Re: ipv6 gateway on different subnet

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

On Sat, Jan 18, 2025 at 12:27:54PM -0600, Peter Miller wrote:
> On Sat, Jan 18, 2025 at 11:51 AM Christof Meerwald <cmeerw%cmeerw.org@localhost> wrote:
> 
> > > on the other address with 100% packet loss
> > > ping6 -S 2602:fed2:7116:d82c::2 google.com
> > >
> > > 10:37:17.595359 IP6 fe80::da67:d9ff:fe58:3d1b > ff02::1:ff00:0: ICMP6,
> > > neighbor solicitation, who has 2604:f440:3:17::, length 32
> > > 10:37:17.851412 IP6 2602:fed2:7116:d82c::2 > 2607:f8b0:4023:1002::71:
> > > ICMP6, echo request, seq 0, length 16
> >
> > The interesting thing here is that there is neither an echo reply nor
> > a neighbor solicitation from the router.
> 
> It's possible I just didn't copy enough of the output. I wasn't sure
> what I was looking for.
> 
> > To me it seems your VPS acts as expected, but there must be something
> > weird going on in that network.
> >
> > Have you actually tested that it works when running Linux? (I am
> > assuming your provider will just blame it on your NetBSD configuration
> > otherwise) Maybe you can just temporarily boot into something like an
> > Alpine Linux live image via netboot.xzy to test?
> 
> I have tested with debian and everything worked fine. I kept
> thinking there's something wrong with my configs, but
> maybe not. I signed up with a different provider and everything
> works fine there, so I'm starting to think this provider has
> a network problem.
> 
> I will put linux back on and tcpdump with that. Is there
> any other info I should get?

The test I would run would be (for both NetBSD and Linux):

  - use tcpdump to dump icmp6 packets to a file (so they can be
    analysed later byte by byte)

  - add a new IPv6 alias (maybe even use a completely new random IPv6
    address to make sure it definitely isn't in some cache)

  - ping that new IPv6 address from the outside (one or two pings
    should be fine)

  - compare the relevant tcpdump output byte by byte (or at least use
    -ev with tcpdump) for Linux vs. NetBSD (there should be a neighbor
    solicitation from the router in both cases and a neighbor
    advertisement from the VPS - there must be some difference
    somewhere)


Christof

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