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I-D on operational MTU/fragmentation issues in tunneling

  • From: Pekka Savola
  • Date: Mon Oct 11 04:15:21 2004

Hi all,

I've written a very short (about 5 pages of meat)  Internet-Draft
describing the issues and operational approaches to the problems faced
with doing tunneling in the network -- as these issues kept coming up
again and again with IP-in-IP, GRE, L2TP, etc.  The approaches may be
different for passive monitoring ('wiretapping' etc.) and 'active'

The document is about to be IETF Last Called for Informational RFC,
but prior to that, I'd like to solicit comments/feedback/review from
the people here because I'm 100% sure a lot of people have been faced
with these issues (we certainly have..).

Please send comments to me by the end of this week, either on- of
off-list, as you deem appropriate.

Find it at:

   Tunneling techniques such as IP-in-IP when deployed in the middle of
   the network, typically between routers, have certain issues regarding
   how large packets can be handled: whether such packets would be
   fragmented and reassembled (and how), whether Path MTU Discovery
   would be used, or how this scenario could be operationally avoided.
   This memo justifies why this is a common, non-trivial problem, and
   goes on to describe the different solutions and their characteristics
   at some length.

Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings