CNAME records having MX

[Michael Kjorling]

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I am getting seriously confused here. Where is the MX pointing to a
CNAME in that example?

Let's analyze it as a mail server wanting to send mail to the domain
in question would. For simplicity, I'll just use unqualified names -
append $ORIGIN as you please.

	* SMTP: RCPT TO:<someone at foo>

	* Look up MX record for foo. Find "foo IN MX 0 mail"

	* Look up A record for mail. Find "mail IN A 192.168.1.10"

	* Connect to 192.168.1.10 and send mail

Web browser going to bar (the name server is uncooperative so we have
to ask it about whatever the RHS of the CNAME is):

	* Look up A record for bar. Find "bar IN CNAME foo"

	* Look up A record for foo. Find no A record. Bail out with
	  domain not found or similar error.

If we allow ourselves to work with IPv6 as well, there will be similar
queries for AAAA and A6 records, but still the motions are the same.


Michael Kjörling


On Dec 17 2001 11:47 -0500, Mathieu Chouquet-Stringer wrote:

> > Technically (and I think that the other responders have the same idea),
> > it is not "an example of 'CNAME can point to an MX'".
> > It is a CNAME and an MX record pointing to the same RHS nodename.
> > I believe that if you had
> >
> >      foo     IN  MX  0   mail
> >      mail    IN  A       192.168.1.10
> >      bar     IN  CNAME   foo
> >
> > where there was no "A" record for "foo", then this would be an invalid
> > configuration.  I am not sure what "pointing to an MX" really means.
>
> You usually you don't want your mx field to be a cname because the mail
> servers will have to do an extra lookup every time they want to send a mail
> to you. That is the only reason as far as I know...

- -- 
Michael Kjörling  --  Programmer/Network administrator  ^..^
Internet: michael at kjorling.com -- FidoNet: 2:204/254.4   \/
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