DNS issues

[Christopher Beland]

I'll throw out some ideas, though others may have more experience with
this code.  Anne, I'm not sure you are experiencing the same problem, if
a reboot fixes it for you but not for Richard.  Are your other symptoms
similar?

On Thu, 2009-04-23 at 00:56 +0200, Richard Körber wrote:
> When I use Firefox, Thunderbird, wget, whatever, I always get an error message 
> that the domain name could not be resolved. Anyhow the network is up, DNS 
> server IPs are set correctly and I can even use dig and ping to successfully 
> resolve domain names. When I enter a plain IP address at Firefox, it also 
> fetches the page correctly.
> 
> Configuration files seem to be correct, there are no hints in the log files, I 
> even checked that there is no proxy set, but I found nothing. I created a 
> clean user to make sure there is no configuration messed up. I rebooted the 
> system, but still got that issue. I'm totally clueless now...

Could your applications be somehow caching bad lookups or bad network
connections?  It might be worthwhile to carefully document the sequence
of events (what you start when) after reboot, and see if the order or
timing makes any difference.  Does restarting e.g. Firefox help?

Good DNS lookups can also be cached locally, so it is easy to be fooled
into thinking DNS is working when it is really not.  (You can work
around that by thinking up a truly new domain name for each test.)

Different programs can certainly use different DNS resolution
mechanisms, so it could be that one of them is somehow malfunctioning or
reacting badly to external intermittent DNS failure.  If you have
another machine you can test on the same subnet, that can help rule
external DNS hiccups in or out.  You can also sniff your own network
traffic using wireshark, to see what's going on behind the scenes, if
necessary.

You might also sanity check your /etc/hosts and /etc/resolv.conf.  There
are a few Bugzilla reports related to having unusually large lists or
using NFS, but I assume you don't have either.

If none of the below bugs match your symptoms, I would recommend filing
a new bug with as much diagnostic detail as you can document.

https://bugzilla.redhat.com/show_bug.cgi?id=478760 
Host lookup fails after suspend

https://bugzilla.redhat.com/show_bug.cgi?id=473785
NetworkManager generates useless /etc/resolv.conf

https://bugzilla.redhat.com/show_bug.cgi?id=489371
removal of fedora-lsb irrevocably causes hostname resolution failure for
a lot of tools

Good luck!

Beland