Re: ipv6 gateway on different subnet

[Christof Meerwald <cmeerw%cmeerw.org@localhost>]

On Wed, Jan 22, 2025 at 07:30:43AM -0500, Greg Troxel wrote:
> Christof Meerwald <cmeerw%cmeerw.org@localhost> writes:
> 
> > On Tue, Jan 21, 2025 at 08:31:58PM -0600, Peter Miller wrote:
> 
> > And comparing the neighbor advertisements:
> >
> > Debian
> >> 10:33:23.197053 00:16:3e:d7:cf:50 > d8:67:d9:58:3d:1b, ethertype
> >> IPv6 (0x86dd), length 86: (hlim 255, next-header ICMPv6 (58) payload
> >> length: 32) 2602:fed2:7116:d82c::5 > fe80::da67:d9ff:fe58:3d1b:
> >> [icmp6 sum ok] ICMP6, neighbor advertisement, length 32, tgt is
> >> 2602:fed2:7116:d82c::5, Flags [solicited, override]
> >
> > NetBSD
> >> 05:01:13.467620 00:16:3e:d7:cf:50 > d8:67:d9:58:3d:1b, ethertype
> >> IPv6 (0x86dd), length 86: (hlim 255, next-header ICMPv6 (58) payload
> >> length: 32) fe80::216:3eff:fed7:cf50 > fe80::da67:d9ff:fe58:3d1b:
> >> [icmp6 sum ok] ICMP6, neighbor advertisement, length 32, tgt is
> >> 2602:fed2:7116:d82c::6, Flags [solicited, override]
> >
> > I am seeing this difference:
> >
> > 2602:fed2:7116:d82c::5 > fe80::da67:d9ff:fe58:3d1b
> > vs.
> > fe80::216:3eff:fed7:cf50 > fe80::da67:d9ff:fe58:3d1b
> 
> See netinet6/nd6_nbr.c and netinet6/nd6_rtr.c which might be
> enlightening.

Sorry, but not really sure what you are trying to get at.

We have two cases where the VPS receives a neighbor solicitation, and
responds with a neighbor advertisement. There is a difference in the
neighbor advertisement being sent, and only in the first case the VPS
then receives a ping request, whereas in the second case no ping
request is forwarded, but another neighbor solicitation.

To me that means that something doesn't like the neighbor
advertisement being sent in the second case (note, I am not saying
that one of these neighbor advertisements is incorrect, I am only
saying that something doesn't like that neighbor advertisement - maybe
because of a misconfiguration in the network outside of the VPS).


Christof

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