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.
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 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.
|1433||SQL Server (default instance)||TCP|
|1434||SQL Server (dedicated admin connection)||TCP|
|1434||SQL Server (browser service)||UDP|