AAAA record
An IPv6 Address record maps a domain name to a 128-bit IPv6 address. The name is pronounced "quad A".
Category glossary
Search all termsIPv6
46 definitions associated with IPv6.
DAD
Duplicate Address Detection, the Neighbor Discovery procedure a node uses before assigning an IPv6 unicast address to an interface. It helps detect another node already using the same address on the link.
DHCPv6
The DHCP protocol for IPv6. It uses UDP ports 546 and 547, DUID-based identities, identity associations, and messages such as SOLICIT, ADVERTISE, REQUEST, and REPLY.
DNS64
A resolver function that synthesizes AAAA records from IPv4 A records using a configured IPv6 prefix, allowing IPv6-only clients to reach IPv4 services through NAT64.
EUI-64
A 64-bit Extended Unique Identifier format. Modified EUI-64 was historically used to form IPv6 interface identifiers from MAC addresses, though modern systems often use privacy or stable-random identifiers instead.
Global scope
The address scope intended for reachability beyond the local link, subject to routing and policy. Global unicast addresses normally come from 2000::/3, though the concept of scope is broader than that allocation block.
Global unicast address (GUA)
An IPv6 unicast address designed for global routing, generally allocated from 2000::/3 at present. A GUA can still be filtered or used only internally depending on routing policy.
Happy Eyeballs
A client connection strategy that quickly races or sequences IPv6 and IPv4 attempts so users are not delayed by a broken path for one family. It affects how A and AAAA answers translate into observed connections.
ICMPv6
The IPv6 control protocol used for errors, diagnostics, Neighbor Discovery, Router Advertisements, multicast listener functions, and other essential operations. Blocking it broadly can break IPv6.
IID
Interface Identifier, the lower-order portion of an IPv6 unicast address used to identify an interface within a subnet prefix. Modern IID generation may use stable-random or temporary privacy methods rather than embedding a MAC address.
Ip6.arpa
The DNS reverse-mapping domain for IPv6. Each hexadecimal nibble of the 128-bit address is reversed as a label beneath ip6.arpa.
IPv4-mapped IPv6 address
An IPv6 representation of an IPv4 address in ::ffff:0:0/96, commonly used by APIs and dual-stack software. It does not by itself provide network translation.
IPv6 address scope
The reachability boundary associated with an IPv6 address, such as interface-local, link-local, or global. Scope identifiers may be required when using link-local addresses on a multi-interface host.
IPv6 Router Advertisement
An ICMPv6 message sent by routers to announce prefixes, default-router information, lifetimes, MTU, flags, and optional configuration such as recursive DNS. Hosts use it for on-link determination and often for SLAAC.
IPv6 subnet
An on-link IPv6 prefix, conventionally /64 for ordinary LANs that use SLAAC and Neighbor Discovery. Different prefix lengths are possible for specific link types and designs.
IPv6-only network
A network where endpoints are not assigned native IPv4 addresses. Access to IPv4-only services may be provided through NAT64, DNS64, 464XLAT, proxies, or application gateways.
LLA
Common abbreviation for IPv6 link-local address. Every IPv6-enabled interface generally has one, and routing protocols and Neighbor Discovery frequently use it.
Managed address configuration flag (M flag)
A Router Advertisement flag indicating that hosts should use DHCPv6 for stateful address configuration. Host behavior can vary by operating system and network policy.
NA
Neighbor Advertisement, an ICMPv6 Neighbor Discovery message used to answer Neighbor Solicitations, announce address or link-layer changes, and support reachability and duplicate-address procedures.
NAT64
A translation mechanism that lets IPv6 clients communicate with IPv4 servers by mapping between an IPv6 prefix and IPv4 addresses. DNS64 is commonly paired with it to synthesize reachable AAAA answers.
Neighbor Advertisement
The expanded name of the ICMPv6 NA message. It carries target and link-layer information and can be solicited or unsolicited.
Neighbor cache
A per-interface table mapping IPv6 neighbors to link-layer addresses and reachability states. It is the IPv6 counterpart to the IPv4 ARP cache, with richer state tracking.
