Behaviour of a recursive DNS server

[yjchu]

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I am trying IPv6 NAT-PT, so I wish my DNS server (my ISP DNS server) can be
purely recursive.

So, I send a recursive query, and my DNS server does reply recursively but
with strange behaviors described as following:

 

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Sometimes, the DNS server will have two replies for single one query.

The first reply will only contain the CNAME but no A or AAAA record
(address) information for the CNAME.

Then, the second reply has all the information, including CNAME and A/AAAA
record information.

 

My NAT-PT box seems to have problems with the first extra reply. So, does
anybody know why this happens? 

And, the most important,  how to remove the first extra reply in the DNS
server, such as Bind?

 

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I have tried to build up my own DNS server using Bind 9.2.1 and make it
support recursive reply.

I find that sometimes, the reply of my DNS server just contains CNAME record
for my query name, no further information. (No second reply with address
information).

However, from the sniffer, the recursive flag in DNS reply is set !!!!

The condition also bothers me a lot.

 

Chu