[c-nsp] MLD snooping breaks IPv6 neighbor discovery

[Alexander Gall]

On Mon, 28 Aug 2006 14:33:14 +0200, Bernhard Schmidt <berni at birkenwald.de> said:

> If I disable MLD snooping by adding "no ipv6 mld snooping" either on
> SVI level or globally neighbor discovery for the loadbalancer works, but
> now router advertisement packets are not sent anymore and all boxes in
> this VLAN/all VLANs lose their defaultroute. This problem is
> reproducible, when I enable MLD snooping RAs are sent but the ND to the
> loadbalancer fail, if I disable MLD snooping ND works but RA packets are
> not sent anymore.

Are you sure the RA packets are not sent at all?  I know that at least
12.2(18)SXD1 had a bug that caused *all* traffic sent to the ALL-NODES
address FF02::1 to be blackholed when MLD snooping was disabled.  You
can verify this by pinging FF02::1.  The bug came in various guises,
sometimes breaking FF02::1 on SVIs, sometimes even on p2p links.  It
drove me nuts.  I sent a bug report in late 2004, but I don't think it
was ever officially acknowledged, at least I don't find any reference
in my archive.  It's very well possible that it is still present in
SXD7.  I do remember seeing it with some later SXD images.  I haven't
seen it with SXF so far and keep my fingers crossed.  So, like Gert
suggested, upgrading is probably your only chance.

I never saw the symptoms you report with regard to the solicited-node
addresses.  But nothing really surprises me with MLD snooping on this
platform.

--
Alex