Neighbor Discovery (ND)
The ICMPv6 framework used for router discovery, prefix discovery, address resolution, neighbor reachability, redirects, and Duplicate Address Detection. It replaces ARP and several IPv4 control mechanisms.
Neighbor Solicitation
An ICMPv6 message used to resolve a neighbor's link-layer address, verify reachability, or perform Duplicate Address Detection. It is commonly abbreviated NS.
Nibble boundary
A boundary aligned on a four-bit hexadecimal digit. IPv6 reverse DNS is simplest when prefixes are delegated on nibble boundaries because each label in ip6.arpa represents one hexadecimal digit.
NUD
Neighbor Unreachability Detection, the Neighbor Discovery process that tracks whether a neighbor is reachable and probes when necessary. Neighbor-cache entries move through states such as REACHABLE, STALE, DELAY, and PROBE.
O flag
The Other Configuration flag in a Router Advertisement, indicating that hosts should use DHCPv6 for information other than addresses, such as DNS or domain search data. Host behavior is implementation-dependent.
Pref64
An IPv6 prefix used by NAT64 to embed or represent IPv4 destinations. Networks can advertise a Pref64 in Router Advertisements, and DNS64 uses a configured prefix for synthesis.
Preferred lifetime
The period during which an IPv6 address or prefix is preferred for new communication. After it expires but before valid lifetime ends, the resource is deprecated and should generally not be selected for new sessions.
Prefix Information Option (PIO)
A Router Advertisement option describing an IPv6 prefix, its valid and preferred lifetimes, and whether it is on-link or autonomous for SLAAC.
Prefix policy
Host rules that rank source and destination address pairs, influencing address selection when multiple IPv4 and IPv6 choices exist. Policy can affect which DNS answer a client actually uses.
RA
Router Advertisement, an ICMPv6 message that communicates default-router and prefix information and can provide DNS, MTU, route, and Pref64 options.
RDNSS
Recursive DNS Server option in IPv6 Router Advertisements. It allows routers to advertise recursive resolver addresses without DHCPv6.
Router Advertisement
The full name for RA, an ICMPv6 message that announces routers, prefixes, lifetimes, flags, MTU, DNS information, routes, and other link configuration.
Router Solicitation
An ICMPv6 message sent by a host to prompt routers to send Router Advertisements sooner than the normal unsolicited interval. It is commonly abbreviated RS.
RS
Router Solicitation, an ICMPv6 message that asks local routers to send Router Advertisements.
SAVI
Source Address Validation Improvement, a family of mechanisms that binds IP source addresses to attachment points to reduce spoofing. SAVI can use DHCP, Neighbor Discovery, or other control-plane evidence.
Site-local address
A deprecated IPv6 unicast scope formerly associated with fec0::/10. It was replaced operationally by Unique Local Addresses and should not be used in new designs.
SLAAC
Stateless Address Autoconfiguration, by which an IPv6 host forms addresses from Router Advertisement prefixes without a DHCPv6 address lease. DHCPv6 can still provide other configuration, and address registration can improve visibility.
Source address selection
Host logic for choosing the most appropriate source address for a destination based on scope, deprecation, label, precedence, and prefix matching. Incorrect choices can cause asymmetric or failed connectivity.
SSAC
A mistaken or informal rendering sometimes used for SLAAC. The standardized acronym is SLAAC, Stateless Address Autoconfiguration.
Tentative address
An IPv6 address assigned to an interface but not yet usable for normal communication while Duplicate Address Detection is in progress.
ULA
Unique Local Address, an IPv6 unicast address from fc00::/7 intended for local communications and not expected to be globally routed. Locally assigned ULAs normally use fd00::/8 with a pseudo-random global ID.
Unique Local Address
The expanded name of ULA. It provides organization-local IPv6 addressing without relying on provider-assigned global prefixes, though collision avoidance remains important during network mergers.
Valid lifetime
The period during which an IPv6 address or delegated prefix remains valid for existing and new use, subject to preferred-state rules. When it expires, the resource must not be used.
Zone ID
An interface or scope identifier appended to a scoped IPv6 address in local APIs, such as fe80::1%eth0. It disambiguates which link is intended for a non-global address.