Can MX records point to multiple cnames

[Barry Margolin]

In article <s77np4bjnfg131 at corp.supernews.com>,
Ben Davies <ben_davies at oxy.com> wrote:
>I want to use oxymail.oxy.com as my mx record for all my external machines.
>I also want oxymail to be a cname for each of two firewalls.  Can I do this:
>
>server1.oxy.com.     in     a     1.1.1.1
>server1.oxy.com .    in    mx    10  oxymail.oxy.com.
>
>firewall1.oxy.com.    in    a    1.1.1.2
>oxymail.oxy.com.    in    cname    firewall1.oxy.com
>
>firewall2.oxy.com.    in    a    1.1.1.3
>oxymail.oxy.com.    in    cname    firewall2.oxy.com.
>
>
>or does the machine reverenced by the cname need to be an "A" record
>
>We get too much mail to just do this and the DNS and BIND book does not
>address this clearly.

MX records are supposed to point to A records.  RFC 1034 section 3.6.2
says:

   Domain names in RRs which point at another name should always point at
   the primary name and not the alias.

And multiple CNAME records for the same name are not supposed to be
allowed, either (BIND 8 requires you to use the "multiple-cnames yes"
option to override this restriction).

Your proposed configuration violates both rules, so I suggest you not use
it.

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