[Gllug] * on mail exchanger records

[home at alexhudson.com]

Hi all.

I'm having something of an argument with my ISP over their dns setup (naming
no names :). Basically, the source of my frustration is their inclusion of

	* 	IN MX [their mail servers]

in all of the domains for which they are authoratitive. Which isn't
necessarily a problem, in and of itself. However.. with domain/search set in
the resolv.conf, this throws up an interesting problem.

Let's say, for example, that they have foo.com on their name servers, and we
have a machine which is in the domain foo.com. (This is where my knowledge
of DNS falls down - please correct me in the following...) 

We want to look up bar.com, for example. Given we're in foo.com, we lookup
bar.com.foo.com (we're looking up an A record - want to go to a webpage for
example), and this doesn't return NXDOMAIN but NOERROR with no answers. We
hunt on for bar.com - but this time, the lookup for bar.com fails with
NXDOMAIN because it doesn't exist (in this hypothetical world, all the
three-letter .com domains aren't all taken :). And Lynx is unable to view
the document (except it goes through all the interations of bar.com.com etc,
first, and probably bar.com.com.foo.com as well... :( ). An nslookup for
bar.com returns bar.com.foo.com, but with no answer obviously, and this
seems to confuse a number of programs.

The  seems to be even worse with e-mail - now, a domain which shouldn't
exist suddenly has mail exchangers, because we've used the search path.
Obviously, this isn't email which is going to be delivered anyway, but now
instead of failing because of an invalid domain name, it fails because the
user does not exist at the mail server (or, worse, it succeeds and there is
no error generated :((( )

Can anyone please make an argument for why this setup is valid? It's not
entirely _invalid_, but it does seem to suck for no good reason (* IN MX ..
is certainly valid, but I would say only for domains with no machines in
them for reasons of sanity - and our domains have machines in them!).

Cheers,

Alex.

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