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.
tcpflow is similar to ‘tcpdump’, in that both process packets from the wire or from a stored file. But it’s different in that it reconstructs the actual data streams and stores each flow in a separate file for later analysis.
tcpflow understands sequence numbers and will correctly reconstruct data streams regardless of retransmissions or out-of-order delivery.
Jeremy Elson developed the first version of tcpflow in 1999 but stopped maintaining it in 2003. In 2006 Simson Garfinkel took over maintenance of the program and added:
- support for VLANs
- support for IPv6
- DFXML output of the connections in a report.xml file.
- Improved performance through the use of the C++ STL classes.
- Support for continuous operation (tcpflow now purges out old flows).
- Variable Filename specifications.
- A plug-in architecture.
tcpflow is based on the LBL Packet Capture Library (available from LBL) and therefore supports the same rich filtering expressions that programs like ‘tcpdump’ support. It should compile under most popular versions of UNIX; see the INSTALL file for details. tcpflow stores all captured data in files that have names of the form:
where the contents of the above file would be data transmitted from host 126.96.36.199 port 2345, to host 10.11.12.13 port 45103. VLAN information, if provided is stored in brackets.
tcpflow stores all captured data in files that have names of the form
where the contents of the above file would be data transmitted from host 188.8.131.52 port 2345, to host 10.11.12.13 port 45103.
- tcpflow does not understand IP fragments;
- tcpflow does not understand 802.11 headers.