Subject: RE: AN interesting article. FYI... contd

From: Dan Lanciani <[email-masked]>
Date: Sat, 28 Aug 1999 15:45:50 -0400 (EDT)

"Mike Zintel (Exchange)" <[email-masked]> wrote:

|I don't understand how DDNS alone will solve this in the absence of some
|sticky address for every end node. 
|
|If client initiated DDNS updates must occur, say, everytime PPP or DHCP
|gives me a new address, how can we build a network where my moher can call
|me when I'm not connected? 

Ah, I assumed you were referring to the case of a transient connection
while that connection was up.  Clearly for the true dynamic outcall case
you want an address identifier that is as stable as possible, but that
applies equally to IPv4 and IPv6.  Of course, for IPv4 that identifier
could in fact be your IP address (at least it could when end-user allocations
of portable address space were still allowed).  Whether this was a good thing
or a bad thing seems to be a philosophical debate. :)  Who knows what the
first-class identifier will turn out to be under IPv6?  It's certainly handy
in many applications to have a stable identifier that you can ``own'' and
that won't change out from under you.  To be useful that identifier may
need to be at a lower level than a domain name but at a higher level than
a dynamic address.  Evolution will probably provide...

				Dan Lanciani
				[email-masked]
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From: Robert Honore <[email-masked]>
Date: Sun, 29 Aug 1999 10:45:05 -0400

Dear Dan,

> Who knows what the

Have we come full circle to the question of Session Stability as we had been
discussing in another thread a few weeks ago?

Yours sincerely,
Robert Honore.

---

From: Thomas Narten <[email-masked]>
Date: Mon, 30 Aug 1999 08:10:31 -0400

> Ah, I assumed you were referring to the case of a transient
> connection while that connection was up.  Clearly for the true
> dynamic outcall case you want an address identifier that is as
> stable as possible, but that applies equally to IPv4 and IPv6.  Of
> course, for IPv4 that identifier could in fact be your IP address
> (at least it could when end-user allocations of portable address
> space were still allowed).  Whether this was a good thing or a bad
> thing seems to be a philosophical debate. :)

Philosophical desires aside, the reality today is that the IPv4
addresses are no longer the stable identifiers that folks find
covenient. Wishing it otherwise won't make it so.

> Who knows what the first-class identifier will turn out to be under
> IPv6?  It's certainly handy in many applications to have a stable
> identifier that you can ``own'' and that won't change out from under
> you.  To be useful that identifier may need to be at a lower level
> than a domain name but at a higher level than a dynamic address.
> Evolution will probably provide...

The hard problem with stable identifiers is that for identifiers to be
useful, one needs to be able to map them into a network address that
IP can use to actually deliver a packet to the destination
corresponding to that identifier. An identifier by itself, with no
idea how to deliver a packet to the node corresponding to an
identifier is close to useless.

If one stores the identifier, presumably one will want to use it again
in the future. But then it needs to be mappable into a network layer
address so packets can be delivered to it. And if addresses change
over time, than the mapping changes over time as well.

In the old days of IPv4, having the address carry both the identifier
and locator in the same enitity (i.e., the address) made the mapping
problem trivial.

How to do the mapping in a world where network address can change is a
very hard problem, if one wants a solution that scales to the size of
the Internet. DNS names come to mind because there we have a scalable
distributed database that maps identifiers (DNS names) to arbitrary
information (e.g., the current address corresponding to the
identifier). But how to keep the DNS up-to-date in a world where
addresses change frequently is a non-trivial problem. This becomes
particularly apparent when one understands that the DNS is glued
together by hard-wired addresses (pointers to DNS servers for a
zone). You can't change network addresses without fixing up the DNS
pointers simultanenously (if you want the mapping function to always
work). While this could in theory be done, there are some non-trivial
details to work out before this can be made practical, and to my
knowledge, no one has sat down and tried to work through a detailed
design (though it would certainly be useful if someone did!).

Thomas