The Internet is an interconnected collection of separate IPv4 and IPv6 networks, all communicating over a series of standardised protocols conceptualised in the OSI model. Traffic is routable between these separate networks.
Types of network
- A LAN, or Local Area Network, refers to a single site.
- WLAN refers to a Wireless LAN.
- WAN, or Wide Area Network, typically refers to a network of LANs connected across the Internet via a VPN or via a private backbone.
- PAN refers to a Personal Area Network, e.g. a mobile hotspot.
Transports
There are two commonly used transports on the Internet today:
- TCP/IP provides reliable, ordered transmission of segments over sessions.
- UDP offers lighter weight communication with lesser delivery guarantees.
Ports
Ports are used to expose multiple services from the same host address. They're grouped into defined ranges:
- Source ports assigned to clients for sessions are in the ephemeral range (49,152–65,535)
- Well-known ports between 0–1,023
- Registered port numbers between 1,024–49,151
Common port numbers
More common services can be located in /etc/services
on most BSD, Linux and Unix systems.
Port number | Service | Dependencies | |
---|---|---|---|
20 | FTP (data) | TCP | |
21 | FTP (command) | TCP | |
22 | SFTP | TCP | |
22 | SSH | TCP | |
23 | Telnet | TCP | |
25 | SMTP (insecure) | TCP | |
67 | DHCP (server) | UDP | |
68 | DHCP (client) | UDP | |
69 | TFTP | UDP | |
80 | [[HTTP | net.http]] | TCP |
110 | POP3 (insecure) | TCP | |
135 | Windows RPC | TCP/UDP | |
143 | IMAP | TCP | |
389 | LDAP | TCP/UDP | |
443 | HTTPS | TCP | |
445 | SMB | TCP | |
587 | SMTP (secure) | TCP | |
636 | LDAPs | TCP | |
993 | IMAP (secure) | TCP | |
995 | POP3 (secure) | TCP | |
1433 | SQL Server (default instance) | TCP | |
1434 | SQL Server (dedicated admin connection) | TCP | |
1434 | SQL Server (browser service) | UDP | |
2376 | Docker engine | TCP | |
3306 | MySQL | TCP | |
5432 | PostgreSQL | TCP/UDP |