceiling) {
      DPRINTF(2, ("receive: AM_MANYCAST drop: unsync/stratum\n"));
      sys_declined++;
      return;     /* no help */
    }
    cast_flags = MDF_UCAST;
    if (MDF_POOL & peer2->cast_flags) {
      cast_flags |= MDF_PCLNT;
    }
    peer = newpeer(&rbufp->recv_srcadr, NULL, rbufp->dstadr,
             r4a.ippeerlimit, MODE_CLIENT, hisversion,
             peer2->minpoll, peer2->maxpoll,
             (FLAG_PREEMPT | (POOL_FLAG_PMASK & peer2->flags)),
             cast_flags, 0, skeyid, sys_ident);
    if (NULL == peer) {
      DPRINTF(2, ("receive: AM_MANYCAST drop: duplicate\n"));
      sys_declined++;
      return;     /* ignore duplicate */
    }

    /*
     * After each preemptible pool association is spun,
     * accelerate the next poll for the pool solicitor so
     * the pool will fill promptly.
     */
    if (MDF_POOL & peer2->cast_flags) {
      peer2->nextdate = current_time + 1;
    }
    /*
     * Further processing of the solicitation response would
     * simply detect its origin timestamp as bogus for the
     * brand-new association (it matches the prototype
     * association) and tinker with peer->nextdate delaying
     * first sync.
     */
    return;   /* solicitation response handled */

  /*
   * This is the first packet received from a broadcast server. If
   * the packet is authentic and we are enabled as broadcast
   * client, mobilize a broadcast client association. We don't
   * kiss any frogs here.
   *
   * There are cases here where we do not call record_raw_stats().
   */
  case AM_NEWBCL:

#ifdef AUTOKEY
    /*
     * Do not respond if not the same group.
     */
    if (group_test(groupname, sys_ident)) {
      DPRINTF(2, ("receive: AM_NEWBCL drop: groupname mismatch\n"));
      sys_declined++;
      return;
    }
#endif /* AUTOKEY */
    if (!sys_bclient && !sys_mclient) {
      DPRINTF(2, ("receive: AM_NEWBCL drop: not a bclient/mclient\n"));
      sys_restricted++;
      return;     /* not enabled */
    }
    if (!AUTH(sys_authenticate | (restrict_mask &
        (RES_NOPEER | RES_DONTTRUST)), is_authentic)
        /* NEWBCL: RES_NOEPEER? */
       ) {
      DPRINTF(2, ("receive: AM_NEWBCL drop: AUTH failed\n"));
      sys_restricted++;
      return;     /* access denied */
    }

    /*
     * Do not respond if unsynchronized or stratum is below
     * the floor or at or above the ceiling.
     */
    if (   hisleap == LEAP_NOTINSYNC
        || hisstratum < sys_floor
        || hisstratum >= sys_ceiling) {
      DPRINTF(2, ("receive: AM_NEWBCL drop: Unsync or bad stratum\n"));
      sys_declined++;
      return;     /* no help */
    }

#ifdef AUTOKEY
    /*
     * Do not respond if Autokey and the opcode is not a
     * CRYPTO_ASSOC response with association ID.
     */
    if (   crypto_flags && skeyid > NTP_MAXKEY
        && (opcode & 0xffff0000) != (CRYPTO_ASSOC | CRYPTO_RESP)) {
      DPRINTF(2, ("receive: AM_NEWBCL drop: Autokey but not CRYPTO_ASSOC\n"));
      sys_declined++;
      return;     /* protocol error */
    }
#endif  /* AUTOKEY */

    /*
     * Broadcasts received via a multicast address may
     * arrive after a unicast volley has begun
     * with the same remote address.  newpeer() will not
     * find duplicate associations on other local endpoints
     * if a non-NULL endpoint is supplied.  multicastclient
     * preemptible associations are unique across all local
     * endpoints.
     */
    if (!(INT_MCASTOPEN & rbufp->dstadr->flags)) {
      match_ep = rbufp->dstadr;
    } else {
      match_ep = NULL;
    }
    /*
     * Determine whether to execute the initial volley.
     */
    if (sys_bdelay > 0.0) {
#ifdef AUTOKEY
      /*
       * If a two-way exchange is not possible,
       * neither is Autokey.
       */
      if (crypto_flags && skeyid > NTP_MAXKEY) {
        sys_restricted++;
        DPRINTF(2, ("receive: AM_NEWBCL drop: Autokey but not 2-way\n"));
        return;   /* no autokey */
      }
#endif  /* AUTOKEY */

      /*
       * Do not execute the volley. Start out in
       * broadcast client mode.
       */
      peer = newpeer(&rbufp->recv_srcadr, NULL, match_ep,
          r4a.ippeerlimit, MODE_BCLIENT, hisversion,
          pkt->ppoll, pkt->ppoll,
          FLAG_PREEMPT, MDF_BCLNT, 0, skeyid, sys_ident);
      if (NULL == peer) {
        DPRINTF(2, ("receive: AM_NEWBCL drop: duplicate\n"));
        sys_restricted++;
        return;   /* ignore duplicate */

      } else {
        peer->delay = sys_bdelay;
        peer->bxmt = p_xmt;
      }
      break;
    }

    /*
     * Execute the initial volley in order to calibrate the
     * propagation delay and run the Autokey protocol.
     *
     * Note that the minpoll is taken from the broadcast
     * packet, normally 6 (64 s) and that the poll interval
     * is fixed at this value.
     */
    peer = newpeer(&rbufp->recv_srcadr, NULL, match_ep,
             r4a.ippeerlimit, MODE_CLIENT, hisversion,
             pkt->ppoll, pkt->ppoll,
             FLAG_BC_VOL | FLAG_IBURST | FLAG_PREEMPT, MDF_BCLNT,
             0, skeyid, sys_ident);
    if (NULL == peer) {
      DPRINTF(2, ("receive: AM_NEWBCL drop: empty newpeer() failed\n"));
      sys_restricted++;
      return;     /* ignore duplicate */
    }
    peer->bxmt = p_xmt;
#ifdef AUTOKEY
    if (skeyid > NTP_MAXKEY)
      crypto_recv(peer, rbufp);
#endif  /* AUTOKEY */

    return;       /* hooray */

  /*
   * This is the first packet received from a potential ephemeral
   * symmetric active peer.  First, deal with broken Windows clients.
   * Then, if NOEPEER is enabled, drop it.  If the packet meets our
   * authenticity requirements and is the first he sent, mobilize
   * a passive association.
   * Otherwise, kiss the frog.
   *
   * There are cases here where we do not call record_raw_stats().
   */
  case AM_NEWPASS:

    DEBUG_REQUIRE(MODE_ACTIVE == hismode);

#ifdef AUTOKEY
    /*
     * Do not respond if not the same group.
     */
    if (group_test(groupname, sys_ident)) {
      DPRINTF(2, ("receive: AM_NEWPASS drop: Autokey group mismatch\n"));
      sys_declined++;
      return;
    }
#endif /* AUTOKEY */
    if (!AUTH(sys_authenticate | (restrict_mask &
        (RES_NOPEER | RES_DONTTRUST)), is_authentic)
       ) {
      /*
       * If authenticated but cannot mobilize an
       * association, send a symmetric passive
       * response without mobilizing an association.
       * This is for drat broken Windows clients. See
       * Microsoft KB 875424 for preferred workaround.
       */
      if (AUTH(restrict_mask & RES_DONTTRUST,
         is_authentic)) {
        fast_xmit(rbufp, MODE_PASSIVE, skeyid,
            restrict_mask);
        return;     /* hooray */
      }
      /* HMS: Why is this next set of lines a feature? */
      if (is_authentic == AUTH_ERROR) {
        fast_xmit(rbufp, MODE_PASSIVE, 0,
            restrict_mask);
        sys_restricted++;
        return;
      }

      if (restrict_mask & RES_NOEPEER) {
        DPRINTF(2, ("receive: AM_NEWPASS drop: NOEPEER\n"));
        sys_declined++;
        return;
      }

      /* [Bug 2941]
       * If we got here, the packet isn't part of an
       * existing association, either isn't correctly
       * authenticated or it is but we are refusing
       * ephemeral peer requests, and it didn't meet
       * either of the previous two special cases so we
       * should just drop it on the floor.  For example,
       * crypto-NAKs (is_authentic == AUTH_CRYPTO)
       * will make it this far.  This is just
       * debug-printed and not logged to avoid log
       * flooding.
       */
      DPRINTF(2, ("receive: at %ld refusing to mobilize passive association"
            " with unknown peer %s mode %d/%s:%s keyid %08x len %d auth %d\n",
            current_time, stoa(&rbufp->recv_srcadr),
            hismode, hm_str, am_str, skeyid,
            (authlen + has_mac), is_authentic));
      sys_declined++;
      return;
    }

    if (restrict_mask & RES_NOEPEER) {
      DPRINTF(2, ("receive: AM_NEWPASS drop: NOEPEER\n"));
      sys_declined++;
      return;
    }

    /*
     * Do not respond if synchronized and if stratum is
     * below the floor or at or above the ceiling. Note,
     * this allows an unsynchronized peer to synchronize to
     * us. It would be very strange if he did and then was
     * nipped, but that could only happen if we were
     * operating at the top end of the range.  It also means
     * we will spin an ephemeral association in response to
     * MODE_ACTIVE KoDs, which will time out eventually.
     */
    if (   hisleap != LEAP_NOTINSYNC
           && (hisstratum < sys_floor || hisstratum >= sys_ceiling)) {
      DPRINTF(2, ("receive: AM_NEWPASS drop: Remote stratum (%d) out of range\n",
          hisstratum));
      sys_declined++;
      return;     /* no help */
    }

    /*
     * The message is correctly authenticated and allowed.
     * Mobilize a symmetric passive association, if we won't
     * exceed the ippeerlimit.
     */
    if ((peer = newpeer(&rbufp->recv_srcadr, NULL, rbufp->dstadr,
            r4a.ippeerlimit, MODE_PASSIVE, hisversion,
            pkt->ppoll, NTP_MAXDPOLL, 0, MDF_UCAST, 0,
            skeyid, sys_ident)) == NULL) {
      DPRINTF(2, ("receive: AM_NEWPASS drop: newpeer() failed\n"));
      sys_declined++;
      return;     /* ignore duplicate */
    }
    break;


  /*
   * Process regular packet. Nothing special.
   *
   * There are cases here where we do not call record_raw_stats().
   */
  case AM_PROCPKT:

#ifdef AUTOKEY
    /*
     * Do not respond if not the same group.
     */
    if (group_test(groupname, peer->ident)) {
      DPRINTF(2, ("receive: AM_PROCPKT drop: Autokey group mismatch\n"));
      sys_declined++;
      return;
    }
#endif /* AUTOKEY */

    if (MODE_BROADCAST == hismode) {
      int bail = 0;
      l_fp  tdiff;
      u_long  deadband;

      DPRINTF(2, ("receive: PROCPKT/BROADCAST: prev pkt %ld seconds ago, ppoll: %d, %d secs\n",
            (current_time - peer->timelastrec),
            peer->ppoll, (1 << peer->ppoll)
            ));
      /* Things we can check:
       *
       * Did the poll interval change?
       * Is the poll interval in the packet in-range?
       * Did this packet arrive too soon?
       * Is the timestamp in this packet monotonic
       *  with respect to the previous packet?
       */

      /* This is noteworthy, not error-worthy */
      if (pkt->ppoll != peer->ppoll) {
        msyslog(LOG_INFO, "receive: broadcast poll from %s changed from %u to %u",
          stoa(&rbufp->recv_srcadr),
          peer->ppoll, pkt->ppoll);
      }

      /* This is error-worthy */
      if (   pkt->ppoll < peer->minpoll
          || pkt->ppoll > peer->maxpoll) {
        msyslog(LOG_INFO, "receive: broadcast poll of %u from %s is out-of-range (%d to %d)!",
          pkt->ppoll, stoa(&rbufp->recv_srcadr),
          peer->minpoll, peer->maxpoll);
        ++bail;
      }

      /* too early? worth an error, too!
       *
       * [Bug 3113] Ensure that at least one poll
       * interval has elapsed since the last **clean**
       * packet was received.  We limit the check to
       * **clean** packets to prevent replayed packets
       * and incorrectly authenticated packets, which
       * we'll discard, from being used to create a
       * denial of service condition.
       */
      deadband = (1u << pkt->ppoll);
      if (FLAG_BC_VOL & peer->flags)
        deadband -= 3; /* allow greater fuzz after volley */
      if ((current_time - peer->timereceived) < deadband) {
        msyslog(LOG_INFO, "receive: broadcast packet from %s arrived after %lu, not %lu seconds!",
          stoa(&rbufp->recv_srcadr),
          (current_time - peer->timereceived),
          deadband);
        ++bail;
      }

      /* Alert if time from the server is non-monotonic.
       *
       * [Bug 3114] is about Broadcast mode replay DoS.
       *
       * Broadcast mode *assumes* a trusted network.
       * Even so, it's nice to be robust in the face
       * of attacks.
       *
       * If we get an authenticated broadcast packet
       * with an "earlier" timestamp, it means one of
       * two things:
       *
       * - the broadcast server had a backward step.
       *
       * - somebody is trying a replay attack.
       *
       * deadband: By default, we assume the broadcast
       * network is trustable, so we take our accepted
       * broadcast packets as we receive them.  But
       * some folks might want to take additional poll
       * delays before believing a backward step.
       */
      if (sys_bcpollbstep) {
        /* pkt->ppoll or peer->ppoll ? */
        deadband = (1u << pkt->ppoll)
             * sys_bcpollbstep + 2;
      } else {
        deadband = 0;
      }

      if (L_ISZERO(&peer->bxmt)) {
        tdiff.l_ui = tdiff.l_uf = 0;
      } else {
        tdiff = p_xmt;
        L_SUB(&tdiff, &peer->bxmt);
      }
      if (   tdiff.l_i < 0
          && (current_time - peer->timereceived) < deadband)
      {
        msyslog(LOG_INFO, "receive: broadcast packet from %s contains non-monotonic timestamp: 0x%x.%08x -> 0x%x.%08x",
          stoa(&rbufp->recv_srcadr),
          peer->bxmt.l_ui, peer->bxmt.l_uf,
          p_xmt.l_ui, p_xmt.l_uf
          );
        ++bail;
      }

      if (bail) {
        DPRINTF(2, ("receive: AM_PROCPKT drop: bail\n"));
        peer->timelastrec = current_time;
        sys_declined++;
        return;
      }
    }

    break;

  /*
   * A passive packet matches a passive association. This is
   * usually the result of reconfiguring a client on the fly. As
   * this association might be legitimate and this packet an
   * attempt to deny service, just ignore it.
   */
  case AM_ERR:
    DPRINTF(2, ("receive: AM_ERR drop.\n"));
    sys_declined++;
    return;

  /*
   * For everything else there is the bit bucket.
   */
  default:
    DPRINTF(2, ("receive: default drop.\n"));
    sys_declined++;
    return;
  }

#ifdef AUTOKEY
  /*
   * If the association is configured for Autokey, the packet must
   * have a public key ID; if not, the packet must have a
   * symmetric key ID.
   */
  if (   is_authentic != AUTH_CRYPTO
      && (   ((peer->flags & FLAG_SKEY) && skeyid <= NTP_MAXKEY)
          || (!(peer->flags & FLAG_SKEY) && skeyid > NTP_MAXKEY))) {
    DPRINTF(2, ("receive: drop: Autokey but wrong/bad auth\n"));
    sys_badauth++;
    return;
  }
#endif  /* AUTOKEY */

  peer->received++;
  peer->flash &= ~PKT_TEST_MASK;
  if (peer->flags & FLAG_XBOGUS) {
    peer->flags &= ~FLAG_XBOGUS;
    peer->flash |= TEST3;
  }

  /*
   * Next comes a rigorous schedule of timestamp checking. If the
   * transmit timestamp is zero, the server has not initialized in
   * interleaved modes or is horribly broken.
   *
   * A KoD packet we pay attention to cannot have a 0 transmit
   * timestamp.
   */

  kissCode = kiss_code_check(hisleap, hisstratum, hismode, pkt->refid);

  if (L_ISZERO(&p_xmt)) {
    peer->flash |= TEST3;     /* unsynch */
    if (kissCode != NOKISS) {   /* KoD packet */
      peer->bogusorg++;   /* for TEST2 or TEST3 */
      msyslog(LOG_INFO,
        "receive: Unexpected zero transmit timestamp in KoD from %s",
        ntoa(&peer->srcadr));
      return;
    }

  /*
   * If the transmit timestamp duplicates our previous one, the
   * packet is a replay. This prevents the bad guys from replaying
   * the most recent packet, authenticated or not.
   */
  } else if (   ((FLAG_LOOPNONCE & peer->flags) && L_ISEQU(&peer->nonce, &p_xmt))
       || (!(FLAG_LOOPNONCE & peer->flags) && L_ISEQU(&peer->xmt, &p_xmt))
  ) {
    DPRINTF(2, ("receive: drop: Duplicate xmit\n"));
    peer->flash |= TEST1;     /* duplicate */
    peer->oldpkt++;
    return;

