Subject: RE: Why IPv6 is a must?

From: [email-masked] (Sean Doran)
Date: Mon, 12 Nov 2001 22:51:25 +0100 (CET)

Peter Ford post ROAD writes:

| I concur that the routing guys have some work in front of them.   May I
| suggest people take a closer look at hierarchical routing, combined
| provider and geographic hierarchies, and adult supervision?

All of these have been well-studied with IPv4.

Unfortunately, there is no known (to the IETF) way of preserving
hierarchy in the absence of host renumbering (of locator-part), 
careful use of multiple locators by hosts, or NAT, which is a way a 
middle-box can  "spoof" one of the previous two options.

The problem of maintaining hierarchical routing is identical with
ANY way of describing a device in ANY network: the locator MUST
change with a change in location.

Keeping the location independent of the identity of a device
makes this task much easier, especially when a minimal number
of things running on the host have to know about the location
at all.  (i.e., it's great if the host doesn't need to know its
location at all, at any time, thus allowing in-flight mutations
of the locator at will as the network changes shape -- the host
should not reject packets meant for itself (identity) just because
they have been sent to a "surprising" (to the host) location).

There are alternatives to a complete separation of identity and
location, but most of them result in NAT-like localization of
identity (i.e., identity is not end-to-end) or things like UUCP bang
paths or vaguely CLNS-style names, and unfortunately, variable-length
addresses are not supported by IPv6.

	Sean.

---

From: Keith Moore <[email-masked]>
Date: Mon, 12 Nov 2001 17:13:54 -0500

> change with a change in location.

perhaps, but the locator doesn't have to be exposed in the address.
if you expose the locator in the address then every time the location
changes you have to somehow inform all parties that are using that 
location that there's a new location for that address.

at present our locators are AS numbers.  they are not exposed in the
address or to hosts; instead there is a mapping function from address 
prefixes to AS numbers that is maintained by routers.

if we change the system to use a different kind of locator we still
need stable addresses, we still have to maintain the mapping 
function from addresses to locators, and we still need that mapping
function to be current and reliable.

what we are arguing about is the appropriate granularity of the 
mapping function, and the appropriate place to maintain that mapping.

Keith