Subject: Re: [Int-area] [rrg] Please respond: Questions from the IESG as to whether a WG forming BOF is necessary for LISP

From: [email-masked] (Noel Chiappa)
Date: Wed, 28 Jan 2009 23:05:19 -0500 (EST)

> From: Christian Vogt <[email-masked]>

    > Portability of EID prefixes requires that the ALT topology follows
    > EID-addressing. This leads to potentially longer-than-optimal paths
    > along the ALT topology. Vice versa, if path stretch is to be limited,
    > then portability of EID prefixes must be restricted.

Yes, but this is only for the first packet(s), until the mapping gets back to
the ITR. Do you really think a few extra hops there are going to be a
problem? (Especially given that due to EGP/IGP information flow barriers,
paths probably aren't completely optimal anyway....)

Also, what percentage of DNS resolutions take more than one round-trip
(because of the use of multi-level DNS names)? Surely that's an even worse
delay (several round-trips, as opposed to simply a few extra hops), but I
don't think I've heard complaints about that?

	Noel
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From: Christian Vogt <[email-masked]>
Date: Sat, 31 Jan 2009 22:57:22 -0800

[ Forked from thread:  "Please respond: Questions from the IESG as to
whether a WG forming BOF is necessary for LISP". ]

On Jan 28, 2009, Noel Chiappa wrote:

> (because of the use of multi-level DNS names)? Surely that's an even
> worse delay (several round-trips, as opposed to simply a few extra
> hops), but I don't think I've heard complaints about that?

Noel -

There are two significant differences between the delays introduced by
DNS during hostname resolution, and the delays introduced by a pull-
based mapping system:

- DNS-related delays do not affect transport protocols, whereas pull-
   based mapping systems do.

- DNS does not create off-path dependencies for routing, whereas a
   pull-based mapping system does.  In pull-based mapping systems, at
   least the mapping requests must travel via an overlay because the
   direct routing path is not yet known at the request time.  This
   creates an off-path dependency for routing.

The first bullet is a performance issue.  Experimentation could help in
finding out how much of a problem this is.  The second bullet is a
robustness issue.  More analysis and discussion would help to better
understand the consequences of this.

- Christian