[Pkg-utopia-maintainers] Bug#414569: Confusion

[Mike Crowe]

I think that there are separate problems here that are getting
intermingled in this bug report and others
(e.g. https://bugs.launchpad.net/ubuntu/+source/avahi/+bug/94940 )

The particular variant that the original bug reporter appears to be
suffering from (and I happen to also be suffering from) is that even
if you have a DNS server that authoritatively claims that no reverse
mapping is available for a particular IP address mdns4 still times out
trying to find a name via Multicast DNS. It does this even if the IP
address is not even on the local network (I can imagine a situation
where this might actually be useful but I doubt it occurs in
practice.)

I was able to stop reverse lookups gettings as far as mdns4 in this
situation by changing /etc/nsswitch.conf to say:

 hosts: files mdns4_minimal [NOTFOUND=return] dns [NOTFOUND=return] mdns4

The idea is that if a definitive failure is returned by DNS then it
won't go on to try Multicast DNS. If DNS times out or is unconfigured
then Multicast DNS is tried (and may then go on to time out.)

This works for me (on lenny) in avoiding the timeout when the DNS
server responds with NXDOMAIN. In theory it should also support the
AutoIP ad-hoc network with no DNS server situation too but I can't
easily test that. It does break when there is a DNS server that
doesn't know about every host on the network but only for reverse
mapping so it may not be the end of the world.

I agree with Martin in message #29 and Trent in message #34 that the
only decent way to solve this is to rely on avahi to cache mDNS
information as hosts come and go and rely on that cache only for
reverse lookups. The answer will then always be (almost) instant.

Mike.