Large packets lost between Onsala and Stockholm

PTS Case 11

Background

Onsala observatory contacted the PERT about a problem with traceroute - it did not work as expected between an end-system in Onsala (a Mk5A system) and a SUNET test server in Stockholm. It seemed that traceroute packets between the Onsala Mk5A and the SUNET test system were being dropped.

Investigation

Discussions between the PERT and SUNET determined there were no MTU problems (which had been the primes suspect) on the path between the test server and Onsala Mk5A - the SUNET network core had an MTU of 8192 bytes and the end-systems Gigabit Ethernet cards used an MTU 4470.
It was determined that traceroute only did not work when run after iperf test, and this was true when running iperf and traceroute between the Onsala Mk5A and any other end system, not just the SUNET test system. To 'cure' traceroute the Mk5A had to be re-booted. It was also determined that the problem was particular to traceroute and did not affect, for example, tracepath.

Outcome

Given that this problem only affected this Mk5A, and because there was a perfectly good work-around (which was, to use tracepath instead of traceroute), the end-user (Onsala Observatory) agreed that no further investigation was necessary and the case could be closed.

– Main.TobyRodwell - 31 Jan 2007