Service Ports: The entrance to the Programs/Application/Web on Your Systems

A port is an application or process specific software construct serving as a communications endpoint used by Transport Layer protocols of the Internet Protocol Suite such as TCP and UDP. A specific port is identified by its number, commonly known as the port number, the IP address it is associated with, and the protocol used for communication. Transport Layer protocols such as TCP and UDP specify a source and destination port number in their packet headers. A port number is a 16-bit unsigned integer ranging from 0 to 65535.

An advertised service is simply a service/application/web available over the Internet from its assigned port. If your machine isn’t offering a particular service, and someone tries to connect to the port associated with that service, nothing will happen. Someone is knocking on the door, but no one lives there to answer. For example, HTTP is assigned to port 80 though, again, there’s no reason why you couldn’t run it on port 8080 or any available port. If your machine isn’t running an HTTP-based web server and someone tries to connect to port 80, the client program receives a connection shutdown message as an error message from your machine indicating that the service isn’t offered.

By historical convention, major network services are assigned well-known, or famous, port numbers in the lower range from 1 to 1023. These port numbers to service mappings are coordinated by the Internet Assigned Numbers Authority (IANA) as a set of universally agreed-on conventions or standards.

The higher port numbers from 1024 to 65535 are called unprivileged ports. They serve a dual purpose. For the most part, these ports are dynamically assigned to the client end of a connection. The combination of client and server port number pairs, along with their respective IP host addresses, and the Transport protocol used, uniquely identifies the connection. Additionally, ports in the 1024 through 49151 ranges are registered with the IANA. These ports can be used as part of the general unprivileged pool, but they are also associated with particular services such as SOCKS or X Window servers. There are also ports registered to the specific computer vendor or manufacturer for specific purposes. Very Common officially used Port numbers are:

Port Name Port Number Description
FTP 21/TCP command
FTP 20/TCP Documents
SMTP 25/TCP Mail
IMAP 143/TCP & UDP Internet Message Access Protocol
Telnet 23/TCP  
SSH 22/TCP Secure Shell
LDAP 389/TCP & UDP  
HTTP Alt 8080/TCP  
HTTPS 443/TCP Secure WWW
VMware Console 901, 902 TCP & UDP  
VMware Server Management 8222, 8333  
DNS 42/TCP & UDP Name Server
DNS Service 53/TCP & UDP  
DHCP Server 67/UDP  
DHCP Client 68/UDP  
WINS 1512/TCP & UDP Windows Internet Name Service
NTP 123/UDP  
NNTP 119/TCP Network News Transfer Protocol
113/TCP authentication
Nick name 43/TCP Whois
MTP 57/TCP Mail transfer
Gopher Protocol 70/TCP  
Kerberos Authentication 88/TCP & UDP  
RPC 135/TCP & UDP  
Netbios 137-139 TCP & UDP  NETBIOS Name Service   
SNMP 161/TCP & UDP  Simple Network Management Protocol
RPC 135 & 530/TCP & UDP  
IPSec 1293/TCP,UDP  
MSSQL database Server 1433/TCP  MS SQL
MSSQL database Monitor 1434/UDP  MS SQL
Radius Server 1812,1645/TCP,UDP1813, 1646/TCP & UDP  AuthenticationAccounting
NFS 2049/UDP  Network File Systems
RDP 3389/TCP  Remote Desktop Protocol
YAHOO! Messenger 5050/TCP  
AOL Messenger 5190/TCP  
Windows Live Messenger 6891–6900/TCP,UDP  
VNC 5800/TCP, 5500/TCP  
EMC Clarion 6389/TCP  
L2TP 1701/TCP & UDP Layer Two Tunnelling Protocol
PPTP 1723/TCP & UDP Point to Point Tunnelling Protocol
AD Windows Share
445/TCP & UDP  Windows Share
SCOM, MOM 1270/TCP & UDP Microsoft Operations Manager

Further Study:

Internet Corporation for Assigned Names and Numbers

Microsoft Documentation for well known Port

Keywords: TCP, UDP, Ports, IANA

2 thoughts on “Service Ports: The entrance to the Programs/Application/Web on Your Systems

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