Brian,
After having discussed with others, please see attached
for a proposal that addresses the MTU issues for 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
- 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
The proposal updates existing tunneling mechanisms
(including IPv6/*/IPv4) and also offers a solution for
the RAM/RRG tunnel MTU problem space. Should this be
discussed here, or take it over to the ram/rrg lists?
Thanks - Fred
[EMAIL PROTECTED]
> -----Original Message-----
> From: Brian E Carpenter [mailto:[EMAIL PROTECTED]
> Sent: Thursday, September 13, 2007 12:54 PM
> To: IPv6
> Subject: [Fwd: Re: [RRG] Re: [RAM] Tunneling overheads and
> fragmentation]
>
> For those who aren't following the routing & addressing
> discussions, there's been some discussion on MTU size
> issues and tunnel-based solutions. See below, but it did
> strike me that 2460 doesn't *explicitly* say "don't send
> more than 1280 bytes unless you determine that a larger
> MTU will work." It's implied but not stated.
>
> Brian
>
> -------- Original Message --------
> Subject: Re: [RRG] Re: [RAM] Tunneling overheads and fragmentation
> Date: Thu, 13 Sep 2007 10:23:06 -0700
> From: Dino Farinacci <[EMAIL PROTECTED]>
> To: Brian E Carpenter <[EMAIL PROTECTED]>
> CC: Gert Doering <[EMAIL PROTECTED]>, Robin Whittle
> <[EMAIL PROTECTED]>, RRG <[EMAIL PROTECTED]>
>
> > I just re-read RFC 2460 section 5. Admittedly things are less
> > clear for IPv4, but it seems clear that IPv6 senders should not
> > exceed 1280 bytes (pre-encapsulation) unless they have succeeded
> > in discovering a larger path MTU.
>
> Nice to hear some good news for a change. ;-)
>
> Thanks,
> Dino
>
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--- Begin Message ---
A New Internet-Draft is available from the on-line Internet-Drafts
directories.
Title : Packetization Layer Path MTU Discovery for
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:
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