  /*
   * If this is a broadcast mode packet, make sure hisstratum
   * is appropriate.  Don't do anything else here - we wait to
   * see if this is an interleave broadcast packet until after
   * we've validated the MAC that SHOULD be provided.
   *
   * hisstratum cannot be 0 - see assertion above.
   * If hisstratum is 15, then we'll advertise as UNSPEC but
   * at least we'll be able to sync with the broadcast server.
   */
  } else if (hismode == MODE_BROADCAST) {
    /* 0 is unexpected too, and impossible */
    if (STRATUM_UNSPEC <= hisstratum) {
      /* Is this a ++sys_declined or ??? */
      msyslog(LOG_INFO,
        "receive: Unexpected stratum (%d) in broadcast from %s",
        hisstratum, ntoa(&peer->srcadr));
      return;
    }

  /*
   * Basic KoD validation checking:
   *
   * KoD packets are a mixed-blessing.  Forged KoD packets
   * are DoS attacks.  There are rare situations where we might
   * get a valid KoD response, though.  Since KoD packets are
   * a special case that complicate the checks we do next, we
   * handle the basic KoD checks here.
   *
   * Note that we expect the incoming KoD packet to have its
   * (nonzero) org, rec, and xmt timestamps set to the xmt timestamp
   * that we have previously sent out.  Watch interleave mode.
   */
  } else if (kissCode != NOKISS) {
    DEBUG_INSIST(!L_ISZERO(&p_xmt));
    if (   L_ISZERO(&p_org)    /* We checked p_xmt above */
        || L_ISZERO(&p_rec)) {
      peer->bogusorg++;
      msyslog(LOG_INFO,
        "receive: KoD packet from %s has a zero org or rec timestamp.  Ignoring.",
        ntoa(&peer->srcadr));
      return;
    }

    if (   !L_ISEQU(&p_xmt, &p_org)
        || !L_ISEQU(&p_xmt, &p_rec)) {
      peer->bogusorg++;
      msyslog(LOG_INFO,
        "receive: KoD packet from %s has inconsistent xmt/org/rec timestamps.  Ignoring.",
        ntoa(&peer->srcadr));
      return;
    }

    /* Be conservative */
    if (peer->flip == 0 && !L_ISEQU(&p_org, &peer->aorg)) {
      peer->bogusorg++;
      msyslog(LOG_INFO,
        "receive: flip 0 KoD origin timestamp 0x%x.%08x from %s does not match 0x%x.%08x - ignoring.",
        p_org.l_ui, p_org.l_uf,
        ntoa(&peer->srcadr),
        peer->aorg.l_ui, peer->aorg.l_uf);
      return;
    } else if (peer->flip == 1 && !L_ISEQU(&p_org, &peer->borg)) {
      peer->bogusorg++;
      msyslog(LOG_INFO,
        "receive: flip 1 KoD origin timestamp 0x%x.%08x from %s does not match interleave 0x%x.%08x - ignoring.",
        p_org.l_ui, p_org.l_uf,
        ntoa(&peer->srcadr),
        peer->borg.l_ui, peer->borg.l_uf);
      return;
    }

    /*
     * Basic mode checks:
     *
     * If there is no origin timestamp, it's either an initial
     * packet or we've already received a response to our query.
     * Of course, should 'aorg' be all-zero because this really
     * was the original transmit timestamp, we'll ignore this
     * reply.  There is a window of one nanosecond once every
     * 136 years' time where this is possible.  We currently
     * ignore this situation, as a completely zero timestamp
     * is (quietly?) disallowed.
     *
     * Otherwise, check for bogus packet in basic mode.
     * If it is bogus, switch to interleaved mode and
     * resynchronize, but only after confirming the packet is
     * not bogus in symmetric interleaved mode.
     *
     * This could also mean somebody is forging packets claiming
     * to be from us, attempting to cause our server to KoD us.
     *
     * We have earlier asserted that hisstratum cannot be 0.
     * If hisstratum is STRATUM_UNSPEC, it means he's not sync'd.
     */

    /* XXX: FLAG_LOOPNONCE */
    DEBUG_INSIST(0 == (FLAG_LOOPNONCE & peer->flags));

    if (RATEKISS == kissCode) {
      msyslog(LOG_INFO, "RATE KoD from %s poll %u",
        ntoa(&peer->srcadr), 1u << pkt->ppoll);
    } else {
      msyslog(LOG_INFO, "KoD %s from %s",
        refid_str(pkt->refid, -1),
        ntoa(&peer->srcadr));
    }
  } else if (peer->flip == 0) {
    if (0) {
    } else if (L_ISZERO(&p_org)) {
      const char *action;

#ifdef BUG3361
      msyslog(LOG_INFO,
        "receive: BUG 3361: Clearing peer->aorg ");
      L_CLR(&peer->aorg);
      /* Clear peer->nonce, too? */
#endif
      /**/
      switch (hismode) {
        /* We allow 0org for: */
          case UCHAR_MAX:
        action = "Allow";
        break;
        /* We disallow 0org for: */
          case MODE_UNSPEC:
          case MODE_ACTIVE:
          case MODE_PASSIVE:
          case MODE_CLIENT:
          case MODE_SERVER:
          case MODE_BROADCAST:
        action = "Drop";
        peer->bogusorg++;
        peer->flash |= TEST2; /* bogus */
        break;
          default:
        action = "";  /* for cranky compilers / MSVC */
        INSIST(!"receive(): impossible hismode");
        break;
      }
      /**/
      msyslog(LOG_INFO,
        "receive: %s 0 origin timestamp from %s@%s xmt 0x%x.%08x",
        action, hm_str, ntoa(&peer->srcadr),
        ntohl(pkt->xmt.l_ui), ntohl(pkt->xmt.l_uf));
    } else if (   L_ISZERO(&peer->aorg) && MODE_CLIENT != hismode
         && !memcmp("STEP", &peer->refid, 4)) {
      /* response came in just after we stepped clock, normal */
    } else if (!L_ISEQU(&p_org, &peer->aorg)) {
      /* are there cases here where we should bail? */
      /* Should we set TEST2 if we decide to try xleave? */
      peer->bogusorg++;
      peer->flash |= TEST2; /* bogus */
      msyslog(LOG_INFO, 
        "duplicate or replay: org 0x%x.%08x does not match 0x%x.%08x from %s@%s",
        ntohl(pkt->org.l_ui), ntohl(pkt->org.l_uf),
        peer->aorg.l_ui, peer->aorg.l_uf,
        hm_str, ntoa(&peer->srcadr));
      if (  !L_ISZERO(&peer->dst)
          && L_ISEQU(&p_org, &peer->dst)) {
        /* Might be the start of an interleave */
        if (dynamic_interleave) {
          peer->flip = 1;
          report_event(PEVNT_XLEAVE, peer, NULL);
        } else {
          msyslog(LOG_INFO,
            "receive: Dynamic interleave from %s@%s denied",
            hm_str, ntoa(&peer->srcadr));
        }
      }
    } else {
      L_CLR(&peer->aorg);
      /* XXX: FLAG_LOOPNONCE */
    }

  /*
   * Check for valid nonzero timestamp fields.
   */
  } else if (   L_ISZERO(&p_org)
       || L_ISZERO(&p_rec)
       || L_ISZERO(&peer->dst)) {
    peer->flash |= TEST3;   /* unsynch */

  /*
   * Check for bogus packet in interleaved symmetric mode. This
   * can happen if a packet is lost, duplicated or crossed. If
   * found, flip and resynchronize.
   */
  } else if (   !L_ISZERO(&peer->dst)
       && !L_ISEQU(&p_org, &peer->dst)) {
    DPRINTF(2, ("receive: drop: Bogus packet in interleaved symmetric mode\n"));
    peer->bogusorg++;
    peer->flags |= FLAG_XBOGUS;
    peer->flash |= TEST2;   /* bogus */
#ifdef BUG3453
    return; /* Bogus packet, we are done */
#endif
  }

  /**/

  /*
   * If this is a crypto_NAK, the server cannot authenticate a
   * client packet. The server might have just changed keys. Clear
   * the association and restart the protocol.
   */
  if (crypto_nak_test == VALIDNAK) {
    report_event(PEVNT_AUTH, peer, "crypto_NAK");
    peer->flash |= TEST5;   /* bad auth */
    peer->badauth++;
    if (peer->flags & FLAG_PREEMPT) {
      if (unpeer_crypto_nak_early) {
        unpeer(peer);
      }
      DPRINTF(2, ("receive: drop: PREEMPT crypto_NAK\n"));
      return;
    }
#ifdef AUTOKEY
    if (peer->crypto) {
      peer_clear(peer, "AUTH");
    }
#endif  /* AUTOKEY */
    DPRINTF(2, ("receive: drop: crypto_NAK\n"));
    return;

  /*
   * If the digest fails or it's missing for authenticated
   * associations, the client cannot authenticate a server
   * reply to a client packet previously sent. The loopback check
   * is designed to avoid a bait-and-switch attack, which was
   * possible in past versions. If symmetric modes, return a
   * crypto-NAK. The peer should restart the protocol.
   */
  } else if (!AUTH(peer->keyid || has_mac ||
       (restrict_mask & RES_DONTTRUST), is_authentic)) {

    if (peer->flash & PKT_TEST_MASK) {
      msyslog(LOG_INFO,
        "receive: Bad auth in packet with bad timestamps from %s denied - spoof?",
        ntoa(&peer->srcadr));
      return;
    }

    report_event(PEVNT_AUTH, peer, "digest");
    peer->flash |= TEST5;   /* bad auth */
    peer->badauth++;
    if (   has_mac
        && (   hismode == MODE_ACTIVE
      || hismode == MODE_PASSIVE))
      fast_xmit(rbufp, MODE_ACTIVE, 0, restrict_mask);
    if (peer->flags & FLAG_PREEMPT) {
      if (unpeer_digest_early) {
        unpeer(peer);
      }
    }
#ifdef AUTOKEY
    else if (peer_clear_digest_early && peer->crypto) {
      peer_clear(peer, "AUTH");
    }
#endif  /* AUTOKEY */
    DPRINTF(2, ("receive: drop: Bad or missing AUTH\n"));
    return;
  }

  /*
   * For broadcast packets:
   *
   * HMS: This next line never made much sense to me, even
   * when it was up higher:
   *   If an initial volley, bail out now and let the
   *   client do its stuff.
   *
   * If the packet has not failed authentication, then
   * - if the origin timestamp is nonzero this is an
   *   interleaved broadcast, so restart the protocol.
   * - else, this is not an interleaved broadcast packet.
   */
  if (hismode == MODE_BROADCAST) {
    if (   is_authentic == AUTH_OK
        || is_authentic == AUTH_NONE) {
      if (!L_ISZERO(&p_org)) {
        if (!(peer->flags & FLAG_XB)) {
          msyslog(LOG_INFO,
            "receive: Broadcast server at %s is in interleave mode",
            ntoa(&peer->srcadr));
          peer->flags |= FLAG_XB;
          peer->aorg = p_xmt;
          peer->borg = rbufp->recv_time;
          report_event(PEVNT_XLEAVE, peer, NULL);
          return;
        }
      } else if (peer->flags & FLAG_XB) {
        msyslog(LOG_INFO,
          "receive: Broadcast server at %s is no longer in interleave mode",
          ntoa(&peer->srcadr));
        peer->flags &= ~FLAG_XB;
      }
    } else {
      msyslog(LOG_INFO,
        "receive: Bad broadcast auth (%d) from %s",
        is_authentic, ntoa(&peer->srcadr));
    }

    /*
     * Now that we know the packet is correctly authenticated,
     * update peer->bxmt.
     */
    peer->bxmt = p_xmt;
  }


  /*
  ** Update the state variables.
  */
  if (peer->flip == 0) {
    if (hismode != MODE_BROADCAST)
      peer->rec = p_xmt;
    peer->dst = rbufp->recv_time;
  }
  peer->xmt = p_xmt;

  /*
   * Set the peer ppoll to the maximum of the packet ppoll and the
   * peer minpoll. If a kiss-o'-death, set the peer minpoll to
   * this maximum and advance the headway to give the sender some
   * headroom. Very intricate.
   */

  /* HMS: XXX
  ** make sure NTP_MINPOLL <= pkt->ppoll <= NTP_MAXPOLL
  **
  ** Remember that data minimized or broken implementations
  ** may send a packet with a 0 ppoll.  How sure are we that
  ** peer->minpoll is in a valid range?
  */
  if (peer->ppoll != max(peer->minpoll,pkt->ppoll)) {
    msyslog(LOG_INFO,
      "receive: peer->ppoll changing from %d to max(peer->minpoll (%d), pkt->ppoll (%d)) per %s",
      peer->ppoll, peer->minpoll, pkt->ppoll,
      stoa(&rbufp->recv_srcadr));
  }
  peer->ppoll = max(peer->minpoll, pkt->ppoll);

  /*
   * Check for any kiss codes. Note this is only used when a server
   * responds to a client request.
   *
   * Note Well: by this time, we've already just used pkt->ppoll...
   * Harlan thinks that for RATEKISS (at least) we might want to
   * delay setting peer->ppoll until after we validate pkt->ppoll.
   *
   * HMS: Best to make sure we've sanity checked pkt->ppoll already,
   * and data minimizing and broken folks may send a 0 pkt->ppoll.
   */
  if (kissCode == RATEKISS) {
    if (   pkt->ppoll < NTP_MINPOLL
        || pkt->ppoll > NTP_MAXPOLL) {
      DPRINTF(2, ("Ignoring ppoll %d RATE KoD from %s\n",
            pkt->ppoll, stoa(&rbufp->recv_srcadr)));
      sys_badlength++;
      return;     /* invalid packet poll */
    }
    peer->selbroken++;  /* Increment the KoD count */
    report_event(PEVNT_RATE, peer, NULL);
    peer->minpoll = peer->ppoll;
    peer->burst = peer->retry = 0;
    peer->throttle = (NTP_SHIFT + 1) * (1 << peer->minpoll);
    poll_update(peer, pkt->ppoll, 0);
    return;       /* kiss-o'-death */

  } else if (kissCode != NOKISS) {
    peer->selbroken++;  /* Increment the KoD count */
    return;   /* Drop any other kiss code packets */
  }


  /*
   * XXX
   */


  /*
   * If:
   *  - this is a *cast (uni-, broad-, or m-) server packet
   *  - and it's symmetric-key authenticated
   * then see if the sender's IP is trusted for this keyid.
   * If it is, great - nothing special to do here.
   * Otherwise, we should report and bail.
   *
   * Autokey-authenticated packets are accepted.
   */

  switch (hismode) {
      case MODE_SERVER:   /* server mode */
      case MODE_BROADCAST: /* broadcast mode */
      case MODE_ACTIVE:   /* symmetric active mode */
      case MODE_PASSIVE:   /* symmetric passive mode */
    if (   is_authentic == AUTH_OK
        && skeyid
        && skeyid <= NTP_MAXKEY
        && !authistrustedip(skeyid, &peer->srcadr)) {
      report_event(PEVNT_AUTH, peer, "authIP");
      peer->badauth++;
      return;
    }
    break;

      case MODE_CLIENT:   /* client mode */
#if 0   /* At this point, MODE_CONTROL is overloaded by MODE_BCLIENT */
      case MODE_CONTROL:    /* control mode */
#endif
      case MODE_PRIVATE:   /* private mode */
      case MODE_BCLIENT:   /* broadcast client mode */
    break;

      case MODE_UNSPEC:   /* unspecified (old version) */
      default:
    msyslog(LOG_INFO,
      "receive: Unexpected mode (%d) in packet from %s",
      hismode, ntoa(&peer->srcadr));
    break;
  }


  /*
   * That was hard and I am sweaty, but the packet is squeaky
   * clean. Get on with real work.
   */
  peer->timereceived = current_time;
  peer->timelastrec = current_time;
  if (is_authentic == AUTH_OK)
    peer->flags |= FLAG_AUTHENTIC;
  else
    peer->flags &= ~FLAG_AUTHENTIC;

