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[RRG] Fwd: Tunnel MTU
(Fwd'd from 'int-area'):
Please see below for a proposal that addresses the MTU issues
for *-in-IPv4 tunnels. It also addresses the multi-mtu subnet
issue, since it does not rely on ICMP "packet too big" messages
from the last-hop router. Elements of the proposal include:
- trailing "footer" and data as part of encapsulation
- tiny echo requests wrapped in encapsulation headers
and trailing padding - used as probes to elicit tiny
echo replies
- tunnel endpoint discovers tunnel far end EMTU_R and
reassemby timeout values in initial probes=20
- periodic probing to discover the tunnel path MTU,
plus EMTU_R; reassembly timeout fluctuations
- inner fragmentation to create inner packets no larger
than EMTU_R
- outer fragmentation to create outer packets no larger
than the tunnel path MTU
- coservative use of fragmentation to avoid packet loss
within the tunnel
- TE drops unfragmentable packets larger than EMTU_R
and sends ICMP PTB w/o wasting tunnel resources
- protection against fragment misassociations
- protection against off-path attacks
- protection against wrapped ip_id
- backwards compatibility
- incremental deployment
- NAT traversal
Please review and send comments.
Thanks - Fred
fred.l.templin@boeing.com
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A New Internet-Draft is available from the on-line Internet-Drafts=20
directories.
Title : Packetization Layer Path MTU Discovery for=20
IP/*/IPv4 Tunnels
Author(s) : F. Templin
Filename : draft-templin-inetmtu-00.txt
Pages : 20
Date : 2007-9-18
The nominal Maximum Transmission Unit (MTU) MTU of the Internet has
become 1500 bytes, but existing IP/*/IPv4 tunneling mechanisms impose
an encapsulation overhead that can reduce the effective path MTU to
smaller values. Additionally, existing IP/*/IPv4 tunneling
mechanisms are limited in their ability to discover and utilize
larger MTUs. This document specifies new mechanisms for conveying
packets over IP/*/IPv4 tunnels that address these issues.
A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-templin-inetmtu-00.txt
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