Cisco CNS Network Registrar User's Guide, 6.0
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Table Of Contents


A record
DNS Address resource record. Maps a host's name to its address and specifies the Internet Protocol address (in dotted decimal form) of the host. There should be one A record for each host address.
address block
Block of IP addresses to use with DHCP subnet allocation that uses on-demand address pools.
Pointer from one domain name to the official (canonical) domain name.
Asynchronous Transfer Mode (ATM)
International standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells.
authoritative name server
DNS name server that possesses complete information about a zone.
Full DNS zone transfer. See also zone transfer and IXFR.

Berkeley Internet Name Domain
Berkeley Internet Name Domain. Implementation of the Domain Name System (DNS) protocols.
Collection of DHCP client options and lease information, managed by the main and backup DHCP servers. A binding database is a collection of configuration parameters associated with all DHCP clients. This database holds configuration information about all the datasets.
Bootstrap Protocol. Used by a network node to determine the IP address of its Ethernet interfaces, so that it can affect network booting.

cable modem termination system
Data stored in indexed disk files to reduce the amount of physical memory.
caching name server
Type of DNS server that caches information learned from other name servers so that it can answer requests quickly, without having to query other servers for each transaction.
Values in Network Registrar are not case-sensitive, with the exception of passwords.
DHCP client hardware (MAC) address. Sent in an RFC 2131 packet between the client and server.
DHCP client IP address. Sent in an RFC 2131 packet between the client and server.
class of address
Category of an IP address that 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.
Cisco CNS Network Registrar feature that provides differentiated services to users that are connected to a common network. You can thereby group your user community based on administrative criteria, and then ensure that each user receives the appropriate class of service.
In Network Registrar, a group of DNS, DHCP, and TFTP servers that share the same database.
Cable modem termination system. Either a router or bridge, typically at the cable headend.
CNAME record
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.
Name of one of the Network Registrar internal databases. The others are changeset database and MCD.

Data Over Cable Service Interface Specification
Act of assigning responsibility for managing a DNS subzone to another server.
Dynamic Host Configuration Protocol. Designed by the Internet Engineering Task Force (IETF) to reduce the amount of configuration that is required when using TCP/IP. DHCP allocates IP addresses to hosts. It also provides all the parameters that hosts require to operate and exchange information on the Internet network to which they are attached.
DHCP option
DHCP configuration parameter and other control information stored in the options field of a DHCP message. DHCP clients determine what options get requested and sent in a DHCP packet.
Acknowledgment used in a positive response to a DHCP request.
Initial request for an IP address from the DHCP client to the server.
Acknowledgment used in a negative response to a DHCP request.
Offer of an IP address sent by the DHCP server after receiving a DHCPDISCOVER from the client.
Request from the DHCP client to the server for the renewal of an IP address.
Client request for an IP address after receiving a DHCPOFFER from the DHCP server.
Digital Subscriber Line
Public network technology that delivers high bandwidth over conventional copper wiring at limited distances.
Domain Name System. Handles the growing number of Internet users. DNS translates names, such as, into Internet Protocol (IP) addresses, such as, so that computers can communicate with each other.
Data Over Cable Service Interface Specification. Standard created by cable companies in 1995 to work toward an open cable system standard and that resulted in specifications for connection points, called interfaces.
Portion of the DNS naming hierarchy tree that refers to general groupings of networks based on organization type or geography. The hierarchy is root, top- or first-level, and second-level domain.
domain name
DNS name that can be either 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.
Domain Name System
See DNS.
dotted decimal notation
Syntactic representation of a 32-bit integer that consists of four eight-bit numbers written in base 10 with dots separating them for a representation of IP addresses. Many TCP/IP application programs accept dotted decimal notation in place of destination machine names.
dynamic DNS update
Protocol (RFC 2136) that integrates DNS with DHCP.
Dynamic Host Configuration Protocol

extension point
In Network Registrar, element of a script written in TCP, C, or C++ that customizes handling DHCP packets as the server processes them, and which supports additional levels of customizing DHCP clients.

Network Registrar feature (as described in RFC 2131) that provides for multiple, redundant DHCP servers, whereby one server can take over in case of a failure. DHCP clients can continue to keep and renew their leases without needing to know or care which server is responding to their requests.
DNS server designated to handle all offsite queries. Using forwarders relieves other DNS servers from having to send packets offsite.
Fully qualified domain name. Absolute domain name that unambiguously specifies a host's location in the DNS hierarchy.
fully qualified domain name

DHCP gateway (relay agent) IP address. Sent in an RFC 2131 packet between the client and server.
glue record
DNS 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
DNS Host Information resource record. Provides information about the hardware and software of the host machine.
hint server
Any network device with a TCP/IP network address.

