Understanding TCP Ports

Robert Ramstetter By Robert Ramstetter, 19th Feb 2015 | Follow this author | RSS Feed | Short URL http://nut.bz/tm6tu5cv/
Posted in Wikinut>Guides>Internet

This is a quick How To guide on understanding TCP ports on networks. The subject is tested heavily on the Net + exam, so understanding the concept is crucial to passing the exam. It is also pertinent for network administrators in order to ensure network security..

Ports: What are they?

The term TCP Ports can be a bit confusing. You have probably been conditioned to think of a port as an access point, or a point of entry. As an example, think of the back of your computer. You have USB ports, VGA ports, serial ports, HDMI ports, etc. TCP ports, however, are something different entirely. For instance, the most commonly used port is port 80. This port is for http traffic, the basic Internet communication port. I will cite more examples later on.
When dealing with TCP ports, there is no physical or even digital access point within your computer that is designated as port 80 or any other port. For TCP purposes, a port is simply a number that is used to determine the type of service that is required. In other words, the computer will have to know if an incoming file is encrypted to not, or what its intended use is. Port 80 will designate a file as a standard, non-encrypted file, but port 443 signals that it is encrypted. That way, the computer knows whether it needs to decrypt the file or not.

Common Ports

Here are some of the most commonly used ports:

Port 20: FTP. The File Transfer Protocol. Used for downloading or uploading files over the Internet.

Port 22: SSH. Remote Log In Protocol: This is used for logging into a remote computer, transferring files to or from a remote computer, and remotely controlling a computer.

Port 23: Telnet. This is a terminal emulation protocol.

Port 25: SMTP: Simple Mail Transfer Protocol. For sending and receiving email messages from one server to another.

Port 110: POP3. Post Office Protocol. This port is used to retrieve email from an email server. Pop3 (as opposed to port 109 POP2) does not need SMTP to retrieve email.

Port 143: ICMP: Internet Mail Access Protocol.

Port 53: DNS: Domain Name System. DNS is used to translate domain names (such AS Microsoft.com) to an IP address. Domain names are easier for users to understand, but computers communicate through numbers. DNS servers are used to translate names to IP addresses.

Port 118: SQL Services. Used to communicate with a SQL server.

Port 389: LDAP: Lightweight Directory Access Protocol. Used to access information directories. This port can be used to access lists of email addresses or any public keys.

Port 546: DHCP Client: Dynamic Host Configuration Protocol. This port is used by a client computer on a network to communicate with a DHCP server to obtain an IP address. This is to simplify network administration by relieving the administrator of the burden of assigning manual IP addresses to every client workstation on a network.

Port 80: HTTP. This is the basic port for communicating over the Internet. Port 80 will fetch a web page from a server and deliver it to the client workstation that requested it.

Port 443: HTTPS: This port establishes a secure transmission over the Internet.

Security Concerns

This is only a small sampling of the many ports that are used with TCP transmissions. There are many more. Some, such as Port 37 (time) and Port 7 (echo), are no longer used. Some were found to contain security vulnerabilities, while others simply became obsolete with new technology. Ports are an integral part of network communication. Blocking certain ports on a computer can increase security. Some viruses and malware will open up ports on a computer, thus increasing their ability to exploit the device.
It is good practice to view open ports and understand the function of each, particularly those that are unfamiliar. An unfamiliar open port on a computer would be the equivalent of letting someone into your house who posed as a repair person. Unknown to you, they would then leave a door or window unlocked to gain access later on. Ports on a computer function the same way.


Net, Network, Network Communication, Tcp Ports

Meet the author

author avatar Robert Ramstetter
Robert Ramstetter is a world traveler and writer of short stories, full length novels, and a vast array of technical articles.

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author avatar Kingwell
19th Feb 2015 (#)

So much information here. Thank You for sharing.

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author avatar Robert Ramstetter
19th Feb 2015 (#)

You're welcome. I plan on publishing more in the near future. I hope you find it helpful.

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author avatar Carol Roach
20th Feb 2015 (#)

thank you for this explanation I am not very savvy in computer technology

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author avatar Robert Ramstetter
22nd Feb 2015 (#)

I am glad I can help!

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