[165328] in North American Network Operators' Group
RE: IP Fragmentation - Not reliable over the Internet?
daemon@ATHENA.MIT.EDU (Christopher Palmer)
Thu Aug 29 20:51:33 2013
From: Christopher Palmer <Christopher.Palmer@microsoft.com>
To: William Herrin <bill@herrin.us>
Date: Fri, 30 Aug 2013 00:51:20 +0000
In-Reply-To: <CAP-guGUhVyRqNfAyHYegVtZf5H493to=2Kh-SPaN15G2V+A_mg@mail.gmail.com>
Cc: North American Network Operators' Group <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
This is what I'm concerned about:
"""
1. If I originate IP packet fragments, such as an 8000 byte NFS packet brok=
en into 1500 byte fragments, what's the probability of some host before the=
other endpoint dropping one or all of those fragments?
"""
Big thanks to everyone who has sent thoughts already, really quite helpful.
-----Original Message-----
From: wherrin@gmail.com [mailto:wherrin@gmail.com] On Behalf Of William Her=
rin
Sent: Tuesday, August 27, 2013 10:45 AM
To: Christopher Palmer
Cc: North American Network Operators' Group
Subject: Re: IP Fragmentation - Not reliable over the Internet?
On Mon, Aug 26, 2013 at 8:01 PM, Christopher Palmer <Christopher.Palmer@mic=
rosoft.com> wrote:
> What is the probability that a random path between two Internet hosts=20
> will traverse a middlebox that drops or otherwise barfs on fragmented=20
> IPv4 packets?
Hi Christopher,
I think there might be three rather different questions here:
1. If I originate IP packet fragments, such as an 8000 byte NFS packet brok=
en into 1500 byte fragments, what's the probability of some host before the=
other endpoint dropping one or all of those fragments?
2. If I send an IP packet that's too large for the path and *don't* set the=
don't-fragment bit, what' the chance that the router with the too-small ne=
xt hop will fail to correctly fragment that packet (or that the correctly f=
ragmented packet will fall into trap #1 above)?
3. If I send an IP packet that's too large for the path and *do* set the do=
n't-fragment bit, what's the chance of failing to receive the "packet too b=
ig" message it causes the intermediate router to send?
Are you after the answer to one in particular?
Regards,
Bill Herrin
--
William D. Herrin ................ herrin@dirtside.com bill@herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls C=
hurch, VA 22042-3004
