IP Addresses in MX Records?

[Barry Margolin]

In article <7od0o0$d5$1 at nnrp1.deja.com>,
Khalid J Hosein  <kjh1 at my-deja.com> wrote:
>Looking through RFC 974, I can't find anything that says you CAN'T have
>an IP address as the value for an MX record (as opposed to a host name).
>What do you think?

It took me two seconds to find the following:

   Each MX matches a domain name with two pieces of data, a
   preference value (an unsigned 16-bit integer), and the name of a
   host.

It specifically says "name of a host".

Another authority is RFC 1035, the DNS specification:

   3.3.9. MX RDATA format

       +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
       |                  PREFERENCE                   |
       +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
       /                   EXCHANGE                    /
       /                                               /
       +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

   where:

   PREFERENCE      A 16 bit integer which specifies the preference given to
		   this RR among others at the same owner.  Lower values
		   are preferred.

   EXCHANGE        A <domain-name> which specifies a host willing to act as
		   a mail exchange for the owner name.

   MX records cause type A additional section processing for the host
   specified by EXCHANGE.  The use of MX RRs is explained in detail in
   [RFC-974].

This says that the MX record points to a name, and that it then looks up
the A record for that name.

-- 
Barry Margolin, barmar at bbnplanet.com
GTE Internetworking, Powered by BBN, Burlington, MA
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