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Weekly report

18

Mar

2014

A longer run to find black holes in load balancers using our version of fast mapping has been carried out. Instead of 1000 addresses, two lots of 5000 were used. In each case there was an initial traceroute MDA run followed by eight Paris traceroute runs and in turn a final MDA run. The resulting warts files were scanned using the upgraded analysis program which when it finds a short Paris trace, compares the initial and final MDA runs for route changes and checks the Paris end point to see if it is within a load balancer. Some special cases which are flagged are when the destination is inside a load balancer itself and when the Paris stop point is at the convergence point of a load balancer. These special cases explained the possible black holes found in the 1000 destination data, however some true appearance black holes in LBs were found in the 5000 destination data. It may be possible to continue this on planetlab however it is probably necessary to use ICMP probes, and this would reduce the number of per flow load balancers seen, requiring more probing to see the same number of load balancers.

Initial runs were carried out using valgrind callgrind. It took me a while to realise that I could not use my Internet Simulator bash script as callgrind appeared to analyse the bash shell in this case. When I ran the program directly I still couldn't start with no instrumentation and then manually activate it. When I did this there were no events collected. This seems to be a callgrind bug. Another possibility is to try the programmatic activation of callgrind instrumentation by recompiling the simulator with an activation macro included. It turns out that making memory map nodes in the build method starts almost immediately, and I don't know how long it takes before it gets to making links. Running valgrind without a delayed start can help answer this. The objective is still to delay for a day and then run instrumentation for two days.