#ifdef AUTOKEY
  /*
   * More autokey dance. The rules of the cha-cha are as follows:
   *
   * 1. If there is no key or the key is not auto, do nothing.
   *
   * 2. If this packet is in response to the one just previously
   *    sent or from a broadcast server, do the extension fields.
   *    Otherwise, assume bogosity and bail out.
   *
   * 3. If an extension field contains a verified signature, it is
   *    self-authenticated and we sit the dance.
   *
   * 4. If this is a server reply, check only to see that the
   *    transmitted key ID matches the received key ID.
   *
   * 5. Check to see that one or more hashes of the current key ID
   *    matches the previous key ID or ultimate original key ID
   *    obtained from the broadcaster or symmetric peer. If no
   *    match, sit the dance and call for new autokey values.
   *
   * In case of crypto error, fire the orchestra, stop dancing and
   * restart the protocol.
   */
  if (peer->flags & FLAG_SKEY) {
    /*
     * Decrement remaining autokey hashes. This isn't
     * perfect if a packet is lost, but results in no harm.
     */
    ap = (struct autokey *)peer->recval.ptr;
    if (ap != NULL) {
      if (ap->seq > 0)
        ap->seq--;
    }
    peer->flash |= TEST8;
    rval = crypto_recv(peer, rbufp);
    if (rval == XEVNT_OK) {
      peer->unreach = 0;
    } else {
      if (rval == XEVNT_ERR) {
        report_event(PEVNT_RESTART, peer,
            "crypto error");
        peer_clear(peer, "CRYP");
        peer->flash |= TEST9; /* bad crypt */
        if (peer->flags & FLAG_PREEMPT) {
          if (unpeer_crypto_early) {
            unpeer(peer);
          }
        }
      }
      return;
    }

    /*
     * If server mode, verify the receive key ID matches
     * the transmit key ID.
     */
    if (hismode == MODE_SERVER) {
      if (skeyid == peer->keyid)
        peer->flash &= ~TEST8;

    /*
     * If an extension field is present, verify only that it
     * has been correctly signed. We don't need a sequence
     * check here, but the sequence continues.
     */
    } else if (!(peer->flash & TEST8)) {
      peer->pkeyid = skeyid;

    /*
     * Now the fun part. Here, skeyid is the current ID in
     * the packet, pkeyid is the ID in the last packet and
     * tkeyid is the hash of skeyid. If the autokey values
     * have not been received, this is an automatic error.
     * If so, check that the tkeyid matches pkeyid. If not,
     * hash tkeyid and try again. If the number of hashes
     * exceeds the number remaining in the sequence, declare
     * a successful failure and refresh the autokey values.
     */
    } else if (ap != NULL) {
      int i;

      for (i = 0; ; i++) {
        if (   tkeyid == peer->pkeyid
            || tkeyid == ap->key) {
          peer->flash &= ~TEST8;
          peer->pkeyid = skeyid;
          ap->seq -= i;
          break;
        }
        if (i > ap->seq) {
          peer->crypto &=
              ~CRYPTO_FLAG_AUTO;
          break;
        }
        tkeyid = session_key(
            &rbufp->recv_srcadr, dstadr_sin,
            tkeyid, pkeyid, 0);
      }
      if (peer->flash & TEST8)
        report_event(PEVNT_AUTH, peer, "keylist");
    }
    if (!(peer->crypto & CRYPTO_FLAG_PROV)) /* test 9 */
      peer->flash |= TEST8; /* bad autokey */

    /*
     * The maximum lifetime of the protocol is about one
     * week before restarting the Autokey protocol to
     * refresh certificates and leapseconds values.
     */
    if (current_time > peer->refresh) {
      report_event(PEVNT_RESTART, peer,
          "crypto refresh");
      peer_clear(peer, "TIME");
      return;
    }
  }
#endif  /* AUTOKEY */

  /*
   * The dance is complete and the flash bits have been lit. Toss
   * the packet over the fence for processing, which may light up
   * more flashers. Leave if the packet is not good.
   */
  process_packet(peer, pkt, rbufp->recv_length);
  /* Bug 2734: TEST3 prevents initial interleave sync */
  if ((~TEST3 & peer->flash) & PKT_TEST_MASK) {
    return;
  }

  /* [bug 3592] Update poll. Ideally this should not happen in a
   * receive branch, but too much is going on here... at least we
   * do it only if the packet was good!
   */  
  poll_update(peer, peer->hpoll, (peer->hmode == MODE_CLIENT));

  /*
   * In interleaved mode update the state variables. Also adjust the
   * transmit phase to avoid crossover.
   */
  if (peer->flip != 0) {
    peer->rec = p_rec;
    peer->dst = rbufp->recv_time;
    if (peer->nextdate - current_time < (1U << min(peer->ppoll,
        peer->hpoll)) / 2)
      peer->nextdate++;
    else
      peer->nextdate--;
  }
}


/*
 * process_packet - Packet Procedure, a la Section 3.4.4 of RFC-1305
 *  Or almost, at least.  If we're in here we have a reasonable
 *  expectation that we will be having a long term
 *  relationship with this host.
 */
void
process_packet(
  register struct peer *peer,
  register struct pkt *pkt,
  u_int len
  )
{
  double  t34, t21;
  double  p_offset, p_del, p_disp;
  l_fp  p_rec, p_xmt, p_org, p_reftime, ci;
  u_char  pmode, pleap, pversion, pstratum;
#ifdef ASSYM
  int itemp;
  double  etemp, ftemp, td;
#endif /* ASSYM */

  p_del = FPTOD(NTOHS_FP(pkt->rootdelay));
  p_offset = 0;
  p_disp = FPTOD(NTOHS_FP(pkt->rootdisp));
  NTOHL_FP(&pkt->reftime, &p_reftime);
  NTOHL_FP(&pkt->org, &p_org);
  NTOHL_FP(&pkt->rec, &p_rec);
  NTOHL_FP(&pkt->xmt, &p_xmt);
  pmode = PKT_MODE(pkt->li_vn_mode);
  pleap = PKT_LEAP(pkt->li_vn_mode);
  pversion = PKT_VERSION(pkt->li_vn_mode);
  pstratum = PKT_TO_STRATUM(pkt->stratum);

  /*
   * Verify the server is synchronized; that is, the leap bits,
   * stratum and root distance are valid.
   */
  if (   pleap == LEAP_NOTINSYNC    /* test 6 */
      || pstratum < sys_floor || pstratum >= sys_ceiling)
    peer->flash |= TEST6;   /* bad synch or strat */
  if (p_del / 2 + p_disp >= MAXDISPERSE) /* test 7 */
    peer->flash |= TEST7;   /* bad header */

  /*
   * If any tests fail at this point, the packet is discarded.
   * Note that some flashers may have already been set in the
   * receive() routine.
   */
  if (peer->flash & PKT_TEST_MASK) {
    peer->seldisptoolarge++;
    DPRINTF(1, ("packet: flash header %04x\n",
          peer->flash));
    /* [Bug 3592] do *not* update poll on bad packets! */
    return;
  }

  /*
   * update stats, now that we really handle this packet:
   */
  sys_processed++;
  peer->processed++;

  /*
   * Capture the header values in the client/peer association..
   */
  record_raw_stats(&peer->srcadr,
      peer->dstadr ? &peer->dstadr->sin : NULL,
      &p_org, &p_rec, &p_xmt, &peer->dst,
      pleap, pversion, pmode, pstratum, pkt->ppoll, pkt->precision,
      p_del, p_disp, pkt->refid,
      len - MIN_V4_PKT_LEN, (u_char *)&pkt->exten);
  peer->leap = pleap;
  peer->stratum = min(pstratum, STRATUM_UNSPEC);
  peer->pmode = pmode;
  peer->precision = pkt->precision;
  peer->rootdelay = p_del;
  peer->rootdisp = p_disp;
  peer->refid = pkt->refid;   /* network byte order */
  peer->reftime = p_reftime;

  /*
   * First, if either burst mode is armed, enable the burst.
   * Compute the headway for the next packet and delay if
   * necessary to avoid exceeding the threshold.
   */
  if (peer->retry > 0) {
    peer->retry = 0;
    if (peer->reach)
      peer->burst = min(1 << (peer->hpoll -
          peer->minpoll), NTP_SHIFT) - 1;
    else
      peer->burst = NTP_IBURST - 1;
    if (peer->burst > 0)
      peer->nextdate = current_time;
  }

  /*
   * If the peer was previously unreachable, raise a trap. In any
   * case, mark it reachable.
   */
  if (!peer->reach) {
    report_event(PEVNT_REACH, peer, NULL);
    peer->timereachable = current_time;
  }
  peer->reach |= 1;

  /*
   * For a client/server association, calculate the clock offset,
   * roundtrip delay and dispersion. The equations are reordered
   * from the spec for more efficient use of temporaries. For a
   * broadcast association, offset the last measurement by the
   * computed delay during the client/server volley. Note the
   * computation of dispersion includes the system precision plus
   * that due to the frequency error since the origin time.
   *
   * It is very important to respect the hazards of overflow. The
   * only permitted operation on raw timestamps is subtraction,
   * where the result is a signed quantity spanning from 68 years
   * in the past to 68 years in the future. To avoid loss of
   * precision, these calculations are done using 64-bit integer
   * arithmetic. However, the offset and delay calculations are
   * sums and differences of these first-order differences, which
   * if done using 64-bit integer arithmetic, would be valid over
   * only half that span. Since the typical first-order
   * differences are usually very small, they are converted to 64-
   * bit doubles and all remaining calculations done in floating-
   * double arithmetic. This preserves the accuracy while
   * retaining the 68-year span.
   *
   * There are three interleaving schemes, basic, interleaved
   * symmetric and interleaved broadcast. The timestamps are
   * idioscyncratically different. See the onwire briefing/white
   * paper at www.eecis.udel.edu/~mills for details.
   *
   * Interleaved symmetric mode
   * t1 = peer->aorg/borg, t2 = peer->rec, t3 = p_xmt,
   * t4 = peer->dst
   */
  if (peer->flip != 0) {
    ci = p_xmt;       /* t3 - t4 */
    L_SUB(&ci, &peer->dst);
    LFPTOD(&ci, t34);
    ci = p_rec;       /* t2 - t1 */
    if (peer->flip > 0)
      L_SUB(&ci, &peer->borg);
    else
      L_SUB(&ci, &peer->aorg);
    LFPTOD(&ci, t21);
    p_del = t21 - t34;
    p_offset = (t21 + t34) / 2.;
    if (p_del < 0 || p_del > 1.) {
      mprintf_event(PEVNT_XERR, peer,
              "t21 %.9f t34 %.9f", t21, t34);
      return;
    }

  /*
   * Broadcast modes
   */
  } else if (peer->pmode == MODE_BROADCAST) {

    /*
     * Interleaved broadcast mode. Use interleaved timestamps.
     * t1 = peer->borg, t2 = p_org, t3 = p_org, t4 = aorg
     */
    if (peer->flags & FLAG_XB) {
      ci = p_org;     /* delay */
      L_SUB(&ci, &peer->aorg);
      LFPTOD(&ci, t34);
      ci = p_org;     /* t2 - t1 */
      L_SUB(&ci, &peer->borg);
      LFPTOD(&ci, t21);
      peer->aorg = p_xmt;
      peer->borg = peer->dst;
      if (t34 < 0 || t34 > 1.) {
        /* drop all if in the initial volley */
        if (FLAG_BC_VOL & peer->flags)
          goto bcc_init_volley_fail;
        mprintf_event(PEVNT_XERR, peer,
                "offset %.9f delay %.9f",
                t21, t34);
        return;
      }
      p_offset = t21;
      peer->xleave = t34;

    /*
     * Basic broadcast - use direct timestamps.
     * t3 = p_xmt, t4 = peer->dst
     */
    } else {
      ci = p_xmt;   /* t3 - t4 */
      L_SUB(&ci, &peer->dst);
      LFPTOD(&ci, t34);
      p_offset = t34;
    }

    /*
     * When calibration is complete and the clock is
     * synchronized, the bias is calculated as the difference
     * between the unicast timestamp and the broadcast
     * timestamp. This works for both basic and interleaved
     * modes.
     * [Bug 3031] Don't keep this peer when the delay
     * calculation gives reason to suspect clock steps.
     * This is assumed for delays > 50ms.
     */
    if (FLAG_BC_VOL & peer->flags) {
      peer->flags &= ~FLAG_BC_VOL;
      peer->delay = fabs(peer->offset - p_offset) * 2;
      DPRINTF(2, ("broadcast volley: initial delay=%.6f\n",
        peer->delay));
      if (peer->delay > fabs(sys_bdelay)) {
    bcc_init_volley_fail:
        DPRINTF(2, ("%s", "broadcast volley: initial delay exceeds limit\n"));
        unpeer(peer);
        return;
      }
    }
    peer->nextdate = current_time + (1u << peer->ppoll) - 2u;
    p_del = peer->delay;
    p_offset += p_del / 2;


  /*
   * Basic mode, otherwise known as the old fashioned way.
   *
   * t1 = p_org, t2 = p_rec, t3 = p_xmt, t4 = peer->dst
   */
  } else {
    ci = p_xmt;       /* t3 - t4 */
    L_SUB(&ci, &peer->dst);
    LFPTOD(&ci, t34);
    ci = p_rec;       /* t2 - t1 */
    L_SUB(&ci, &p_org);
    LFPTOD(&ci, t21);
    p_del = fabs(t21 - t34);
    p_offset = (t21 + t34) / 2.;
  }
  p_del = max(p_del, LOGTOD(sys_precision));
  p_disp = LOGTOD(sys_precision) + LOGTOD(peer->precision) +
      clock_phi * p_del;

#if ASSYM
  /*
   * This code calculates the outbound and inbound data rates by
   * measuring the differences between timestamps at different
   * packet lengths. This is helpful in cases of large asymmetric
   * delays commonly experienced on deep space communication
   * links.
   */
  if (peer->t21_last > 0 && peer->t34_bytes > 0) {
    itemp = peer->t21_bytes - peer->t21_last;
    if (itemp > 25) {
      etemp = t21 - peer->t21;
      if (fabs(etemp) > 1e-6) {
        ftemp = itemp / etemp;
        if (ftemp > 1000.)
          peer->r21 = ftemp;
      }
    }
    itemp = len - peer->t34_bytes;
    if (itemp > 25) {
      etemp = -t34 - peer->t34;
      if (fabs(etemp) > 1e-6) {
        ftemp = itemp / etemp;
        if (ftemp > 1000.)
          peer->r34 = ftemp;
      }
    }
  }

  /*
   * The following section compensates for different data rates on
   * the outbound (d21) and inbound (t34) directions. To do this,
   * it finds t such that r21 * t - r34 * (d - t) = 0, where d is
   * the roundtrip delay. Then it calculates the correction as a
   * fraction of d.
   */
  peer->t21 = t21;
  peer->t21_last = peer->t21_bytes;
  peer->t34 = -t34;
  peer->t34_bytes = len;
  DPRINTF(2, ("packet: t21 %.9lf %d t34 %.9lf %d\n", peer->t21,
        peer->t21_bytes, peer->t34, peer->t34_bytes));
  if (peer->r21 > 0 && peer->r34 > 0 && p_del > 0) {
    if (peer->pmode != MODE_BROADCAST)
      td = (peer->r34 / (peer->r21 + peer->r34) -
          .5) * p_del;
    else
      td = 0;

    /*
     * Unfortunately, in many cases the errors are
     * unacceptable, so for the present the rates are not
     * used. In future, we might find conditions where the
     * calculations are useful, so this should be considered
     * a work in progress.
     */
    t21 -= td;
    t34 -= td;
    DPRINTF(2, ("packet: del %.6lf r21 %.1lf r34 %.1lf %.6lf\n",
          p_del, peer->r21 / 1e3, peer->r34 / 1e3,
          td));
  }
#endif /* ASSYM */

  /*
   * That was awesome. Now hand off to the clock filter.
   */
  clock_filter(peer, p_offset + peer->bias, p_del, p_disp);

  /*
   * If we are in broadcast calibrate mode, return to broadcast
   * client mode when the client is fit and the autokey dance is
   * complete.
   */
  if (   (FLAG_BC_VOL & peer->flags)
      && MODE_CLIENT == peer->hmode
      && !(TEST11 & peer_unfit(peer))) { /* distance exceeded */
#ifdef AUTOKEY
    if (peer->flags & FLAG_SKEY) {
      if (!(~peer->crypto & CRYPTO_FLAG_ALL))
        peer->hmode = MODE_BCLIENT;
    } else {
      peer->hmode = MODE_BCLIENT;
    }
#else /* !AUTOKEY follows */
    peer->hmode = MODE_BCLIENT;
#endif  /* !AUTOKEY */
  }
}


/*
 * clock_update - Called at system process update intervals.
 */
static void
clock_update(
  struct peer *peer /* peer structure pointer */
  )
{
  double  dtemp;
  l_fp  now;
#ifdef HAVE_LIBSCF_H
  char  *fmri;
#endif /* HAVE_LIBSCF_H */

