[dns-operations] MX record definition?

[Mark Andrews]

In message <20081218052415.GA24753 at vacation.karoshi.com.>, bmanning at vacation.ka
roshi.com writes:
> On Thu, Dec 18, 2008 at 12:36:59PM +1100, Mark Andrews wrote:
> > 
> > In message <a06240800c56f3fcb2752@[10.31.200.207]>, Edward Lewis writes:
> > > That's the place for the definition.
> > > 
> > > Don't know if there's a document that says why/that they are bad.
> > > 
> > > I can only venture a guess - probably because the reason they are bad 
> > > is weakly written application code that assumes the name in the MX 
> > > record is a host name and not a domain name.  (Host names in RFC 
> > > 1123.)  I.e., what do you get if you try to look up the A record for 
> > > 123.321.23.123?
> > 
> > 	Well the description pretty clearly says it it a host.
> > 
> > EXCHANGE        A <domain-name> which specifies a host willing to act as
> >                 a mail exchange for the owner name.
> > 
> > 	Seeing a IP address in the exchange field of a MX record
> > 	in a master file is, almost always, a configuration error.
> > 
> > 	Seeing a IP address with a period at the end in the exchange
> > 	field of a MX record in a master file is also, almost always,
> > 	a configuration error
> 
> 	can you tell me what is behind the "almost always" disclaimers
> 	in both the preceding paragraphs?

	$ORIGIN example.net.
	foo	MX 0 1.2.3.4 

	becomes

 	foo.example.net. MX 0 1.2.3.4.example.net.

	and 1.2.3.4.example.net is a legal hostname.

	$ORIGIN example.net.
	foo     MX 0 1.2.3.4.

	becomes

	foo.example.net. MX 0 1.2.3.4.

	Which would only be legal if you are running in your own private
	namespace.

	Using IPv6 examples ::1 instead of 1.2.3.4.

	foo.example.net. MX 0 ::1.example.net.
	foo.example.net. MX 0 ::1.

	Which would only be legal in your own private namespace.

> 	sounds to me like -in some cases- a fully numeric string that 
> 	-could- be parsed as an IP address would be legal.
> 
> 	i've seen and used fully numeric (domain names) in the past
> 	and may do so in the future... 

	Not on the big I Internet.  Maybe in your own private namespace.

	Mark
 
> > 	MTA that treat a "123.321.23.123." as a IP address are broken.
> > 
> > > As far as being a no-no: they aren't prohibited by the DNS 
> > > specification.  Perhaps there's a mail protocol restriction.
> > > 
> > > At 15:21 -0800 12/17/08, Seth Mattinen wrote:
> > > >Does anyone know offhand where the MX record is defined? The best I 
> > > >can find is section 3.3.9 in RFC 1035. I'm trying to find a 
> > > >reference that says numeric MX records are bad. I'm assuming they're 
> > > >a no-no, at least that's what I've always been told.
> > > >
> > > >~Seth
> > > >_______________________________________________
> > > >dns-operations mailing list
> > > >dns-operations at lists.dns-oarc.net
> > > >https://lists.dns-oarc.net/mailman/listinfo/dns-operations
> > > 
> > > -- 
> > > -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
> =-
> > > Edward Lewis
> > > NeuStar                    You can leave a voice message at +1-571-434-54
> 68
> > > 
> > > Never confuse activity with progress.  Activity pays more.
> > > _______________________________________________
> > > dns-operations mailing list
> > > dns-operations at lists.dns-oarc.net
> > > https://lists.dns-oarc.net/mailman/listinfo/dns-operations
> > -- 
> > Mark Andrews, ISC
> > 1 Seymour St., Dundas Valley, NSW 2117, Australia
> > PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org
> > _______________________________________________
> > dns-operations mailing list
> > dns-operations at lists.dns-oarc.net
> > https://lists.dns-oarc.net/mailman/listinfo/dns-operations
> 
> --bill manning
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org