This program illustrates as simply as possible how to use the resubmit() primitive. This primitive is used to make a packet go twice through the ingress pipeline. For more information, please refer to the P4 specification.

The P4 program only consists of an ingress pipeline, with 2 tables: t_ingress_1 and t_ingress_2. When a packet enters the pipeline, the following happens (based on the P4 program and the [commands.txt] (commands.txt) files):

the packet hits table_ingress_1 and the egress port is set to 2.
the packet hits table_ingress_2, mymeta.f1 is set to 1 and the resubmit() primitive is called. Because mymeta is resubmitted along with the packet, mymeta.f1 will now be equal to 1 for the second pass.
the packet hits table_ingress_1, this time the egress port is set to 3.
the packet hits table_ingress_2 which is a no-op.

Running the demo

We provide a small demo to let you test the program. It consists of the following scripts, which you need to run one after the other, in 2 separate terminals:

[run_switch.sh] (run_switch.sh): compile the P4 program and starts the switch, also configures the data plane by running the CLI [commands] (commands.txt).
[send_and_receive.py] (send_and_receive.py): send a packet on port 0 (veth1), wait for the forwarded packet on port 3 (veth7).