  /*
   * Update the system state variables. We do this very carefully,
   * as the poll interval might need to be clamped differently.
   */
  sys_peer = peer;
  sys_epoch = peer->epoch;
  if (sys_poll < peer->minpoll)
    sys_poll = peer->minpoll;
  if (sys_poll > peer->maxpoll)
    sys_poll = peer->maxpoll;
  poll_update(peer, sys_poll, 0);
  sys_stratum = min(peer->stratum + 1, STRATUM_UNSPEC);
  if (   peer->stratum == STRATUM_REFCLOCK
      || peer->stratum == STRATUM_UNSPEC)
    sys_refid = peer->refid;
  else
    sys_refid = addr2refid(&peer->srcadr);
  /*
   * Root Dispersion (E) is defined (in RFC 5905) as:
   *
   * E = p.epsilon_r + p.epsilon + p.psi + PHI*(s.t - p.t) + |THETA|
   *
   * where:
   *  p.epsilon_r is the PollProc's root dispersion
   *  p.epsilon   is the PollProc's dispersion
   *  p.psi       is the PollProc's jitter
   *  THETA       is the combined offset
   *
   * NB: Think Hard about where these numbers come from and
   * what they mean.  When did peer->update happen?  Has anything
   * interesting happened since then?  What values are the most
   * defensible?  Why?
   *
   * DLM thinks this equation is probably the best of all worse choices.
   */
  dtemp = peer->rootdisp
    + peer->disp
    + sys_jitter
    + clock_phi * (current_time - peer->update)
    + fabs(sys_offset);

  p2_rootdisp = prev_rootdisp;
  prev_rootdisp = sys_rootdisp;
  if (dtemp > sys_mindisp)
    sys_rootdisp = dtemp;
  else
    sys_rootdisp = sys_mindisp;

  sys_rootdelay = peer->delay + peer->rootdelay;

  p2_reftime = prev_reftime;
  p2_time = prev_time;

  prev_reftime = sys_reftime;
  prev_time = current_time + 64 + (rand() & 0x3f);  /* 64-127 s */

  sys_reftime = peer->dst;

  DPRINTF(1, ("clock_update: at %lu sample %lu associd %d\n",
        current_time, peer->epoch, peer->associd));

  /*
   * Comes now the moment of truth. Crank the clock discipline and
   * see what comes out.
   */
  switch (local_clock(peer, sys_offset)) {

  /*
   * Clock exceeds panic threshold. Life as we know it ends.
   */
  case -1:
    msyslog(LOG_ERR, "Clock offset exceeds panic threshold.");
#ifdef HAVE_LIBSCF_H
    /*
     * For Solaris enter the maintenance mode.
     */
    if ((fmri = getenv("SMF_FMRI")) != NULL) {
      if (smf_maintain_instance(fmri, 0) < 0) {
        msyslog(LOG_ERR, "smf_maintain_instance: %s",
             scf_strerror(scf_error()));
        exit(1);
      }
      /*
       * Sleep until SMF kills us.
       */
      msyslog(LOG_ERR, "%s placed into maintenance. "
        "Set system clock by hand before clearing.",
        fmri);
      for (;;)
        pause();
    }
#endif /* HAVE_LIBSCF_H */
    msyslog(LOG_ERR, "Set system clock by hand.");
    exit (-1);
    /* not reached */

  /*
   * Clock was stepped. Flush all time values of all peers.
   */
  case 2:
    clear_all();
    set_sys_leap(LEAP_NOTINSYNC);
    sys_stratum = STRATUM_UNSPEC;
    memcpy(&sys_refid, "STEP", 4);
    sys_rootdelay = 0;
    p2_rootdisp = 0;
    prev_rootdisp = 0;
    sys_rootdisp = 0;
    L_CLR(&p2_reftime);  /* Should we clear p2_reftime? */
    L_CLR(&prev_reftime);  /* Should we clear prev_reftime? */
    L_CLR(&sys_reftime);
    sys_jitter = LOGTOD(sys_precision);
    leapsec_reset_frame();
    break;

  /*
   * Clock was slewed. Handle the leapsecond stuff.
   */
  case 1:

    /*
     * If this is the first time the clock is set, reset the
     * leap bits. If crypto, the timer will goose the setup
     * process.
     */
    if (sys_leap == LEAP_NOTINSYNC) {
      set_sys_leap(LEAP_NOWARNING);
#ifdef AUTOKEY
      if (crypto_flags)
        crypto_update();
#endif  /* AUTOKEY */

    }

    /*
     * If there is no leap second pending and the number of
     * survivor leap bits is greater than half the number of
     * survivors, try to schedule a leap for the end of the
     * current month. (This only works if no leap second for
     * that range is in the table, so doing this more than
     * once is mostly harmless.)
     */
    if (leapsec == LSPROX_NOWARN) {
      if (   leap_vote_ins > leap_vote_del
          && leap_vote_ins > sys_survivors / 2) {
        get_systime(&now);
        leapsec_add_dyn(TRUE, now.l_ui, NULL);
      }
      if (   leap_vote_del > leap_vote_ins
          && leap_vote_del > sys_survivors / 2) {
        get_systime(&now);
        leapsec_add_dyn(FALSE, now.l_ui, NULL);
      }
    }
    break;

  /*
   * Popcorn spike or step threshold exceeded. Pretend it never
   * happened.
   */
  default:
    break;
  }
}


/*
 * poll_update - update peer poll interval
 */
void
poll_update(
  struct peer *peer,  /* peer structure pointer */
  u_char  mpoll,
  u_char  skewpoll
  )
{
  u_long  next, utemp, limit;
  u_char  hpoll;

  /*
   * This routine figures out when the next poll should be sent.
   * That turns out to be wickedly complicated. One problem is
   * that sometimes the time for the next poll is in the past when
   * the poll interval is reduced. We watch out for races here
   * between the receive process and the poll process.
   *
   * Clamp the poll interval between minpoll and maxpoll.
   */
  hpoll = max(min(peer->maxpoll, mpoll), peer->minpoll);

#ifdef AUTOKEY
  /*
   * If during the crypto protocol the poll interval has changed,
   * the lifetimes in the key list are probably bogus. Purge the
   * the key list and regenerate it later.
   */
  if ((peer->flags & FLAG_SKEY) && hpoll != peer->hpoll)
    key_expire(peer);
#endif  /* AUTOKEY */
  peer->hpoll = hpoll;

  /*
   * There are three variables important for poll scheduling, the
   * current time (current_time), next scheduled time (nextdate)
   * and the earliest time (utemp). The earliest time is 2 s
   * seconds, but could be more due to rate management. When
   * sending in a burst, use the earliest time. When not in a
   * burst but with a reply pending, send at the earliest time
   * unless the next scheduled time has not advanced. This can
   * only happen if multiple replies are pending in the same
   * response interval. Otherwise, send at the later of the next
   * scheduled time and the earliest time.
   *
   * Now we figure out if there is an override. If a burst is in
   * progress and we get called from the receive process, just
   * slink away. If called from the poll process, delay 1 s for a
   * reference clock, otherwise 2 s.
   */
  utemp = current_time + max(peer->throttle - (NTP_SHIFT - 1) *
      (1 << peer->minpoll), ntp_minpkt);

  /*[Bug 3592] avoid unlimited postpone of next poll */
  limit = (2u << hpoll);
  if (limit > 64)
    limit -= (limit >> 2);
  limit += peer->outdate;
  if (limit < current_time)
    limit = current_time;

  if (peer->burst > 0) {
    if (peer->nextdate > current_time)
      return;
#ifdef REFCLOCK
    else if (peer->flags & FLAG_REFCLOCK)
      peer->nextdate = current_time + RESP_DELAY;
#endif /* REFCLOCK */
    else
      peer->nextdate = utemp;

#ifdef AUTOKEY
  /*
   * If a burst is not in progress and a crypto response message
   * is pending, delay 2 s, but only if this is a new interval.
   */
  } else if (peer->cmmd != NULL) {
    if (peer->nextdate > current_time) {
      if (peer->nextdate + ntp_minpkt != utemp)
        peer->nextdate = utemp;
    } else {
      peer->nextdate = utemp;
    }
#endif  /* AUTOKEY */

  /*
   * The ordinary case. If a retry, use minpoll; if unreachable,
   * use host poll; otherwise, use the minimum of host and peer
   * polls; In other words, oversampling is okay but
   * understampling is evil. Use the maximum of this value and the
   * headway. If the average headway is greater than the headway
   * threshold, increase the headway by the minimum interval.
   */
  } else {
    if (peer->retry > 0)
      hpoll = peer->minpoll;
    else
      hpoll = min(peer->ppoll, peer->hpoll);
#ifdef REFCLOCK
    if (peer->flags & FLAG_REFCLOCK)
      next = 1 << hpoll;
    else
#endif /* REFCLOCK */
      next = ((0x1000UL | (ntp_random() & 0x0ff)) <<
          hpoll) >> 12;
    next += peer->outdate;
    /* XXX: bug3596: Deal with poll skew list? */
    if (skewpoll) {
      psl_item psi;

      if (0 == get_pollskew(hpoll, &psi)) {
        int sub = psi.sub;
        int qty = psi.qty;
        int msk = psi.msk;
        int val;

        if (   0 != sub
            || 0 != qty) {
          do {
            val = ntp_random() & msk;
          } while (val > qty);

          next -= sub;
          next += val;
        }
      } else {
        /* get_pollskew() already logged this */
      }
    }
    if (next > utemp)
      peer->nextdate = next;
    else
      peer->nextdate = utemp;
    if (peer->throttle > (1 << peer->minpoll))
      peer->nextdate += ntp_minpkt;
  }

  /*[Bug 3592] avoid unlimited postpone of next poll */
  if (peer->nextdate > limit) {
    DPRINTF(1, ("poll_update: clamp reached; limit %lu next %lu\n",
          limit, peer->nextdate));
    peer->nextdate = limit;
  }
  DPRINTF(2, ("poll_update: at %lu %s poll %d burst %d retry %d head %d early %lu next %lu\n",
        current_time, ntoa(&peer->srcadr), peer->hpoll,
        peer->burst, peer->retry, peer->throttle,
        utemp - current_time, peer->nextdate -
        current_time));
}


/*
 * peer_clear - clear peer filter registers.  See Section 3.4.8 of the
 * spec.
 */
void
peer_clear(
  struct peer *peer,    /* peer structure */
  const char *ident   /* tally lights */
  )
{
  static u_long earliest;
  u_char    u;
  l_fp    bxmt = peer->bxmt;  /* bcast clients retain this! */

#ifdef AUTOKEY
  /*
   * If cryptographic credentials have been acquired, toss them to
   * Valhalla. Note that autokeys are ephemeral, in that they are
   * tossed immediately upon use. Therefore, the keylist can be
   * purged anytime without needing to preserve random keys. Note
   * that, if the peer is purged, the cryptographic variables are
   * purged, too. This makes it much harder to sneak in some
   * unauthenticated data in the clock filter.
   */
  key_expire(peer);
  if (peer->iffval != NULL)
    BN_free(peer->iffval);
  value_free(&peer->cookval);
  value_free(&peer->recval);
  value_free(&peer->encrypt);
  value_free(&peer->sndval);
  if (peer->cmmd != NULL)
    free(peer->cmmd);
  if (peer->subject != NULL)
    free(peer->subject);
  if (peer->issuer != NULL)
    free(peer->issuer);
#endif /* AUTOKEY */

  /*
   * Clear all values, including the optional crypto values above.
   */
  memset(CLEAR_TO_ZERO(peer), 0, LEN_CLEAR_TO_ZERO(peer));
  peer->ppoll = peer->maxpoll;
  peer->hpoll = peer->minpoll;
  peer->disp = MAXDISPERSE;
  peer->flash = peer_unfit(peer);
  peer->jitter = LOGTOD(sys_precision);

  /* Don't throw away our broadcast replay protection */
  if (peer->hmode == MODE_BCLIENT)
    peer->bxmt = bxmt;

  /*
   * If interleave mode, initialize the alternate origin switch.
   */
  if (peer->flags & FLAG_XLEAVE)
    peer->flip = 1;
  for (u = 0; u < NTP_SHIFT; u++) {
    peer->filter_order[u] = u;
    peer->filter_disp[u] = MAXDISPERSE;
  }
#ifdef REFCLOCK
  if (!(peer->flags & FLAG_REFCLOCK)) {
#endif
    peer->leap = LEAP_NOTINSYNC;
    peer->stratum = STRATUM_UNSPEC;
    memcpy(&peer->refid, ident, 4);
#ifdef REFCLOCK
  } else {
    /* Clear refclock sample filter */
    peer->procptr->codeproc = 0;
    peer->procptr->coderecv = 0;
  }
#endif

  /*
   * During initialization use the association count to spread out
   * the polls at one-second intervals. Unconfigured associations'
   * first poll is delayed by the "discard minimum" plus 1 to avoid
   * rate limiting. Other post-startup new or cleared associations
   * randomize the first poll over the minimum poll interval to
   * avoid implosion.
   */
  peer->nextdate = peer->update = peer->outdate = current_time;
  if (initializing) {
    peer->nextdate += peer_associations;
  } else if (!(FLAG_CONFIG & peer->flags)) {
    peer->nextdate += ntp_minpkt + 1;
    /* space out manycastclient first polls */
    if (peer->nextdate < earliest) {
      peer->nextdate = earliest;
    }
    earliest = peer->nextdate + 1;
  } else {
    peer->nextdate += ntp_random() % (1 << peer->minpoll);
  }
#ifdef AUTOKEY
  peer->refresh = current_time + (1 << NTP_REFRESH);
#endif  /* AUTOKEY */
  DPRINTF(1, ("peer_clear: at %ld next %ld associd %d refid %s\n",
        current_time, peer->nextdate, peer->associd,
        ident));
}


/*
 * clock_filter - add incoming clock sample to filter register and run
 *      the filter procedure to find the best sample.
 */
void
clock_filter(
  struct peer *peer,    /* peer structure pointer */
  double  sample_offset,    /* clock offset */
  double  sample_delay,   /* roundtrip delay */
  double  sample_disp   /* dispersion */
  )
{
  double  dst[NTP_SHIFT];   /* distance vector */
  u_char  ord[NTP_SHIFT];   /* index vector */
  short i, j;
  u_char  k, m;
  double  dtemp, etemp;

  /*
   * A sample consists of the offset, delay, dispersion and epoch
   * of arrival. The offset and delay are determined by the on-
   * wire protocol. The dispersion grows from the last outbound
   * packet to the arrival of this one increased by the sum of the
   * peer precision and the system precision as required by the
   * error budget. First, shift the new arrival into the shift
   * register discarding the oldest one.
   */
  j = peer->filter_nextpt;
  peer->filter_offset[j] = sample_offset;
  peer->filter_delay[j] = sample_delay;
  peer->filter_disp[j] = sample_disp;
  peer->filter_epoch[j] = current_time;
  j = (j + 1) % NTP_SHIFT;
  peer->filter_nextpt = (u_char)j;

  /*
   * Update dispersions since the last update and at the same
   * time initialize the distance and index lists. Since samples
   * become increasingly uncorrelated beyond the Allan intercept,
   * only under exceptional cases will an older sample be used.
   * Therefore, the distance list uses a compound metric. If the
   * dispersion is greater than the maximum dispersion, clamp the
   * distance at that value. If the time since the last update is
   * less than the Allan intercept use the delay; otherwise, use
   * the sum of the delay and dispersion.
   */
  dtemp = clock_phi * (current_time - peer->update);
  peer->update = current_time;
  for (i = NTP_SHIFT - 1; i >= 0; i--) {
    if (i != 0)
      peer->filter_disp[j] += dtemp;
    if (peer->filter_disp[j] >= MAXDISPERSE) {
      peer->filter_disp[j] = MAXDISPERSE;
      dst[i] = MAXDISPERSE;
    } else if (peer->update - peer->filter_epoch[j] >
        (u_long)ULOGTOD(allan_xpt)) {
      dst[i] = peer->filter_delay[j] +
          peer->filter_disp[j];
    } else {
      dst[i] = peer->filter_delay[j];
    }
    ord[i] = (u_char)j;
    j = (j + 1) % NTP_SHIFT;
  }

  /*
   * If the clock has stabilized, sort the samples by distance.
   */
  if (freq_cnt == 0) {
    for (i = 1; i < NTP_SHIFT; i++) {
      for (j = 0; j < i; j++) {
        if (dst[j] > dst[i]) {
          k = ord[j];
          ord[j] = ord[i];
          ord[i] = k;
          etemp = dst[j];
          dst[j] = dst[i];
          dst[i] = etemp;
        }
      }
    }
  }

  /*
   * Copy the index list to the association structure so ntpq
   * can see it later. Prune the distance list to leave only
   * samples less than the maximum dispersion, which disfavors
   * uncorrelated samples older than the Allan intercept. To
   * further improve the jitter estimate, of the remainder leave
   * only samples less than the maximum distance, but keep at
   * least two samples for jitter calculation.
   */
  m = 0;
  for (i = 0; i < NTP_SHIFT; i++) {
    peer->filter_order[i] = ord[i];
    if (   dst[i] >= MAXDISPERSE
        || (m >= 2 && dst[i] >= sys_maxdist))
      continue;
    m++;
  }

  /*
   * Compute the dispersion and jitter. The dispersion is weighted
   * exponentially by NTP_FWEIGHT (0.5) so it is normalized close
   * to 1.0. The jitter is the RMS differences relative to the
   * lowest delay sample.
   */
  peer->disp = peer->jitter = 0;
  k = ord[0];
  for (i = NTP_SHIFT - 1; i >= 0; i--) {
    j = ord[i];
    peer->disp = NTP_FWEIGHT * (  peer->disp
              + peer->filter_disp[j]);
    if (i < m) {
      peer->jitter += DIFF(peer->filter_offset[j],
               peer->filter_offset[k]);
    }
  }

