# Re: DNS lookups for URLs (was: URN functionality from URLs)

Keith Moore (moore@cs.utk.edu)
Wed, 15 Dec 1993 00:40:44 -0500

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    Message-Id: <199312150540.AAA09385@CS.UTK.EDU>

    From: Keith Moore <moore@cs.utk.edu>

    To: dupuy@smarts.com (Alexander Dupuy)

    Subject: Re: DNS lookups for URLs (was: URN functionality from URLs)

    In-Reply-To: Your message of "Tue, 14 Dec 1993 22:54:59 +0500."

                 <9312150354.AA05849@brainy.smarts.com>

    Date: Wed, 15 Dec 1993 00:40:44 -0500

> Date: Tue, 14 Dec 1993 22:54:59 +0500
> From: dupuy@smarts.com (Alexander Dupuy)
>
> In <199312142059.PAA03573@wilma.cs.utk.edu> Keith Moore <moore@cs.utk.edu> says:
> > Not everyone thinks this [DNS search paths] is a nice feature. Some people
> > would even call it broken. Domain names (like URLs) are supposed to be
> > absolute.
>
> In <9312142028.AA21530@rodan.UU.NET> stripes@uunet.uu.net (Josh Osborne) agrees:
> > I don't think you really want to use search paths that way. (Why? I don't
> > know, it just seems unclean). If just want caching, just use a caching
> > nameserver. (or for more aggressive caching be an unoffical secondary for
> > the domain...) No problem there.
>
> The purpose of putting in local DNS IX records for STANF URLs in other domains
> is to provide caches for the files (objects) referenced by the URLs, not
> caches for the IX records themselves (in that case, a caching nameserver would
> be better). This sort of local cache for common references (RFCs,
> dictionaries, etc.) will be very important, and is one of the reasons for
> URNs, which are supposed to be location-independent.

Local cacheing is a good idea. Using the DNS for this purpose is not.

Files should be referenced by URN (not URL). Then the DNS should be used
to find the "official" URN->URL lookup service. If you have a local cache,
you should consult it first to see if it has a cached copy of the file
indicated by a particular URN.

> Now, as for whether DNS search paths are nice, well, look at RFC 1535 to see
> how search paths (as implemented by all but the most recent BIND releases)
> have a major problem (hint: what happens when you create an edu.com domain?).
> Nonetheless, sometimes things which aren't nice are still useful.

This happens a lot: someone creates a hack to solve a local problem,
without considering its effect on the net as a whole. DNS search paths
seem to solve local problems (users don't have to type long domain names),
but they create users have problems talking to hosts on the other side of
the world. Let's not legitimize that mistake by using it for URN/URL lookup.
> So it seems unlikely that a new DNS record type would be adopted by any
> significant fraction of domains anytime soon. One approach to this problem
> would be to use TXT records, which have the advantage that they are supported
> by a significant fraction of DNS servers (though probably still not most of
> them). But even in this case, it isn't clear that people will actually go to
> the trouble of setting up this information on a wide enough scale for it to be
> useful.
>
> So although I feel that using DNS is the more elegant approach, I'm not yet
> convinced that it is a good idea to tie URNs into a naming system that has a
> lot of administrative inertia.

Agreed that a new DNS type is hard to get going. Especially since (so I'm
told) many DNS implementations can't cache RRs that they don't know about.
This needs to be fixed, but URNs can't wait on it. We should probably
just use TXT records and put URN->URL mappings in a different class
or top-level domain.

Keith Moore

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