Re: VRF and UDP broadcast frames

[David Ahern <dsahern@kernel.org>]

[ cc'ed Ido ]

On 8/22/25 1:16 PM, Ben Greear wrote:
> Hello,
> 
> Assume I have a network interface assigned to a VRF (wifi AP interface
> is what I'm testing now).
> I would like to have it be able to send and receive UDP broadcast
> frames.  I am binding the socket
> to the AP netdev with SO_BINDTODEVICE.  From what I can tell, the socket
> at least cannot receive
> UDP broadcasts sent to it.  I do see the broadcast arriving on the AP
> interface if I run tshark.
> 
> Is there any particular issue with UDP broadcast sockets in VRF?  Do I
> have to instead
> bind to the vrf netdev instead of the ap netdev?

I am not aware of any issues with VRF and broadcast, but the fcnal-test
suite (covers permutations across the uapi) is lacking broadcast tests.

As I recall you tend to run relatively new kernels, so either device
should work.

I use the fib:* tracepoints as a start point for debugging cases like this.

> 
> And always possible I doing something wrong in my socket code, my
> current test setup
> is quite complicated.
> 
> Thanks,
> Ben
>