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Emulab FAQ: Troubleshooting: I get a WARNING message from linktest, what does it mean?

Emulab FAQ: Troubleshooting: I get a WARNING message from linktest, what does it mean?

There are currently two warning messages that you might get from Linktest:

  • *** WARNING: some hosts do not support linktest, skipping links between those hosts
    This means that one or more of the hosts in your experiment are running an OS that does not support Linktest. You can find our for sure by visiting the OSID List, looking up your image(s), and seeing if it has an osfeature of linktest. Other links in your experiment will be tested.
  • *** WARNING: tb-set-noshaping used on one or more links, skipping BW tests for those links.
    You have specified tb-set-noshaping for one or more links or LANs in your NS file. Since these commands will disable bandwidth shaping on the indicated links, Linktest will not test their bandwidth. All other links in your experiment will be tested.
  • *** May see BW errors for ''node-link'' to ''node-link'' (...)
    In a nutshell, the link in question has some combination of low-bandwidth, high-latency, and high-lossrate that might result in an inaccurate bandwidth reading. Linktest uses an iperf run on each link for measuring bandwidth and it limits the length of each such run in order to bound the maximum runtime for the entire Linktest session. When an iperf run completes, the sender expects a final acknowledgement from the receiver before it stops the clock in order to calculate the observed bandwidth. The longer it takes to receive the ACK, the less accurate the bandwidth reading will be. Linktest calculates how long it should reasonably wait to receive the ACK, based on the bandwidth, delay and loss rate of the link and possibly lengthens the iperf run to minimize the effect of the ACK wait. If the required run time exceeds the maximum per-test runtime, this warning is given.