BlueCatのA to Z of DNS へようこそ






A record

A DNS record that maps domain names to IPv4 addresses.

AAA (Authentication, Authorization and Accounting)

Refers to a family of protocols that mediate network access.

AAAA record

A DNS record that maps domain names to IPv6 addresses.

ACI (Cisco Application Centric Infrastructure)

Cisco’s software-defined networking (SDN) solution for data center and cloud networks.

ACL (Access Control List)

Limits which entities are allowed to perform certain functions against a DNS server, such as sending queries or performing dynamic updates.

Active Directory

A Microsoft directory service for Windows domain networks that is included in most Windows Server operating systems as a set of processes and services.


A traffic routing algorithm used for the speedy delivery of website content that advertises individual IP addresses on multiple nodes.

Authoritative DNS server / Authoritative name server

Provides original and definitive answers to DNS queries.


BAM (BlueCat Address Manager)

BlueCat’s IPAM solution that brings all IP address, DNS, and DHCP information into a single pane of glass.

BDDS (BlueCat DNS, DHCP Server)

The DNS and DHCP servers that get their data from BAM and serve it to clients.

BGP (Border Gateway Protocol)

A standardized exterior gateway protocol to exchange routing and reachability information among autonomous systems on the internet.


Widely-used software that allows you to publish your DNS information on the internet, and to resolve DNS queries for your users.

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Bridgehead server

A domain controller that functions as the primary route of Active Directory replication data moving into and out of sites.

Broadcast routing

Packets are sent to all nodes even if they do not want it.


Caching DNS server

A server that handles recursive requests from clients.

CIDR (Classless Inter-Domain Routing)

A method for allocating IP addresses and IP routing introduced by the ITEF 1993 to replace classful networks.

Classful networks

A previous network addressing architecture that divided the IP address space for IPv4 into five address classes based on the leading four address bits.


A type of DNS record that redirects a domain to a different domain.

Crossover high availability (xHA)

Aims to ensure a certain level of operational performance or uptime for a system.

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The integration of DNS, DHCP, and IPAM into one management solution.

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DHCP (Dynamic Host Configuration Protocol)

The standard mechanism to dynamically assign IP addresses within a network.

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Sent by the server to the client in response to a DHCPREQUEST indicating that the server acknowledges the request.


Sent by the client as the first step of the DHCP client/server interaction to discover what servers exist.


Sent by the server to the client in response to a DHCPREQUEST indicating that the server does not acknowledge the request.


Sent by the server to the client in response to a DHCPDISCOVER to offer an IP address, lease time, and network configuration parameters.


Sent by the client to the server in response to a DHCPOFFER indicating which server the client has chosen to further interact with.

DHS Root Server

A name server that directly answers requests for records in the root zone and answers other requests by returning a list of authoritative name servers for the appropriate top-level domain.

DMZ (Demilitarized zone)

A subnetwork that contains and exposes an organization’s external-facing services to an untrusted, usually larger, network such as the internet.

DNA Center (Cisco DNA Center)

Uses intent-based networking to simplify network management.

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DNS – Domain Name System

A hierarchical naming system that enables communication across devices in a network.

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DNS hijacking

IP addresses of your domain’s DNS servers are changed to IP addresses of attacker-controlled servers.

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DNS namespace

Identifies the structure of the domains that combine to form a complete domain name.

DNS query / DNS request

Demand for information sent from a user’s computer (DNS client) to a DNS server.

DNS record

Tells servers precisely how to respond to a DNS query.

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DNS root server

A name server that directly answers requests for records in the root zone and answers other requests by returning a list of authoritative name servers for the appropriate top-level domain.

DNS server

Also called a DNS nameserver, it stores DNS records and responds to and resolves DNS queries from devices.

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DNS sinkhole

A DNS server that gives out a false result for a domain name.

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DNS stub resolver

The part of the client device that facilitates DNS queries.

DNS tunneling

Exploits the DNS protocol to tunnel malware and other data through a client-server model.

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DNS zone

A distinct, contiguous portion of the domain name space for which administrative responsibility has been delegated to a single manager.

DNSSEC (Domain Name Service Security Extension)

A mechanism that uses cryptography to provide authentication and integrity for DNS queries.

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DORA process

The sequence of discover, offer, request, and acknowledge messages exchanged between client and server for DHCP.

Dynamic IP Address

An IP address that changes from time to time, unlike a static IP address.


Enhanced Interior Gateway Routing Protocol (EIGRP)

An advanced distance-vector routing protocol that is used on a computer network for automating routing decisions and configuration.


The unauthorized transfer of data from a computer; DNS tunneling is a common menthod of DNS-based exfiltration.

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Forwarding DNS Server

A DNS server on a network that forwards DNS queries for external DNS names to DNS servers outside that network.

Fully Qualified Domain Name (FQDN)

A domain name that specifies its exact location in the tree hierarchy of DNS.



The delivery of information to a group of destinations in a network identified by their geographical locations; a specialized form of multicast addressing.

GUID (Globally Unique Identifier)

A128-bit number used to identify information in computer systems, typically in software created by Microsoft.


High Availability (HA)

It aims to ensure a certain level of operational performance or uptime for a system.

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Intent-Based Networking

A model to leverage automation and software-defined networking in day-to-day management and operations.

