[170795] in North American Network Operators' Group
Re: real-world data about fragmentation
daemon@ATHENA.MIT.EDU (Dan Wing)
Wed Apr 9 15:43:35 2014
From: Dan Wing <dwing@cisco.com>
In-Reply-To: <253521C4-EA53-4CF3-BC5F-EBC424989DFC@hopcount.ca>
Date: Wed, 9 Apr 2014 12:42:29 -0700
To: Joe Abley <jabley@hopcount.ca>
Cc: NANOG Mailing List <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Apr 2, 2014, at 11:14 AM, Joe Abley <jabley@hopcount.ca> wrote:
> Hi all,
>=20
> 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.
>=20
> Is anybody aware of any wide-scale studies that examine the =
probability of fragmentation of datagrams of different sizes?
>=20
> 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.
>=20
> What does the curve look like between 576 bytes and 10,000 bytes?
>=20
> I might expect exciting curve action around 1500 bytes (because =
ethernet), 1492 (PPPoE), 1480 (GRE), etc. But I'm interested in actual =
data.
>=20
> 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
