[f-nsp] Problem with IPv6 anycast

[Wido den Hollander]

Hi Philipp,

Well, In my setup it is not working.

I have a /64, where ::1 is my first router, ::2 my second and ::3 a
anycast address.

I'm trying to use ::3 as my default gateway, so that when one of the
RX-8's goes down, my Linux machines (2.6.32 kernel) still have
connectivity.

When analyzing the traffic with Wireshark I see that the RX-8 responds
to the ND with it's unicast address, the ::2 in this case.

In the original thread I saw the same behaviour:

https://puck.nether.net/pipermail/foundry-nsp/2010-September/002637.html

Quote:
"Now when I try to ping that address from a client within the network
2001:db8:f1:c::/64, I get a neighbour advertisement from the MLX announcing
it's UNIcast address:"

"This causes the asking client to create an entry in its neighbour cache
for the routers unicast address, but not realising, that this was the
answer to its question, hence it keeps on sending solicitation messages for
the anycast address.
In my understanding the neighbour advertisement should have the unicast
address as source, but should announce the anycast address."

That's the issue I'm seeing here too.

Strange thing is, a Windows 2k3 machine works fine with the anycast address as it's default gateway.

Regards,

Wido den Hollander

On Tue, 2010-11-30 at 14:49 +0100, Philipp Geschke wrote:
> Hi,
> 
> On Tue, 30 Nov 2010 14:15:20 +0100, Wido den Hollander <wido at widodh.nl>
> wrote:
> > One of our network administrators found out that anycast might be a
> > solution, well, it partially is. A Windows machine does work, but a
> > Linux machine won't accept the anycast address as a gateway (Or even
> > ping it.)
> 
> A current Linux should accept the anycast address without any issues. Did
> you have a look at the ICMP packets that get exchanged during Neighbour
> Solicitation?
> All Brocade devices I have under my administration do not handle IPv6
> Neighbour Discorvery correctly (sad...), so maybe the RX8 is also buggy.
> 
> > Has anybody made any progress with using anycast as a gateway for a
> > Linux machine? Kernel tweaks / settings which make it work?
> 
> If you have a gateway that handles ND correctly Linux accepts that just
> fine, so I don't think that you need any Kernel tweaks.
> 
> 
> Regards,
> Philipp
>