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real-world data about fragmentation

daemon@ATHENA.MIT.EDU (Joe Abley)
Wed Apr 2 14:15:11 2014

From: Joe Abley <jabley@hopcount.ca>
Date: Wed, 2 Apr 2014 14:14:22 -0400
To: NANOG Mailing List <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org

Hi all,

It's common wisdom that a datagram that needs to be fragmented between =
endpoints (because it is bigger than the path MTU) will demonstrate less =
reliable delivery and reassembly than a datagram that doesn't need to be =
fragmented, because math, firewall, other, take your pick.

Is anybody aware of any wide-scale studies that examine the probability =
of fragmentation of datagrams of different sizes?

For example, I could reasonable expect an IPv4 packet of 576 bytes not =
to be fragmented very often (to choose a size not at random). The =
probability of a 10,000 octet IPv4 packet getting fragmented seems =
likely to be 100%, if we're talking about arbitrary paths across the =
Internet.

What does the curve look like between 576 bytes and 10,000 bytes?

I might expect exciting curve action around 1500 bytes (because =
ethernet), 1492 (PPPoE), 1480 (GRE), etc. But I'm interested in actual =
data.

Anybody have any pointers? IPv4 and IPv6 are both interesting.


Joe=


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