  /*
   * If no acceptable samples remain in the shift register,
   * quietly tiptoe home leaving only the dispersion. Otherwise,
   * save the offset, delay and jitter. Note the jitter must not
   * be less than the precision.
   */
  if (0 == m) {
    clock_select();
    return;
  }
  etemp = fabs(peer->offset - peer->filter_offset[k]);
  peer->offset = peer->filter_offset[k];
  peer->delay = peer->filter_delay[k];
  if (m > 1) {
    peer->jitter /= m - 1;
  }
  peer->jitter = max(SQRT(peer->jitter), LOGTOD(sys_precision));

  /*
   * If the the new sample and the current sample are both valid
   * and the difference between their offsets exceeds CLOCK_SGATE
   * (3) times the jitter and the interval between them is less
   * than twice the host poll interval, consider the new sample
   * a popcorn spike and ignore it.
   */
  if (   peer->disp < sys_maxdist
      && peer->filter_disp[k] < sys_maxdist
      && etemp > CLOCK_SGATE * peer->jitter
      &&   peer->filter_epoch[k] - peer->epoch
         < 2. * ULOGTOD(peer->hpoll)) {
    mprintf_event(PEVNT_POPCORN, peer, "%.9f s", etemp);
    return;
  }

  /*
   * A new minimum sample is useful only if it is later than the
   * last one used. In this design the maximum lifetime of any
   * sample is not greater than NTP_SHIFT (8) times the poll
   * interval, so the maximum interval between minimum samples is
   * NTP_SHIFT packets.
   */
  if (peer->filter_epoch[k] <= peer->epoch) {
    DPRINTF(2, ("clock_filter: old sample %lu s\n",
          current_time - peer->filter_epoch[k]));
    return;
  }
  peer->epoch = peer->filter_epoch[k];

  /*
   * The mitigated sample statistics are saved for later
   * processing. If not synchronized or not in a burst, tickle the
   * clock select algorithm.
   */
  record_peer_stats(&peer->srcadr, ctlpeerstatus(peer), peer->offset,
        peer->delay, peer->disp, peer->jitter);
  DPRINTF(1, ("clock_filter: n %hu off %.9f del %.9f dsp %.9f jit %.9f\n",
        (u_short)m, peer->offset, peer->delay, peer->disp,
        peer->jitter));
  if (0 == peer->burst || LEAP_NOTINSYNC == sys_leap) {
    clock_select();
  }
}


/*
 * clock_select - find the pick-of-the-litter clock
 *
 * LOCKCLOCK: (1) If the local clock is the prefer peer, it will always
 * be enabled, even if declared falseticker, (2) only the prefer peer
 * can be selected as the system peer, (3) if the external source is
 * down, the system leap bits are set to 11 and the stratum set to
 * infinity.
 */
void
clock_select(void)
{
  struct peer *peer;
  int i, j, k, n;
  int nlist, nl2;
  int allow;
  int speer;
  double  d, e, f, g;
  double  high, low;
  double  speermet;
  double  lastresort_dist = MAXDISPERSE;
  double  orphmet = 2.0 * U_INT32_MAX; /* 2x is greater than */
  struct endpoint endp;
  struct peer *osys_peer;
  struct peer *sys_prefer = NULL; /* prefer peer */
  struct peer *typesystem = NULL;
  struct peer *typelastresort = NULL;
  struct peer *typeorphan = NULL;
#ifdef REFCLOCK
  struct peer *typeacts = NULL;
  struct peer *typelocal = NULL;
  struct peer *typepps = NULL;
#endif /* REFCLOCK */
  static struct endpoint *endpoint = NULL;
  static int *indx = NULL;
  static peer_select *peers = NULL;
  static u_int endpoint_size = 0;
  static u_int peers_size = 0;
  static u_int indx_size = 0;
  size_t octets;

  /*
   * Initialize and create endpoint, index and peer lists big
   * enough to handle all associations.
   */
  osys_peer = sys_peer;
  sys_survivors = 0;
#ifdef LOCKCLOCK
  set_sys_leap(LEAP_NOTINSYNC);
  sys_stratum = STRATUM_UNSPEC;
  memcpy(&sys_refid, "DOWN", 4);
#endif /* LOCKCLOCK */

  /*
   * Allocate dynamic space depending on the number of
   * associations.
   */
  nlist = 1;
  for (peer = peer_list; peer != NULL; peer = peer->p_link)
    nlist++;
  endpoint_size = ALIGNED_SIZE(nlist * 2 * sizeof(*endpoint));
  peers_size = ALIGNED_SIZE(nlist * sizeof(*peers));
  indx_size = ALIGNED_SIZE(nlist * 2 * sizeof(*indx));
  octets = endpoint_size + peers_size + indx_size;
  endpoint = erealloc(endpoint, octets);
  peers = INCR_PTR(endpoint, endpoint_size);
  indx = INCR_PTR(peers, peers_size);

  /*
   * Initially, we populate the island with all the rifraff peers
   * that happen to be lying around. Those with seriously
   * defective clocks are immediately booted off the island. Then,
   * the falsetickers are culled and put to sea. The truechimers
   * remaining are subject to repeated rounds where the most
   * unpopular at each round is kicked off. When the population
   * has dwindled to sys_minclock, the survivors split a million
   * bucks and collectively crank the chimes.
   */
  nlist = nl2 = 0;  /* none yet */
  for (peer = peer_list; peer != NULL; peer = peer->p_link) {
    peer->new_status = CTL_PST_SEL_REJECT;

    /*
     * Leave the island immediately if the peer is
     * unfit to synchronize.
     */
    if (peer_unfit(peer)) {
      continue;
    }

    /*
     * If we have never been synchronised, look for any peer 
     * which has ever been synchronised and pick the one which 
     * has the lowest root distance. This can be used as a last 
     * resort if all else fails. Once we get an initial sync 
     * with this peer, sys_reftime gets set and so this 
     * function becomes disabled.
     */
    if (L_ISZERO(&sys_reftime)) {
      d = root_distance(peer);
      if (!L_ISZERO(&peer->reftime) && d < lastresort_dist) {
        typelastresort = peer;
        lastresort_dist = d;
      }
    }

    /*
     * If this peer is an orphan parent, elect the
     * one with the lowest metric defined as the
     * IPv4 address or the first 64 bits of the
     * hashed IPv6 address.  To ensure convergence
     * on the same selected orphan, consider as
     * well that this system may have the lowest
     * metric and be the orphan parent.  If this
     * system wins, sys_peer will be NULL to trigger
     * orphan mode in timer().
     */
    if (peer->stratum == sys_orphan) {
      u_int32 localmet;
      u_int32 peermet;

      if (peer->dstadr != NULL)
        localmet = ntohl(peer->dstadr->addr_refid);
      else
        localmet = U_INT32_MAX;
      peermet = ntohl(addr2refid(&peer->srcadr));
      if (peermet < localmet && peermet < orphmet) {
        typeorphan = peer;
        orphmet = peermet;
      }
      continue;
    }

    /*
     * If this peer could have the orphan parent
     * as a synchronization ancestor, exclude it
     * from selection to avoid forming a
     * synchronization loop within the orphan mesh,
     * triggering stratum climb to infinity
     * instability.  Peers at stratum higher than
     * the orphan stratum could have the orphan
     * parent in ancestry so are excluded.
     * See http://bugs.ntp.org/2050
     */
    if (peer->stratum > sys_orphan) {
      continue;
    }
#ifdef REFCLOCK
    /*
     * The following are special cases. We deal
     * with them later.
     */
    if (!(peer->flags & FLAG_PREFER)) {
      switch (peer->refclktype) {
      case REFCLK_LOCALCLOCK:
        if (   current_time > orphwait
            && typelocal == NULL)
          typelocal = peer;
        continue;

      case REFCLK_ACTS:
        if (   current_time > orphwait
            && typeacts == NULL)
          typeacts = peer;
        continue;
      }
    }
#endif /* REFCLOCK */

    /*
     * If we get this far, the peer can stay on the
     * island, but does not yet have the immunity
     * idol.
     */
    peer->new_status = CTL_PST_SEL_SANE;
    f = root_distance(peer);
    peers[nlist].peer = peer;
    peers[nlist].error = peer->jitter;
    peers[nlist].synch = f;
    nlist++;

    /*
     * Insert each interval endpoint on the unsorted
     * endpoint[] list.
     */
    e = peer->offset;
    endpoint[nl2].type = -1;  /* lower end */
    endpoint[nl2].val = e - f;
    nl2++;
    endpoint[nl2].type = 1;   /* upper end */
    endpoint[nl2].val = e + f;
    nl2++;
  }
  /*
   * Construct sorted indx[] of endpoint[] indexes ordered by
   * offset.
   */
  for (i = 0; i < nl2; i++)
    indx[i] = i;
  for (i = 0; i < nl2; i++) {
    endp = endpoint[indx[i]];
    e = endp.val;
    k = i;
    for (j = i + 1; j < nl2; j++) {
      endp = endpoint[indx[j]];
      if (endp.val < e) {
        e = endp.val;
        k = j;
      }
    }
    if (k != i) {
      j = indx[k];
      indx[k] = indx[i];
      indx[i] = j;
    }
  }
  for (i = 0; i < nl2; i++)
    DPRINTF(3, ("select: endpoint %2d %.6f\n",
      endpoint[indx[i]].type, endpoint[indx[i]].val));

  /*
   * This is the actual algorithm that cleaves the truechimers
   * from the falsetickers. The original algorithm was described
   * in Keith Marzullo's dissertation, but has been modified for
   * better accuracy.
   *
   * Briefly put, we first assume there are no falsetickers, then
   * scan the candidate list first from the low end upwards and
   * then from the high end downwards. The scans stop when the
   * number of intersections equals the number of candidates less
   * the number of falsetickers. If this doesn't happen for a
   * given number of falsetickers, we bump the number of
   * falsetickers and try again. If the number of falsetickers
   * becomes equal to or greater than half the number of
   * candidates, the Albanians have won the Byzantine wars and
   * correct synchronization is not possible.
   *
   * Here, nlist is the number of candidates and allow is the
   * number of falsetickers. Upon exit, the truechimers are the
   * survivors with offsets not less than low and not greater than
   * high. There may be none of them.
   */
  low = 1e9;
  high = -1e9;
  for (allow = 0; 2 * allow < nlist; allow++) {

    /*
     * Bound the interval (low, high) as the smallest
     * interval containing points from the most sources.
     */
    n = 0;
    for (i = 0; i < nl2; i++) {
      low = endpoint[indx[i]].val;
      n -= endpoint[indx[i]].type;
      if (n >= nlist - allow)
        break;
    }
    n = 0;
    for (j = nl2 - 1; j >= 0; j--) {
      high = endpoint[indx[j]].val;
      n += endpoint[indx[j]].type;
      if (n >= nlist - allow)
        break;
    }

    /*
     * If an interval containing truechimers is found, stop.
     * If not, increase the number of falsetickers and go
     * around again.
     */
    if (high > low)
      break;
  }

  /*
   * Clustering algorithm. Whittle candidate list of falsetickers,
   * who leave the island immediately. The TRUE peer is always a
   * truechimer. We must leave at least one peer to collect the
   * million bucks.
   *
   * We assert the correct time is contained in the interval, but
   * the best offset estimate for the interval might not be
   * contained in the interval. For this purpose, a truechimer is
   * defined as the midpoint of an interval that overlaps the
   * intersection interval.
   */
  j = 0;
  for (i = 0; i < nlist; i++) {
    double  h;

    peer = peers[i].peer;
    h = peers[i].synch;
    if ((   high <= low
         || peer->offset + h < low
         || peer->offset - h > high
        ) && !(peer->flags & FLAG_TRUE))
      continue;

#ifdef REFCLOCK
    /*
     * Eligible PPS peers must survive the intersection
     * algorithm. Use the first one found, but don't
     * include any of them in the cluster population.
     */
    if (peer->flags & FLAG_PPS) {
      if (typepps == NULL)
        typepps = peer;
      if (!(peer->flags & FLAG_TSTAMP_PPS))
        continue;
    }
#endif /* REFCLOCK */

    if (j != i)
      peers[j] = peers[i];
    j++;
  }
  nlist = j;

  /*
   * If no survivors remain at this point, check if the modem
   * driver, local driver or orphan parent in that order. If so,
   * nominate the first one found as the only survivor.
   * Otherwise, give up and leave the island to the rats.
   */
  if (nlist == 0) {
    peers[0].error = 0;
    peers[0].synch = sys_mindisp;
#ifdef REFCLOCK
    if (typeacts != NULL) {
      peers[0].peer = typeacts;
      nlist = 1;
    } else if (typelocal != NULL) {
      peers[0].peer = typelocal;
      nlist = 1;
    } else
#endif /* REFCLOCK */
    if (typeorphan != NULL) {
      peers[0].peer = typeorphan;
      nlist = 1;
    } else if (typelastresort != NULL) {
      peers[0].peer = typelastresort;
      nlist = 1;
    }
  }

  /*
   * Mark the candidates at this point as truechimers.
   */
  for (i = 0; i < nlist; i++) {
    peers[i].peer->new_status = CTL_PST_SEL_SELCAND;
    DPRINTF(2, ("select: survivor %s %f\n",
      stoa(&peers[i].peer->srcadr), peers[i].synch));
  }

  /*
   * Now, vote outliers off the island by select jitter weighted
   * by root distance. Continue voting as long as there are more
   * than sys_minclock survivors and the select jitter of the peer
   * with the worst metric is greater than the minimum peer
   * jitter. Stop if we are about to discard a TRUE or PREFER
   * peer, who of course have the immunity idol.
   */
  while (1) {
    d = 1e9;
    e = -1e9;
    g = 0;
    k = 0;
    for (i = 0; i < nlist; i++) {
      if (peers[i].error < d)
        d = peers[i].error;
      peers[i].seljit = 0;
      if (nlist > 1) {
        f = 0;
        for (j = 0; j < nlist; j++)
          f += DIFF(peers[j].peer->offset,
              peers[i].peer->offset);
        peers[i].seljit = SQRT(f / (nlist - 1));
      }
      if (peers[i].seljit * peers[i].synch > e) {
        g = peers[i].seljit;
        e = peers[i].seljit * peers[i].synch;
        k = i;
      }
    }
    g = max(g, LOGTOD(sys_precision));
    if (   nlist <= max(1, sys_minclock)
        || g <= d
        || ((FLAG_TRUE | FLAG_PREFER) & peers[k].peer->flags))
      break;

    DPRINTF(3, ("select: drop %s seljit %.9f jit %.9f\n",
      ntoa(&peers[k].peer->srcadr), g, d));
    if (nlist > sys_maxclock)
      peers[k].peer->new_status = CTL_PST_SEL_EXCESS;
    for (j = k + 1; j < nlist; j++)
      peers[j - 1] = peers[j];
    nlist--;
  }

  /*
   * What remains is a list usually not greater than sys_minclock
   * peers. Note that unsynchronized peers cannot survive this
   * far.  Count and mark these survivors.
   *
   * While at it, count the number of leap warning bits found.
   * This will be used later to vote the system leap warning bit.
   * If a leap warning bit is found on a reference clock, the vote
   * is always won.
   *
   * Choose the system peer using a hybrid metric composed of the
   * selection jitter scaled by the root distance augmented by
   * stratum scaled by sys_mindisp (.001 by default). The goal of
   * the small stratum factor is to avoid clockhop between a
   * reference clock and a network peer which has a refclock and
   * is using an older ntpd, which does not floor sys_rootdisp at
   * sys_mindisp.
   *
   * In contrast, ntpd 4.2.6 and earlier used stratum primarily
   * in selecting the system peer, using a weight of 1 second of
   * additional root distance per stratum.  This heavy bias is no
   * longer appropriate, as the scaled root distance provides a
   * more rational metric carrying the cumulative error budget.
   */
  e = 1e9;
  speer = 0;
  leap_vote_ins = 0;
  leap_vote_del = 0;
  for (i = 0; i < nlist; i++) {
    peer = peers[i].peer;
    peer->unreach = 0;
    peer->new_status = CTL_PST_SEL_SYNCCAND;
    sys_survivors++;
    if (peer->leap == LEAP_ADDSECOND) {
      if (peer->flags & FLAG_REFCLOCK)
        leap_vote_ins = nlist;
      else if (leap_vote_ins < nlist)
        leap_vote_ins++;
    }
    if (peer->leap == LEAP_DELSECOND) {
      if (peer->flags & FLAG_REFCLOCK)
        leap_vote_del = nlist;
      else if (leap_vote_del < nlist)
        leap_vote_del++;
    }
    if (peer->flags & FLAG_PREFER)
      sys_prefer = peer;
    speermet = peers[i].seljit * peers[i].synch +
        peer->stratum * sys_mindisp;
    if (speermet < e) {
      e = speermet;
      speer = i;
    }
  }

