real-world data about fragmentation

Wed Apr 9 19:42:29 UTC 2014

On Apr 2, 2014, at 11:14 AM, Joe Abley <jabley at hopcount.ca> wrote:

> 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.

Seems a good thing for RIPE Atlas probes to measure.  But they are probably not generally connected to representative networks (read: poor networks).

-d