BIND 9.6 Flaw - CNAME vs. A Record in MX Records are NOT "Illegal"

[bsfinkel at anl.gov]

I have not copied the entire thread.

>You've added an additional step in your second paragraph that is  
>prohibited by the section you quoted in the first.  The section from  
>the RFC describes a situation where A is queried for and an MX record  
>pointing to B is returned.  When B is queried for, an address record  
>MUST be the answer.   The situation you have described is that A is  
>queried for resulting in an MX record pointing to B.  When B is  
>queried for, a CNAME pointing to C is returned, and that when C is  
>queried an address record is returned.  Do you see the difference?
>
>The RFCs are quite clear that CNAMEs are not permitted in the RDATA  
>for an MX.

If I have in DNS

     cn IN CNAME realname

and I query for cn, the DNS resolver will return "realname".
BIND also returns the "A" record for realname.  Is this a requirement?
If not, then

     mx IN 10 MX cn

will result in:

     1) the MX query returning cn,

     2) the cn query returning realname,

     3) a third (and RFC-breaking) query to get the "A" for realname.

There are only two queries if the resolver returns the "A" record along
with the realname of the CNAME record.
----------------------------------------------------------------------
Barry S. Finkel
Computing and Information Systems Division
Argonne National Laboratory          Phone:    +1 (630) 252-7277
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