RA
Router Advertisement, an ICMPv6 message that communicates default-router and prefix information and can provide DNS, MTU, route, and Pref64 options.
Read definitionAlphabetical glossary
R glossary terms
70 definitions beginning with R.
70 terms
Race condition
A timing problem in which concurrent processes read the same available resource and both attempt to allocate or modify it. Transactional allocation or server-side next-available functions help avoid duplicate assignments.
Read definitionRandom subdomain attack
A denial-of-service technique that generates many unique labels beneath a target domain, defeating positive caching and forcing repeated authoritative work. It is also called DNS water torture.
Read definitionRARP
Reverse Address Resolution Protocol, an obsolete method for a host to learn its IPv4 address from its link-layer address. BOOTP and then DHCP replaced it.
Read definitionRBAC
Role-Based Access Control, which grants permissions according to job roles rather than individually. DDI RBAC should separate read, change, approval, key management, and platform-administration duties.
Read definitionRCODE
The DNS response code indicating the outcome of a query or operation, such as NOERROR, FORMERR, SERVFAIL, NXDOMAIN, NOTIMP, or REFUSED. EDNS extends the original four-bit field.
Read definitionRD bit
The Recursion Desired bit in a query asks the server to perform recursive resolution if it supports and permits it. The server's RA bit indicates whether recursion is available.
Read definitionRDATA
The type-specific data portion of a resource record, such as an IPv4 address in an A record or the fields of an SOA record.
Read definitionRDLENGTH
The resource-record field giving the length in octets of RDATA in the wire-format message.
Read definitionRDNSS
Recursive DNS Server option in IPv6 Router Advertisements. It allows routers to advertise recursive resolver addresses without DHCPv6.
Read definitionReconciliation
The process of comparing records from multiple systems and resolving differences to maintain a trustworthy source of truth. Inputs may include DDI databases, network discovery, cloud inventory, CMDB, and security telemetry.
Read definitionRECONFIGURE
A server-initiated DHCPv6 message asking a client to initiate Renew or Information-request processing. Clients must indicate and follow the applicable reconfigure acceptance and authentication rules.
Read definitionRecursive answer
An answer produced after a server performs or forwards resolution on behalf of a client. It is normally non-authoritative from the responding resolver's perspective.
Read definitionRecursive query
A query requesting that the server obtain a final answer or error on the client's behalf rather than returning only a referral. Recursion is requested with the RD bit and controlled by server policy.
Read definitionRecursive resolver
A server that accepts recursive queries, follows referrals or uses forwarders, caches results, and returns final answers to clients. It may also validate DNSSEC and apply policy.
Read definitionRedundancy
Duplication of components, paths, data, or services so a single failure does not cause total outage. Redundancy only improves availability when failure modes are independent and recovery is tested.
Read definitionReferral
A response that directs a resolver to authoritative name servers closer to the requested name, normally through NS records in the authority section and optional glue in the additional section.
Read definitionRefresh interval
In an SOA, the interval after which a secondary checks the primary source for a new serial. In Microsoft DNS aging, the refresh interval is the period during which eligible refreshes update a record timestamp.
Read definitionRegistered domain
A domain registered through a registrar beneath a registry-controlled suffix. Application security often uses the concept of an organizational or registrable domain, which may require public-suffix policy data.
Read definitionRegistrant
The person or organization that holds registration rights for a domain name under a registry and registrar agreement.
Read definitionRegistrar
An organization accredited or authorized to register domain names for customers and submit data to a registry. Registrar account security is critical because compromise can change delegation and DNSSEC data.
Read definitionRegistry
The operator and database for a top-level domain or other registration zone. It maintains delegations and registration data submitted through registrars or direct processes.
Read definitionRegistry lock
A registry-level protection that prevents selected domain changes until an out-of-band unlock process is completed. It reduces the risk of unauthorized transfer or delegation change.
Read definitionRelative domain name
A domain name interpreted relative to an origin or search suffix rather than the root. In a zone file, names without a trailing dot are usually relative to the current $ORIGIN.
Read definitionRelay agent
An intermediary that forwards DHCP traffic between clients and servers on different links and supplies link or subscriber context. DHCPv4 and DHCPv6 relay formats differ.
Read definitionRelay Agent Information option
The full name of DHCP option 82. Its suboptions can identify circuit, remote device, subscriber, link selection, and other relay-supplied context.
Read definitionRelay-forward
A DHCPv6 message created by a relay agent to encapsulate a client message or another relay message on its way to a server. Multiple relays can create a relay chain.
Read definitionRelay-reply
A DHCPv6 message sent from a server or upstream relay back through the relay chain toward the client. It contains the encapsulated response in the Relay Message option.
Read definitionRelease
A client indication that it no longer needs an assigned address or prefix. Because release messages can be lost, leases still require finite lifetimes and expiration handling.
Read definitionRemote ID
An option 82 suboption identifying the remote access device, subscriber unit, or relay context. The exact value format is implementation-specific.
Read definitionRenew
The process by which a client asks to extend an existing binding before it expires. DHCPv4 normally starts renewal at T1, while DHCPv6 uses a RENEW message to the server that supplied the binding.
Read definitionRenewing state
The client state entered at T1 when it attempts to renew its lease directly with the original server. If renewal fails until T2, the client enters REBINDING.
Read definitionRequesting router
A router that asks a delegating router for one or more IPv6 prefixes using DHCPv6 Prefix Delegation. It assigns subnets from the delegated space to downstream links.
Read definitionReservation
A configured association between a client identity and a specific address or set of options. Product semantics vary regarding whether the reserved address is inside a dynamic pool and whether it creates DNS data.
