Network+ Exam Objectives 1.2

1.2 Identify commonly used TCP and UDP default ports

Since like people, computers are able to perform a variety of tasks at one time, there is a need for both TCP and UDP ports. These ports are able to identify packets so that they can be identified, processed, and used properly. Each packet is identified using a set port number, which allows each packet to receive the specific services they need. Port numbers can also be used to filter traffic amongst a network.

• TCP ports – Transmission control protocol ports are a core protocol of the IPS suite. There are 65,536 TCP ports available today. Some ports are used much more commonly than others while some are rarely used much at all. TCP ports are divided in three types: well-known ports, registered ports, and dynamic/private ports. Often times an application is designed to connect to a well known port and then move to a dynamic or private port to continue a connection.

• FTP – 20, 21 – Well known TCP port used for data transfer and data control.

• SSH – 22 – Well known TCP port used for SSH purposes to ensure secure logins, file transfers, and port forwarding.

• TELNET – 23 – Well known TCP port used for unencrypted text communications.

• SMTP – 25 – Well known TCP port used for used for e-mail routing between mail servers.

• DNS – 53 – DNS is a TCP and UDP port. Domain name system often known as the Internet’s phone book as it translates website addresses into IP addresses. On the TCP level DNS is needed when the response data size exceeds 512 bytes.

• HTTP – 80 – Well known TCP/UDP port; hypertext transfer protocol. It is the port that controls the basic foundation and structure of the Internet.

• POP3 – 110 – Well known TCP port; post office protocol version 3. POP3 is mostly used by local e-mail clients in order to retrieve e-mail from a remote server over a TCP/IP connection.

• NTP – 123 – Well known TCP port used for used for time synchronization.

• IMAP4 – 143 – Well known TCP port used for managing email messages.

• HTTPS – 443 – Well known TCP port needed to create an encrypted communication and secure identification of a network’s web server.

• UDP ports – UDP, user datagram protocol ports, are used and needed so that computer applications are able to send messages to other hosts on an IP network. With UDP, applications do not require any type of prior communication in order to create special transmission channels or data paths.

• TFTP – 69 – TFTP (Trivial File Transfer Protocol), a UDP port, is extremely limited and simple and is mostly used for the automated transfer of configuration or boot files between machines locally.

• DNS – 53 – Domain name system often known as the Internet’s phone book as it translates website addresses into IP addresses.

• BOOTPS/DHCP – BOOTPS is needed to obtain an IP address from a configuration server. DHCP is needed so that a computer is able to automatically configure itself. With DHCP, a network administrator is not needed to intervene.