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This is a list of TCP and UDP port numbers used by protocols for operation of network applications. The Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) only need one port for bidirectional traffic. TCP usually uses port numbers that match the services of the corresponding UDP implementations, if they exist, and vice versa.
Telnet consists of two components: (1) the protocol itself and (2) the service component. The telnet protocol is a client-server protocol, based on a reliable connection-oriented transport. [2] This protocol is used to establish a connection to Transmission Control Protocol (TCP) port number 23 or 2323, where a Telnet server application is ...
For example, listing the hosts that respond to TCP and/or ICMP requests or have a particular port open. Port scanning – Enumerating the open ports on target hosts. Version detection – Interrogating network services on remote devices to determine application name and version number. [11] Ping Scan – Check host by sending ping requests.
Banner grabbing is a technique used to gain information about a computer system on a network and the services running on its open ports. Administrators can use this to take inventory of the systems and services on their network.
A reverse connection is usually used to bypass firewall restrictions on open ports. [1] A firewall usually blocks incoming connections on closed ports, but does not block outgoing traffic . In a normal forward connection, a client connects to a server through the server's open port , but in the case of a reverse connection, the client opens the ...
Port knocking is a flexible, customisable system add-in. If the administrator chooses to link a knock sequence to an activity such as running a shell script, other changes such as implementing additional firewall rules to open ports for specific IP addresses can easily be incorporated into the script. Simultaneous sessions are easily accommodated.
The above use of the terms "open" and "closed" can sometimes be misleading, though; it blurs the distinction between a given port being reachable (unfiltered) and whether there is an application actually listening on that port. Technically, a given port being "open" (in this context, reachable) is not enough for a communication channel to be ...
NCSA Telnet was released as free and open source software (although the term "open source" was not yet in use), and as such spawned a number of spin-off products including BetterTelnet; Brown tn3270 [4] BYUTelnet; InterCon's TCP/Connect series; MacBlue Telnet (Chinese-language version) MacTelnet; NCSA Telnet-J (Japanese-language version)