Objectives: Learn common port numbers and services, and which transport protocol they use.
Prerequisites: you have to know about TCP/IP protocols in general.
Key terms: port numbers, network, common, protocol, services
Network ports are provided by the TCP or UDP protocols at the Transport layer. They are used by protocols in the upper layers of the OSI model. Port numbers are used to determine what protocol incoming traffic should be directed to. Ports allow a single host with a single IP address to run network services. Each port number identifies a distinct service, and each host can have 65535 ports per IP address. Port use is regulated by the Internet Corporation for Assigning Names and Numbers (ICANN). By ICANN there are three categories for ports:
- From 0 to 1023 — well known ports assigned to common protocols and services
- From 1024 to 49151 — registered ports assigned by ICANN to a specific service
- From 49152 to 65 535 — dynamic (private, high) ports range from 49,152 to 65,535. Can be used by any service on an ad hoc basis. Ports are assigned when a session is established, and released when the session ends.
Well known ones are:
Port Service name Transport protocol 20, 21 File Transfer Protocol (FTP) TCP 22 Secure Shell (SSH) TCP and UDP 23 Telnet TCP 25 Simple Mail Transfer Protocol (SMTP) TCP 50, 51 IPSec 53 Domain Name System (DNS) TCP and UDP 67, 68 Dynamic Host Configuration Protocol (DHCP) UDP 69 Trivial File Transfer Protocol (TFTP) UDP 80 HyperText Transfer Protocol (HTTP) TCP 110 Post Office Protocol (POP3) TCP 119 Network News Transport Protocol (NNTP) TCP 123 Network Time Protocol (NTP) UDP 135–139 NetBIOS TCP and UDP 143 Internet Message Access Protocol (IMAP4) TCP and UDP 161, 162 Simple Network Management Protocol (SNMP) TCP and UDP 389 Lightweight Directory Access Protocol TCP and UDP 443 HTTP with Secure Sockets Layer (SSL) TCP and UDP 3389 Remote Desktop Protocol TCP and UDP