  /*
   * Unless there are at least sys_misane survivors, leave the
   * building dark. Otherwise, do a clockhop dance. Ordinarily,
   * use the selected survivor speer. However, if the current
   * system peer is not speer, stay with the current system peer
   * as long as it doesn't get too old or too ugly.
   */
  if (nlist > 0 && nlist >= sys_minsane) {
    double  x;

    typesystem = peers[speer].peer;
    if (osys_peer == NULL || osys_peer == typesystem) {
      sys_clockhop = 0;
    } else if ((x = fabs(typesystem->offset -
        osys_peer->offset)) < sys_mindisp) {
      if (0 == sys_clockhop)
        sys_clockhop = sys_mindisp;
      else
        sys_clockhop *= .5;
      DPRINTF(1, ("select: clockhop %d %.9f %.9f\n",
        j, x, sys_clockhop));
      if (x < sys_clockhop)
        typesystem = osys_peer;
      else
        sys_clockhop = 0;
    } else {
      sys_clockhop = 0;
    }
  }

  /*
   * Mitigation rules of the game. We have the pick of the
   * litter in typesystem if any survivors are left. If
   * there is a prefer peer, use its offset and jitter.
   * Otherwise, use the combined offset and jitter of all kitters.
   */
  if (typesystem != NULL) {
    if (sys_prefer == NULL) {
      typesystem->new_status = CTL_PST_SEL_SYSPEER;
      clock_combine(peers, sys_survivors, speer);
    } else {
      typesystem = sys_prefer;
      sys_clockhop = 0;
      typesystem->new_status = CTL_PST_SEL_SYSPEER;
      sys_offset = typesystem->offset;
      sys_jitter = typesystem->jitter;
    }
    DPRINTF(1, ("select: combine offset %.9f jitter %.9f\n",
      sys_offset, sys_jitter));
  }
#ifdef REFCLOCK
  /*
   * If a PPS driver is lit and the combined offset is less than
   * 0.4 s, select the driver as the PPS peer and use its offset
   * and jitter. However, if this is the atom driver, use it only
   * if there is a prefer peer or there are no survivors and none
   * are required.
   */
  if (   typepps != NULL
      && fabs(sys_offset) < 0.4
      && (   typepps->refclktype != REFCLK_ATOM_PPS
    || (   typepps->refclktype == REFCLK_ATOM_PPS
        && (   sys_prefer != NULL
      || (typesystem == NULL && sys_minsane == 0))))) {
    typesystem = typepps;
    sys_clockhop = 0;
    typesystem->new_status = CTL_PST_SEL_PPS;
    sys_offset = typesystem->offset;
    sys_jitter = typesystem->jitter;
    DPRINTF(1, ("select: pps offset %.9f jitter %.9f\n",
      sys_offset, sys_jitter));
  }
#endif /* REFCLOCK */

  /*
   * If there are no survivors at this point, there is no
   * system peer. If so and this is an old update, keep the
   * current statistics, but do not update the clock.
   */
  if (typesystem == NULL) {
    if (osys_peer != NULL) {
      orphwait = current_time + sys_orphwait;
      report_event(EVNT_NOPEER, NULL, NULL);
    }
    sys_peer = NULL;
    for (peer = peer_list; peer != NULL; peer = peer->p_link)
      peer->status = peer->new_status;
    return;
  }

  /*
   * Do not use old data, as this may mess up the clock discipline
   * stability.
   */
  if (typesystem->epoch <= sys_epoch)
    return;

  /*
   * We have found the alpha male. Wind the clock.
   */
  if (osys_peer != typesystem)
    report_event(PEVNT_NEWPEER, typesystem, NULL);
  for (peer = peer_list; peer != NULL; peer = peer->p_link)
    peer->status = peer->new_status;
  clock_update(typesystem);
}


static void
clock_combine(
  peer_select * peers,  /* survivor list */
  int   npeers, /* number of survivors */
  int   syspeer /* index of sys.peer */
  )
{
  int i;
  double  x, y, z, w;

  y = z = w = 0;
  for (i = 0; i < npeers; i++) {
    x = 1. / peers[i].synch;
    y += x;
    z += x * peers[i].peer->offset;
    w += x * DIFF(peers[i].peer->offset,
        peers[syspeer].peer->offset);
  }
  sys_offset = z / y;
  sys_jitter = SQRT(w / y + SQUARE(peers[syspeer].seljit));
}


/*
 * root_distance - compute synchronization distance from peer to root
 */
static double
root_distance(
  struct peer *peer /* peer structure pointer */
  )
{
  double  dtemp;

  /*
   * Root Distance (LAMBDA) is defined as:
   * (delta + DELTA)/2 + epsilon + EPSILON + D
   *
   * where:
   *  delta   is the round-trip delay
   *  DELTA   is the root delay
   *  epsilon is the peer dispersion
   *      + (15 usec each second)
   *  EPSILON is the root dispersion
   *  D       is sys_jitter
   *
   * NB: Think hard about why we are using these values, and what
   * the alternatives are, and the various pros/cons.
   *
   * DLM thinks these are probably the best choices from any of the
   * other worse choices.
   */
  dtemp = (peer->delay + peer->rootdelay) / 2
    + peer->disp
      + clock_phi * (current_time - peer->update)
    + peer->rootdisp
    + peer->jitter;
  /*
   * Careful squeak here. The value returned must be greater than
   * the minimum root dispersion in order to avoid clockhop with
   * highly precise reference clocks. Note that the root distance
   * cannot exceed the sys_maxdist, as this is the cutoff by the
   * selection algorithm.
   */
  if (dtemp < sys_mindisp)
    dtemp = sys_mindisp;
  return (dtemp);
}


/*
 * peer_xmit - send packet for persistent association.
 */
static void
peer_xmit(
  struct peer *peer /* peer structure pointer */
  )
{
  struct pkt xpkt;  /* transmit packet */
  size_t  sendlen, authlen;
  keyid_t xkeyid = 0; /* transmit key ID */
  l_fp  xmt_tx, xmt_ty;

  if (!peer->dstadr) { /* can't send */
    return;
  }
  xpkt.li_vn_mode = PKT_LI_VN_MODE(sys_leap, peer->version,
      peer->hmode);
  xpkt.stratum = STRATUM_TO_PKT(sys_stratum);
  xpkt.ppoll = peer->hpoll;
  xpkt.precision = sys_precision;
  xpkt.refid = sys_refid;
  xpkt.rootdelay = HTONS_FP(DTOFP(sys_rootdelay));
  xpkt.rootdisp =  HTONS_FP(DTOUFP(sys_rootdisp));
  /* Use sys_reftime for peer exchanges */
  HTONL_FP(&sys_reftime, &xpkt.reftime);
  HTONL_FP(&peer->rec, &xpkt.org);
  HTONL_FP(&peer->dst, &xpkt.rec);

  /*
   * If the received packet contains a MAC, the transmitted packet
   * is authenticated and contains a MAC. If not, the transmitted
   * packet is not authenticated.
   *
   * It is most important when autokey is in use that the local
   * interface IP address be known before the first packet is
   * sent. Otherwise, it is not possible to compute a correct MAC
   * the recipient will accept. Thus, the I/O semantics have to do
   * a little more work. In particular, the wildcard interface
   * might not be usable.
   */
  sendlen = LEN_PKT_NOMAC;
  if (
#ifdef AUTOKEY
      !(peer->flags & FLAG_SKEY) &&
#endif  /* !AUTOKEY */
      peer->keyid == 0) {

    /*
     * Transmit a-priori timestamps
     */
    get_systime(&xmt_tx);
    if (peer->flip == 0) { /* basic mode */
      peer->aorg = xmt_tx;
      HTONL_FP(&xmt_tx, &xpkt.xmt);
    } else {   /* interleaved modes */
      if (peer->hmode == MODE_BROADCAST) { /* bcst */
        HTONL_FP(&xmt_tx, &xpkt.xmt);
        if (peer->flip > 0)
          HTONL_FP(&peer->borg,
              &xpkt.org);
        else
          HTONL_FP(&peer->aorg,
              &xpkt.org);
      } else { /* symmetric */
        if (peer->flip > 0)
          HTONL_FP(&peer->borg,
              &xpkt.xmt);
        else
          HTONL_FP(&peer->aorg,
              &xpkt.xmt);
      }
    }
    peer->t21_bytes = sendlen;
    sendpkt(&peer->srcadr, peer->dstadr,
      sys_ttl[(peer->ttl >= sys_ttlmax) ? sys_ttlmax : peer->ttl],
      &xpkt, sendlen);
    peer->sent++;
    peer->throttle += (1 << peer->minpoll) - 2;

    /*
     * Capture a-posteriori timestamps
     */
    get_systime(&xmt_ty);
    if (peer->flip != 0) {   /* interleaved modes */
      if (peer->flip > 0)
        peer->aorg = xmt_ty;
      else
        peer->borg = xmt_ty;
      peer->flip = -peer->flip;
    }
    L_SUB(&xmt_ty, &xmt_tx);
    LFPTOD(&xmt_ty, peer->xleave);
    DPRINTF(1, ("peer_xmit: at %ld %s->%s mode %d len %zu xmt 0x%x.%08x\n",
          current_time, latoa(peer->dstadr),
          stoa(&peer->srcadr), peer->hmode, sendlen,
          xmt_tx.l_ui, xmt_tx.l_uf));
    return;
  }

  /*
   * Authentication is enabled, so the transmitted packet must be
   * authenticated. If autokey is enabled, fuss with the various
   * modes; otherwise, symmetric key cryptography is used.
   */
#ifdef AUTOKEY
  if (peer->flags & FLAG_SKEY) {
    struct exten *exten;  /* extension field */

    /*
     * The Public Key Dance (PKD): Cryptographic credentials
     * are contained in extension fields, each including a
     * 4-octet length/code word followed by a 4-octet
     * association ID and optional additional data. Optional
     * data includes a 4-octet data length field followed by
     * the data itself. Request messages are sent from a
     * configured association; response messages can be sent
     * from a configured association or can take the fast
     * path without ever matching an association. Response
     * messages have the same code as the request, but have
     * a response bit and possibly an error bit set. In this
     * implementation, a message may contain no more than
     * one command and one or more responses.
     *
     * Cryptographic session keys include both a public and
     * a private componet. Request and response messages
     * using extension fields are always sent with the
     * private component set to zero. Packets without
     * extension fields indlude the private component when
     * the session key is generated.
     */
    while (1) {

      /*
       * Allocate and initialize a keylist if not
       * already done. Then, use the list in inverse
       * order, discarding keys once used. Keep the
       * latest key around until the next one, so
       * clients can use client/server packets to
       * compute propagation delay.
       *
       * Note that once a key is used from the list,
       * it is retained in the key cache until the
       * next key is used. This is to allow a client
       * to retrieve the encrypted session key
       * identifier to verify authenticity.
       *
       * If for some reason a key is no longer in the
       * key cache, a birthday has happened or the key
       * has expired, so the pseudo-random sequence is
       * broken. In that case, purge the keylist and
       * regenerate it.
       */
      if (peer->keynumber == 0)
        make_keylist(peer, peer->dstadr);
      else
        peer->keynumber--;
      xkeyid = peer->keylist[peer->keynumber];
      if (authistrusted(xkeyid))
        break;
      else
        key_expire(peer);
    }
    peer->keyid = xkeyid;
    exten = NULL;
    switch (peer->hmode) {

    /*
     * In broadcast server mode the autokey values are
     * required by the broadcast clients. Push them when a
     * new keylist is generated; otherwise, push the
     * association message so the client can request them at
     * other times.
     */
    case MODE_BROADCAST:
      if (peer->flags & FLAG_ASSOC)
        exten = crypto_args(peer, CRYPTO_AUTO |
            CRYPTO_RESP, peer->associd, NULL);
      else
        exten = crypto_args(peer, CRYPTO_ASSOC |
            CRYPTO_RESP, peer->associd, NULL);
      break;

    /*
     * In symmetric modes the parameter, certificate,
     * identity, cookie and autokey exchanges are
     * required. The leapsecond exchange is optional. But, a
     * peer will not believe the other peer until the other
     * peer has synchronized, so the certificate exchange
     * might loop until then. If a peer finds a broken
     * autokey sequence, it uses the autokey exchange to
     * retrieve the autokey values. In any case, if a new
     * keylist is generated, the autokey values are pushed.
     */
    case MODE_ACTIVE:
    case MODE_PASSIVE:

      /*
       * Parameter, certificate and identity.
       */
      if (!peer->crypto)
        exten = crypto_args(peer, CRYPTO_ASSOC,
            peer->associd, hostval.ptr);
      else if (!(peer->crypto & CRYPTO_FLAG_CERT))
        exten = crypto_args(peer, CRYPTO_CERT,
            peer->associd, peer->issuer);
      else if (!(peer->crypto & CRYPTO_FLAG_VRFY))
        exten = crypto_args(peer,
            crypto_ident(peer), peer->associd,
            NULL);

      /*
       * Cookie and autokey. We request the cookie
       * only when the this peer and the other peer
       * are synchronized. But, this peer needs the
       * autokey values when the cookie is zero. Any
       * time we regenerate the key list, we offer the
       * autokey values without being asked. If for
       * some reason either peer finds a broken
       * autokey sequence, the autokey exchange is
       * used to retrieve the autokey values.
       */
      else if (   sys_leap != LEAP_NOTINSYNC
         && peer->leap != LEAP_NOTINSYNC
         && !(peer->crypto & CRYPTO_FLAG_COOK))
        exten = crypto_args(peer, CRYPTO_COOK,
            peer->associd, NULL);
      else if (!(peer->crypto & CRYPTO_FLAG_AUTO))
        exten = crypto_args(peer, CRYPTO_AUTO,
            peer->associd, NULL);
      else if (   peer->flags & FLAG_ASSOC
         && peer->crypto & CRYPTO_FLAG_SIGN)
        exten = crypto_args(peer, CRYPTO_AUTO |
            CRYPTO_RESP, peer->assoc, NULL);

      /*
       * Wait for clock sync, then sign the
       * certificate and retrieve the leapsecond
       * values.
       */
      else if (sys_leap == LEAP_NOTINSYNC)
        break;

      else if (!(peer->crypto & CRYPTO_FLAG_SIGN))
        exten = crypto_args(peer, CRYPTO_SIGN,
            peer->associd, hostval.ptr);
      else if (!(peer->crypto & CRYPTO_FLAG_LEAP))
        exten = crypto_args(peer, CRYPTO_LEAP,
            peer->associd, NULL);
      break;

    /*
     * In client mode the parameter, certificate, identity,
     * cookie and sign exchanges are required. The
     * leapsecond exchange is optional. If broadcast client
     * mode the same exchanges are required, except that the
     * autokey exchange is substitutes for the cookie
     * exchange, since the cookie is always zero. If the
     * broadcast client finds a broken autokey sequence, it
     * uses the autokey exchange to retrieve the autokey
     * values.
     */
    case MODE_CLIENT:

      /*
       * Parameter, certificate and identity.
       */
      if (!peer->crypto)
        exten = crypto_args(peer, CRYPTO_ASSOC,
            peer->associd, hostval.ptr);
      else if (!(peer->crypto & CRYPTO_FLAG_CERT))
        exten = crypto_args(peer, CRYPTO_CERT,
            peer->associd, peer->issuer);
      else if (!(peer->crypto & CRYPTO_FLAG_VRFY))
        exten = crypto_args(peer,
            crypto_ident(peer), peer->associd,
            NULL);

      /*
       * Cookie and autokey. These are requests, but
       * we use the peer association ID with autokey
       * rather than our own.
       */
      else if (!(peer->crypto & CRYPTO_FLAG_COOK))
        exten = crypto_args(peer, CRYPTO_COOK,
            peer->associd, NULL);
      else if (!(peer->crypto & CRYPTO_FLAG_AUTO))
        exten = crypto_args(peer, CRYPTO_AUTO,
            peer->assoc, NULL);

      /*
       * Wait for clock sync, then sign the
       * certificate and retrieve the leapsecond
       * values.
       */
      else if (sys_leap == LEAP_NOTINSYNC)
        break;

      else if (!(peer->crypto & CRYPTO_FLAG_SIGN))
        exten = crypto_args(peer, CRYPTO_SIGN,
            peer->associd, hostval.ptr);
      else if (!(peer->crypto & CRYPTO_FLAG_LEAP))
        exten = crypto_args(peer, CRYPTO_LEAP,
            peer->associd, NULL);
      break;
    }

    /*
     * Add a queued extension field if present. This is
     * always a request message, so the reply ID is already
     * in the message. If an error occurs, the error bit is
     * lit in the response.
     */
    if (peer->cmmd != NULL) {
      u_int32 temp32;

      temp32 = CRYPTO_RESP;
      peer->cmmd->opcode |= htonl(temp32);
      sendlen += crypto_xmit(peer, &xpkt, NULL,
          sendlen, peer->cmmd, 0);
      free(peer->cmmd);
      peer->cmmd = NULL;
    }

