Purpose: iftop displays current bandwidth usage by pairs of hosts on a network interface.
Traffic capture: iftop listens on a named interface or, if none is specified, the first interface it finds that looks like an external interface.
Permissions: iftop must be run with sufficient permissions to monitor all network traffic on the interface.
Filtering: It supports packet filter code and display filters, with display filters affecting what is shown rather than what is captured.
Traffic views: The display can show host names, port numbers, bandwidth bars, totals, and traffic rates averaged over 2, 10, and 40 seconds.
Configuration: iftop can read settings from a configuration file, defaulting to ~/.iftoprc when no alternate file is specified.
Terminal output: A text interface without ncurses is available, with options to print a single output after a specified number of seconds and limit the number of lines.
Network support: Configuration options include an IPv4 network boundary and display of link-local IPv6 traffic.
Promiscuous mode: iftop can put the interface into promiscuous mode to capture traffic between other hosts on the same network segment.
Integration: The manual lists tcpdump, pcap, and driftnet as related tools; it does not state integrations with external services.
Security and license: The manual identifies iftop as free software under the GNU General Public License, version 2 or any later version, and provides it without warranty.
Notable limitation: After changing the capture filter, existing display entries may remain for up to 40 seconds because the display reflects a recent capture window.
Maker: The manual names Paul Warren as the author.
Price from: Free

Where it ranks on Freedom251

Best Bandwidth Monitoring Software in 2026#11 of 31

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Sources

sources.debian.org/src/iftop/1.0~pre4-7/iftop.cat· checked 4 Oct 2026