Subject: [RRG] Map-encap, fragmentation, PMTUD etc.

From: Robin Whittle <[email-masked]>
Date: Tue, 29 Jul 2008 09:53:39 +1000

I haven't been keeping up with the list of late, but noticed this
message, in the "Re: [RRG] Six/One Router Design Clarifications"
thread.  Quoting Pekka, Tony wrote:

> |As a result for encap/decap schemes I specifically want to see
> |how they 100% avoid fragmentation, or describe how they deal with
> |it.
>
> Cue Fred.  ;-)

  http://tools.ietf.org/html/draft-templin-seal-22

Please also take a look at:

  http://www.firstpr.com.au/ip/ivip/pmtud-frag/

My approach is intended to cope gracefully with transition to
jumboframes in the DFZ - so it goes well beyond coping with the
immediate problem of the encapsulation overhead pushing the final
packet length over the 1500 byte limit.  I explain it in terms of
Ivip but I think the principles apply just as well to LISP, APT or TRRP.

    - Robin

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---

From: "Templin, Fred L" <[email-masked]>
Date: Mon, 28 Jul 2008 17:17:46 -0700

>-----Original Message-----
>From: Robin Whittle [mailto:[email-masked]] 
>Sent: Monday, July 28, 2008 4:54 PM
>To: Routing Research Group; Routing Research Group
>Cc: Pekka Savola
>Subject: [RRG] Map-encap, fragmentation, PMTUD etc.
>

Also the Linux kernel code is here:

  http://osprey67.com/seal

To Pekka's question, fragmentation is not 100%
avoided however it is "tuned out" as early as
possible so as to avoid RFC4963-type problems
(using a "report fragmentation" mechanism).
 
>Ivip but I think the principles apply just as well to LISP, 

SEAL also supports graceful accommodation of larger
path MTUs. Just to be clear, the 2KB reassembly limit
in SEAL is there *only* to accommodate paths with
marginal MTUs. But, larger path MTUs will still be
naturally discovered and utilized.

Fred
[email-masked]

---

From: Robin Whittle <[email-masked]>
Date: Tue, 29 Jul 2008 11:17:39 +1000

Hi Pekka,

I haven't kept up with the pace of SEAL development since writing
this message in April:

  SEAL & IPTM: differing goals
  http://psg.com/lists/rrg/2008/msg01207.html

This was 2008-04-22 - I thought there were significant differences
in the scope and goals of Fred's and my proposals.

That was for SEAL-11, but there have been many revisions to create
the current version:

I am not sure how relevant the above message is to Fred's work now,
but it might help you understand the differences between the
proposals in April.

The LISP-ALT team's interest in solving the PMTUD problems does not
seem to be as fervent as Fred's or mine.

In March, I wrote a critique of the LISP-ALT approach, based on
draft-farinacci-lisp-06 (2008-02-27):

   LISP PMTU & fragmentation problems
   http://psg.com/lists/rrg/2008/msg00678.html

some followup messages are linked to from:

   http://www.firstpr.com.au/ip/ivip/lisp-links/#pmtud

My impression is that the changes from 06 to the current version 08
do not concern MTU problems.

Fred recently discussed applying SEAL to LISP on the LISP-Interest list:

  Archives: www.queuefull.net/lisp-interest/
  To subscribe, send a message with the subject line "subscribe" to
  <lisp-interest@ lists.civil-tongue.net>.

  http://www.queuefull.net/lisp-interest/msg00031.html  FT
  http://www.queuefull.net/lisp-interest/msg00032.html  DF
  http://www.queuefull.net/lisp-interest/msg00033.html  FT
  http://www.queuefull.net/lisp-interest/msg00034.html  DF
  http://www.queuefull.net/lisp-interest/msg00035.html  FT

  - Robin