A record
An Address record maps a domain name to a 32-bit IPv4 address. It is one of the most common DNS data types and is normally used for forward name resolution.
Read definitionAlphabetical glossary
A glossary terms
49 definitions beginning with A.
49 terms
AA flag
The Authoritative Answer bit in a DNS response indicates that the responding server is authoritative for the name in the answer section. It does not mean every item in the response is authoritative, such as some additional-section data.
Read definitionAAAA record
An IPv6 Address record maps a domain name to a 128-bit IPv6 address. The name is pronounced "quad A".
Read definitionAbandoned lease
A lease state used when a DHCP server believes an address is already in use or has failed conflict detection. The server normally avoids offering that address until an administrator clears the state or the implementation retries it.
Read definitionAbsolute domain name
A domain name expressed relative to the DNS root, usually shown with a trailing dot, such as host.example.com. The trailing dot prevents a resolver or tool from appending a local search suffix.
Read definitionAccess control list (ACL)
A rule set that permits or denies operations based on attributes such as source address, identity, network, or transaction type. DNS and DHCP ACLs commonly control recursion, zone transfers, updates, queries, and administrative access.
Read definitionActive Directory-integrated zone
A Microsoft DNS zone whose data is stored in Active Directory and replicated through AD replication rather than only through DNS zone transfers. It can support secure dynamic updates and multi-writer operation on eligible domain controllers.
Read definitionActive lease
A lease currently assigned to a client and not yet expired, released, or invalidated. The lease database normally records the address, client identifier, start time, duration, and state.
Read definitionActive leasequery
A protocol mechanism that streams DHCP lease state changes to a requesting system after an initial synchronization. It is commonly used by access, security, accounting, or IPAM systems that need near-real-time binding information.
Read definitionActive-active
An architecture in which multiple service nodes actively answer traffic at the same time. In DDI, the term can describe anycast DNS, load-balanced DHCP, or multi-primary management, but the exact behavior depends on the product.
Read definitionActive-passive
An architecture in which one node serves traffic while a standby node waits to take over after a failure. State synchronization and failover detection determine how much disruption or data loss can occur.
Read definitionAD bit
The Authenticated Data bit in a DNS response signals that the validating resolver considers the included answer and relevant proof data authentic according to DNSSEC. A stub should only trust the bit when it trusts the resolver and the transport path.
Read definitionAddress allocation
The process of selecting an address or prefix from a larger pool and making it available for use. Allocation does not always mean the address has been configured on a device yet.
Read definitionAddress assignment
The act of associating an allocated IP address or prefix with a specific interface, device, customer, service, or purpose. IPAM systems track assignments to reduce duplication and preserve ownership history.
Read definitionAddress block
A contiguous range of IP addresses represented by a network and prefix length, such as 192.0.2.0/24 or 2001:db8::/32. Blocks may be allocated, assigned, reserved, delegated, or subdivided.
Read definitionAddress conflict
A condition in which two interfaces attempt to use the same IP address on the same logical network. Symptoms can include intermittent connectivity, ARP or Neighbor Discovery instability, and DHCP declines.
Read definitionAddress family
A classification for network address formats and protocol behavior. DDI work most often distinguishes IPv4 from IPv6.
Read definitionAddress management
The policies, workflows, records, and automation used to plan, assign, reclaim, audit, and report on IP addresses and prefixes. It is broader than simply maintaining a spreadsheet of free addresses.
Read definitionAddress pool
A set of addresses available for dynamic allocation. A pool is normally associated with a subnet or link and may be restricted by policies, classes, exclusions, or utilization thresholds.
Read definitionAddress registration
A mechanism by which a host informs a DHCPv6 infrastructure component about an IPv6 address it configured through another method, such as SLAAC. This can help DDI systems maintain address visibility and DNS registration.
Read definitionAddress reservation
A policy that associates a particular address with a known client identity so the server consistently offers that address. Some products distinguish a reservation from a fixed address that sits outside a dynamic pool.
Read definitionAddress scope
The reachability domain of an address. IPv6 explicitly defines scopes such as interface-local, link-local, and global, while operational IPAM tools may also use scope to mean an administrative partition or DHCP range.
Read definitionAddress space
The complete set of addresses being considered, such as all IPv4 addresses, a private enterprise block, or a tenant-specific VRF. Address space can overlap when routing domains are isolated.
Read definitionAddress utilization
A measurement of how much of a network, pool, or prefix is assigned, reserved, leased, or otherwise unavailable. The numerator and denominator should be defined because products may treat network, broadcast, excluded, and reserved addresses differently.
