FreeBSD does not reply to IPv6 Neighbor Solicitations

[John-Mark Gurney]

Andrey V. Elsukov wrote this message on Wed, Jan 13, 2021 at 11:42 +0300:
> On 13.01.2021 00:37, John-Mark Gurney wrote:
> >> when this will happen again, it would be nice to make sure that NS
> >> packets hit the IP stack. E.g. with attached dtrace script.
> > 
> > Ok, I ran the dtrace script when I reproduced the problem, and it did
> > not produce any output.
> > 
> > These are effectively what the script does:
> > 9) configure inet6 addresses on ure and bge (duplicating the addresses
> >    already configured)
> 
> Does it mean that you just reconfigure address without removing it? It
> looks like the problem, that was discussed here
> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=233535

Yeah, I guess it is the same...

> > bge0:
> >         inet6 fe80::12e7:c6ff:fexx:xxxx%bge0 scopeid 0x2
> >         mldv2 flags=2<USEALLOW> rv 2 qi 125 qri 10 uri 3
> >                 group ff01::1%bge0 scopeid 0x2 mode exclude
> >                         mcast-macaddr 33:33:00:00:00:01
> >                 group ff02::1%bge0 scopeid 0x2 mode exclude
> >                         mcast-macaddr 33:33:00:00:00:01
> >                 group ff02::1:ffxx:xxxx%bge0 scopeid 0x2 mode exclude
> >                         mcast-macaddr 33:33:ff:xx:xx:xx
> > 
> > so, I made things works, and ran ifmcstat again, and this time it has
> > an additional group in the output:
> > [...]
> > bge0:
> >         inet6 fe80::12e7:c6ff:fexx:xxxx%bge0 scopeid 0x2
> >         mldv2 flags=2<USEALLOW> rv 2 qi 125 qri 10 uri 3
> >                 group ff02::1:ff00:c43c%bge0 scopeid 0x2 mode exclude
> >                         mcast-macaddr 33:33:ff:00:c4:3c
> >                 group ff01::1%bge0 scopeid 0x2 mode exclude
> >                         mcast-macaddr 33:33:00:00:00:01
> >                 group ff02::1%bge0 scopeid 0x2 mode exclude
> >                         mcast-macaddr 33:33:00:00:00:01
> >                 group ff02::1:ffxx:xxxx%bge0 scopeid 0x2 mode exclude
> >                         mcast-macaddr 33:33:ff:xx:xx:xx
> > 
> > and the tcpdump output:
> > 21:10:53.938655 IP6 fc00:b5d:41c:7e37::7e37 > ff02::1:ff00:c43c: ICMP6, neighbor solicitation, who has fc00:b5d:41c:7e37::c43c, length 32
> > 21:10:55.001428 IP6 fc00:b5d:41c:7e37::7e37 > ff02::1:ff00:c43c: ICMP6, neighbor solicitation, who has fc00:b5d:41c:7e37::c43c, length 32
> 
> Since ff02::1:ff00:c43c%bge0 is not configured in first case, IP stack
> just ignores NS messages and they don't hit ND6 code.
> 
> In the PR 233535 the problem was reproducible with MLDv1, so if you
> disable MLDv2 will it work (to reduce possible scope of problematic code)?
> 
> net.inet6.mld.v2enable=0

I just tested this, and it does not fix the problem for me.

Do I need to reboot or something?  If I set it to 0, the bug
still appears, and also the ifmcstat has the line:
mldv2 flags=2<USEALLOW> rv 2 qi 125 qri 10 uri 3

is there something else that needs to be done to disable mldv2?

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."