[f-nsp] Problem with IPv6 anycast

[Philipp Geschke]

Hello,

On Tue, 30 Nov 2010 15:36:20 +0100, Wido den Hollander <wido at widodh.nl>
wrote:
> 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.

Depending on what you mean this is a wrong behaviour.
The router MUST respond with it's UNIcast address as source address (as
anycast addresses must not be the source address of an IPv6 packet, see
RFC
3513 section 2.6) but the Target field of the ICMP message MUST be the
Target field of the Neighbor solicitation that prompted the advertisement
(See RFC2461 Section 4.4). If you specified the anycast address as the
gateway this should be the anycast address.

So a correct Neighbor Solicitation for an IPv6 anycast address with a
Linux client that has ::10 would basically look like this:

Client: Source ::10, Target field ::3
Router: Source ::2, Target field ::3

This would work with Linux, at least tested with Debian.

What NI MLX does is:

Client: Source ::10, Target field ::3
Router: Source ::2, Target field ::2

This will not work and is a bug. I have opened a bug report with Brocade
and it's a confirmed defect.

If you want, send me a pcap or tcpdump output of your Neighbor
Solicitation and I will tell you what the RX does wrong.

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

I have no working knowledge of IPv6 behaviour of Windows, so I really
can't tell you why it is working. :(


Regards,
Philipp