[P4-dev] Does simple router support user-defined p4 source file? If so, how to use it correctly?

Antonin Bas antonin at barefootnetworks.com
Thu Aug 10 14:45:55 EDT 2017


Hi,

For the vast majority of people, simple_switch is the only bmv2 target they
want to be using. You CAN write your own P4 programs for simple_router but
they MAY not be compatible with simple_switch. In other words, a P4 program
that runs correctly on simple_router may not run correctly on
simple_switch, and vice-versa.
simple_router should be ignored by most people. It is just meant as an
example to demonstrate how bmv2 can be used to implement different switch
architectures. P4 programs written for a given architecture are generally
not compatible with other architectures. I would recommend running the
P4_16 specification (
https://p4lang.github.io/p4-spec/docs/P4-16-v1.0.0-spec.html) if you are
not familiar with the notion of architecture.

About your specific problem:
simple_router was updated in bmv2 version 1.6 to be more compatible with
simple_switch (
https://github.com/p4lang/behavioral-model/commit/2106979fb700792dca1a3aed7351899acae7a696),
since the differences between the 2 were confusing for a lot of people. If
you update to a more recent version (1.5 is pretty old), you may be able to
run your forward.p4 program on both targets. However, I would not recommend
it, stick to simple_switch unless you have a very good reason to use
simple_router.

Thanks,

Antonin

On Wed, Aug 9, 2017 at 10:13 PM, Wu, Xiaoban <Xiaoban_Wu at student.uml.edu>
wrote:

> Hi,
>
>
> I am trying to run the behavioral model simple router https://github.com/
> p4lang/behavioral-model/tree/master/targets/simple_router, it is of
> version 1.5.0, but I am facing an unknown issue.
>
>
> Traffic flow: eth1 at machine1-->eth1 at machine2-->eth2 at machine2-->eth2@
> machine1
>
>
> The simple router is running on machine2, with "sudo ./simple_router -i
> 0 at eth1 -i 1 at eth2 forward.json", where the forward.json is generated by "python
> /p4c-bm/p4c_bm/__main__.py --json forward.json forward.p4". The p4c-bm is
> also of version 1.5.0. The forward.p4 is in the attached.
>
>
> After the simple router is running, I open another terminal on
> machine2 and run "./runtime_CLI < commands.txt", where the commands.txt
> in the attached.
>
>
> Then I use scapy on machine1 to send packet out of interface eth1,
>
> p = Ether(dst="aa:bb:cc:dd:ee:ff", src="aa:bb:cc:dd:ee:ff") /
> IP(src="10.0.1.1", dst="10.0.0.1") / TCP() / "aaaaaaaaaaaaaaaaaaa"
>
> sendp(p, iface = "eth1")
>
>
> Then on machine1, I use "tcpdump -i eth2" to monitor the traffic. However,
> I see nothing.
>
>
> Some debugging info,
>
> (1) I have tested the attached forward.p4 and commands.txt in the
> simple_switch, it works just fine.
>
> (2)In the function "transmit_thread" of the simple_router.cpp
>
>     1.The "packet->get_egress_port()" always return 0.
>
>     2. If I manually change it with 1, then "transmit_fn(1, packet->data(),
> packet->get_data_size())" just works fine, since I can see the traffic with "tcpdump
> -i eth2" on machine2. This means all the connections are good.
>
>
> Hence I am wondering if some issues are in the ingress match-action
> pipeline, but I could not find a clue. Hence I am wondering if the simple
> router support user-defined p4 source file?
>
>
> Can anybody please explain what are the main differences between
> simple_router and simple_switch? I could not understand why forward.p4
> works fine in simple_switch but not the simple_router.
>
>
> Thank you very for your help.
>
>
> Warm regards,
>
> Xiaoban
>
>
>
> _______________________________________________
> P4-dev mailing list
> P4-dev at lists.p4.org
> http://lists.p4.org/mailman/listinfo/p4-dev_lists.p4.org
>



-- 
Antonin
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