[157580] in North American Network Operators' Group
Re: IP tunnel MTU
daemon@ATHENA.MIT.EDU (Chris Woodfield)
Mon Oct 29 19:40:43 2012
From: Chris Woodfield <rekoil@semihuman.com>
In-Reply-To: <E1829B60731D1740BB7A0626B4FAF0A65E0E03E73E@XCH-NW-01V.nw.nos.boeing.com>
Date: Mon, 29 Oct 2012 16:40:22 -0700
To: "Templin, Fred L" <Fred.L.Templin@boeing.com>
Cc: NANOG list <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
True, but it could be used as an alternative PMTUD algorithm - raise the =
segment size and wait for the "I got this as fragments" option to show =
up...
Of course, this only works for IPv4. IPv6 users are SOL if something in =
the middle is dropping ICMPv6.
-C
On Oct 29, 2012, at 4:02 PM, Templin, Fred L wrote:
> Hi Bill,
>=20
>> Maybe something as simple as clearing the don't fragment flag and
>> adding a TCP option to report receipt of a fragmented packet along
>> with the fragment sizes back to the sender so he can adjust his mss =
to
>> avoid fragmentation.
>=20
> That is in fact what SEAL is doing, but there is no guarantee
> that the size of the largest fragment is going to be an accurate
> reflection of the true path MTU. RFC1812 made sure of that when
> it more or less gave IPv4 routers permission to fragment packets
> pretty much any way they want.
>=20
> Thanks - Fred
> fred.l.templin@boeing.com
>=20
