Glossary of networking terms

Every term used across the Networking & the Internet path, defined in plain language and linked to the lesson where it’s explained in full. Skim it as a refresher, or use your browser’s find (Ctrl/Cmd-F) to jump to a word. Terms are grouped by theme, roughly in the order the path introduces them.

How networks work

Network — Devices (nodes) connected by links so they can share data. See What is a network?

LAN / WAN — A Local Area Network (home or office) versus a Wide Area Network spanning distance; the internet interconnects countless networks. See What is a network?

Packet — A small chunk of data with a header (addresses, sequence) wrapped around a payload; data is split into packets to travel the network. See Packets & switching

Router / switch — A switch moves packets within a local network; a router moves them between networks, forwarding each toward its destination. See Packets & switching

Protocol — An agreed set of rules two machines follow to communicate; both ends must speak the same one. See Protocols & layers

Layers (TCP/IP model) — Networking split into stacked layers — link, internet, transport, application — each with its own job and protocols. See Protocols & layers

Client / server — The client initiates a request; the server listens and responds. See Clients, servers & peers

Peer-to-peer — A model with no central server, where peers connect directly and both request and serve. See Clients, servers & peers

Addressing

IP address — A number identifying a device on a network so packets can be routed to it. See IP addresses & subnets

IPv4 / IPv6 — The older 32-bit addressing (dotted quad, ~4 billion addresses) and its vastly larger successor. See IP addresses & subnets

Subnet / CIDR — A block of addresses; CIDR notation like /24 marks how many bits are the network part versus the host part. See IP addresses & subnets

Public vs. private IP — Publicly routable addresses versus private ranges (10.x, 172.16–31.x, 192.168.x) reused inside home and office networks. See NAT & private networks

DNS — The internet’s phone book, translating names like example.com into IP addresses. See DNS — names to addresses

DNS record — An entry in DNS: A (name→IPv4), AAAA (→IPv6), CNAME (alias), MX (mail), TXT (verification). See DNS — names to addresses

Port — A numbered door on a machine so it can run many network services at once (80 = HTTP, 443 = HTTPS, 22 = SSH). See Ports & sockets

Socket — An address + port + protocol that ties a connection to a specific program; a connection is a pair of sockets. See Ports & sockets

NAT (network address translation) — How a router maps many private addresses onto one public IP, so all your devices share it. See NAT & private networks

DHCP — The protocol that automatically leases a joining device its IP address, gateway, and DNS settings. See DHCP & joining a local network

Default gateway — The router a device sends traffic to when the destination is outside its own subnet. See DHCP & joining a local network

Protocols

TCP — A reliable, ordered, connection-based transport protocol (with a three-way handshake) used by the web, SSH, and email. See TCP vs. UDP

UDP — A fast, connectionless transport protocol with no delivery guarantees, used for DNS, voice, and video. See TCP vs. UDP

HTTP — The request/response protocol of the web — methods, headers, and status codes. See HTTP — the web’s protocol

Status code — HTTP’s result number by class: 2xx success, 3xx redirect, 4xx client error, 5xx server error. See HTTP — the web’s protocol

TLS / HTTPS — TLS encrypts and authenticates a connection; HTTPS is HTTP over TLS — the padlock. See TLS & HTTPS

Certificate / CA — A certificate binds a domain to a public key and is signed by a Certificate Authority your device trusts. See TLS & HTTPS

Web API / REST — Programs talking over HTTP; REST addresses resources by URL and uses HTTP methods as verbs, usually with JSON. See Web APIs & REST

WebSocket — A persistent, two-way connection (upgraded from HTTP) that lets the server push data any time. See WebSockets & real-time connections

Connecting & securing

Firewall — A control that allows or blocks traffic by port, address, and protocol; safest set to deny-by-default. See Firewalls & controlling access

Port forwarding — A router rule mapping a public port to a device’s private address and port, so outside traffic can reach it. See Port forwarding & dynamic DNS

Dynamic DNS — A service that keeps a hostname pointed at your changing home IP address. See Port forwarding & dynamic DNS

VPN — An encrypted tunnel to a VPN server, hiding your traffic from the local network and ISP — but not true anonymity. See VPNs & tunnels

Proxy / reverse proxy — A middleman that forwards requests; a reverse proxy sits in front of servers to terminate TLS, route, and hide backends. See Proxies, reverse proxies & load balancers

Load balancer — Spreads incoming traffic across several backend servers and skips unhealthy ones. See Proxies, reverse proxies & load balancers

Man-in-the-middle — An attacker positioned to read or alter traffic between two parties; encryption defends against it. See Network security basics

Command-line tools

ping — Tests whether a host is reachable and how long a round trip takes. See Testing connectivity

traceroute — Shows the sequence of hops between you and a destination. See Testing connectivity

dig / nslookup — Queries DNS to see what address (and records) a name resolves to. See Testing connectivity

ss / netstat — Lists network connections and which ports your machine is listening on. See Inspecting your network

curl — Sends HTTP requests from the shell to test an API or a site and read the response. See Making requests with curl

SSH tunnel — Carrying another service’s traffic securely inside an SSH connection (ssh -L / -R / -D). See SSH tunnels & transfers

tcpdump / Wireshark — Tools that capture and inspect the actual packets on a network for debugging. See Packet capture basics

Running a service

Bind / listen — A server binds to an address and port and listens there for incoming connections. See Running a server — binding & reachability

localhost vs. 0.0.0.0 — Binding to localhost (127.0.0.1) allows only the same machine; 0.0.0.0 allows every network interface. See Running a server — binding & reachability

Reverse proxy (TLS termination) — The standard front door for a self-hosted web service — it handles HTTPS and forwards to the app. See Exposing a service safely

Self-hosting — Running your own services on hardware you control, often on a home network. See Self-hosting on a home network