Port Number and Address

Introduction

• The list of port numbers is specified in RFC (Both client and server must state the HTTP version of their request or response in the first line of their message. Internet Society and IETF (Internet Engineering Task Force) Request for Comments documents (known as RFCs) provide the official definitions for the HTTP protocol: HTTP/1.0.)1700.
• The concept of port numbers was established by the early developers of the ARPANET.
• The Internet Assigned Numbers Authority (IANA) is responsible for maintaining the official assignments of port numbers for specific uses.

Definition

• Port/Network/Communication Port

  • In computer networking, a port is a communication endpoint.
  • The ports are used by TCP and UDP to deliver the data to the right application.
  • The term port is an identifier number that specifies an individual process or user program running on the destination computer.
  • Ports are typically used to map data to a particular process running on a client.
  • As software, for an operating system, a port is a logical construct that identifies a specific process or a type of network service.
  • A network port is a process/application-specific software construct serving as a communication endpoint.
  • A communication port is a medium through which, an application establishes a connection with another application by binding a socket to a port number.
  • In computer and telecommunication devices, a port is generally a specific place for being physically connected to some other device. It is usually a socket and plug of some kind. Typically, a personal computer has one or more serial ports and usually one/few parallel ports.

• Port Number

  • When a process starts up, it registers/creates a unique port number with the protocol stack. It is the logical address of each application or process that uses a network or the Internet to communicate. 
  • Every service in a network has a unique port number.
  • In Computer Networks, ports are identified for each protocol and IP address as 16-bit unsigned positive integer numbers, commonly known as the port number.
  • It is a way to identify a specific process/application that uses a network or the Internet to communicate via the server.
  • The port number is used to direct the data to the correct location within this device.
  • The port number identifies what type/category of port an application/process is.
  • Port number permits unique identification of several simultaneous processes using
    TCP/UDP

• Port Address

  • A port address is a logical address (in the form of an integer number ranging from 0 to 65535) of each application or process that uses a network or the Internet to communicate.

Features

• A port identifies a specific application running on a machine. A port is identified by port number.
• The most common protocols that use port numbers are the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) i.e. port numbers are mainly used in TCP and UDP-based networks.
• A port number is always associated with an IP address of a host and the protocol type of the communication.
• The port numbers are specified by a 16-bit number i.e. the port number ranges from 0 to 65535(2¹⁶ = 65536).
• There are a total of 65,535 TCP Ports and another 65,535 UDP ports.
• IANA maintains the official list of well-known and registered ports.
• A port number uniquely identifies a network-based application on a computer. Each application/program is allocated a 16-bit integer port number. In other words, the IP address identifies the computer host, and the port number specifies the particular process running on that host.
• This number is assigned automatically by the OS, manually by the user, or is set as a default for some popular applications.
• The port number works with the IP address where the IP address is used to identify the destination computer/node in a network, whereas the port number further specifies the destination end of an application/program in that computer.
• Only one process per protocol can listen/work on a given port i.e., two different processes, one using UDP and another TCP can both listen on a unique port number. However, two processes using the same transport protocol cannot listen on the same port number.
• All outgoing data packets contain application/process port numbers in the packet header to enable the receiver to distinguish the specific application on receiving end.

Types

There are 3 types of ports –

(A) Well Known/System/Global/Reserved/Common/Restricted Port : 

• • The port numbers in the range from 0 to 1023 are the well-known ports.
  • These ports are registered & controlled by IANA i.e. these are official ports.
  • They are used by system processes that provide widely-used types of network services i.e. these port numbers are assigned to the server side of an application and are already reserved for specific applications by IANA (Internet Assigned Number Authority).
  • They are reserved for privileged services.
  • For example – 
    • Application/Process Name  –  Working Port Number/Associated Protocol
      • FTP  –  20 (For data) & 21(For Control)/TCP
      • TFTP  –  69/UDP
      • Telnet  –  23/TCP
      • SMTP  –  25/TCP
      • DNS – 53/UDP(mostly) or TCP
      • IMAP  –  143
      • POP2 – 109/TCP
      • POP3  –  110/TCP
      • Gopher  –  70
      • HTTP  –  80/TCP
      • HTTPS  –  443/TCP
      • DHCP  –  67 – for data & 68 – for control/UDP. 
      • IRC  –  194
      • SNMP  –  161/UDP
      • BOOTPS  –  67 (for Server)/UDP
      • BOOTPC – 68 (for Client)/UDP
      • LOGIN  –  513/TCP
      • BGP – 179/TCP
      • TIME – 37/UDP
      • WHOIS –  43/TCP
      • ECHO – 7/TCP or UDP
      • SSH – 22/TCP
      • NTP – 123/UDP
      • RIP -520/UDP

(B) Registered Ports :

• • These ports are not registered with IANA hence these are unofficial ports.
  • These port numbers have been publicly defined as a convenient service for the Internet community to help them avoid vendor conflicts.
  • The range of port numbers from 1024 to 49151 are the registered ports.
  • User-level processes/services generally use port number value >= 1024.

(C) Dynamic/Private/ Ephemeral Port

• • These ports are conflicts i.e. these ports are in use for multiple applications (which may be official or unofficial).
  • These ports are ranges from 49152–65535.
  • It can be used freely by any client or server application.