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Packet capture is the process of intercepting and logging traffic. As data streams flow across the network, the analyzer captures each packet and, if needed, decodes the packet's raw data, showing the values of various fields in the packet, and analyzes its content according to the appropriate RFC or other specifications.
[1] [2] [3] It accepts as input files produced by packet-capture programs, including tcpdump, Wireshark, and snoop. tcptrace can produce several different types of output containing information on each connection seen, such as elapsed time, bytes and segments sent and received, retransmissions, round trip times , window advertisements, and ...
A capture file saved in the format that libpcap, WinPcap, and Npcap use can be read by applications that understand that format, such as tcpdump, Wireshark, CA NetMaster, or Microsoft Network Monitor 3.x. The file format is described by Internet-Draft draft-ietf-opsawg-pcap; [5] the current editors' version of the draft is also available. [6]
Wireshark is very similar to tcpdump, but has a graphical front-end and integrated sorting and filtering options.. Wireshark lets the user put network interface controllers into promiscuous mode (if supported by the network interface controller), so they can see all the traffic visible on that interface including unicast traffic not sent to that network interface controller's MAC address.
The following tables compare general and technical information for several packet analyzer software utilities, also known as network analyzers or packet sniffers. Please see the individual products' articles for further information.
tcpdump prints the contents of network packets. It can read packets from a network interface card or from a previously created saved packet file. tcpdump can write packets to standard output or a file. It is also possible to use tcpdump for the specific purpose of intercepting and displaying the communications of another user or computer.
ECN allows end-to-end notification of network congestion without dropping packets. ECN is an optional feature that may be used between two ECN-enabled endpoints when the underlying network infrastructure also supports it. Conventionally, TCP/IP networks signal congestion by dropping packets.
It includes all commands that are standardized by the Internet Engineering Task Force (IETF) in RFC 959, plus extensions. Note that most command-line FTP clients present their own non-standard set of commands to users. For example, GET is the common user command to download a file instead of the raw command RETR.