glossary

A

A record

A DNS Address resource record that maps a host's name to its address. It specifies the Internet Protocol address (in dotted decimal form) of the host. There should be one A record for each host address.

alias

Pointer from one domain name to the official (canonical) domain name.

anonymous FTP

An FTP session that uses login name anonymous to access public files. A server that permits anonymous FTP often allows password@, signifying an e-mail address.

authoritative name server

A DNS name server that possesses complete information about a zone.

B

binding

A collection of DHCP client options and lease information, managed by the main and backup DHCP servers.

binding database

A collection of configuration parameters associated with all DHCP clients. This database holds configuration information about all the datasets.

bit swiping

Separating the IP address in the middle of an octet.

C

caching name server

This type of DNS server retains information (cache) learned from other name servers so that it can answer requests quickly, without having to query other servers for each transaction.

class

Address classes are used to identify networks of varying sizes. The class membership is specified in the first octet of the Internet address. There are five classes: A, B, C, D, and E.

class of address

The category of an IP address. This determines the location of the boundary between network prefix and host suffix. Internet addresses can be A, B, C, D, or E level addresses. Class D addresses are used for multicasting and are not used on hosts. Class E addresses are for experimental use only.

cluster

In Network Registrar, a group of DNS, DHCP, and TFTP servers that share the same database.

CNAME record

A DNS Canonical Name resource record used for nicknames or aliases. The name associated with the resource record is the nickname. The data portion is the official or canonical name.

connectionless service

This service treats each packet or datagram as a separate entity that contains the source and destination addresses. The alternative is a connection-based service using a protocol, such as TCP. The IP protocol UDP is often used to implement connectionless services.

delegation

The act of assigning responsibility for managing a DNS subzone to another server.

DHCP option

A DHCP configuration parameter and other control information that is stored in the options field of a DHCP message. DHCP clients determine what options get requested and sent in a DHCP packet.

DNS refresh interval

This interval tells the secondary server how often to check the accuracy of its data by sending an AXFR packet to the primary DNS server.

domain level

A top-level or first-level is a child of the root. A second-level domain is a child of the first-level domain.

domain name

A name that can be of two types: absolute or relative. An absolute name is the fully qualified domain name (FQDN) and is terminated with a period. A relative name is relative to the current domain and does not end with a period.

dotted decimal notation

The syntactic representation for a 32-bit integer that consists of four 8-bit numbers written in base 10 with periods (dots) separating them for a representation of IP addresses. Many TCP/IP application programs accept dotted decimal notation in place of destination machine names.

epoch date

A point in history chosen as the data from which time is measured. TCP/IP uses January 1, 1990, Universal Time (formerly called Greenwich Mean Time) as its epoch date. When TCP/IP programs exchange date or time of day, they express time as the number of seconds past the epoch date.

forwarder

A DNS server designated to handle all off-site queries. Using forwarders relieves other DNS servers from having to send packets off-site.

FQDN

The fully qualified domain name, the absolute domain name that unambiguously specifies a host's location in the DNS hierarchy.

glue record

An A (address) resource record that specifies the address of a subdomain's authoritative name server. You only need glue records in the server delegating a domain, not in the domain itself.

HINFO record

A DNS Host Information resource record that provides information about the hardware and software of the host machine.

in-addr.arpa

The DNS address mapping domain that allows you to index host addresses and names. It allows the Internet to convert IP addresses back to host names.

iterative query

When a DNS query is iterative, the name server returns the closest answer to the querying server.

IXFR

Incremental zone transfer, a standard that allows Network Registrar to update a slave (secondary) server by transferring only the change data from the primary server.

lame delegation

This occurs when DNS servers listed in a zone were not configured to be authoritative for the zone.

lease

Used to specify how long a DHCP client can use an assigned IP address. When the lease expires, the computer has to negotiate a new lease with the DHCP server.

lease grace period

The length of time the lease is retained in the DHCP server's database after it expired. This grace period protects a client's lease in cases where the client and server are in different time zones, the computer's clocks are not synchronized, or the client was not on the network when the lease expired.

loopback address

A zone that enables the server to direct traffic to itself. The host number is almost always 127.0.0.1.

mail exchanger

A computer that accepts electronic mail. Some mail exchangers forward the mail to other computers. DNS has a separate resource record type (MZ) for mail exchangers.

master name server

An authoritative name server (primary or secondary) that transfers zone data to secondary servers through zone transfers.

