[dns-operations] MX record definition?

[bmanning at vacation.karoshi.com]

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?

	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... 

	
> 
> 	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
> > >_______________________________________________
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> > 
> > -- 
> > -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
> > Edward Lewis
> > NeuStar                    You can leave a voice message at +1-571-434-5468
> > 
> > Never confuse activity with progress.  Activity pays more.
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> -- 
> Mark Andrews, ISC
> 1 Seymour St., Dundas Valley, NSW 2117, Australia
> PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org
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--bill manning