Last Updated on March 5, 2026
tcpflow is a program that captures data transmitted as part of TCP connections (flows), and stores the data in a way that is convenient for protocol analysis and debugging.
Each TCP flow is stored in its own file. Thus, the typical TCP flow will be stored in two files, one for each direction. tcpflow can also process stored ‘tcpdump’ packet flows.
This is free and open source software.
tcpflow stores all captured data in files that have names of the form:
[timestampT]sourceip.sourceport-destip.destport[--VLAN][cNNNN]
where: timestamp is an optional timestamp of the time that the first packet was seen T is a delimiter that indicates a timestamp was provided sourceip is the source IP address sourceport is the source port destip is the destination ip address destport is the destination port VLAN is the VLAN port c is a delimiter indicating that multiple connections are present NNNN is a connection counter, when there are multiple connections with the same [time]/sourceip/sourceport/destip/destport combination.
Website: github.com/simsong/tcpflow
Support:
Developer: Simson L. Garfinkel and contributors
License: GNU General Public License v3.0
tcpflow is written in C++. Learn C++ with our recommended free books and free tutorials.
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