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From: romkey@asylum.asylum.sf.ca.us (John Romkey)
Newsgroups: comp.protocols.tcp-ip
Subject: re: name handling in DNS resolvers
Message-ID: <9105171533.AA01010@asylum.asylum.sf.ca.us>
Date: 17 May 91 15:33:27 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: romkey@asylum.sf.ca.us
Organization: The Internet
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As the person who designed the way DNS lookup works in PC/TCP, I'll
explain to you why it's done that way.

Suppose you do your domain name lookup by working your way up the
domain name. Your host's domain name is W.X.Y.Z. It's presented with
name A; so first it tries A.X.Y.Z, then it tries A.Y.Z, etc.

Or, perhaps you present it with A.B and it tries A.B, A.B.Z, A.B.Y.Z.

There are other searches it could do, too.

In any of these cases, the user can have the name resolve into a
system that's not the one they expected, and then have no way to
specify that name. By the principle of least astonishment, you
shouldn't allow that to happen.

For instance, if I'm using the name LEEDS.AC.UK, and I'm inside
MIT.EDU and MIT happens to have a LEEDS.AC.UK.MIT.EDU, I may never be
able to contact the true LEEDS.AC.UK because my searching-DNS resolver
decides that it should use the one inside MIT.

And, if you say "Well, let's first try the top level domain
interpretation rather than the path", then you'll have people who
expect consistent behaviour and are rather shocked that when they type
LEEDS.AC.UK they get the top level host, rather than
LEEDS.AC.UK.MIT.EDU.

Before you argue that nobody has name duplication like that, let me
make two points:

1. Such names have existed. The Media Lab at MIT had several names
like EDU.MIT.EDU for a while.

2. Nothing prevents them from existing; and if software you provide
won't work with them, you WILL find sites that create them and them
are functionally cursed because of an implementation decision you
made.

Basically, I agree that doing the searching is handy, but I think it's
also brain damaged because it can lead to ambiguous cases and wall off
the users from sections of the DNS so that they can no longer access
chunks of the name space, because their searching algorithms find
the incorrect ones first.
		- john romkey			Epilogue Technology
USENET/UUCP/Internet:  romkey@asylum.sf.ca.us	voice/fax: 415 594-1141