Networking Glossary: 100+ Terms Defined

A comprehensive reference of networking, internet, and security terms. Definitions are concise and practical, with links to full articles where available.

A

ACL (Access Control List): A set of rules that determines which network traffic is allowed or denied through a router, firewall, or network device.

AES (Advanced Encryption Standard): A symmetric encryption algorithm used to secure data. AES-128 and AES-256 are the standard choices for TLS, VPN, and disk encryption.

Anycast: A routing method where the same IP address is advertised from multiple locations. Traffic is routed to the nearest location. Used by CDNs and DNS providers for global load distribution.

ARP (Address Resolution Protocol): Resolves IP addresses to MAC addresses on a local network. ARP spoofing is a common technique in man-in-the-middle attacks.

ASN (Autonomous System Number): A unique number identifying a network or group of networks under single administrative control. Used in BGP routing. Full article →

B

Bandwidth: The maximum rate of data transfer across a network path, measured in bits per second (bps). Not the same as speed; bandwidth is capacity, latency is speed.

BGP (Border Gateway Protocol): The routing protocol that connects autonomous systems on the internet. Determines the path traffic takes between networks. Full article →

Blacklist (DNSBL): A database of IP addresses known for spam, malware, or abuse. Email servers check blacklists to filter incoming mail. Full article →

Broadcast: A packet sent to all devices on a network. IPv4 uses broadcast addresses; IPv6 replaces broadcast with multicast.

Browser Fingerprinting: Tracking technique that identifies users by combining unique browser attributes like screen resolution, fonts, and GPU. Full article →

C

Cache: A temporary storage that keeps copies of frequently accessed data for faster retrieval. DNS caches, browser caches, and CDN caches all speed up the internet.

CDN (Content Delivery Network): A distributed network of servers that delivers content from locations geographically close to users. Full article →

CGNAT (Carrier-Grade NAT): NAT performed by an ISP, sharing a single public IP among multiple customers. Causes issues with port forwarding and IP reputation.

CIDR (Classless Inter-Domain Routing): A method of IP address allocation that replaces the old class-based system. Uses prefix notation like /24. Full article →

CNAME (Canonical Name): A DNS record that creates an alias, pointing one domain name to another domain name instead of directly to an IP.

D

DDoS (Distributed Denial of Service): An attack that overwhelms a target with traffic from many sources, making it unavailable to legitimate users. Full article →

DHCP (Dynamic Host Configuration Protocol): Automatically assigns IP addresses and network configuration to devices. Full article →

DNS (Domain Name System): Translates human-readable domain names into IP addresses. The internet’s phone book. Full article →

DNS Leak: When DNS queries bypass a VPN and go through the ISP’s resolver, exposing which domains you visit. Full article →

DNSSEC (DNS Security Extensions): Adds cryptographic signatures to DNS records to verify their authenticity. Full article →

DoH (DNS over HTTPS): Encrypts DNS queries inside HTTPS traffic, preventing eavesdropping on domain lookups. Full article →

DoT (DNS over TLS): Encrypts DNS queries using TLS on port 853. Alternative to DoH with different tradeoffs.

E

Egress: Outbound network traffic (leaving a network). Often charged by cloud providers.

Encryption: The process of converting data into a format that can only be read by authorized parties with the correct decryption key.

Ethernet: The most common wired local area networking technology. Defines cabling, data formats, and protocols for LAN communication.

F

Firewall: Hardware or software that monitors and controls network traffic based on predefined rules. Essential for network security.

Forward Proxy: A proxy server that sits between clients and the internet, forwarding requests on behalf of the client.

FQDN (Fully Qualified Domain Name): The complete domain name including all levels (e.g., www.whatismyip.wiki.), ending with the root domain (represented by a trailing dot).

G

Gateway: A network device that serves as an entry/exit point between two networks. Your router is the gateway between your home network and the internet.

Geolocation: The process of determining a physical location from an IP address. Full article →

H

HSTS (HTTP Strict Transport Security): A security header that tells browsers to only connect via HTTPS, preventing SSL stripping attacks.

HTTP (Hypertext Transfer Protocol): The application protocol for web communication. Sends data in plain text. Full article →

HTTPS: HTTP secured with TLS encryption. The standard for web traffic since the mid-2010s. Full article →

I

ICMP (Internet Control Message Protocol): Protocol used for diagnostics (ping, traceroute) and error reporting in IP networks.

Ingress: Inbound network traffic (entering a network).

IP Address: A numerical label assigned to each device on a network, used for identification and routing. Full article →

IP Spoofing: Forging the source IP address in packets to disguise the sender’s identity. Full article →

IPv4: Internet Protocol version 4. Uses 32-bit addresses (4.3 billion total). The current standard, but running out. Full article →

IPv6: Internet Protocol version 6. Uses 128-bit addresses (340 undecillion total). The successor to IPv4. Full article →

ISP (Internet Service Provider): Company that provides internet connectivity to consumers and businesses. Full article →

J

Jitter: Variation in packet arrival times. Low jitter is critical for real-time applications like VoIP and gaming.

