caching questions

Kevin Darcy kcd at daimlerchrysler.com
Tue Aug 1 23:26:23 UTC 2000


Read RFC 2308. The last field of the SOA record is no longer the minimum or
even the default TTL of all records in the zone. It is now interpreted as
the negative caching TTL. In later versions of BIND, the $TTL directive is
what controls the default TTL value, but it's not something you can discern
from a remote server via normal DNS queries, since it's only a master file
directive. And, besides, even $TTL is not a reliable guide to the TTL value
of a given RR, since it is always possible to override the default value in
the master file.

You can, however, peek at individual TTL values. Just run "dig" or (if you
must) "nslookup" in debug mode: this will show the TTL values of the
records. Chances are, each record which you keep having to re-fetch has a
low TTL value, probably because the domain owner is implementing some kind
of DNS-based failover and/or load-balancing. If this is the case, there is
not a lot you can do about it, short of becoming a slave to the zone and
arranging to receive NOTIFYs whenever the zone's serial number changes...


- Kevin

Charlie Romero wrote:

> Can anyone give me any pointers on why my BIND 8.2.2 doesn't seem to
> cache my requests?
>
> I can make a request for a domain and then go back 15 minutes later
> and make the same request and BIND has to do a lookup again.  I don't
> see where I can modify any configs that define this parameter.
>
> bmwcentral.com                SOA   86400   ns4.jumpinc.com
>                                              dnsmaster.jumpinc.com
>                                              Serial  2000072903
>                                              Refresh 10800 (3 hours)
>                                              Retry   3600 (60 minutes)
>                                              Expire  604800 (7 days)
>                                              Minimum TTL 86400 (24 hours)
>
> This is a snippet of my config. This is standard stuff as per
> O'Reilly's book so where can I change this caching value?
>
> I'm confused on why some domains seem to cache and some don't. When I
> look up their BIND config. info. it's the same as mine???
>
> TIA,
>
> Charlie






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