Course glossary

Networking terms, in context.

Definitions for terms used in How Networks Work. Each one points back to the session where it becomes useful.

ARP

Address Resolution Protocol maps an IPv4 address on the local link to a link-layer address.

Why it matters: Ethernet needs a destination MAC address. Level 1-5.

MAC address

A link-layer identifier carried in an Ethernet frame.

Why it matters: switches learn and forward using these addresses. Level 1-4.

Frame

A unit of link-layer data, such as Ethernet, that can carry an IP packet.

Level 1-4.

Packet

A unit of network-layer data. An IP packet carries transport data between IP endpoints.

Level 1-1.

Route

A rule that tells a host or router which interface and next hop to use for matching destinations.

Level 2-1.

Default gateway

The next-hop router used when no more-specific route matches a destination.

Level 1-2.

NAT

Network Address Translation rewrites address information and often ports while tracking a flow.

Level 2-2.

Port

A transport-layer number that helps TCP or UDP deliver data to the right application endpoint.

Level 2-3.

TCP

A connection-oriented transport protocol that provides an ordered, reliable byte stream.

Levels 2-3 and 2-4.

DNS

The Domain Name System maps names to records through a distributed, cached system.

Level 2-5.

TLS

A protocol that authenticates peers and protects application data in transit.

Level 2-6.

Certificate

A signed document that binds identity information to a public key, subject to validation rules.

Level 2-6.

Firewall

A policy enforcement point that permits or blocks traffic using packet and connection state.

Level 3-2.

Load balancer

A system that distributes connections or requests across available backends.

Level 3-3.

Autonomous system

A network or group of networks operated under one routing policy and identified by an ASN.

Level 3-5.

BGP

The Border Gateway Protocol exchanges reachability and path information between routing systems.

Levels 3-5 and 3-6.