Glossary

DNS record that maps a domain name to an IPv4 address.

DNS record that maps a domain name to an IPv6 address.

Addressing technique in which the same IP prefix is announced from multiple locations, so traffic is routed to the topologically nearest one.

Globally unique number identifying an autonomous system (routing domain) on the internet.

Name server that is the official source for the records in a DNS zone.

Path-vector routing protocol that exchanges reachability information between autonomous systems on the internet.

Last address in an IPv4 subnet, used to send traffic to every host at once.

Distributed edge network that caches and delivers content from points of presence close to the user.

Notation for describing IP networks and prefix lengths using a slash, for example 192.168.1.0/24.

DNS record that points one domain name to another as its canonical name.

Protocol that automatically assigns IP addresses and network configuration to devices.

Time-limited assignment of an IP address from a DHCP server to a client, renewed periodically until it expires.

Email authentication that cryptographically signs messages with a domain's private key.

Policy built on SPF and DKIM that tells receivers how to handle unauthenticated email.

The system that translates domain names to IP addresses.

The time it takes for a DNS change to become visible everywhere as cached records expire on recursive resolvers.

Server that performs DNS lookups on behalf of clients and applications.

DNS extension that signs records so resolvers can verify they came from the real zone and were not modified in transit.

Human-readable name that represents an IP address via DNS.

Configuration where a device or network supports both IPv4 and IPv6 simultaneously.

The first address in a subnet that can be assigned to a host.

Fully Qualified Domain Name — an absolute DNS name that includes every label up to the root.

HTTP transported inside a TLS session — the modern default for web traffic.

Numeric identifier assigned to a device on an IP network so that data can be routed to and from it.

The most widely used version of IP addressing based on 32-bit.

Modern IP protocol using 128-bit addresses to replace IPv4 address limitations.

128-bit Internet Protocol address written as eight hexadecimal hextets, designed to replace the exhausted IPv4 space.

Leading portion of an IPv6 address that identifies a network, written in CIDR notation as `address/length`.

Internet service provider that gives access to the internet.

The last address in a subnet that can be assigned to a host.

Address that always refers to the local host and never leaves the machine — `127.0.0.1` in IPv4 and `::1` in IPv6.

DNS record that specifies the mail server for a domain.

Technique that translates between private and public IP addresses.

Transition mechanism that lets IPv6-only clients reach services that still only exist on IPv4.

First address in a subnet that identifies the network.

DNS record that specifies authoritative name servers for a domain.

NAT variant that lets many internal hosts share one public IPv4 by rewriting source ports per flow.

Direct interconnection between two autonomous systems to exchange traffic, usually for their own networks and customers.

Diagnostic that measures reachability and round-trip time using ICMP Echo Request and Echo Reply.

The number of leading bits in an IP address that define the network portion, written after the slash in CIDR notation.

IP address reserved for internal networks and not routable on the public internet.

DNS record used for reverse DNS lookups, mapping an IP address back to a domain name.

Globally routable IP address used to communicate over the public internet.

Network mechanisms that prioritise some traffic over other traffic to control latency, jitter and packet loss.

HTTPS/JSON protocol for registration data, designed as a structured successor to WHOIS.

DNS resolver that fully resolves a query on behalf of the client.

Address range set aside by IANA or an RFC for a specific purpose and excluded from normal public routing.

Lookup that finds the domain name associated with an IP address using PTR records.

The process of selecting paths and forwarding IP packets between networks until they reach the destination.

Mechanism that allows IPv6 devices to configure their own address without DHCP.

DNS record that holds the authoritative metadata for a zone.

DNS TXT record that lists which servers are allowed to send email for a domain.

Division of an IP network into smaller segments.

32-bit value in dotted-decimal notation that separates the network portion from the host portion of an IPv4 address.

Cryptographic protocol that provides encryption, authentication and integrity for TCP-based traffic.

The total number of IP addresses in a subnet including network and broadcast addresses.

Diagnostic that lists the routers on the path to a host by sending probes with incrementing IP TTLs.

Service in which one autonomous system pays another to deliver its traffic to and from the rest of the internet.

Value that tells resolvers how long a DNS record may be cached before re-querying.

DNS record for arbitrary text, used for SPF, DKIM and verification.

IP addresses in a subnet that can actually be assigned to hosts.

An encrypted tunnel that carries network traffic between two endpoints over an untrusted network such as the Internet.

Legacy plain-text query protocol for retrieving domain, IP and ASN registration data.

Inverted subnet mask used in ACLs and routing to match ranges of IP addresses.