MCD

The name of one of the Network Registrar internal databases. The other is CNRDB.

MX record

A DNS Mail Exchanger resource record that specifies where mail for a domain name should be delivered. You can have multiple MX records for a single domain name, ranked in preference order.

NACK

No Acknowledgment, used in responding to a DHCP request. A positive acknowledgement is an ACK.

namespace

All the nodes in a domain's large inverted tree, beginning at the root (.) domain.

network ID

The portion of the 32-bit IP address that identifies which network a particular system is on. It is determined by performing an AND operation of the subnet mask and the IP address.

NOTIFY

An RFC standard that enables DNS master servers to inform their slaves that changes were made to their zones. This initiates a zone transfer.

policy

A group of DHCP attributes or options applied to a single scope or group of scopes.

primary masters

The server from which secondary servers receive data through a zone transfer request.

PTR record

A DNS Pointer resource record used to enable special names to point to some other location in the domain tree. They are used in in-addr.arpa records for translation of addresses to names. PTRs should refer to official (canonical) names and not aliases.

recursive query

A DNS query where the name server asks other DNS server for any nonauthoritative data not in its own cache. Recursive queries continue to query all name servers until receiving an answer or an error.

reservation

An IP address that is reserved for a specific DHCP client.

resolver

The client part of the DNS client-server mechanism. A resolver creates queries sent across a network to a name server, interprets responses, and returns information to the requesting programs.

resource record types

These include SOA, NS, A, CNAME, HINFO, WKS, MX and PTR. (For more information, see "Resource Records.")

reverse zone

A DNS zone that uses names as addresses in order to support address queries (see also in-addr.arpa).

root name server

This name server is at the top of the hierarchy for all root name queries. A root name server knows the addresses of the authoritative name servers for all the top-level domains. Resolution of nonauthoritative or noncached data must start at the root servers.

round-robin

When a DNS server rearranges the order of its multiple same-type records each time it is queried.

scope

An administrative grouping of TCP/IP addresses on a DHCP server.

secondary master

A DNS name server that gets it zone data from another name server authoritative for the zone. When a secondary name server starts up, it contacts the name server from which it receives updates and pulls over the zone data.

secondary subnet

A single LAN might have more than one subnet number applicable to the same LAN or network segment in a router. Typically, one subnet is designated as primary, the others as secondary. A site might support addresses on more than one subnet number associated with a single interface. You must configure the DHCP server with the necessary information about your secondary subnets.

slave forwarder

A DNS server that behaves like a stub resolver and passes most queries on to another name server for resolution (see also stub resolver).

slave servers

A DNS server that always forwards queries it cannot answer from its cache to a fixed list of forwarding servers instead of querying the root name servers for answers.

SOA record

A DNS Start of Authority resource record that designates the start of a zone.

stable storage

Contains information about address bindings so that information is not lost when a server fails.

stub resolver

A DNS server that hands off queries to another server instead of performing the full resolution itself.

subnetting

Dividing any network class into multiple subnetworks.

subnet pool

A set of IP addresses associated with a network number and subnet mask, including secondary subnets.

subzone

A partition of a domain that was delegated. It is represented as a child of the parent node. It always ends with the name of its parent, for example, engineering.cisco.com. is a subzone of cisco.com.

supernet

An aggregation of IP network addresses advertised as a single classless network address.

Universal Time (UT)

The international standard time reference that was formerly called Greenwich Mean Time. It is also called universal coordinated time or UCT.

well-known port

Any set of IP protocol port numbers preassigned for specific uses by transport level protocols, for example, TCP and UDP. Each server listens at a well-known port so clients can locate it.

WKS record

A DNS Well Known Service resource record in a DNS zone that is used to list the services provided by the host. The common protocols are TCP or UDP

Z

zone

A delegation point in the DNS tree hierarchy. It contains all the names from a certain point downward except for those names that were delegated to other zones. A zone defines the contents of a contiguous section of the domain space, usually bounded by administrative boundaries. Each zone has configuration data composed of entries called resource records. A zone can map exactly to a single domain, but can also include only part of a domain, with the remainder delegated another subzone.

zone of authority

A term used in DNS to refer to the group of names for which a given name server is an authority.

zone transfer

This occurs when a secondary DNS server starts up and updates itself from the primary server. A secondary DNS server queries a primary name server with a specific packet type called AXFR (transfer all) or IXFR (transfer incrementally) and initiates a transfer of a copy of the database.