[dns-operations] BIND forwarders question

Michael Monnerie michael.monnerie at is.it-management.at
Wed Jul 29 22:31:03 UTC 2009

On Mittwoch 29 Juli 2009 Tom Daly wrote:
> I'm not quite sure I understand your question, but it sounds like
> your goal is to keep your caches as hot as possible.

Our spamfilters do a lot of lookups. Having both primary and secondary 
MX servers on both sites, I expect to have similiar lookups, e.g. for 
RBLs, on both DNS servers. In order to speedup the lookups, I want that 
DNS1 first asks DNS2 if he knows the answer already, and if not lookup 
the usual way. That's the simple forwarding.
But I also want DNS2 to lookup DNS1, as it could be that DNS1 already 
knows a record DNS2 doesn't know. That's also simple forwarding, just 
from the other side.

The question is: When both servers have the other as a forwarder, will 
there be a mess? I can imagine the following:
DNS1 asks DNS2: tell me "A www.orf.at"
DNS2 doesn't know, so he asks his forwarder, DNS1
DNS1 doesn't know, so asks DNS2, and so on.

Or is BIND clever enough to just:
DNS1 asks DNS2: tell me "A www.orf.at"
DNS2 says "no".
DNS1 lookups the usual hierarchy way.

mfg zmi
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