DNS newbie question

[David Botham]

bind-users-bounce at isc.org wrote on 05/11/2005 12:02:09 PM:
> 
> Chris wrote:
> > <iceman80231 at yahoo.com> wrote in message
> news:d5qruk$nck$1 at sf1.isc.org...
> > > Hello everyone,
> > >
> > > I have two DNS servers external to my firewall, running BIND 9.2.2.
> > > Any hostnames that they cannot resolve are being forwarded to my
> ISP's
> > > DNS servers.  My servers have zone data files and I wanted to see
> if
> > > caching was enabled and, if not, to configure BIND so that it is
> > > enabled.  After endless searching on Google, I have heard very bad
> > > things about nscd and BIND not working well together so I want to
> > > reconfigure BIND to continue to resolve hostnames with its own zone
> > > data files, forward requests it cannot handle to the ISP's DNS
> servers,
> > > AND cache the latter results to cut down on requests made to the
> ISP's
> > > DNS servers.  Many thanks.
> > >
> > >
> >
> > Why use forwarders at all. You have a fully capable DNS server so
> don't send
> > recursive queries to your ISP's servers. Let yours do the leg work.
> >
> > Chris.
> 
> Chris, thanks for the advice.  At the same time, at least for my
> knowledge, I am very curious about the following:
> 
> a)The earlier respondent said that BIND caches by default.  How do we
> know this, i.e. is there a configuration setting/switch in which this
> feature is turned on/off?  If so, what is it and in what file is it
> stored?

We know this (that BIND caches by default) because we read the 
Administrators Reference Manual (ARM) that comes with BIND.  You can get 
it at www.isc.org.  If you are interested in tuning how the cache is 
handled, search for the word "cache" in Chapter 6 of the ARM.

> 
> b)Is there a way to see the cache data?  How is it stored, e.g. is it

Yes.  To see the cache use:

"rndc dumpdb"


The cache will be dumped to the file specified by the "dump-file" option 
in named.conf (see the ARM, chapter 6).

> written to a file whose contents are wiped based upon the TTL specified
> on the DNS server in question or is it memory-resident and wiped out
> after a systemm reboot?

Yes, it is stored in RAM and wiped when:
- The system is reboot
- The name server process is stopped
- You flush the cache with "rndc flush [view]"

Yes, as the TTL on RR's in the cache expire, those RR's are removed.


Perhaps you should invest a little time into reading the ARM.  You have 
some great questions.  Most of the answers are in the docs...


hth,


Dave...


> 
> Thanks.
> 
>