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Re: multi-homing

  • From: Eliot Lear
  • Date: Fri Aug 31 12:24:39 2001


> 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

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