Subject: Re: [lisp] Comments about the LISP header

From: [email-masked] (Noel Chiappa)
Date: Wed, 27 May 2009 09:44:40 -0400 (EDT)

> From: "Templin, Fred L" <[email-masked]>

    > how can ITR I know that the path to ETR E is down without testing it? 

Without sending _some_ packets across it, it can't, as far as I can see.

    > if the ping is piggybacked on top of ordinary data packets the overhead
    > is perhaps not so much.

Exactly; that's why there's been some thinking recently about piggybacking
reachability detection on user data traffic.

	Noel

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From: [email-masked] (Noel Chiappa)
Date: Thu, 28 May 2009 12:05:22 -0400 (EDT)

<Lots of email to catch up on from yesterday... replies to a couple of things
together...>

    > From: Sam Hartman <[email-masked]>

    Noel> The _protocol_ mechanism is very simple and cheap. The
    Noel> algorithms to use it inside the nodes can change over time,
    Noel> and in a trivially interoperable way.

    > it sounds like you believe that the protocol bits are simple enough
    > that we can look at them today?

Very close, yes. (I've been thinking about this for a while, since the issue
of reachability was flagged as a problem a while back.)

There are a couple of _really_ minor technical protocol issues I'd like to
think through, so the proposal that comes up is fully baked, but that should
only take a few days.

    > From: "Darrel Lewis (darlewis)" <[email-masked]>

    > Link Aggregation schemes for core routers use 5 tuple hashes which
    > include s-port and d-port fields of udp/tcp protocols. ISP operators
    > early in the specification processes provided explicit and animated
    > feedback saying that UDP encapsulation was a critical feature.

Indeed; since our goal is to get something actually deployed widely, my take
would be 'anything the people who are going to actually deploy it ask for, we
should do, if it is at all feasible'.

So if there's not a huge technical downside to option A as opposed to B, and
the people who are actually going to deploy prefer A, A is what we do...

	Noel

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From: [email-masked] (Noel Chiappa)
Date: Thu, 28 May 2009 12:55:27 -0400 (EDT)

> From: Margaret Wasserman <[email-masked]>

    > if we think that using additional UDP ports would be the best
    > extensibility mechanism for LISP (which I could be convinced that it
    > is), I think we should just make a note of that in the spec.

I'm not sure it's wise to go quite that far. See, I think exactly what we do
in the future, if we need to make changes, will depend a lot on what the
situation is. E.g. if LISP does not catch on, not a problem, there is no need
to worry about it! :-) And if all the ISPs are using it, maybe a new
data-handling protocol would be better. Etc, etc.

But I have no idea what the detailed future will look like, so I don't know
how the various factors will weigh in together. How about we just recognize
that there are a number of potential ways to handle that issue, and it's not
necessarily possible to say now which will be best then, and then place it
down for the moment?

Less is more... :-)

	Noel