real-world data about fragmentation

[Joe Abley <jabley () hopcount ca>]

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