tcpflow – TCP Flow Recorder for Protocol Analysis and Debugging

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. 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 port 2345, to host port 45103.

The only downside to this tool is that it’s not being actively maintained, the last version was released in 2003.

The upside is that the TCP protocol hasn’t changed, so the tool still work just fine.

Definitely extremely useful for network forensics, it’s one of the tools I use to demo network dissection in classes.

You can download it here:

Version 0.21 source tarball
Version 0.21 Source RPM

Or read more here.

Posted in: Forensics, Networking Hacking

, , ,

Latest Posts:

SecLists - Usernames, passwords, URLs, sensitive data patterns, fuzzing payloads, web shells SecLists – Usernames, passwords, URLs, sensitive data patterns, fuzzing payloads, web shells
SecLists is the security tester's companion. It's a collection of multiple types of lists used during security assessments, collected in one place.
DeepSound - Audio Steganography Tool DeepSound – Audio Steganography Tool
DeepSound is an audio steganography tool and audio converter that hides secret data into audio files, the application also enables you to extract from files.
2019 High Severity Vulnerabilities What are the MOST Critical Web Vulnerabilities in 2019?
So what is wild on the web this year? Need to know about the most critical web vulnerabilities in 2019 to protect your organization?
GoBuster - Directory/File & DNS Busting Tool in Go GoBuster – Directory/File & DNS Busting Tool in Go
GoBuster is a tool used to brute-force URIs (directories and files) in web sites and DNS subdomains (inc. wildcards) - a directory/file & DNS busting tool.
BDFProxy - Patch Binaries via MITM - BackdoorFactory + mitmProxy BDFProxy – Patch Binaries via MiTM – BackdoorFactory + mitmproxy
BDFProxy allows you to patch binaries via MiTM with The Backdoor Factory combined with mitmproxy enabling on the fly patching of binary downloads
Domained - Multi Tool Subdomain Enumeration Domained – Multi Tool Subdomain Enumeration
Domained is a multi tool subdomain enumeration tool that uses several subdomain enumeration tools and wordlists to create a unique list of subdomains.

6 Responses to tcpflow – TCP Flow Recorder for Protocol Analysis and Debugging

  1. Goodpeople November 26, 2007 at 12:29 pm #

    Can’t wait to have my students play with it.

  2. dirty November 26, 2007 at 5:25 pm #

    oldie but goodie…thanks for the info Darknet

  3. Pantagruel November 26, 2007 at 9:59 pm #

    A golden oldie, should be part of anyones network traffic analysis kit.
    A better maintained package with similar features is WireShark ( The website even sports some tutorials and other nice tools.

  4. Reticent November 27, 2007 at 12:10 am #

    I figure you’d be better off using the still-maintained application ‘argus’ for this type of stuff. It captures tcp flow information but also comes with a suite of applications to manipulate that data – service distribution, host analysis, and even has a graphing function.

    correction: It seems tcpflow does full packet captures rather than just summaries like argus does. Regardless, check it out if you’re into network security monitoring

  5. Darknet November 27, 2007 at 6:54 am #

    I still like tcpflow when I’m doing network forensics from tcpdump files. Wireshark is pretty nice for graphical interface too. Sometimes it’s just easier and faster on the commandline though.

    I’ll check argus out, thanks!

  6. dirty November 29, 2007 at 5:31 pm #

    I spoke (email) with the author of TCPFlow briefly…
    When asked if a new version was coming out, he said “probably not” and that he hadnt worked on it in years…

    oh well…as long as it still works huh?