Troubleshooting Procedures

PERT Troubleshooting Procedures, as used in the earlier centralised PERT in GN2 (2004-2008), are laid down in GN2 Deliverable DS3.5.2 (see references section), which also contains the User Guide for using the (now-defunct) PERT Ticket System (PTS).

Standard tests

  • Ping - simple RTT/loss measurement using ICMP ECHO requests
  • Fping - ping variant with concurrent measurement of multiple destinations

End-user tests

tweak tools http://www.dslreports.com/tweaks is able to run a simple end-user test, checking such parameters as TCP options, receive window size, data transfer rates. It is all done through the user's web-browser making it a simple test for them to do.

Linux Tools and Checks

ip route show cache

Linux is able to apply specific conditions (MSS, ssthresh) to specific routes. Some parameters (such as MSS, ssthresh) can be set manually (with ip route add|replace ...) whilst others are changed automatically by Linux in response to what it learns from TCP (such parameters include estimated rtt, cwnd and re-ordering). The learned info is stored in the route cache and thus can be shown with ip route show cache. Note, this learning behaviour can actually limit TCP performance - if the last transfer was poor, then the starting TCP parameters will be be pessimistic. For this reason some tools, e.g. bwctl, always flush the route cache before starting a test.

References

  • PERT Troubleshooting Procedures - 2nd Edition, B. Belter, A. Harding, T. Rodwell, GN2 deliverable D3.5.2, August 2006 (PDF)

-- SimonLeinen - 18 Sep 2005 - 17 Aug 2010
-- BartoszBelter - 28 Mar 2006

Topic revision: r25 - 2010-08-17 - SimonLeinen
 
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