This glossary is organized around relationships rather than one-line dictionary definitions. A term is useful when it tells you what device performs the function, what information it acts on, and what symptom appears when it fails.

Addressing and routing

IP address: a layer-3 address used for routed communication. Subnet/prefix: the part of the address plan that lets a host decide which destinations are local. Default gateway: the router a client uses for destinations outside its local routes. DHCP: a protocol that can supply address, gateway, DNS and lease information automatically. NAT: translation between address/port spaces, commonly at the home edge for IPv4.

Local-link terms

MAC address: a link-layer interface identity used on technologies such as Ethernet/Wi-Fi. ARP: the IPv4 mechanism that discovers the link-layer address associated with a local IPv4 destination or gateway. SSID: the Wi-Fi network name clients select; multiple access points can advertise the same SSID. BSSID: identifies a specific Wi-Fi basic service set/radio instance.

Name and service discovery

DNS: the naming system that maps domain names and other records. mDNS: multicast DNS used for local-link naming/discovery without a conventional unicast DNS server. TTL: in DNS, a caching lifetime; in IP, a hop-limit style field with a different purpose despite the shared abbreviation.

Security and reachability

Firewall: policy that permits or blocks traffic. Port forwarding: an inbound translation/rule that sends selected traffic to an internal service. VPN: an authenticated/encrypted tunnel that creates a routed path between endpoints or networks. CGNAT: provider-side IPv4 address sharing, often visible through 100.64/10 shared address space. WPA2/WPA3: Wi-Fi security generations for network authentication/encryption.

Study the terms in context

Use every term as a troubleshooting question

Ask who owns the value, where it is valid, and what observation changes when it fails. DHCP changes addressing, DNS changes name resolution, the default gateway changes the next hop, and NAT changes address/port state across a boundary. That relationship is more useful than memorizing isolated definitions.

Do not collapse different jobs into one word?

Router, modem, gateway, access point, DNS server, firewall, and ISP can coexist in one physical box but remain different functions. The same is true for Wi-Fi password versus router administrator password, public IP versus default gateway, and bridge mode versus access-point mode.

Video walkthrough for Networking Glossary: Router, Wi-Fi, IP, DNS & Security Terms

Explains common DNS record types and how they fit together. DNS resolution is only one layer; a resolved hostname can still have a web, TLS or routing problem.