IP Fragmentation - Not reliable over the Internet?

Christopher Palmer Christopher.Palmer at microsoft.com
Fri Aug 30 00:51:20 UTC 2013


This is what I'm concerned about:

"""
1. If I originate IP packet fragments, such as an 8000 byte NFS packet broken 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 at gmail.com [mailto:wherrin at gmail.com] On Behalf Of William Herrin
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 at microsoft.com> wrote:
> What is the probability that a random path between two Internet hosts 
> will traverse a middlebox that drops or otherwise barfs on fragmented 
> 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 broken 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 next hop will fail to correctly fragment that packet (or that the correctly fragmented 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 don't-fragment bit, what's the chance of failing to receive the "packet too big" message it causes the intermediate router to send?

Are you after the answer to one in particular?

Regards,
Bill Herrin



--
William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004



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