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

[Matus UHLAR - fantomas]

On 26.01.09 09:19, bsfinkel at anl.gov wrote:
> 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.

according to RFC1035 sect. 3.3.9

"MX records cause type A additional section processing for the host
specified by EXCHANGE."

according to RFC2181 sect 10.3. 

"The domain name used as the value of a NS resource record, or part of the
value of a MX resource record must not be an alias."

"It can also have other RRs, but never a CNAME RR."

"Additional section processing does not include CNAME records"...

"Thus, if an alias is used as the value of an NS or MX record, no address
will be returned with the NS or MX value."


-- 
Matus UHLAR - fantomas, uhlar at fantomas.sk ; http://www.fantomas.sk/
Warning: I wish NOT to receive e-mail advertising to this address.
Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu.
"The box said 'Requires Windows 95 or better', so I bought a Macintosh".