"John A. Tamplin" <jat@traveller.com> writes:

With the larger address space of IPv6, there is the capacity for an arbitrary number of levels in the hierarchy.

"Arbitrary" is overstating it, considering that the addresses are fixed-length fields.

Obviously, making use of those levels to improve on the inefficiency noted above will require more routes to be propagated, so there is a tradeoff.

Kleinrock and Kamoun ("Stochastic Performance Evaluation of Hierarchical Routing for Large Networks") demonstrated that the optimal number of levels in a hierarchically addressed Internetwork with k routers is ln k, and so e ln k routing entries are needed per router to provide routing with acceptable amounts of non-optimality. Consequently, a scheme which can provide for this optimal number of levels also neatly bounds the amount of routing information necessary for nearly optimal routing. A fixed address length clearly can be a scaling constraint on the number of levels that can be encoded into the address itself, and one that is too short, therefore, naturally requires an Internet to carry larger numbers of routes. (One that is too long is merely wasteful of resources). Note, however, that the important thing is that such a scalable Internetwork is _hierarchically addressed_; this constraint is necessary to make any Internetwork scale, independent of the routing protocol(s) used.

I don't think we want either a routing table contaning one route per AS

ASes are an EGPism, and the deaths of EGP and its cosmetically improved descendents are long overdue. Despite all the problems with BGP, at least with respect to addressing the problem is not in the protocol, but in the need for hierarchical routing. Sean.