Read definitionRESINFO record
The Resolver Information record lets a resolver publish information about its capabilities or configuration through key-value data. Clients can discover it using the resolver.arpa framework.
Read definitionResolver
Software or a service that receives DNS questions and obtains answers from local data, cache, forwarding, or iterative queries. A resolver may be a stub, caching recursive resolver, forwarding resolver, or validating resolver.
Read definitionResolver operator
The organization or team responsible for a recursive resolver service, including policy, privacy, logging, security, capacity, and upstream connectivity.
Read definitionResource record (RR)
The basic typed data element in DNS, containing an owner name, type, class, TTL, and RDATA. Records with the same owner, type, and class form an RRset.
Read definitionResource record set (RRset)
All resource records with the same owner name, class, and type. DNSSEC signs an RRset as a unit, and authoritative servers should return the complete set subject to protocol rules.
Read definitionResponse
A DNS message sent in reply to a query, containing a status code and possibly answer, authority, or additional data. A response can be authoritative, recursive, referred, truncated, or policy-generated.
Read definitionResponse policy zone (RPZ)
A DNS zone format and resolver policy mechanism used to distribute rules for blocking, redirecting, or otherwise modifying answers based on queried names, answer addresses, name servers, or client context.
Read definitionResponse rate limiting
A server technique that limits repeated similar responses to reduce reflection and amplification abuse. It is commonly abbreviated RRL.
Read definitionREST
Representational State Transfer, a common API style using HTTP methods and resource representations. DDI REST APIs often support CRUD operations, search, pagination, authentication, and asynchronous tasks.
Read definitionReverse delegation
Delegation of authority for part of in-addr.arpa or ip6.arpa to the organization responsible for an address block. IPv4 prefixes not aligned on octet boundaries may require RFC 2317 techniques.
Read definitionReverse DNS
The use of PTR records in in-addr.arpa or ip6.arpa to map an IP address to a domain name. Reverse data is independently managed from forward A and AAAA records.
Read definitionReverse lookup
A query that converts an IP address into its reverse-domain name and requests a PTR record. The result is descriptive and does not by itself prove ownership or trust.
Read definitionReverse zone
An authoritative zone beneath in-addr.arpa or ip6.arpa containing PTR records and delegations for address space.
Read definitionRFC
Request for Comments, the archival publication series containing Internet standards, best practices, informational documents, experiments, and historical material. An RFC's category and current status matter as much as its number.
Read definitionRIR
Regional Internet Registry, one of the organizations that allocate and register IP address and autonomous system number resources within a service region. The five RIRs are AFRINIC, APNIC, ARIN, LACNIC, and RIPE NCC.
Read definitionRisk-based authentication
Authentication controls that adjust requirements based on context such as device, network, behavior, location, or operation sensitivity. DDI management changes involving DNSSEC keys or global configuration may justify stronger controls.
Read definitionrndc
The remote name daemon control utility used to manage BIND named, including reload, retransfer, freeze, thaw, flush, and status operations. It uses an authenticated control channel.
Read definitionRoot hints
A bootstrap list of root name server names and addresses used by a full resolver to begin iterative resolution. Resolvers update their working root-server information from DNS responses.
Read definitionRoot label
The zero-length label at the top of the DNS hierarchy. It is shown as the trailing dot in an absolute domain name and as a single dot when written alone.
Read definitionRoot name server
An authoritative server for the DNS root zone. The named root-server identities are served by many anycast instances distributed worldwide.
Read definitionRoot priming
The process by which a recursive resolver queries a root server using hints to obtain the current root NS RRset and associated addresses.
Read definitionRoot zone
The zone at the top of the DNS hierarchy, represented by a single dot. It delegates top-level domains and contains DNSSEC trust-chain data for signed delegations.
Read definitionRoute aggregation
Combining multiple contiguous prefixes into a larger summary route. Hierarchical address planning preserves aggregation and reduces routing-table size and policy complexity.
Read definitionRoute leak
The unintended propagation of routing information beyond its intended scope, potentially diverting or exposing traffic. DDI service anycast prefixes and BYOIP routes require filtering to prevent leaks.
Read definitionRoute object
An IRR database object declaring that an autonomous system intends to originate a prefix. It is used for routing-policy documentation and filter generation.
Read definitionRouter Advertisement
The full name for RA, an ICMPv6 message that announces routers, prefixes, lifetimes, flags, MTU, DNS information, routes, and other link configuration.
Read definitionRouter option
DHCP option 3, which supplies one or more default gateway addresses in order of preference. It should not be confused with classless static route option 121.
Read definitionRouter 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.
Read definitionRouting domain
A set of interfaces and prefixes sharing a routing table or routing policy context. VRFs and tenants can create separate domains with overlapping address space.
Read definitionRPZ
Abbreviation for Response Policy Zone. It is used by recursive resolvers to apply distributed DNS response policies.
Read definitionRRL
Common abbreviation for DNS Response Rate Limiting. It reduces the volume of repeated spoofable responses while trying to preserve legitimate service.
Read definitionRRset
Common abbreviation for Resource Record Set, the records sharing owner name, class, and type.
Read definitionRRSIG record
A DNSSEC signature record covering an RRset. It identifies the covered type, algorithm, signer, key tag, inception and expiration times, and cryptographic signature.
Read definitionRRTYPE
The numeric resource-record type code identifying the format and meaning of RDATA, such as A=1, AAAA=28, or HTTPS=65. IANA maintains the registry.
Read definitionRS
Router Solicitation, an ICMPv6 message that asks local routers to send Router Advertisements.
Read definitionRTT
Round-trip time, the elapsed time for a request to travel to a destination and a response to return. DNS RTT measurements should distinguish client-to-resolver and resolver-to-authoritative paths.
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