Re: Malformed Zone?

Jonathan Duncan <[email protected]> wrote:
> Just for my education, why would the CNAME record and the MX record
> clash?  I know that Matthew said, "CNAME records can't coexist at
> the same name with other records."  Why is this?  The A record
> "+pennypix.net" is the same name as "@pennypix.net" but they do not
> clash.  What is different about CNAME records?

The short answer is "because the RFC says so".

A CNAME isn't just a subsitute for an A record; it substitutes for all
records--when a resolver is looking for a record of type X for the
name foo, and it sees a CNAME for foo pointing to bar (possibly
already cached, from earlier when it was looking for a Y record for
foo), then it looks for a record of type X for bar instead.  If foo
also had its own X record, the resolver wouldn't be able to use its
cached knowledge; it would have to check with foo's server
specifically about the X record.  So this requirement saves on network
traffic and resolution time.


paul