[Dnsmasq-discuss] [PATCH] --dont-mirror-queries option

[Chris Novakovic]

I have a (rather odd, and perhaps ill-advised) network setup in which
names in a particular domain (e.g. example.com) are split across three
sites, and I need three dnsmasq servers to be mutually dependent in the
following hierarchy to resolve names for that domain:

          master
           / \
          /   \
      area1   area2

If a client sends a query for x.example.com to area1 that area1 can't
answer, or if another client sends a query for y.example.com to area2
that area2 can't answer, both servers will forward the query to master,
which is configured (with --server) to be the sole upstream DNS server
for example.com on both area1 and area2. If master can't answer a query
for example.com, it is configured to forward the query to area1 and
area2. Clearly, master shouldn't forward queries that originate from
area1 back to area1: this would lead to an infinite forwarding loop.

The attached patch implements a new option, --dont-mirror-queries. When
enabled, this option prevents dnsmasq from forwarding a request to an
upstream server if its IP address matches that of the sender of the
query. I suppose this could be considered a dynamic, per-query version
of the --dns-loop-detect option that is only capable of detecting 1-hop
loops.

Kurt H Maier <khm at sciops.net> was the brains of this operation, helping
me figure out the part of forward.c that needed patching.

Cheers,
Chris
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