    /*
     * Add an extension field created above. All but the
     * autokey response message are request messages.
     */
    if (exten != NULL) {
      if (exten->opcode != 0)
        sendlen += crypto_xmit(peer, &xpkt,
            NULL, sendlen, exten, 0);
      free(exten);
    }

    /*
     * Calculate the next session key. Since extension
     * fields are present, the cookie value is zero.
     */
    if (sendlen > (int)LEN_PKT_NOMAC) {
      session_key(&peer->dstadr->sin, &peer->srcadr,
          xkeyid, 0, 2);
    }
  }
#endif  /* AUTOKEY */

  /*
   * Transmit a-priori timestamps
   */
  get_systime(&xmt_tx);
  if (peer->flip == 0) {   /* basic mode */
    peer->aorg = xmt_tx;
    HTONL_FP(&xmt_tx, &xpkt.xmt);
  } else {     /* interleaved modes */
    if (peer->hmode == MODE_BROADCAST) { /* bcst */
      HTONL_FP(&xmt_tx, &xpkt.xmt);
      if (peer->flip > 0)
        HTONL_FP(&peer->borg, &xpkt.org);
      else
        HTONL_FP(&peer->aorg, &xpkt.org);
    } else {   /* symmetric */
      if (peer->flip > 0)
        HTONL_FP(&peer->borg, &xpkt.xmt);
      else
        HTONL_FP(&peer->aorg, &xpkt.xmt);
    }
  }
  xkeyid = peer->keyid;
  authlen = authencrypt(xkeyid, (u_int32 *)&xpkt, sendlen);
  if (authlen == 0) {
    report_event(PEVNT_AUTH, peer, "no key");
    peer->flash |= TEST5;   /* auth error */
    peer->badauth++;
    return;
  }
  sendlen += authlen;
#ifdef AUTOKEY
  if (xkeyid > NTP_MAXKEY)
    authtrust(xkeyid, 0);
#endif  /* AUTOKEY */
  if (sendlen > sizeof(xpkt)) {
    msyslog(LOG_ERR, "peer_xmit: buffer overflow %u", (u_int)sendlen);
    exit(EX_SOFTWARE);
  }
  peer->t21_bytes = sendlen;
  sendpkt(&peer->srcadr, peer->dstadr,
    sys_ttl[(peer->ttl >= sys_ttlmax) ? sys_ttlmax : peer->ttl],
    &xpkt, sendlen);
  peer->sent++;
  peer->throttle += (1 << peer->minpoll) - 2;

  /*
   * Capture a-posteriori timestamps
   */
  get_systime(&xmt_ty);
  if (peer->flip != 0) {     /* interleaved modes */
    if (peer->flip > 0)
      peer->aorg = xmt_ty;
    else
      peer->borg = xmt_ty;
    peer->flip = -peer->flip;
  }
  L_SUB(&xmt_ty, &xmt_tx);
  LFPTOD(&xmt_ty, peer->xleave);
#ifdef AUTOKEY
  DPRINTF(1, ("peer_xmit: at %ld %s->%s mode %d keyid %08x len %zu index %d\n",
        current_time, latoa(peer->dstadr), stoa(&peer->srcadr),
        peer->hmode, xkeyid, sendlen, peer->keynumber));
#else /* !AUTOKEY follows */
  DPRINTF(1, ("peer_xmit: at %ld %s->%s mode %d keyid %08x len %zu\n",
        current_time, peer->dstadr ?
        ntoa(&peer->dstadr->sin) : "-",
        ntoa(&peer->srcadr), peer->hmode, xkeyid, sendlen));
#endif  /* !AUTOKEY */

  return;
}


#ifdef LEAP_SMEAR

static void
leap_smear_add_offs(
  l_fp *t,
  l_fp *t_recv
  )
{

  L_ADD(t, &leap_smear.offset);

  /*
  ** XXX: Should the smear be added to the root dispersion?
  */

  return;
}

#endif /* LEAP_SMEAR */


/*
 * fast_xmit - Send packet for nonpersistent association. Note that
 * neither the source or destination can be a broadcast address.
 */
static void
fast_xmit(
  struct recvbuf* rbufp,  /* receive packet pointer */
  int xmode,    /* receive mode */  /* XXX: HMS: really? */
  keyid_t xkeyid,   /* transmit key ID */
  int flags   /* restrict mask */
)
{
  struct pkt xpkt;  /* transmit packet structure */
  struct pkt* rpkt; /* receive packet structure */
  l_fp  xmt_tx, xmt_ty;
  size_t  sendlen;
#ifdef AUTOKEY
  u_int32 temp32;
#endif

  /*
   * Initialize transmit packet header fields from the receive
   * buffer provided. We leave the fields intact as received, but
   * set the peer poll at the maximum of the receive peer poll and
   * the system minimum poll (ntp_minpoll). This is for KoD rate
   * control and not strictly specification compliant, but doesn't
   * break anything.
   */
  rpkt = &rbufp->recv_pkt;
  /*
   * If the packet was received on an endpoint open only on
   * a multicast address, the response needs to go out from
   * a unicast endpoint.
   */
#ifndef MULTICAST_NONEWSOCKET
  if (rbufp->dstadr->flags & INT_MCASTOPEN) {
    rbufp->dstadr = findinterface(&rbufp->recv_srcadr);
    if (NULL == rbufp->dstadr ||
        ANY_INTERFACE_CHOOSE(&rbufp->recv_srcadr) /* wildcard */
          == rbufp->dstadr) {
      DPRINTF(2, ("No unicast local address found for"
            " reply to %s mcast.",
            stoa(&rbufp->recv_srcadr)));
      return;
    }
  }
#endif

  /*
   * If this is a kiss-o'-death (KoD) packet, show leap
   * unsynchronized, stratum zero, reference ID the four-character
   * kiss code and (???) system root delay. Note we don't reveal
   * the local time, so these packets can't be used for
   * synchronization.
   */
  if (flags & RES_KOD) {
    sys_kodsent++;
    xpkt.li_vn_mode = PKT_LI_VN_MODE(LEAP_NOTINSYNC,
        PKT_VERSION(rpkt->li_vn_mode), xmode);
    xpkt.stratum = STRATUM_PKT_UNSPEC;
    xpkt.ppoll = max(rpkt->ppoll, ntp_minpoll);
    xpkt.precision = rpkt->precision;
    memcpy(&xpkt.refid, "RATE", 4);
    xpkt.rootdelay = rpkt->rootdelay;
    xpkt.rootdisp = rpkt->rootdisp;
    xpkt.reftime = rpkt->reftime;
    xpkt.org = rpkt->xmt;
    xpkt.rec = rpkt->xmt;
    xpkt.xmt = rpkt->xmt;

  /*
   * This is a normal packet. Use the system variables.
   */
  } else {
    double this_rootdisp;
    l_fp this_ref_time;

#ifdef LEAP_SMEAR
    /*
     * Make copies of the variables which can be affected by smearing.
     */
    l_fp this_recv_time;
#endif

    /*
     * If we are inside the leap smear interval we add
     * the current smear offset to:
     * - the packet receive time,
     * - the packet transmit time,
     * - and eventually to the reftime to make sure the
     *   reftime isn't later than the transmit/receive times.
     */
    xpkt.li_vn_mode = PKT_LI_VN_MODE(xmt_leap,
        PKT_VERSION(rpkt->li_vn_mode), xmode);

    xpkt.stratum = STRATUM_TO_PKT(sys_stratum);
    xpkt.ppoll = max(rpkt->ppoll, ntp_minpoll);
    xpkt.precision = sys_precision;
    xpkt.refid = sys_refid;
    xpkt.rootdelay = HTONS_FP(DTOFP(sys_rootdelay));

    /*
    ** Server Response Fuzzing
    **
    ** Which values do we want to use for reftime and rootdisp?
    */

    if (   MODE_SERVER == xmode
        && RES_SRVRSPFUZ & flags) {
      if (current_time < p2_time) {
        this_ref_time = p2_reftime;
        this_rootdisp = p2_rootdisp;
      } else if (current_time < prev_time) {
        this_ref_time = prev_reftime;
        this_rootdisp = prev_rootdisp;
      } else {
        this_ref_time = sys_reftime;
        this_rootdisp = sys_rootdisp;
      }

      SRVRSP_FUZZ(this_ref_time);
    } else {
      this_ref_time = sys_reftime;
      this_rootdisp = sys_rootdisp;
    }

    /*
    ** ROOT DISPERSION
    */

    xpkt.rootdisp = HTONS_FP(DTOUFP(this_rootdisp));

    /*
    ** REFTIME
    */

#ifdef LEAP_SMEAR
    if (leap_smear.in_progress) {
      /* adjust the reftime by the same amount as the
       * leap smear, as we don't want to risk the
       * reftime being later than the transmit time.
       */
      leap_smear_add_offs(&this_ref_time, NULL);
    }
#endif

    HTONL_FP(&this_ref_time, &xpkt.reftime);

    /*
    ** REFID
    */

#ifdef LEAP_SMEAR
    if (leap_smear.in_progress) {
      xpkt.refid = convertLFPToRefID(leap_smear.offset);
      DPRINTF(2, ("fast_xmit: leap_smear.in_progress: refid %8x, smear %s\n",
        ntohl(xpkt.refid),
        lfptoa(&leap_smear.offset, 8)
        ));
    }
#endif

    /*
    ** ORIGIN
    */

    xpkt.org = rpkt->xmt;

    /*
    ** RECEIVE
    */
#ifdef LEAP_SMEAR
    this_recv_time = rbufp->recv_time;
    if (leap_smear.in_progress)
      leap_smear_add_offs(&this_recv_time, NULL);
    HTONL_FP(&this_recv_time, &xpkt.rec);
#else
    HTONL_FP(&rbufp->recv_time, &xpkt.rec);
#endif

    /*
    ** TRANSMIT
    */

    get_systime(&xmt_tx);
#ifdef LEAP_SMEAR
    if (leap_smear.in_progress)
      leap_smear_add_offs(&xmt_tx, &this_recv_time);
#endif
    HTONL_FP(&xmt_tx, &xpkt.xmt);
  }

#ifdef HAVE_NTP_SIGND
  if (flags & RES_MSSNTP) {
    send_via_ntp_signd(rbufp, xmode, xkeyid, flags, &xpkt);
    return;
  }
#endif /* HAVE_NTP_SIGND */

  /*
   * If the received packet contains a MAC, the transmitted packet
   * is authenticated and contains a MAC. If not, the transmitted
   * packet is not authenticated.
   */
  sendlen = LEN_PKT_NOMAC;
  if (rbufp->recv_length == sendlen) {
    sendpkt(&rbufp->recv_srcadr, rbufp->dstadr, 0, &xpkt,
        sendlen);
    DPRINTF(1, ("fast_xmit: at %ld %s->%s mode %d len %lu\n",
          current_time, stoa(&rbufp->dstadr->sin),
          stoa(&rbufp->recv_srcadr), xmode,
          (u_long)sendlen));
    return;
  }

  /*
   * The received packet contains a MAC, so the transmitted packet
   * must be authenticated. For symmetric key cryptography, use
   * the predefined and trusted symmetric keys to generate the
   * cryptosum. For autokey cryptography, use the server private
   * value to generate the cookie, which is unique for every
   * source-destination-key ID combination.
   */
#ifdef AUTOKEY
  if (xkeyid > NTP_MAXKEY) {
    keyid_t cookie;

    /*
     * The only way to get here is a reply to a legitimate
     * client request message, so the mode must be
     * MODE_SERVER. If an extension field is present, there
     * can be only one and that must be a command. Do what
     * needs, but with private value of zero so the poor
     * jerk can decode it. If no extension field is present,
     * use the cookie to generate the session key.
     */
    cookie = session_key(&rbufp->recv_srcadr,
        &rbufp->dstadr->sin, 0, sys_private, 0);
    if ((size_t)rbufp->recv_length > sendlen + MAX_MAC_LEN) {
      session_key(&rbufp->dstadr->sin,
          &rbufp->recv_srcadr, xkeyid, 0, 2);
      temp32 = CRYPTO_RESP;
      rpkt->exten[0] |= htonl(temp32);
      sendlen += crypto_xmit(NULL, &xpkt, rbufp,
          sendlen, (struct exten *)rpkt->exten,
          cookie);
    } else {
      session_key(&rbufp->dstadr->sin,
          &rbufp->recv_srcadr, xkeyid, cookie, 2);
    }
  }
#endif  /* AUTOKEY */
  get_systime(&xmt_tx);
  sendlen += authencrypt(xkeyid, (u_int32 *)&xpkt, sendlen);
#ifdef AUTOKEY
  if (xkeyid > NTP_MAXKEY)
    authtrust(xkeyid, 0);
#endif  /* AUTOKEY */
  sendpkt(&rbufp->recv_srcadr, rbufp->dstadr, 0, &xpkt, sendlen);
  get_systime(&xmt_ty);
  L_SUB(&xmt_ty, &xmt_tx);
  sys_authdelay = xmt_ty;
  DPRINTF(1, ("fast_xmit: at %ld %s->%s mode %d keyid %08x len %lu\n",
        current_time, ntoa(&rbufp->dstadr->sin),
        ntoa(&rbufp->recv_srcadr), xmode, xkeyid,
        (u_long)sendlen));
}


/*
 * pool_xmit - resolve hostname or send unicast solicitation for pool.
 */
static void
pool_xmit(
  struct peer *pool /* pool solicitor association */
  )
{
#ifdef WORKER
  struct pkt  xpkt; /* transmit packet structure */
  struct addrinfo hints;
  int   rc;
  endpt *   lcladr;
  sockaddr_u *  rmtadr;
  u_short   af;
  struct peer * p;
  l_fp    xmt_tx;

  DEBUG_REQUIRE(pool);
  if (NULL == pool->ai) {
    if (pool->addrs != NULL) {
      /* free() is used with copy_addrinfo_list() */
      free(pool->addrs);
      pool->addrs = NULL;
    }
    af = AF(&pool->srcadr);
    if (   (AF_INET == af && !nonlocal_v4_addr_up)
        || (AF_INET6 == af && !nonlocal_v6_addr_up)
        || (   AF_UNSPEC == af
      && !nonlocal_v4_addr_up
      && !nonlocal_v6_addr_up)) {

      /* POOL DNS query would be useless [Bug 3845] */
      return;
    }
    ZERO(hints);
    hints.ai_family = AF(&pool->srcadr);
    hints.ai_socktype = SOCK_DGRAM;
    hints.ai_protocol = IPPROTO_UDP;
    /* ignore getaddrinfo_sometime() errors, we will retry */
    rc = getaddrinfo_sometime(
      pool->hostname,
      "ntp",
      &hints,
      0,      /* no retry */
      &pool_name_resolved,
      (void *)(intptr_t)pool->associd);
    if (!rc)
      DPRINTF(1, ("pool DNS lookup %s started\n",
        pool->hostname));
    else
      msyslog(LOG_ERR,
        "unable to start pool DNS %s: %m",
        pool->hostname);
    return;
  }

  do {
    /* copy_addrinfo_list ai_addr points to a sockaddr_u */
    rmtadr = (sockaddr_u *)(void *)pool->ai->ai_addr;
    pool->ai = pool->ai->ai_next;
    /* do not solicit when hopeless [Bug 3845] */
    if (   (IS_IPV4(rmtadr) && !nonlocal_v4_addr_up)
        || (IS_IPV6(rmtadr) && !nonlocal_v6_addr_up)) {
      continue;
    }
    p = findexistingpeer(rmtadr, NULL, NULL, MODE_CLIENT, 0, NULL);
  } while (p != NULL && pool->ai != NULL);
  if (p != NULL) {
    return; /* out of addresses, re-query DNS next poll */
  }
  restrict_source(rmtadr, FALSE, 1 + POOL_SOLICIT_WINDOW);
  lcladr = findinterface(rmtadr);
  memset(&xpkt, 0, sizeof(xpkt));
  xpkt.li_vn_mode = PKT_LI_VN_MODE(sys_leap, pool->version,
           MODE_CLIENT);
  xpkt.stratum = STRATUM_TO_PKT(sys_stratum);
  xpkt.ppoll = pool->hpoll;
  xpkt.precision = sys_precision;
  xpkt.refid = sys_refid;
  xpkt.rootdelay = HTONS_FP(DTOFP(sys_rootdelay));
  xpkt.rootdisp = HTONS_FP(DTOUFP(sys_rootdisp));
  /* Bug 3596: What are the pros/cons of using sys_reftime here? */
  HTONL_FP(&sys_reftime, &xpkt.reftime);

  get_systime(&xmt_tx);
  pool->aorg = xmt_tx;

  if (FLAG_LOOPNONCE & pool->flags) {
    l_fp nonce;

    do {
      nonce.l_ui = ntp_random();
    } while (0 == nonce.l_ui);
    do {
      nonce.l_uf = ntp_random();
    } while (0 == nonce.l_uf);
    pool->nonce = nonce;
    HTONL_FP(&nonce, &xpkt.xmt);
  } else {
    L_CLR(&pool->nonce);
    HTONL_FP(&xmt_tx, &xpkt.xmt);
  }
  pool->sent++;
  pool->throttle += (1 << pool->minpoll) - 2;
  DPRINTF(1, ("pool_xmit: at %ld %s->%s pool\n",
        current_time, latoa(lcladr), stoa(rmtadr)));
  msyslog(LOG_INFO, "Soliciting pool server %s", stoa(rmtadr));
  sendpkt(rmtadr, lcladr,
    sys_ttl[(pool->ttl >= sys_ttlmax) ? sys_ttlmax : pool->ttl],
    &xpkt, LEN_PKT_NOMAC);
#endif  /* WORKER */
}


