ports

This field is used along with internal load balancing and network load balancer when the forwarding rule references a backend service and when protocol is not L3_DEFAULT. A single port or a comma separated list of ports can be configured. Only packets addressed to these ports will be forwarded to the backends configured with this forwarding rule. You can only use one of ports and portRange, or allPorts. The three are mutually exclusive. You may specify a maximum of up to 5 ports, which can be non-contiguous.