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

  • Page ID
    40128
  • 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

    Usage

    20

    File Transfer Protocol (FTP) Data Transfer

    21

    File Transfer Protocol (FTP) Command Control

    22

    Secure Shell (SSH)

    23

    Telnet - Remote login service, unencrypted text messages

    25

    Simple Mail Transfer Protocol (SMTP) E-mail Routing

    53

    Domain Name System (DNS) service

    80

    Hypertext Transfer Protocol (HTTP) used in World Wide Web

    110

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

    119

    Network News Transfer Protocol (NNTP)

    123

    Network Time Protocol (NTP)

    143

    Internet Message Access Protocol (IMAP) Management of Digital Mail

    161

    Simple Network Management Protocol (SNMP)

    194

    Internet Relay Chat (IRC)

    443

    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, OpenSource.com is licensed under CC BY-SA 4.0

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