Subject: Measuring Path MTU Discovery Behaviour

From: Lars Eggert <[email-masked]>
Date: Mon, 1 Nov 2010 16:53:22 +1100

An ACM IMC paper of potential interest to the TSV area:

Measuring Path MTU Discovery Behaviour
Matthew Luckie (University of Waikato)
Ben Stasiewicz (University of Waikato)
http://conferences.sigcomm.org/imc/2010/papers/p102.pdf

Path MTU Discovery (PMTUD) is widely believed to be un- reliable because of firewalls that discard ICMP “Packet Too Big” messages. This paper measures PMTUD behaviour for 50,000 popular websites and finds the failure rate in IPv4 is much less than previous studies. We measure the overall failure rate between 5% and 18%, depending on the MTU of the constraining link. We explore methods webserver oper- ators are using to reduce their dependence on PMTUD, and find 11% limit themselves to sending packets no larger than 1380 bytes. We identify a number of common behaviours that seem to be software bugs rather than filtering by fire- walls. If these are corrected PMTUD failures could be re- duced by 63%. We further find the IPv6 failure rate is less than the IPv4 rate even with more scope for failure in IPv6.

Lars