net/tcpflow - The NetBSD Packages Collection

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
or debugging. A program like 'tcpdump' shows a summary of packets seen on the
wire, but usually doesn't store the data that's actually being transmitted.
In contrast, tcpflow 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. However, it
currently does not understand IP fragments; flows containing IP fragments will
not be recorded properly.

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.