Institute of Electrical and Electronics Engineers. Professional organization whose activities include developing communications and network standards.
DNS address mapping domain with which you can index host addresses and names. The Internet can thereby convert IP addresses back to host names. See also reverse zone.
incremental zone transfer
IP address
Internet Protocol address. For example,
IP history
Network Registrar tool that records the lease history of IP addresses in a database.
Internet Service Provider. Company that provides leased line, dialup, and DSL (Point-to-Point over Ethernet and DHCP) access to customers.
iterative query
Type of DNS query whereby the name server returns the closest answer to the querying server.
Incremental zone transfer. Standard that allows Network Registrar to update a slave (secondary) server by transferring only the changed data from the primary server.

lame delegation
Condition when DNS servers listed in a zone are not configured to be authoritative for the zone.
Lightweight Directory Access Protocol. Method that provides directory services to integrate Network Registrar client and lease information.
IP address assignment to a DHCP client that also specifies how long the client can use the address. When the lease expires, the client must negotiate a new one with the DHCP server.
lease grace period
Length of time the lease is retained in the DHCP server's database after it expires. This protects a client's lease in case the client and server are in different time zones, their clocks are not synchronized, or the client is not on the network when the lease expires.
lease query
Process by which a relay agent can request lease (and reservation) data directly from a DHCP server in addition to gleaning it from client/server transactions.
Lightweight Directory Access Protocol
The distinguished name referring to the name of the current machine. Localhost is useful for applications requiring a host name.
loopback zone
DNS zone that enables the server to direct traffic to itself. The host number is almost always

MAC address
Standardized data link layer address. Required for every port or device that connects to a LAN. Other devices in the network use these addresses to locate specific ports on the network and to create and update routing tables and data structures. MAC addresses are six bytes long and are controlled by the IEEE. Also known as a hardware address, MAC layer address, and physical address. A typical MAC address is 1,6,00:d0:ba:d3:bd:3b.
maximum client lead time
mail exchanger
Host that accepts electronic mail, some of which act as mail forwarders. See also MX record.
master name server
Authoritative DNS name server that transfers zone data to secondary servers through zone transfers.
Name of one of the Network Registrar internal databases. The other is CNRDB.
Maximum client lead time. In DHCP failover, a type of lease insurance that controls how much ahead of the backup server's lease expiration the client's lease expiration should be.
Multiple Service Operator. Provides subscribers Internet access using cable or wireless technologies.
State of having multiple DHCP scopes on one subnet or several LAN segments.
Process of performing multiple server tasks.
MX record
DNS Mail Exchanger resource record. 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.

Negative acknowledgment used in responding to a DHCP request.
All the nodes in a domain's large inverted tree, beginning at the root (.) domain. In a virtual private network, the informal name for the addresses contained in it.
DNS Naming Authority Pointer resource record. Helps with name resolution in a particular namespace and are processed to get to a resolution service. Based on proposed standard RFC 2915.
negative cache time
Memory cache the DNS server maintains for a quick response to repeated requests for negative information, such as "no such name" or "no such data." Network Registrar discard this information at intervals.
network ID
Portion of the 32-bit IP address that identifies which network a particular system is on, determined by performing an AND operation of the subnet mask and the IP address.
Standard (RFC 1996) whereby DNS master servers can inform their slaves that changes were made to their zones, and which initiates a zone transfer.
The Network Registrar command line interface (CLI).

on-demand address pool
Wholesale IP address pool issued to a client (usually a VPN router or other provisioning device), from which it can draw for lease assignments. Also known as DHCP subnet allocation.
Organizationally Unique Identifier (OUI)
Assigned by the IEEE to identify the owner or ISP of a VPN. See also IEEE and VPN.

Packet Internetwork Groper. A common method for troubleshooting device accessibility that uses a series of Internet Control Message Protocol (ICMP) Echo messages to determine if a remote host is active or inactive, and the round-trip delay in communicating with the host.
Group of DHCP attributes or options applied to a single scope or group of scopes.
primary master
DNS server from which a secondary server receive data through a zone transfer request.
PTR record
DNS Pointer resource record. Used to enable special names to point to some other location in the domain tree. Should refer to official (canonical) names and not aliases. See also

