27 and 28 January 2011

Download the video file - matthew-l.mp4

WAND Update

Matthew Luckie


Matthew Luckie's talk on Measuring Path MTU Discovery Behaviour reports on measurements of PMTUD behaviour for ~50k popular IPv4 websites and ~1k popular IPv6 websites.  We measure the IPv4 failure rate between 5% and 18% depending on the MTU of the constraining link, and 2.4% and 56% in IPv6.  We explore methods webserver operators are using to reduce their dependence on PMTUD, and find 11% limit themselves to sending packets no larger than 1420 bytes, but a disproportionate 27% of these systems fail PMTUD for links smaller than 1420 bytes.  We identify a number of behaviours that seem to be software bugs rather than filtering by firewalls.

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