Re: [RRG] LISP-NERD reachability and MTU detection

[Scott Brim <swb@employees.org>]

Excerpts from Eliot Lear at 11:53:33 +0100 on Mon 17 Dec 2007:
> > The ETR receiving the packet sees the "please respond" message and
> > sends back info to the originating ITR that could encompass
> > current locator preference information (for traffic engineering),
> > the up/down status of other ETRs, the maximum packet size the ETR
> > is prepared to receive, possibly (if the ETR supports reassembly)
> > the maximum packet size the ETR is prepared to reassemble from
> > fragments.
> 
> The ETR really only has its interface MTU.  It doesn't look a whole
> lot different than any other router.  Again, I think this is a
> general tunneling problem, and not something that is specific to
> LISP.  I do think the problem is worth considering in LISP's
> context, but we should be thinking in more general terms when it
> comes to solutions (e.g, L2TP, IPSEC, IP over HTTP, etc., etc.).

This is where I come to.  (1) LISP itself cannot and should not keep
track of path MTU; (2) whatever mechanisms we use for path MTU should
work for all packets, whether crossing a LISP encap/decap point or
not.

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