egress_spec documentation

[AndreasVoellmy]

The P4 spec says the standard_metadata.egress_spec field is target specific. So it seems that the behavioral target should specify how to write to this field in order to accomplish various tasks, such as forwarding to a specific port or to a subset of ports.

[antoninbas]

This is not supported by the behavioral model. If you want to use the egress_spec to send to an arbitrary subset of ports, you need to modify the code.
What I suggest you do is use the clone action primitives instead. The supported ones are clone_ingress_pkt_to_egress and clone_egress_pkt_to_egress. Their behavior is described in the P4 spec, but I am not sure the behavior of clone_egress_pkt_to_egress (looking at it now, it seems to be cloning the packet which is submitted to the egress pipeline, not the packet after egress processing). If you choose to go that way, I can provide more details. However, it seems that the easiest thing for you to do may be to use multicast. The behavioral model includes a Packet Replication Engine, which is not too difficult to use.