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10-A.1.3: TCP/IP Fundamentals - Ports and Segments

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  • Network Ports

    The physical ports on your computer allow it to communicate with peripheral devices such as your keyboard and mouse and to connect with internet devices via Ethernet cables.

    Within computer networking, ports serve a similar purpose. When a computer system seeks to connect to another computer, the port serves as a communication endpoint. It is also possible for different services running on the same computer to expose various ports and communicate with one another using these ports. In simple terms, if a software application or service needs to communicate with others, it will expose a port. Ports are identified with positive 16-bit unsigned integers, ranging from 0 to 65535. Other services use this port number to communicate with the service or app. Port numbers are divided into three ranges: well-known ports, registered ports, and dynamic or private ports.

    Well-known Port Numbers

    Port Number



    File Transfer Protocol (FTP) Data Transfer


    File Transfer Protocol (FTP) Command Control


    Secure Shell (SSH)


    Telnet - Remote login service, unencrypted text messages


    Simple Mail Transfer Protocol (SMTP) E-mail Routing


    Domain Name System (DNS) service


    Hypertext Transfer Protocol (HTTP) used in World Wide Web


    Post Office Protocol (POP3) used by e-mail clients to retrieve e-mail from a server


    Network News Transfer Protocol (NNTP)


    Network Time Protocol (NTP)


    Internet Message Access Protocol (IMAP) Management of Digital Mail


    Simple Network Management Protocol (SNMP)


    Internet Relay Chat (IRC)


    HTTP Secure (HTTPS) HTTP over TLS/SSL

    Network Segments

    Network segments are used to divide a network into multiple segments or subnets, each acting as its own small network. By doing this network administrators can control the flow of traffic between subnets, improve monitoring, boost performance, localize technical issues and enhance security. Below is an example of a network segment from Cisco's Packet Tracer. One segment is on the left, and another segment is on the right.

    Each of the segments has its own network ID, which is part of the IP address that is assigned to the devices in each subnet.

    2 Network segments. The segments are separated by a router. Each segment has its own network number, which is part of the IP address.
    Figure \(\PageIndex{1}\): Network Segments. ("Network Segments" by Patrick McClanahan is licensed under CC BY-SA 4.0)

    Adapted from:
    "14 common network ports you should know" by Kedar Vijay Kulkarni, is licensed under CC BY-SA 4.0

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