K

Keepalive: A signal sent between two devices to maintain an idle connection, preventing timeouts.

L

Latency: The time it takes for a packet to travel from source to destination. Measured in milliseconds (ms). Lower is better.

Link-Local Address: An IP address valid only within a single network segment. IPv4 uses 169.254.x.x; IPv6 uses fe80::/10.

Load Balancer: Distributes incoming traffic across multiple servers to ensure no single server is overwhelmed.

M

MAC Address (Media Access Control): A unique hardware identifier assigned to network interfaces by the manufacturer. 48-bit address written in hexadecimal (e.g., AA:BB:CC:DD:EE:FF).

Man-in-the-Middle (MITM): An attack where the attacker intercepts communication between two parties. Full article →

MTU (Maximum Transmission Unit): The largest packet size that can be transmitted over a network without fragmentation. Standard Ethernet MTU is 1500 bytes.

Multicast: Sending data to a specific group of interested receivers, not all devices (broadcast) or a single device (unicast).

MX Record (Mail Exchange): DNS record specifying which mail servers handle email for a domain.

N

NAT (Network Address Translation): Allows multiple devices to share a single public IP address by translating between private and public addresses. Full article →

Nameserver: A DNS server that stores DNS records for a domain and responds to queries about that domain.

NTP (Network Time Protocol): Synchronizes clocks across devices on a network. Critical for logging, authentication, and certificate validation.

O

OSI Model: A 7-layer conceptual model for network communication: Physical, Data Link, Network, Transport, Session, Presentation, Application.

P

Packet: A unit of data transmitted over a network. Contains a header (source, destination, protocol info) and a payload (actual data).

Peering: Direct interconnection between two networks for traffic exchange, bypassing third-party transit providers.

Phishing: Social engineering attack using fake emails or websites to steal credentials. Full article →

Ping: Network tool that tests host reachability and measures round-trip latency using ICMP. Full article →

Port: A virtual endpoint identifying a specific process or service (0 to 65535). Full article →

Proxy: A server that acts as intermediary between client and destination server. Full article →

PTR Record (Pointer): DNS record that maps an IP address to a domain name (reverse DNS).

Q

QUIC: A modern transport protocol built on UDP that powers HTTP/3. Reduces latency and eliminates head-of-line blocking. Full article →

R

RDAP (Registration Data Access Protocol): The modern replacement for WHOIS, providing structured JSON responses for domain and IP registration queries.

Reverse DNS: Looking up the domain name associated with an IP address (opposite of normal DNS).

Reverse Proxy: A proxy that sits in front of servers, handling incoming requests before they reach the origin server. Used for load balancing, caching, and security.

Round-Trip Time (RTT): The time for a packet to travel from source to destination and back. What ping measures.

RPKI (Resource Public Key Infrastructure): A cryptographic framework for verifying that BGP route announcements are authorized by the IP address block owner.

S

SLAAC (Stateless Address Autoconfiguration): IPv6 mechanism allowing devices to configure their own addresses without a DHCP server.

SNI (Server Name Indication): TLS extension that includes the target hostname in the handshake, allowing multiple HTTPS sites on one IP.

SSL (Secure Sockets Layer): The predecessor to TLS. Deprecated due to security vulnerabilities. Full article →

Subnet: A logical division of an IP network into smaller segments. Full article →

T

TCP (Transmission Control Protocol): Reliable, connection-oriented transport protocol. Guarantees delivery and ordering. Full article →

TLS (Transport Layer Security): The encryption protocol securing HTTPS connections. Successor to SSL. Full article →

TLD (Top Level Domain): The last segment of a domain name (.com, .org, .wiki, .io, etc).

Tor (The Onion Router): An anonymity network that routes traffic through three relays, each stripping one encryption layer. Full article →

Traceroute: Network diagnostic tool showing the path packets take between source and destination. Full article →

TTL (Time to Live): In IP packets: the number of router hops before a packet is discarded. In DNS: how long a record should be cached (in seconds).

U

UDP (User Datagram Protocol): Fast, connectionless transport protocol with no delivery guarantees. Used for gaming, streaming, DNS. Full article →

Unicast: Communication between a single sender and a single receiver. The most common type of network communication.

V

VLAN (Virtual LAN): A logical network segmentation that allows devices on different physical network segments to behave as if they’re on the same LAN.

VPN (Virtual Private Network): Creates an encrypted tunnel between your device and a remote server, hiding your IP and encrypting traffic. Full article →

W

WebRTC (Web Real-Time Communication): Browser API for peer-to-peer audio/video communication. Can leak your real IP even with a VPN. Full article →

WHOIS: Protocol and databases for looking up domain and IP registration information. Full article →

WireGuard: A modern VPN protocol with only ~4,000 lines of code. Fast, simple, and secure. Full article →

Z

Zero Trust: Security model requiring strict verification for every user and device, regardless of network location. Full article →

Zone File: A text file containing all DNS records for a domain. Hosted on authoritative nameservers.