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Well-Known Port Numbers

This table provides common networking protocols and what default ports are assigned to them. This is by no means an exhaustive list, but merely an example of what may be required for the 2009 version of the CompTIA Network+ exam.

I have utilized the resources of Wikipedia as a primary knowledge base and included references and links to the appropriate topics for further study. Wikipedia can also be easily translated for those that do not use English as their first language.

CompTIA Network+ (2009 Edition) Certification

Domain 1.2 - Identify commonly used TCP and UDP default ports

TCP ports

FTP - 20, 21 - FTP commands and responses are usually passed on the well-known port number 21. Data connections usually use port number 20.
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SSH - 22 - Used for secure logins, file transfers (scp, sftp) and port forwarding, the standard TCP port 22 has been assigned for SSH servers to be contacted on.
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TELNET - 23 - Telnet is a client-server protocol, based on a reliable connection-oriented transport. Typically this protocol is used to establish a connection to Transmission Control Protocol (TCP) port number 23, where a Telnet server application (telnetd) is listening.
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SMTP - 25 - The SMTP client typically initiates a Transmission Control Protocol (TCP) connection to the SMTP server on the well-known port designated for SMTP, port number 25.
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DNS - 53 - DNS primarily uses User Datagram Protocol (UDP) on port number 53 to serve requests. The Transmission Control Protocol (TCP) is used when the response data size exceeds 512 bytes, or for such tasks as zone transfers.
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HTTP - 80 - Typically, an HTTP client initiates a request. It establishes a Transmission Control Protocol (TCP) connection to a particular port on a host (port 80 by default).
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POP3 - 110 - POP3 works over a TCP/IP connection using TCP on network port number 110.
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NTP - 123 - The Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. NTP uses UDP on port 123 as its transport layer.
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IMAP4 - 143 - Internet Message Access Protocol (IMAP) is an Application Layer Internet protocol operating on port 143.
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HTTPS - 443 - HTTPS URLs begin with "https://" and use port 443 by default.
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UDP Ports

TFTP - 69 - TFTP uses UDP port 69 as its transport protocol.
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DNS - 53 - DNS primarily uses User Datagram Protocol (UDP) on port number 53 to serve requests.
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BOOTPS/DHCP - 67 - All DHCP packets travel as UDP datagrams; all client-sent packets have source port 68 and destination port 67; all server-sent packets have source port 67 and destination port 68.
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SNMP - 161 - Typically, SNMP uses UDP ports 161 for the agent and 162 for the manager.
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