[Int-area] FW: [RRG] Subnetwork Encapsulation and Adaptation Layer (SEAL)

["Templin, Fred L" <Fred.L.Templin at boeing.com>]

This message is forwared from the Routing Research Group
mailing list. A new document with int-area implications
is available and titled:

  "Subnetwork Encapsulation and Adaptation Layer (SEAL)"
  http://www.ietf.org/internet-drafts/draft-templin-seal-03.txt

SEAL in part specifies an MTU determination scheme based
on the Report Fragmentation (RF) concept that was first
proposed by Charles Lynn on the tcp-ip mailing list in
1987 and re-introduced by Steve Deering on the Path MTU
working group mailing list in 1989. Digests from those
lists are found at:

  http://ipvlx.com/tcp_ip.txt
  http://gatekeeper.dec.com/pub/DEC/WRL/mogul/mtudwg-log

Based on the list discussions, the Report Fragmentation
(RF) method seemed to be the most attractive approach
under consideration for IPv4 path MTU discovery, but was
abandoned in favor of the (Don't Fragment/Fragmentation
Needed) method that eventually became RFC1191. The RF
method seems to have been abandoned due in part to
difficulty in procuring an "RF" bit in the IPv4 header,
difficulty in defining an ICMP Fragmentation Report
message and the concern that not all hosts at that time
correctly implemented IP reassembly.

The SEAL proposal addresses all of these points (as well
as others) and shows that a Report Fragmentation-based path
MTU discovery capability for router-to-router tunneling
in the Internet is still possible and could correct the
operational difficulties associated with traditional path
MTU discovery approaches. Moreover, the SEAL approach
supports true diversity, especially for subnetworks that
contain heterogeneous link types with diverse MTUs and/or
L2 address formats.

Please review and comment,

Fred
fred.l.templin at boeing.com
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