Subject: Re: Taking two steps back (Was: Re: one question...)

From: Keith Moore <[email-masked]>
Date: Tue, 15 Jul 2003 19:23:35 -0400

On Wed, 22 Jan 2003 03:34:19 +0100 (CET)
Erik Nordmark <[email-masked]> wrote:

] Granted that this is a hard problem, but we seem to be spending emails
] on multiple subsets of this problem (in different WGs) thus I think it
] would be worth-while to concentrate thinking on the identifier/locator
] separation problem.

Mumble.  If you really want to split identifiers and locators then you need a
fast, accurate, scalable, highly available, and robust mapping function
between the two.  That turns out to be very difficult, especially when you
want things to continue working on isolated or ad hoc networks or on networks 
with intermittent connectivity to the outside world.

Even then, there will still be cases where the right thing to do is to talk
directly to a locator.  And there will also be lots of apps for which a
locator is "good enough" that probably shoudn't be made dependent on the
mapping service.

So I lean towards a view where you can use identifiers or locators
interchangably - you can specify an identifier as a connection endpoint if
that's what you want, or you can specify a locator, and the higher layer
protocols mostly shouldn't care about the difference (though things like
TCP might want to know if the locator changes so they can discard RTT
estimates and initiate slow-start, and some apps protocols may have a
preference as to which to use and may not perform as well if the preferred
kind of name is not available).  Which further implies that identifiers and
locators look a lot like IP addresses.

As for identifier-to-locator mapping, I think we'll have to be able to
tolerate multiple coexisting mapping systems, one that works with global
connectivity, another that works bottom-up.  So if your destination happens 
to be near you, so you can still use the identifier to talk to that host even
if the global mapping service is down.  Of course, you'll want to verify the
authenticity of the host you're talking to in either case - you shouldn't
trust the mapping service.  And you can use the locator as a last resort.

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From: Keith Moore <[email-masked]>
Date: Tue, 15 Jul 2003 19:30:35 -0400

sorry about that; I replied to an ancient message.  for some reason my 
mail server had this one marked as unread even though it was read 
a long time ago.

Keith

On Tue, 15 Jul 2003 19:23:35 -0400
Keith Moore <[email-masked]> wrote:

] On Wed, 22 Jan 2003 03:34:19 +0100 (CET)
] Erik Nordmark <[email-masked]> wrote:
] 
] ] Granted that this is a hard problem, but we seem to be spending emails
] ] on multiple subsets of this problem (in different WGs) thus I think it
] ] would be worth-while to concentrate thinking on the identifier/locator
] ] separation problem.
] 
] Mumble.  If you really want to split identifiers and locators then you need a
] fast, accurate, scalable, highly available, and robust mapping function
] between the two.  That turns out to be very difficult, especially when you
] want things to continue working on isolated or ad hoc networks or on networks 
] with intermittent connectivity to the outside world.

etc.