#ifdef AUTOKEY
  /*
   * group_test - test if this is the same group
   *
   * host   assoc   return    action
   * none   none    0   mobilize *
   * none   group   0   mobilize *
   * group  none    0   mobilize *
   * group  group   1   mobilize
   * group  different 1   ignore
   * * ignore if notrust
   */
int
group_test(
  char  *grp,
  char  *ident
  )
{
  if (grp == NULL)
    return (0);

  if (strcmp(grp, sys_groupname) == 0)
    return (0);

  if (ident == NULL)
    return (1);

  if (strcmp(grp, ident) == 0)
    return (0);

  return (1);
}
#endif /* AUTOKEY */


#ifdef WORKER
void
pool_name_resolved(
  int     rescode,
  int     gai_errno,
  void *      context,
  const char *    name,
  const char *    service,
  const struct addrinfo * hints,
  const struct addrinfo * res
  )
{
  struct peer * pool; /* pool solicitor association */
  associd_t assoc;

  if (rescode) {
    msyslog(LOG_ERR,
      "error resolving pool %s: %s (%d)",
      name, gai_strerror(rescode), rescode);
    return;
  }

  assoc = (associd_t)(intptr_t)context;
  pool = findpeerbyassoc(assoc);
  if (NULL == pool) {
    msyslog(LOG_ERR,
      "Could not find assoc %u for pool DNS %s",
      assoc, name);
    return;
  }
  DPRINTF(1, ("pool DNS %s completed\n", name));
  pool->addrs = copy_addrinfo_list(res);
  pool->ai = pool->addrs;
  pool_xmit(pool);

}
#endif  /* WORKER */


#ifdef AUTOKEY
/*
 * key_expire - purge the key list
 */
void
key_expire(
  struct peer *peer /* peer structure pointer */
  )
{
  int i;

  if (peer->keylist != NULL) {
    for (i = 0; i <= peer->keynumber; i++)
      authtrust(peer->keylist[i], 0);
    free(peer->keylist);
    peer->keylist = NULL;
  }
  value_free(&peer->sndval);
  peer->keynumber = 0;
  peer->flags &= ~FLAG_ASSOC;
  DPRINTF(1, ("key_expire: at %lu associd %d\n", current_time,
        peer->associd));
}
#endif  /* AUTOKEY */


/*
 * local_refid(peer) - Check peer refid to avoid selecting peers
 *           currently synced to this ntpd.
 * Note that until 4.2.8p18 and 4.3.1XX ntpd calculated the IPv6
 * refid differently on different-endian systems.  It now calculates
 * the refid the same on both, the same way it did on little-endian
 * in the past.  On big-endian systems, ntpd also calculates a
 * byte-swapped version of each of its IPv6 local addresses' refids,
 * as endpt.old_refid and also detects a loop when seeing it.  This
 * ensures new BE ntpd will detect loops interoperating with older
 * BE ntpd, and keeps the more-common LE old ntpd code detecting
 * loops with IPv6 refids correctly.  Thanks to Hal Murray for
 * the byte-swapping idea.
 */
static int
local_refid(
  struct peer * p
  )
{
  endpt * unicast_ep;

  if (p->dstadr != NULL && !(INT_MCASTIF & p->dstadr->flags))
    unicast_ep = p->dstadr;
  else
    unicast_ep = findinterface(&p->srcadr);

  if (unicast_ep != NULL
      && (   p->refid == unicast_ep->addr_refid
#ifdef WORDS_BIGENDIAN
    || (   IS_IPV6(&unicast_ep->sin)
        && p->refid == unicast_ep->old_refid)
#endif
               )) {
    return TRUE;
  } else {
    return FALSE;
  }
}


/*
 * Determine if the peer is unfit for synchronization
 *
 * A peer is unfit for synchronization if
 * > TEST10 bad leap or stratum below floor or at or above ceiling
 * > TEST11 root distance exceeded for remote peer
 * > TEST12 a direct or indirect synchronization loop would form
 * > TEST13 unreachable or noselect
 */
int       /* FALSE if fit, TRUE if unfit */
peer_unfit(
  struct peer *peer /* peer structure pointer */
  )
{
  int rval = 0;

  /*
   * A stratum error occurs if (1) the server has never been
   * synchronized, (2) the server stratum is below the floor or
   * greater than or equal to the ceiling.
   */
  if (   peer->leap == LEAP_NOTINSYNC
      || peer->stratum < sys_floor
      || peer->stratum >= sys_ceiling) {
    rval |= TEST10;   /* bad synch or stratum */
  }

  /*
   * A distance error for a remote peer occurs if the root
   * distance is greater than or equal to the distance threshold
   * plus the increment due to one host poll interval.
   */
  if (   !(peer->flags & FLAG_REFCLOCK)
      && root_distance(peer) >= sys_maxdist
              + clock_phi * ULOGTOD(peer->hpoll)) {
    rval |= TEST11;   /* distance exceeded */
  }

  /*
   * A loop error occurs if the remote peer is synchronized to the
   * local peer or if the remote peer is synchronized to the same
   * server as the local peer but only if the remote peer is
   * neither a reference clock nor an orphan.
   */
  if (peer->stratum > 1 && local_refid(peer)) {
    rval |= TEST12;   /* synchronization loop */
  }

  /*
   * An unreachable error occurs if the server is unreachable or
   * the noselect bit is set.
   */
  if (!peer->reach || (peer->flags & FLAG_NOSELECT)) {
    rval |= TEST13;   /* unreachable */
  }

  peer->flash &= ~PEER_TEST_MASK;
  peer->flash |= rval;
  return (rval);
}


/*
 * Find the precision of this particular machine
 */
#define MINSTEP   20e-9  /* minimum clock increment (s) */
#define MAXSTEP   1  /* maximum clock increment (s) */
#define MINCHANGES  12  /* minimum number of step samples */
#define MAXLOOPS  ((int)(1. / MINSTEP))  /* avoid infinite loop */

/*
 * This routine measures the system precision defined as the minimum of
 * a sequence of differences between successive readings of the system
 * clock. However, if a difference is less than MINSTEP, the clock has
 * been read more than once during a clock tick and the difference is
 * ignored. We set MINSTEP greater than zero in case something happens
 * like a cache miss, and to tolerate underlying system clocks which
 * ensure each reading is strictly greater than prior readings while
 * using an underlying stepping (not interpolated) clock.
 *
 * sys_tick and sys_precision represent the time to read the clock for
 * systems with high-precision clocks, and the tick interval or step
 * size for lower-precision stepping clocks.
 *
 * This routine also measures the time to read the clock on stepping
 * system clocks by counting the number of readings between changes of
 * the underlying clock.  With either type of clock, the minimum time
 * to read the clock is saved as sys_fuzz, and used to ensure the
 * get_systime() readings always increase and are fuzzed below sys_fuzz.
 */
void
measure_precision(void)
{
  /*
   * With sys_fuzz set to zero, get_systime() fuzzing of low bits
   * is effectively disabled.  trunc_os_clock is FALSE to disable
   * get_ostime() simulation of a low-precision system clock.
   */
  set_sys_fuzz(0.);
  trunc_os_clock = FALSE;
  measured_tick = measure_tick_fuzz();
  set_sys_tick_precision(measured_tick);
  msyslog(LOG_INFO, "proto: precision = %.3f usec (%d)",
    sys_tick * 1e6, sys_precision);
  if (sys_fuzz < sys_tick) {
    msyslog(LOG_NOTICE, "proto: fuzz beneath %.3f usec",
      sys_fuzz * 1e6);
  }
}


/*
 * measure_tick_fuzz()
 *
 * measures the minimum time to read the clock (stored in sys_fuzz)
 * and returns the tick, the larger of the minimum increment observed
 * between successive clock readings and the time to read the clock.
 */
double
measure_tick_fuzz(void)
{
  l_fp  minstep;  /* MINSTEP as l_fp */
  l_fp  val;    /* current seconds fraction */
  l_fp  last;   /* last seconds fraction */
  l_fp  ldiff;    /* val - last */
  double  tick;   /* computed tick value */
  double  diff;
  long  repeats;
  long  max_repeats;
  int changes;
  int i;    /* log2 precision */

  tick = MAXSTEP;
  max_repeats = 0;
  repeats = 0;
  changes = 0;
  DTOLFP(MINSTEP, &minstep);
  get_systime(&last);
  for (i = 0; i < MAXLOOPS && changes < MINCHANGES; i++) {
    get_systime(&val);
    ldiff = val;
    L_SUB(&ldiff, &last);
    last = val;
    if (L_ISGT(&ldiff, &minstep)) {
      max_repeats = max(repeats, max_repeats);
      repeats = 0;
      changes++;
      LFPTOD(&ldiff, diff);
      tick = min(diff, tick);
    } else {
      repeats++;
    }
  }
  if (changes < MINCHANGES) {
    msyslog(LOG_ERR, "Fatal error: precision could not be measured (MINSTEP too large?)");
    exit(1);
  }

  if (0 == max_repeats) {
    set_sys_fuzz(tick);
  } else {
    set_sys_fuzz(tick / max_repeats);
  }

  return tick;
}


void
set_sys_tick_precision(
  double tick
  )
{
  int i;

  if (tick > 1.) {
    msyslog(LOG_ERR,
      "unsupported tick %.3f > 1s ignored", tick);
    return;
  }
  if (tick < measured_tick) {
    msyslog(LOG_ERR,
      "proto: tick %.3f less than measured tick %.3f, ignored",
      tick, measured_tick);
    return;
  } else if (tick > measured_tick) {
    trunc_os_clock = TRUE;
    msyslog(LOG_NOTICE,
      "proto: truncating system clock to multiples of %.9f",
      tick);
  }
  sys_tick = tick;

  /*
   * Find the nearest power of two.
   */
  for (i = 0; tick <= 1; i--)
    tick *= 2;
  if (tick - 1 > 1 - tick / 2)
    i++;

  sys_precision = (s_char)i;
}


/*
 * init_proto - initialize the protocol module's data
 */
void
init_proto(void)
{
  l_fp  dummy;
  int i;

  /*
   * Fill in the sys_* stuff.  Default is don't listen to
   * broadcasting, require authentication.
   */
  set_sys_leap(LEAP_NOTINSYNC);
  sys_stratum = STRATUM_UNSPEC;
  memcpy(&sys_refid, "INIT", 4);
  sys_peer = NULL;
  sys_rootdelay = 0;
  sys_rootdisp = 0;
  L_CLR(&sys_reftime);
  sys_jitter = 0;
  measure_precision();
  get_systime(&dummy);
  sys_survivors = 0;
  sys_manycastserver = 0;
  sys_bclient = 0;
  sys_mclient = 0;
  sys_bdelay = BDELAY_DEFAULT; /*[Bug 3031] delay cutoff */
  sys_authenticate = 1;
  sys_stattime = current_time;
  orphwait = current_time + sys_orphwait;
  proto_clr_stats();
  for (i = 0; i < MAX_TTL; ++i)
    sys_ttl[i] = (u_char)((i * 256) / MAX_TTL);
  sys_ttlmax = (MAX_TTL - 1);
  hardpps_enable = 0;
  stats_control = 1;
}


/*
 * proto_config - configure the protocol module
 */
void
proto_config(
  int item,
  u_long  value,
  double  dvalue,
  sockaddr_u *svalue
  )
{
  /*
   * Figure out what he wants to change, then do it
   */
  DPRINTF(2, ("proto_config: code %d value %lu dvalue %lf\n",
        item, value, dvalue));

  switch (item) {

  /*
   * enable and disable commands - arguments are Boolean.
   */
  case PROTO_AUTHENTICATE: /* authentication (auth) */
    sys_authenticate = value;
    break;

  case PROTO_BROADCLIENT: /* broadcast client (bclient) */
    sys_bclient = (int)value;
    if (!sys_bclient)
      io_unsetbclient();
    else
      io_setbclient();
    break;

#ifdef REFCLOCK
  case PROTO_CAL:   /* refclock calibrate (calibrate) */
    cal_enable = value;
    break;
#endif /* REFCLOCK */

  case PROTO_KERNEL: /* kernel discipline (kernel) */
    select_loop(value);
    break;

  case PROTO_MONITOR: /* monitoring (monitor) */
    if (value)
      mon_start(MON_ON);
    else {
      mon_stop(MON_ON);
      if (mon_enabled)
        msyslog(LOG_WARNING,
          "restrict: 'monitor' cannot be disabled while 'limited' is enabled");
    }
    break;

  case PROTO_NTP:   /* NTP discipline (ntp) */
    ntp_enable = value;
    break;

  case PROTO_MODE7: /* mode7 management (ntpdc) */
    ntp_mode7 = value;
    break;

  case PROTO_PPS:   /* PPS discipline (pps) */
    hardpps_enable = value;
    break;

  case PROTO_FILEGEN: /* statistics (stats) */
    stats_control = value;
    break;

  /*
   * tos command - arguments are double, sometimes cast to int
   */

  case PROTO_BCPOLLBSTEP: /* Broadcast Poll Backstep gate (bcpollbstep) */
    sys_bcpollbstep = (u_char)dvalue;
    break;

  case PROTO_BEACON: /* manycast beacon (beacon) */
    sys_beacon = (int)dvalue;
    break;

  case PROTO_BROADDELAY: /* default broadcast delay (bdelay) */
    sys_bdelay = (dvalue ? dvalue : BDELAY_DEFAULT);
    break;

  case PROTO_CEILING: /* stratum ceiling (ceiling) */
    sys_ceiling = (int)dvalue;
    break;

  case PROTO_COHORT: /* cohort switch (cohort) */
    sys_cohort = (int)dvalue;
    break;

  case PROTO_FLOOR: /* stratum floor (floor) */
    sys_floor = (int)dvalue;
    break;

  case PROTO_MAXCLOCK: /* maximum candidates (maxclock) */
    sys_maxclock = (int)dvalue;
    break;

  case PROTO_MAXDIST: /* select threshold (maxdist) */
    sys_maxdist = dvalue;
    break;

  case PROTO_CALLDELAY: /* modem call delay (mdelay) */
    break;    /* NOT USED */

  case PROTO_MINCLOCK: /* minimum candidates (minclock) */
    sys_minclock = (int)dvalue;
    break;

  case PROTO_MINDISP: /* minimum distance (mindist) */
    sys_mindisp = dvalue;
    break;

  case PROTO_MINSANE: /* minimum survivors (minsane) */
    sys_minsane = (int)dvalue;
    break;

  case PROTO_ORPHAN: /* orphan stratum (orphan) */
    sys_orphan = (int)dvalue;
    break;

  case PROTO_ORPHWAIT: /* orphan wait (orphwait) */
    orphwait -= sys_orphwait;
    sys_orphwait = (dvalue >= 1) ? (int)dvalue : NTP_ORPHWAIT;
    orphwait += sys_orphwait;
    break;

  /*
   * Miscellaneous commands
   */
  case PROTO_MULTICAST_ADD: /* add group address */
    if (svalue != NULL)
      io_multicast_add(svalue);
    sys_mclient = 1;
    break;

  case PROTO_MULTICAST_DEL: /* delete group address */
    if (svalue != NULL)
      io_multicast_del(svalue);
    break;

  /*
   * Peer_clear Early policy choices
   */

  case PROTO_PCEDIGEST: /* Digest */
    peer_clear_digest_early = value;
    break;

  /*
   * Unpeer Early policy choices
   */

  case PROTO_UECRYPTO: /* Crypto */
    unpeer_crypto_early = value;
    break;

  case PROTO_UECRYPTONAK: /* Crypto_NAK */
    unpeer_crypto_nak_early = value;
    break;

  case PROTO_UEDIGEST: /* Digest */
    unpeer_digest_early = value;
    break;

  default:
    msyslog(LOG_NOTICE,
        "proto: unsupported option %d", item);
  }
}


/*
 * proto_clr_stats - clear protocol stat counters
 */
void
proto_clr_stats(void)
{
  sys_stattime = current_time;
  sys_received = 0;
  sys_processed = 0;
  sys_newversion = 0;
  sys_oldversion = 0;
  sys_declined = 0;
  sys_restricted = 0;
  sys_badlength = 0;
  sys_badauth = 0;
  sys_limitrejected = 0;
  sys_kodsent = 0;
  sys_lamport = 0;
  sys_tsrounding = 0;
}

Coverage Report

Created: 2026-08-31 07:18