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 | ||||
| POP3 |
|
pop-3 | |||
| IMAP | 143/TCP & UDP | Internet Message Access Protocol | |||
| Telnet | 23/TCP | ||||
| SSH | 22/TCP | Secure Shell | |||
| LDAP | 389/TCP & UDP | ||||
| HTTP | 80/TCP | WWW, WWW-HTTP | |||
| 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 | |||
| FINGER | 79/TCP | ||||
| 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 SMB |
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
