Leo,

I don't do the IETF thing, but has any development effort there tried to make multihoming / mobility a requirement of a new protocol, and if so why hasn't there been more progress on that front?

There are numerous related activities going on in the IETF to address multihoming and mobility. First, there has been a very long standing effort in the mobility front. MOBILE-IP allows one to hold a single IP address, no matter where one is. It works via tunneling to a known point in the topology, where non-participating nodes rendevous. With IPv6 they're attempting to do one better: there are to be no nodes that are not aware of mobility. That way, once the two end points have connected one can send a rebinding message to the other saying, "I'm over here." The benefit is the elimination of triangular routing. As to multihoming, there are two working groups that are specifically looking at multihoming and its implications. The first is PTOMAIN (don't ask me to expand it. Randy came up with it). PTOMAIN is focused on improving things now through incremental changes to BGP. One of the approaches they're looking at is the scoping of routing updates to a limited number of ASes, after which they would be aggregated into a shorter prefix. MULTI6 is looking at the problem for IPv6. And in this working group things are going a bit slower, but the constraints are looser, since the deployment at this point is, well, limited. There is at least one proposal that talks about NATting and NAT mapping between the end points and within the network. Imagine the edges NATting an address and then unNATing it at an exit. It beats normal NAT in as much as the IP address that the destination sees is the one that the sender used. How it selects addresses, transmits the mapping, and all that are in a draft document. Of course, this stuff is very immature. Our friend Sean Doran is one of the chairs. Perhaps he can comment more. Finally, there are several efforts going on outside of the IETF that may well have very broad implications for both mobility and multihoming. These are research activities of the IRTF. One is the Routing Research Group (RRG), where they're looking at next generation routing. Another effort is the Name Space Research Group, headed by Steve Crocker, Steve Bellovin, and myself. That effort was asked the question "should there be an additional name space above layer 3?" The answer is hard to find, but we are producing an RFC that should be due out in a few months. Finally, there are some more vaguely related things going on. One is SCTP, which is done. It allows for multiple ip addresses per transport end point (as opposed to a single one with TCP). An extension is being considered to allow for addition of transport addresses in the middle of the connection (right now you have to name them all during setup). And finally there is a new working group called HIP (host identiy payload) being run by Bob Moskowitz (see draft-moskowitz-hip-*). Here the idea is to insert a naming layer just as we discussed in the NSRG. Bob has some interesting applications to improve security. There are also mobility possibilities here too. This stuff is fairly early on. Hope this helps, Eliot Lear