Wireshark comes with a wide range of cool analysis tools. But I have yet to find a way to measure jitter and delay  over a network node that works with any kind of traffic. You might be able to utilize Cisco's IP SLA and graph the results using SNMP. But that will require two Cisco routers: one on each side of the node in question. And without any nodes in between. This might not be your topology. And you won't measure the real traffic as IP SLA generates its own traffic for measurement. With TAP devices and the method described below, you will be able to measure directly on TCP or UDP traffic going through the node.

I recently discovered Feedgnuplot. Feedgnuplot is basically a wrapper around Gnuplot, that makes Gnuplot able to plot data fed through a pipe in realtime.  Feedgnuplot is thus able to plot realtime performance counters from headless sytems like routers, firewalls and storage systems. In this short article I will give a few examples on how to use Feedgnuplot for various purposes.

Sure: There are a lot of graphing tools and network monitoring tools available for free. But for quick and dirty troubleshooting, feedgnuplot has quite some advantages, which I will get back to.


Follow log files in real time: tail -f

If you don't know this command by know you might be quite new to the Unix / Linux world. Tail is a classic Unix command. It can be used to show last n lines of a log file. But the command really comes to live, when adding the -f parameter. Try:

tail -f /var/log/apache/access.log.

Tail will stick to the log file and print out lines written to the log file as they are written. Very useful. Tail can even be used for multiple files at once. Just use an asterisk like:

tail -f /var/log/apache/*

This article describes how to configure a point to point PPPoE connection between two Cisco routers.

This article is a part of my article collection: Cisco configuration snippets. The snippets show just and only just how to do a basic configuration on a specific topic.