[CentOS] named server
Steve Huff
shuff at vecna.org
Wed May 18 13:19:07 UTC 2005
On May 18, 2005, at 8:50 AM, Ceg Ryan wrote:
> What is the difference between use forward only+forwarders and
> directly set the nameserver inside resolv.conf ?
resolv.conf is used by the system's name resolution service. BIND
doesn't care about the contents of resolv.conf, as it has its own
mechanism for resolving names (given that that is its primary
function).
here are several scenarios that may illustrate the difference.
scenario 1 - you have set up a forwarding-only nameserver:
other machines can connect to your machine and ask it to resolve names
for them. it will send those queries out to its forwarder, and when
the responses come back, it will relay those responses to the machines
that queried it. (incidentally, this machine's resolv.conf should be
set up so that it queries itself for name resolution.)
scenario 2 - you have configured an external nameserver in resolv.conf,
and you're not running BIND:
your machine will not respond to name service queries; however, it will
still be able to resolve names itself.
scenario 3 - you have set up a forwarding-only nameserver (or any other
instance of BIND), and you've also configured an external nameserver in
resolv.conf:
this scenario is somewhat of a landmine. if other machines are
depending on your machine for name resolution, but your machine uses
the system's name resolution service to resolve names, then the
following conversation can occur when BIND breaks:
User: Hey, I can't resolve www.google.com! Your nameserver isn't
responding!
You : Hmm, I just typed "host www.google.com", and it worked fine for
me.
in a nutshell: resolv.conf and BIND have very little connection. if
your nameserver is using a name resolution service other than itself,
it can be easy to overlook DNS problems. if you're running a
nameserver, its resolv.conf should point to itself (unless you have
some special circumstance that requires otherwise).
does this make sense?
-steve
---
If this were played upon a stage now, I could condemn it as an
improbable fiction. - Fabian, Twelfth Night, III,v
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