FreeBSD does not reply to IPv6 Neighbor Solicitations

[Andrey V. Elsukov]

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


> 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

-- 
WBR, Andrey V. Elsukov