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.

Table of contents

• 5-tuple
• DNS
• Ethernet
• HTTP
• IPv4
• IPv6
• OSI model
• Protocol Buffers
• TCP
• Topologies
• UDP
• gRPC