Subject: [Draft] The PMTU Discovery for IPv6 Using Hop-by-Hop Option Header

From: Soohong Daniel Park <[email-masked]>
Date: Sat, 08 Mar 2003 14:27:50 +0900

Dear folks.

I'd like to discuss this draft "The PMTU Discovery for IPv6 Using
Hop-by-Hop Option Header", it's not submitted yet.
Before I propose, I want to listen some comments and opinion from IPv6
folks.
I'll attack this draft. Please look into and response.

	Daniel

------------------------------------------------------------------------
---------------------------------------------------
  Abstract   

  This document presents a new method for the PMTU discovery for IPv6. 
  To discover the PMTU of a path, a source node measures its actual PMTU
  using the newly defined Hop-by-Hop Option header, whereas a source 
  node initially assumes that the PMTU of a path is the known MTU of 
  the first hop in the path in the previous one [1981]. In order to 
  measure the actual PMTU, the source node sends the IP packet with the
  newly defined Hop-by-Hop Option header to the destination node with 
  the first data packet when node is beginning. This can eliminate the 
  chance of occurrence of several iterations of the somewhat complex 
  discovery cycle (sending a packet, receiving a Packet Too Big message,
  reducing a packet size). Most of all, since existing PMTU has a weak 
  point for security and denial-of-service attacks, this document 
  suggests a security function when PMTU is going on.
  
  All IPv6 nodes, including both hosts and routers, must implement newly
  Options as defined in this specification.

==============================================
     Soohong Daniel Park
     Researcher
     Mobile Platform Lab, Samsung electronics
     TEL:+82-31-200-3728  FAX:+82-31-200-3147
     mailto:[email-masked]

---

From: "Fred L. Templin" <[email-masked]>
Date: Mon, 10 Mar 2003 15:51:03 -0800

Hello Daniel,

It is an interesting draft, but I'm afraid you've re-created RFC 1063 
(albeit using
IPv6 constructs).  RFC 1063 was obsoleted by RFC 1191 at least partly due to
the requirement that all nodes implement the protocol in order for any 
useful path
MTU information to be obtained on a consistent basis - a feature shared 
by your
proposal. RFC 1063 suggested two methods for implementing such a scheme -
Transport Discovery and IP discovery - and it appears you have taken the low
road. But, I have seen some evidence lately that an efficient 
packetization layer
MTU discovery mechanism can be realized with no requirement for feedback
from the network and no requirement for an explicit probe response from the
destination.

That said, your draft does give me an  idea. An issue for the 
packetization layer
scheme is to provide the lower layers with some way of knowing when a probe
is in progress, i.e., so that the lower layers can let the probe 
through. If the
packetization layer were to insert a hop-by-hop (or destination) option that
essentially amounted to a no-op, the lower layers could know that a 
probe was
in progress.

Your thoughts?

Fred Templin
[email-masked]

>I'll attack this draft. Please look into and response.

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