Strange behaviour resolving CNAME's via a forwarder.

[Adam Goodall]

Hi

I am having a strange problem and I'm not sure if i am hitting a bug or
expected behaviour.

Server A on 10.1.1.1 is running BIND 9.7.0-P2-RedHat-9.7.0-5.P2.el6_0.1 on
RHEL6. It is acting as a recursor for its clients and also has a number of
forward zones configured as follows:

zone "testdomain.com" in {
        type forward;
        forwarders { 192.168.1.1; };
        forward only;
};


Server B is on 192.168.1.1 and runs Power DNS, it is authoritative for
testdomain.com and will not service recursive queries.
Some sample entries from that zone are:

ftp IN CNAME www
www IN A 192.168.5.5
mail  IN CNAME mail.someotherdomain.com.


If a client queries server A for www.testdomain.com (type any), the request
is forwarded on to 192.168.1.1 and resolves as expected.
If a client queries server A for ftp.testdomain.com (type any), the request
is forwarded on to 192.168.1.1 and resolves as expected.

However if a client queries server A  for mail.testdomain.com (type any) the
request is not answered. From the logs on server B i can see that server A
is only forwarding on a request of type A. As an A record for
mail.testdomain.com does not exist on server B it does not resolve.

If i then specifically query Server A for mail.testdomain.com of type CNAME,
it resolves as expected. Subsequent requests against server A for
mail.testdomain.com of type any then resolve, presumably because it is
already in the cache.

Hopefully that makes sense! Has anyone had a similar issue and did you come
up with a work around? Is this expected behaviour or a bug?

Thanks for your help on this - its driving me mad!

Adam
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