recursive query
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.
refresh interval
Time interval in which a secondary DNS server checks the accuracy of its data by sending an AXFR packet to the primary server.
relay agent
Device that connects two or more networks or network systems. In DHCP, a router on a virtual private network that is the IP helper for the DHCP server.
Request for Comments
See RFC.
IP address or lease that is reserved for a specific DHCP client.
resolution exception
Selectively forwarding DNS queries for specified domains to internal servers rather than recursively querying Internet root name and external servers.
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
DNS configuration record, such as SOA, NS, A, CNAME, HINFO, WKS, MX and PTR that comprises the data within a DNS zone. For more information, see "Resource Records."
reverse zone
DNS zone that uses names as addresses to support address queries. See also
Request for Comments. TCP/IP set of standards.
root hint server
DNS name server 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 uncached data must start at the root servers. Sometimes called a hint server.
Action when a DNS server rearranges the order of its multiple same-type records each time it is queried.
routed bridge encapsulation
The process by which a stub-bridged segment is terminated on a point-to-point routed interface. Specifically, the router is routing on an IEEE 802.3 or Ethernet header carried over a point-to-point protocol, such as PPP, RFC 1483 ATM, or RFC 1490 Frame Relay.

Action of periodically scanning dynamic updates to the DNS server for stale resource records and purging these records.
Administrative grouping of TCP/IP addresses on a DHCP server.
secondary master
DNS name server that gets it zone data from another name server authoritative for the zone. When a secondary master server starts up, it contacts the primary master, from which it receives updates.
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.
selection tags
The mechanisms that help select DHCP scopes. They represent the selection tags on a DHCP server.
IP address of the server to use in the next step of the DHCP boot process. Sent in an RFC 2131 packet between the client and server.
slave forwarder
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
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.
SNMP notification
Simple Network Management Protocol messages that warn of server error conditions and problems.
SOA record
DNS Start of Authority resource record. Designates the start of a zone.
SRV record
A server (SRV) record is a type of resource record that allows administrators to use several servers for a single domain, to move services from host to host with little difficulty, and to designate some hosts as primary servers for a service and others as backups.
stub resolver
DNS server that hands off queries to another server instead of performing the full resolution itself.
subnet allocation, DHCP
Network Registrar use of on-demand address pools for entire subnet allocation of IP addresses to provisioning devices.
subnet mask
A separate IP address, or part of the host IP address, that determines the part of the host IP address that is its subnet. For example, (or indicates that the first 24 bits of the IP address are its subnet, 192.168.40. In this way, addresses do not need to be divided strictly along network class lines.
subnet pool
Set of IP addresses associated with a network number and subnet mask, including secondary subnets.
subnet sorting
An attribute of the Network Registrar DNS server that by enabling it, the server checks the network address of the client before responding to a query.
Action of dividing any network class into multiple subnetworks.
Partition of a delegated domain, represented as a child of the parent node. A subzone always ends with the name of its parent. For example, is a subzone of
subzone delegation
Dividing a zone into smaller pieces called subzones. You can delegate administrative authority for these subzones, and have them managed by people within those zones or served by separate servers.
Aggregation of IP network addresses advertised as a single classless network address.

A suite of data communication protocols. Its name comes from two of the more important protocols in the suite: the Transmission Control Protocol (TCP) and the Internet Protocol (IP). It forms the basis of Internet traffic.
Trivial File Transfer Protocol. Used to transfer files across the network using UDP. See also UDP.
Trivial File Transfer Protocol

User Datagram Protocol. Connectionless TCP/IP transport layer protocol.
Universal Time (UT)
International standard time reference that was formerly called Greenwich Mean Time, also called Universal Coordinated Time (UCT).

virtual channel identifier (VCI)
16-bit field in the header of an ATM cell. The VCI, together with the VPI, identifies the next destination of a cell as it passes through a series of ATM switches on its way to its destination. ATM switches use the VPI/VCI fields to identify the next network VCL that a cell needs to transit on its way to its final destination. The function of the VCI is similar to that of the DLCI in Frame Relay.
virtual path identifier (VPI)
virtual private network
See VPN.
Virtual private network. Protocol over which IP traffic of private address space can travel securely over a public TCP/IP network. A VPN uses tunneling to encrypt all information at the IP level. See also VRF.
VPN Routing and Forwarding instance. Routing table and forwarding information base table, populated by routing protocol contexts.

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
DNS Well Known Service resource record. Used to list the services provided by the hosts in a zone. Common protocols are TCP and UDP.

"Your" client IP address, or address that the DHCP server offers (and ultimately assigns) the client. Sent in an RFC 2131 packet between the client and server.

Delegation point in the DNS tree hierarchy that 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 to another subzone.
zone of authority
Group of DNS domains for which a given name server is an authority.
zone transfer
Action that 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 (incrementally transfer) and initiates a transfer of a copy of the database.