MX pointing to CNAME
joshl at cisco.com
Tue May 30 17:05:46 UTC 2006
Peter Dambier wrote:
> Tom Del Rosso wrote:
>> Who's right? The ISP says MX records must point to a canonical name, but
>> dnsreport.com says "CNAMEs are prohibited in MX records".
These statements are not in conflict, but are in complete agreement.
The left side name (owner name) of a CNAME RR is not a canonical name,
it is an alias. The right side name (data) of a CNAME RR is supposed to
be a canonical name (not another CNAME), however, CNAME "chaining" is
generally tolerated so some unspecified depth.
A canonical name is a name which owns real data, as opposed to an alias
which owns a CNAME record. See RFC 1034, sec. 3.6.2. The reason the
CNAME record is called that (for "canonical name") is that, like all
other RRs, it refers to what is found on the data side of the name, not
the owner side.
Josh Littlefield Cisco Systems, Inc.
joshl at cisco.com 1414 Massachusetts Avenue
tel: 978-936-1379 fax: 978-936-2226 Boxborough, MA 01719-2205
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