Is there a simple_switch_grpc switch port for P4Runtime PacketIn/PacketOut ?

[jafingerhut]

Is there some either hard-coded or configurable port number that one can send packets to in a P4 program, e.g. using the P4_16 v1model architecture, such that packets sent to that port become PacketIn messages to a P4Runtime client that is connected to simple_switch_grpc (when it is acting as a P4Runtime server) ?

Similarly for PacketOut messages, which I presume would be the same port number according to the P4 code.

[antoninbas]

Yes, it can be set with --cpu-port, which is a target-specific argument. Target-specific arguments are separated from standard bmv2 arguments by --.

simple_switch_grpc <normal args: interfaces, --skip-p4, ...> -- --cpu-port <xyz>

It defaults to 0xffffffff, as per the P4Runtime spec.

[jafingerhut]

Thanks, Antonin. Good to know.

With that default value, I guess the current v1model.p4 included with p4c has an egress_spec value that is only 9 bits wide, and thus cannot use the default cpu port value?

No big worries there, since we can explicitly assign it a value when starting simple_switch_grpc.

[antoninbas]

This is true, and when you write 0xffffffff to a 9-bit value you get 511, which simple_switch uses as the drop port, so it's a bit confusing.

For some resources:

• Stratum starts simple_switch_grpc with a CPU port value of 255: https://github.com/stratum/stratum/blob/master/tools/mininet/stratum.py#L59
• Of course, the same value is used for compiling the fabric.p4 program used by ONOS: https://github.com/opennetworkinglab/onos/blob/master/pipelines/fabric/impl/src/main/resources/bmv2-compile.sh#L5

[antoninbas]

Actually I misread the code: https://github.com/p4lang/behavioral-model/blob/master/targets/simple_switch_grpc/main.cpp#L78. If the option is not provided, cpu_port defaults to 0, which is not a valid CPU port number. Basically, if you do not provide the --cpu-port flag explicitly, no packets will ever be sent to the controller through the P4Runtime stream channel. I guess it is an acceptable behavior, although it would benefit from being documented somewhere.