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From: gandalf@csli.Stanford.EDU (Juergen Wagner)
Newsgroups: comp.protocols.tcp-ip.domains
Subject: Re: Proposed extensions to MX records.
Message-ID: <18490@csli.Stanford.EDU>
Date: 2 Apr 91 13:02:04 GMT
References: <1991Mar28.182232.13467@agate.berkeley.edu> <91Mar28.233847est.6186@neat.cs.toronto.edu> <8341@crash.cts.com>
Organization: Center for the Study of Language and Information, Stanford U.
Lines: 46

So far, the discussion focussed on changes which are visible to clients of
a domain name server. It seems to me that the desired functionality could
also be gained by introducing chnages only on the name server side.

Suppose, a new RR, called VIS (visibility) is defined as follows:

	id	IN	VIS	requestor-domain-1
		IN	VIS	requestor-domain-2
		...	...	...

where 'id' is some non-numeric identifier, possibly domain-style, and where
'requestor-domain-i' is some domain-style name, with the left-most token
possibly being a '*'.

Now, we could tag all traditional RRs in the following way:

	[domain]	[ttl]	class	type	data

changes to

	[domain]	[id] [ttl]	class	type	data

with the semantics that this RR sould only be given to hosts in a domain
listed for the identifier 'id'. Lookup in this table could be done in a
way that the name server looks for the most specific record matching (i.e.
the longer the domain suffix found, the more specific, and the wildcard is
always less specific than any ordinary token).

RRs passed on to clients (mail, news, telnet, etc.) will still have the
same format as before, in fact, they won't notice any difference at all,
except that they now receive less information.

Secondary servers for a domain with VIS records would have to understand
them. This requires updates to all name servers of a domain with VIS RRs.
Listing secondary name servers in VIS records provides a mechanism for
filtering what should be down-loaded on a zone transfer. Of course, we
could also tag VIS records... The name server would use them, anyway, but
some other hosts won't be able to down-load them...

--Juergen Wagner
(gandalf@csli.stanford.edu)
(wagner@iao.fhg.de)

PS: The above reflects some spontaneous ideas I had on this topic. I have
    neither thoroughly thought through all the consequences, nor do I have
    an implementation of it :-).