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.