Query on DNS Bind cache setting

[Sabat Gangadhar]

Hi All,

In DNS bind, two clean the cache, 2 types of cache setting are
there. One is at zone level by default 24hr, and another at server level
such as max-cache-ttl, max-ncache-ttl and cleaning-interval.
Which level setting is effective if both options are set?
Thanks in advance.

Regards,
Gangadhar

[David Botham]

bind-use...@isc.org wrote on 05/18/2005 05:34:50 AM:
> Hi All,
>
> In DNS bind, two clean the cache, 2 types of cache setting are
> there. One is at zone level by default 24hr, and another at server level
> such as max-cache-ttl, max-ncache-ttl and cleaning-interval.
> Which level setting is effective if both options are set?

I think you may be approaching caching from the wrong perspective.

Zone administrators set the TTL on RR's in the zones that they control.
They also set a negative caching TTL for the zone. The negative caching
TTL is used to tell remote name servers how long to *not* come back and
ask about a RR that does not exist.

Now, name server administrators can tell their name server processes to
put bounds on the TTL's set by Zone Administrators. You have mentioned
about the named.conf options used for this purpose.

hth,

Dave...

[Barry Margolin]

In article <d6f3t5$2pnn$1...@sf1.isc.org>,
"Sabat Gangadhar" <sgang...@novell.com> wrote:

> Hi All,
>
> In DNS bind, two clean the cache, 2 types of cache setting are
> there. One is at zone level by default 24hr, and another at server level

No, it's actually at the record level, but when configuring the
authoritative server you can set per-zone defaults. The only zone-level
TTL is the negative cache TTL, which comes from the zone's SOA record.

> such as max-cache-ttl, max-ncache-ttl and cleaning-interval.
> Which level setting is effective if both options are set?
> Thanks in advance.

The max-XXX-ttl server settings are just a maximum. A record's TTL will
be used unless it's longer than the max-XXX-ttl, in which case the
latter will be used instead.

Cleaning-interval has no effect on any of this. It just specifies how
often named will search through the cache looking for entries that have
timed out. But if a record is looked up and it has timed out, it will
be deleted immediate even if the cleaning interval hasn't run out.

--
Barry Margolin, bar...@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***