The Penguin's Practical Network Troubleshooting Guide, Part 2
Tracking Down Network Congestion
June 13, 2006
Last week we used
tcptraceroute to pinpoint connectivity problems, and
nmap to spy on users. Oh yeah, and to map entire subnets with a single command. Today we'll look at ways, when your users crab about "the network is slow", to determine if it's network or server troubles.
mtr, My Traceroute, is a great little tool for giving you a real-time snapshot of network performance. Run it like this:
$ mtr -rc 100 bratgrrl.com
This runs mtr for a count of 100 times and presents the output in a report format. There will always be a bit of packet loss, so one or two percent losses aren't significant. You should see results something like this sample output.
The interesting part of this
mtr report is items 6, 7, 8, and 9, where my poor little packets are rattling around AT&T's servers like dice in a shaker cup. AT&T and Qwest are notorious for behaving more like trampolines than routers.
To see a realtime capture don't use the
-r (report) option. An interesting and useful feature is to toggle the
j key to see jitter statistics, which is helpful for debugging VoIP and other services that require smooth, uninterrupted data streams. We've provided some sample output.
h key at any time to get help,
q to quit.