Subject: Re: [lisp] Fwd: Re: Re: A mapping system design-- specificationof LISP+ALT

From: [email-masked] (Noel Chiappa)
Date: Wed, 2 Dec 2009 14:37:58 -0500 (EST)

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

    > 2) If your data plane notices someone sending to a and you wish they
    > were sending to b, then SMR them in the control plane. Then you can
    > give them a longer prefix when you get their map request.

Interesting idea... I missed that one!

You'd have to make sure the destination ETR for tbe main block knew about the
sub-blocks (so it could check for packet to them), and you'd have to make
sure the Map-Request went to the right ETR, etc, but it might work...

    > the spec currently says that a shorter prefix replaces a longer one in
    > the map cache, so if you ever send to a part of the EID space that has
    > the short prefix, it will replace the long prefix you already have. I
    > think more thought needs to be put into this section of the spec, and
    > perhaps short map replies should not replace longer prefix map replies
    > that have already been verified.

Perhaps. I think this whole thing should be thought through, and we should
_first_ decide it we want to _allow_ overlapping mappings, or just outlaw
them. Only if we decide to keep them would we need to go through and make them
work right (which involves a number of things, not just the 'don't discard
longer entries').

Of course, now that I think about it, how much work it would take to make them
work right, versus how useful they would be, would be a major piece of data
for the 'keep/outlaw' decision... :-)

	Noel

---

From: Sam Hartman <[email-masked]>
Date: Wed, 02 Dec 2009 16:26:43 -0500

>>>>> "Noel" == Noel Chiappa <[email-masked]> writes:

    Noel> Perhaps. I think this whole thing should be thought through,
    Noel> and we should _first_ decide it we want to _allow_ overlapping
    Noel> mappings, or just outlaw them. Only if we decide to keep them
    Noel> would we need to go through and make them work right (which
    Noel> involves a number of things, not just the 'don't discard
    Noel> longer entries').

Agreed.
I tried to implement overlapping mappings because the spec said I
should:-)

The strongest argument for permitting overlapping mappings I've seen is
the default PETR case.