Re: [PATCH bpf-next v3 4/6] selftests/bpf: refactor xdp_context_functional test and bpf program

[Willem de Bruijn]

Marcus Wichelmann wrote:
> Am 24.02.25 um 16:29 schrieb Marcus Wichelmann:
> > [...]
> > +	/* By default, Linux sends IPv6 multicast listener reports which
> > +	 * interfere with this test. Set the IFF_NOARP flag to ensure
> > +	 * silence on the interface.
> > +	 */
> > +	SYS(close, "ip link set dev " RX_NAME " arp off");
> >   	SYS(close, "ip link set dev " RX_NAME " up");
> 
> Hm, setting the NOARP flag seems to have not been sufficient to fix the flaky
> test:
> https://github.com/kernel-patches/bpf/actions/runs/13507111620/job/37739614229
> 
> I was not able to reproduce it locally or with my own CI runs unfortunately, but
> I'll try something else in the next patch version which should definitely stop
> IPv6 multicast listener report packets from messing with the tests.

You probably want to pass nodad to any ip -6 addr add.

This is a common option you'll find in tools/testing/selftests/net.

RFC 3810 section 5.2.13 says

"
   For stateless autoconfiguration, as defined in [RFC2462], a node is
   required to join several IPv6 multicast groups, in order to perform
   Duplicate Address Detection (DAD).
"