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Internet Protocol Address (IP Address)

A numerical label assigned to each device connected to a network that uses IP for communication.

Internet Protocol Host (IP Host)

A computer participating in networks that use the IP suite.

IPAM (IP address management)

A method for planning, tracking, and managing IP address space on a network.

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IPv4 (Internet Protocol version 4)

The fourth version of Internet Protocol that uses 32-bit addresses to route most of today’s internet traffic; the global supply of IPv4 addresses is exhausted.

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IPv6 (Internet Protocol version 6)

The most recent version of Internet Protocol, which uses 128-bit address space; there are 340 undecillion IPv6 addresses.

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Iterative (or non-recursive) query

A DNS request that states, “Give me the answer or give me any information that will help me find the answer.” The nameserver will respond back from its cache or zone files but will not contact other DNS servers.


Lightweight Directory Access Protocol (LDAP)

An open, vendor-neutral, industry standard application protocol for accessing and maintaining distributed directory information services over an IP network.



Group communication where data transmission is addressed to a group of destination computers simultaneously.

MX record

A DNS record that provides the domain names of mail servers that receive emails on behalf of a domain.

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An application for providing responses to queries against a directory service. It translates an often humanly meaningful, text-based identifier to a system-internal, often numeric identification or addressing component. An example of a name server is the server component DNS.

NAT (network address translation)

Remapping one IP address space into another by modifying network address information in the IP header of packets while they are in transit across a traffic routing device.

Non-recursive (or iterative) query

A DNS request that states, “Give me the answer or give me any information that will help me find the answer.” The nameserver will respond back from its cache or zone files but will not contact other DNS servers.

NS record

A DNS record that provides a list of the authoritative name servers responsible for the domain.

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NSD (name server daemon)

An open-source DNS server developed by NLnet labs.

NTP (network time protocol)

A networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks.


DNS response code indicating the DNS query failed because the domain name queried does not exist.

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Open Shortest Path First (OSPF)

A routing protocol for IP networks that uses a link state routing algorithm and falls into the group of interior gateway protocols, operating within a single autonomous system.

OSI model

A conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system.

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PTR record

A DNS record that resolves IPv4 or IPv6 addresses to domain names.

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Recursive DNS server

Responsible for providing the proper IP address of the intended domain name to the requesting host; the first servers contacted as the result of a request.

Recursive query

A kind of query in which the DNS server will do all the job of fetching the answer and giving it back to you; the DNS server might also query other DNS servers on your behalf.

Remote Authentication Dial-In User Service (RADIUS)

A client/server protocol and software that enables remote access servers to communicate with a central server to authenticate dial-in users and authorize their access to the requested system or service.

Reverse DNS lookup

A tool that requires you to enter an IP address to find the domain name associated with the corresponding IP.

RFC 1918 networks

Ranges of IP addresses set aside for private use on TCP/IP networks.

Rogue DNS Server

Translates domain names of desirable websites into IP addresses of sites with unintended content.

Routing Information Protocol

A dynamic routing protocol that uses hop count as a routing metric to find the best path between the source and the destination network.


Simple Network Management Protocol (SNMP)

A protocol for collecting and organizing information about managed devices on IP networks and for modifying that information to change device behavior.

Simple Object Access Protocol (SOAP)

A messaging protocol specification for exchanging structured information in the implementation of web services in computer networks.

SNMP module

An SNMP extension; this should be covered under SNMP entry.

SOA record

A DNS record type that provides important details about a DNS zone; required for every DNS zone.

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SSL (secure sockets layer)

Security technology for establishing an encrypted link between a server and a client.

Static IP address

An IP address that doesn’t change and was manually configured for a device, versus one that was assigned by a DHCP server.

Subnet mask

A 32-bit number that masks an IP address, and divides the IP address into network address and host address.



A protocol that provides reliable, ordered, and error-checked delivery of bytes between applications running on hosts communicating via an IP network; part of the TCP/IP suite.

Time to Live (TTL)

A setting for each DNS record that specifies how long a resolver is supposed to cache the DNS query before it expires.

Top-level domain (TLD)

The last part of the domain name; in the domain name, the top-level domain is com.

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Transaction Signature (TSIG)

A protocol that enables DNS to authenticate updates to a DNS database; most commonly used to update dynamic DNS or a secondary DNS server.

Transport layer security (TLS)

A cryptographic protocol to provide communications security over a computer network.

TXT record

A DNS record that provides any type of descriptive information in text format.

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Unicast (routing)

One-to-one transmission from one point in the network to another point with one sender and one receiver, each identified by a network address.

User Datagram Protocol (UDP)

An alternative protocol to TCP used primarily for establishing low-latency and loss-tolerating connections between applications on the internet.


Virtual IP Address (VIP)

An IP address that doesn’t correspond to an actual physical network interface; uses include network address translation, fault-tolerance, and mobility.

Virtual Realization (vRealize) Automation (vRO)

Now called vRealize Automation. An infrastructure automation platform that enables self-service multicloud environments.

Virtual Sphere (vSphere)

VMware’s cloud computing virtualization platform.


XHA (See Crossover High Availability)

BlueCat’s acronym; aims to ensure a certain level of operational performance or uptime for a system.

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