mutual forwarders in ISC BIND

Damien Fleuriot ml at
Wed Dec 28 09:57:34 UTC 2011

On 12/28/11 8:54 AM, Victor Sudakov wrote:
> Colleagues,
> This question is not directly related to FreeBSD, but perhaps some
> network administrators reading this list know the answer.
> Can I setup several ISC BIND servers to be each other's mutual forwarders?
> Will it work or create an endless loop of DNS queries?
> I have customers using several DNS servers as recursive resolvers. The
> usage pattern is pretty much equal between all the servers. What I
> want is create a cache common to all the recursive servers to reduce
> traffic and response time (much like squid siblings work). 
> Thank you for any input.

If your planned setup is:

DNS A, forward to DNS B on query fail
DNS B, forward to DNS A on query fail

Then this will indeed create a loop in case a query cannot be answered
by both servers.

Also, you won't want to do that.

If you're trying to build up a cache to improve performance and response
time, here's your scenario:

DNS C, forward to DNS A,B for all queries
DNS D, forward to DNS B,A for all queries

Your cache will start building up and only responses that are not cached
will be taken from your NS A and B servers.

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