Read definitionAdministrative domain
A collection of systems, zones, networks, or policies under common operational control. The term is contextual and should not be confused with a DNS domain name.
Read definitionAggressive use of DNSSEC-validated cache
A resolver optimization that reuses validated NSEC or NSEC3 proofs to synthesize negative answers for other names covered by the proof. This can reduce authoritative queries and improve resilience during random-subdomain attacks.
Read definitionAging
A Microsoft DNS mechanism that timestamps eligible dynamically registered records so old data can later be removed by scavenging. Static records normally do not age unless explicitly converted or timestamped.
Read definitionAlias
A name that points to another canonical name or target. CNAME is the standardized alias record for most owner names, while provider-specific ALIAS or ANAME features often synthesize A and AAAA answers at a zone apex.
Read definitionALIAS record
A non-standard provider feature that allows an alias-like configuration where a CNAME is not allowed, often at the zone apex. The authoritative platform follows the target and returns synthesized address records.
Read definitionAllow-query
A policy controlling which clients may ask a DNS server questions. It is commonly enforced globally, per view, or per zone.
Read definitionAllow-recursion
A policy controlling which clients may use a resolver to perform recursive resolution. Restricting recursion prevents an internal resolver from becoming an open resolver.
Read definitionAllow-transfer
A policy controlling which systems may request AXFR or IXFR zone transfers. Transfers should normally be limited to designated secondaries and management systems.
Read definitionANAME record
A proposed or vendor-specific alias-at-apex mechanism that lets an operator point a name to another name while serving address records to clients. It is not a universally standardized DNS resource record type.
Read definitionANY query
A DNS query using QTYPE 255 that asks for whatever records a server chooses to return for a name. It does not reliably mean "all records" and modern servers often minimize or synthesize the response to reduce abuse.
Read definitionAnycast
A routing design in which multiple nodes advertise the same service IP address and the network directs a client to a reachable instance, often the topologically closest one. Anycast is widely used for authoritative and recursive DNS resilience.
Read definitionApex
The top name of a DNS zone. It is also called the zone apex and contains the zone's SOA and authoritative NS record sets.
Read definitionAPI
An application programming interface that lets software read or change DDI objects programmatically. Common styles include REST, vendor-specific web APIs, and standards-based protocols such as DNS UPDATE.
Read definitionAPIPA
Automatic Private IP Addressing, the Microsoft term for self-assignment from 169.254.0.0/16 when a host cannot obtain normal IPv4 configuration. These link-local addresses are not routed.
Read definitionApplication delivery controller (ADC)
A load balancer or traffic-management platform that can proxy application traffic and may also perform DNS-based global server load balancing. ADC-generated DNS queries and health checks often appear in DDI telemetry.
Read definitionARIN
The Regional Internet Registry serving the United States, Canada, parts of the Caribbean, and North Atlantic islands. It allocates and registers Internet number resources within its service region.
Read definitionARP
The Address Resolution Protocol maps an IPv4 address to a link-layer address on a local network. Duplicate IPs, stale caches, and spoofing can cause misleading DDI troubleshooting symptoms.
Read definitionARP probe
An ARP-based check used before assigning or using an IPv4 address to determine whether another device appears to claim it. DHCP servers or clients may use probes as part of conflict detection.
Read definitionAuthoritative answer
A response based on data for which the responding server is authoritative, rather than solely on recursive cache content. The AA bit normally identifies authoritative responses.
Read definitionAuthoritative data
DNS data served from an authoritative zone or a properly configured authoritative data source. Cached copies at resolvers are not authoritative data even when they reproduce the same record set.
Read definitionAuthoritative server
A DNS server that provides authoritative answers for one or more zones. It may obtain data from a primary source, a zone transfer, a database, a catalog, or a hosted control plane.
Read definitionAuthoritative-only server
A server configured to answer only from its authoritative zones and not to provide recursion to clients. Public authoritative infrastructure should normally use this model.
Read definitionAuthorization
A Microsoft Active Directory control that allows approved DHCP servers to provide service in an AD domain environment. An unauthorized Windows DHCP server may stop serving clients.
Read definitionAutomatic allocation
An allocation method in which DHCP permanently assigns an address to a client from a pool, rather than leasing it for a limited period. Dynamic allocation is far more common.
Read definitionAXFR
A full zone transfer that sends the complete contents of a zone from one authoritative server to another authorized system. Large or sensitive transfers should be protected by ACLs, TSIG, and secure transport where supported.
Read definition