tcpdump is a common computer network debugging tool that runs under the command line. It allows the user to intercept and display TCP/IP and other packets being transmitted or received over a network to which the computer is attached. It was originally written by Van Jacobson, Craig Leres and Steven McCanne who were, at the time, working in the Lawrence Berkeley Laboratory Network Research Group. A computer network is a system for communication between computers. ... Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware thus making it behave as expected. ... A command line interface or CLI is a method of interacting with a computer by giving it lines of textual commands (that is, a sequence of characters) either from keyboard input or from a script. ... The Internet protocol suite is the set of communications protocols that implement the protocol stack on which the Internet runs. ... A computer network is a system for communication between computers. ... Van Jacobson is currently chief scientist at Packet Design LLC. Prior to that, he was Chief Scientist at Cisco Systems and group leader for the Network Research Group at Lawrence Berkeley Laboratory. ... The Berkeley Lab is perched on a hill overlooking the Berkeley central campus and San Francisco Bay. ...

Tcpdump works on most Unix-like platforms: Linux, Solaris, BSD, Mac OS X, HP-UX and AIX among others. In those systems, tcpdump is built upon the libpcap packet capture library. A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. ... Tux is the official Linux mascot. ... This article contains information that has not been verified and thus might not be reliable. ... BSD redirects here; for other uses see BSD (disambiguation). ... Mac OS X is the operating system that is included with all currently shipping Apple Macintosh computers in the consumer and professional markets. ... HP-UX (Hewlett Packard UniX) is Hewlett-Packards proprietary implementation of the Unix operating system. ... AIX or Aix may be: Aix, a genus of two species of dabbling ducks, the Wood Duck (Aix sponsa) and the Mandarin Duck (Aix galericulata) AIX operating system Athens Internet Exchange, (AIX) a European IXP a place name: Aix-la-Chapelle, or Aachen, a city in Germany in France: Aix... pcap is an application programming interface for packet capturing. ...

On Windows, WinDump can be used; it's a port of tcpdump to Windows. Microsoft Windows is a series of operating environments and operating systems created by Microsoft for use on personal computers and servers. ...

On Unix and most other operating systems, a user must have superuser privileges to use tcpdump due to its use of promiscuous mode. Wikibooks has more about this subject: Guide to UNIX Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T Bell Labs employees including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. ... Early computers lacked operating systems. ... On many computer operating systems, superuser is the term used for the special user account that is controlled by the system administrator. ... Promiscuous mode, in computer related fields, generally refers to the practice of putting a network card into a setting so that it passes all traffic it receives to the CPU rather than just packets addressed to it. ...

The user may optionally apply any number of filters to render the output more usable on networks with a high volume of traffic.

Common uses of tcpdump

• to debug applications one is writing which utilize the network for communications
• to debug the network setup itself, by determining whether all necessary routing is or is not occurring properly, allowing the user to further isolate the source of a problem
• to intercept and display the communications of another user or computer. Some protocols, such as telnet and HTTP, transmit information unencrypted over the network. A user with control of a router or gateway through which other computers' unencrypted traffic passes can use tcpdump to view login IDs, passwords, the URLs and content of websites being viewed, or any other information.

Microsoft TELNET client animation. ... HTTP (for HyperText Transfer Protocol) is the primary method used to convey information on the World Wide Web. ... This article describes the computer networking device. ... Gateway has several meanings. ... A Uniform Resource Locator, URL (spelled out as an acronym, not pronounced as earl), or Web address, is a standardized address name layout for resources (such as documents or images) on the Internet (or elsewhere). ...

See also

• Ethereal is a similar program with a GUI frontend, and many additional formatting, sorting, and display facilities.
• snoop

This article is about the network traffic analyzer. ... Gui is short for Guilherme or Guilhermo or an iteration of that, in English it translates to Will. ... snoop can stand for: Snoop Dogg SUN Solaris snoop, capture and inspect network packets utility ...

External links

• Official site for tcpdump (and libpcap)
• Official site for WinDump
• ngrep, a tcpdump-like tool