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Re: the "implicit-MX" rule and a proposed BCP

2004-02-14 15:53:20
On Sat, Feb 14, 2004 at 05:41:29PM -0500, Philip Gladstone wrote:

- The resulting addresses MUST have PTR records, and these PTR records
 MUST match the host.  The following lookups will still work but are
 discouraged:
 somehost -> a.b.c.d; a.b.c.d -> otherhost; otherhost -> a.b.c.d

 The following will NOT result in a valid lookup:
 somehost -> a.b.c.d; a.b.c.d -> otherhost; otherhost -> p.q.r.s

This implies that I cannot run a mail server on a cable modem. This is 
uncool. The reason is that the a.b.c.d -> otherhost which typically 
doesn't map to anything.

Why?

d.c.dsl-net-a-b.someprovider.tld  A   a.b.c.d
d.c.b.a.in-addr.arpa              PTR d.c.dsl-net-a-b.someprovider.tld.

Next, you register whatever.tld and setup DNS:

whatever.tld   MX  0 d.c.dsl-net-a-b.someprovider.tld
whatever.tld   TXT "v=spf1 MX -all"

This way, you have a perfectly legal setup, even according to the
proposed items in the BCP.

You have to allow for the case where the a.b.c.d is administratively 
controlled by someone other than the system administrator.

I have.  If your provider sucks and can't get DNS right, well, their
users aren't complaning loudly enough.

cheers,
Alex
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