[PLUG] Spotty DNS Resolution

[Ian Burrell]

On 10/14/06, Daniel Hedlund <daniel at digitree.org> wrote:
> Aaron Ten Clay wrote:
> > This is likely your problem. Most DNS servers these days, it seems, give up
> > after about 2000ms if they can't get the info you want. Especially when just
> > doing forwards. The DNS scheme is that you have multiple servers so if one is
> > down/unreachable you can keep trying all the servers for a zone. Since most
> > software doesn't seem to do that anymore, your listing a non-DNS server as a
> > server for your domain is likely the cause of the problem. Resolvers are
> > probably trying that one first, and giving up.
>
> Timeouts could be a very likely issue and may be my main problem.  There
> is always a possibility on the server that the DNS response might lag by
> a couple of seconds.  This is because I don't have very much memory on
> the machine and some other services on the box might cause BIND to swap
> out of memory at the wrong time.  Good suggestion; not much I can do
> about it besides get more memory or move it to another box (ie. OpenWRT
> router or something).
>

Your main problem is that you listed a non-nameserver as nameserver
for your domain.  Resolvers will randomly choose one of the
nameservers listed for the domain.  They do not try the first and
fallback to the second. If they choose the non-responsive one, they
will wait for the timeout (I think it is 2 sec) until they try the
other one.  Resolvers may be smart enough to cache the fact that one
of the nameservers was non-responsive and use the other one for later
queries.  But the first query for the domain has a 50% chance of being
really slow.

 - Ian