[Systems] IPv6 for buildslave-fedora-11-64bit.sugarlabs.org

[Bernie Innocenti]

I figured out what was wrong with routing of IPv6 traffic *to* the
buildslaves, specifically buildslave-fedora-11-64bit.sugarlabs.org.

The problem was that, oddly, bender's link local address on the
interface virbr0 did not match the mac address of the interface.  This
would cause the IPv6 neighbor resolution protocol to fail on the virtual
LAN.

Restarting virbr0 is somewhat tricky because it is managed by libvirtd,
so instead I fixed the link local address manually:

bender:# ip -6  addr add fe80::9827:56ff:feb1:e7b1/64 dev virbr0
bender:# ip -6  addr add fe80::081c:edff:fedf:8517/64 dev virbr0

Even more strangely, IPv6 traffic originating from the buildslave was
being properly forwarded out, and replies back in, as if it were taking
a different route.

Admittedly, the ipv6 situation on bender is quite tricky because it
interacts in complex ways with all those virtual bridges used by
libvirtd.  We can't directly use br0 because it bridges to eth0 and we
don't want radvd router advertisements to percolate to Develer's LAN.

We did this mess because it was the best we could get.  Now we seem to
have many more hosting options, but for now I'd leave them the
buildslaves where they are because they suck a lot of CPU time and may
slow down other critical infrastructure.  Perhaps we'll reconsider when
we've grow more confidence in KVM resource allocation and
prioritization.

-- 
   // Bernie Innocenti - http://codewiz.org/
 \X/  Sugar Labs       - http://sugarlabs.org/