ietf-mxcomp
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Re: Distilling Wildcards for MARID Monday

2004-05-27 21:03:32

Phill H-B, in a rare failure of vision, writes:

2) Given that DNS wildcards only match on non-existent names
(not name and type), what is the functional difference between
covering a non-existent domain name with a MARID record vs. no
record at all?

What can a wildcard name say that 'name does not exist' does not
shout?

Not to belabor the obvious, but a wildcard says that the name exists.
It's true that wildcard records only match names where there's no
explicit record, but that's not at all the same as saying they don't
exist, it's saying that explicit entries override generic ones.

Using a wildcard for spelling correction like sitefinder is one use
but not the only one.  I find them useful in contexts where there's
too many names to export them all into the DNS, or you can't easily
enumerate all the names, or they change too often to stuff them
individually into the DNS.

Only idea that seemed to make much sense for me would be where 
there is already a wildcard in the zone pointing to some IP address.

Huh?  It makes sense where there's an MX wildcard and the mail flows
both ways.

Imagine, for example, that you're runing a two-way fax gateway along
the lines ot tpc.int with addresses like
Joe(_dot_)Smith(_at_)13115552368(_dot_)iddd(_dot_)tpc(_dot_)int where the phone 
number is part of
the domain, and the local part is cover page info, OCR'd for
fax->email traffic.  You can't list all the phone numbers, so you have
to use wildcards both for the inbound MX and the outbound MARID.

I don't know of any two-way fax gateways, but as I mentioned in an
earlier message, I know plenty of places that have per-user subdomains
and other applications where there really are a whole lot of
subdomains, and valid mail can come from any of them.

Regards,
John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
http://www.taugh.com