Analyzing network traffic with iftop

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The iftop command-line tool captures data traffic on network interfaces and then analyzes which network connections exist and how many data packets are running on each one. In this way, you can quickly determine how much bandwidth each program and service requires and is possibly overloading. Packet filtering is just one of many options that helps.

Table 1

Pcap Filter

Filter Description
dst host All packets with a destination IP address of
src port 22 All packets arriving on port 22
dst portrange 22-33 All packets departing in a range of ports from 22 through 33
gateway All packets with the gateway IP address of


The author thanks Axel Beckert for his help in preparing this article.

The Author

Frank Hofmann ( studied computer science at the Technical University of Chemnitz, Germany. He currently works in Berlin at Buro 2.0, a network of open source experts, as a service provider specializing in printing and typesetting. Frank is also cofounder of the Wizards of FOSS training company and has coordinated meetings of the Linux User Group in the Berlin-Brandenburg region since 2008.

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