Port Numbers

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Based on OSI layer transport is about port addressing, we should know overview of port numbers. The Internet Assigned Numbers Authority (IANA) assigns port numbers. IANA is a standards body that is responsible for assigning various addressing standards.

There are different types of port numbers:

Well Known Ports (Numbers 0 to 1023) – These numbers are reserved for services and applications. They are commonly used for applications such as HTTP (web server) POP3/SMTP (e-mail server) and Telnet. By defining these well-known ports for server applications, client applications can be programmed to request a connection to that specific port and its associated service. Next example of well known ports
TCP ports: ftp port number is 21, telnet port number is 22, SMTP port number is 25, HTTP port number is 80, POP3 port number is 110, IRC (Internet Relay Chat) port number is 194, HTTPS (Secure HTTP) port number is 443.
UDP ports: TFTP port number is 69, RIP port number is 520.

Registered Ports (Numbers 1024 to 49151) – These port numbers are assigned to user processes or applications. These processes are primarily individual applications that a user has chosen to install rather than common applications that would receive a Well Known Port. When not used for a server resource, these ports may also be used dynamically selected by a client as its source port. Next example of registered ports
TCP ports: MSN messenger port number is 1863, Cisco SCCP (VoIP) port number is 2000, Alternate HTTP port number is 8008 or 8080.
UDP ports: RADIUS Authentication Protocol port number is 1812, RTP (Voice and Video Transport Protocol) port number is 5004, SIP (VoIP) port number is 5060.

Dynamic or Private Ports (Numbers 49152 to 65535) – Also known as Ephemeral Ports, these are usually assigned dynamically to client applications when initiating a connection. It is not very common for a client to connect to a service using a Dynamic or Private Port (although some peer-to-peer file sharing programs do).

Some applications may use both TCP and UDP. For example, the low overhead of UDP enables DNS to serve many client requests very quickly. Sometimes, however, sending the requested information may require the reliability of TCP. In this case, the well known port number of 53 is used by both protocols with this service. Next example of TCP/UDP common ports:
Well Known TCP/UDP Ports: DNS port number is 53, SNMP port number is 161, AOL messenger port number is 531.
Registered TCP/UDP Ports: MS SQL port number is 1433, WAP (MMS) port number is 2948.
A current list of port numbers can be found at http://www.iana.org/assignments/port-numbers. Hope after knowing port addressing will make us comfort with computer and internet.

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