Implementations/suggestions for Multihoming IPv6 for DSL sites

Mon Apr 11 16:19:54 UTC 2011

On Mon, Apr 11, 2011 at 11:26 AM, Owen DeLong <owen at delong.com> wrote:
> I'd agree with you if it weren't for the fact I keep thinking I just about understand LISP and then get told
> that my understanding is incorrect (repeatedly).

I agree it is not simple.

At a conceptual level, we can think of existing multi-homing practices
as falling into one of three broad categories:
1) more state in DFZ -- end-site injects a route into BGP

2) triangular routing -- tunnel/circuits/etc to one or more upstream
routers while not injecting anything to DFZ

3) added work/complexity on end-host -- SCTP and friends

LISP is a compromise of all these things, except #3 happens on a
router which does tunneling, not the end-host.  Whether you think it's
"the best of both [three?] worlds," or the worst of them, is up to
you.

I personally believe LISP is a horrible idea that will have trouble
scaling up, because a large table of LISP mappings is not any easier
to store in FIB than a larger DFZ.  The "solution" the LISP folks
think works for this is a side-chain mapping service which the router
can query to setup encapsulation next-hops on-demand, which means if
your FIB isn't big enough to hold every mapping entry, you are
essentially doing flow-based routing, but with "flows" defined as
being toward a remotely-defined end-site rather than toward an
individual IP address (so not quite as bad as "flow-based routing" of
the past, but still bad.)

Maybe I also don't understand LISP and need to RTFM more, but my
current understanding is that it is a dead-end technology without the
ability to dramatically scale up the number of multi-homed end-sites
in a cheaper manner than what is done today with BGP.

I think we would be better off with more work on things like SCTP.

-- 
Jeff S Wheeler <jsw at inconcepts.biz>
Sr Network Operator  /  Innovative Network Concepts