B

B channel

One of the 64 Kbps communications channels on an ISDN circuit. A BRI (Basic Rate Interface) ISDN has two bearer channels and one data channel. A PRI (Primary Rate Interface) ISDN line has 23 bearer channels (in North America) or 30 bearer channels (in Europe) and one data channel. B channel is also called bearer channel. See also Integrated Services Digital Network (ISDN).

backbone

In OSPF, an area common to all other OSPF areas that is used as the transit area for inter-area traffic and for distributing routing information between areas. The backbone must be contiguous. See also Open Shortest Path First (OSPF).

backbone router

In OSPF, a router that is connected to the backbone area. This includes routers that are connected to more than one area (area border routers). However, backbone routers do not have to be area border routers. Routers that have all networks connected to the backbone are internal routers. See also area border router; Open Shortest Path First (OSPF).

backup designated router (BDR)

An OSPF router that forms adjacencies with all other routers on a multiple access network and becomes the designated router when the designated router becomes unavailable.

backup domain controller

In Windows NT Server 4.0 or earlier, a computer running Windows NT Server that receives a copy of the domain's directory database (which contains all account and security policy information for the domain). The copy synchronizes periodically with the master copy on the primary domain controller. A backup domain controller also authenticates user logon information and can be promoted to function as primary domain controllers as needed. Multiple backup domain controllers can exist in a domain. Windows NT 3.51 and 4.0 backup domain controllers can participate in a Windows 2000 domain when the domain is configured in mixed mode. See also mixed mode; primary domain controller.

backup operator

A type of local or global group that contains the user rights needed to back up and restore files and folders. Members of the Backup Operators group can back up and restore files and folders regardless of ownership, access permissions, encryption, or auditing settings. See also auditing; global group; local group; user rights.

backup set

A collection of files, folders, and other data that has been backed up and stored in a file or on one or more tapes.

bad block

A disk sector that can no longer be used for data storage, usually due to media damage or imperfections.

bandwidth

In analog communications, the difference between the highest and lowest frequencies in a given range. For example, a telephone line accommodates a bandwidth of 3,000 Hz, the difference between the lowest (300 Hz) and highest (3,300 Hz) frequencies it can carry. In digital communications, the rate at which information is sent expressed in bits per second (bps).

Bandwidth Allocation Control Protocol (BACP)

A PPP Network Control Protocol that negotiates the election of a favored peer for a multiprocessing connection. If both ends of the multiprocessing connection issue a connection request at the same time, then the connection request of the favored peer is performed.

Bandwidth Allocation Protocol (BAP)

A PPP control protocol that is used on a multiprocessing connection to dynamically add and remove links.

bar code

A machine-readable label that identifies an object, such as physical media.

base DIT

The directory that is installed during a fresh install of a Windows 2000 domain controller.

base search

See search scope.

baseline

A range of measurements derived from performance monitoring that represents acceptable performance under typical operating conditions.

basic disk

A physical disk that contains primary partitions or extended partitions with logical drives used by Windows 2000 and all versions of Windows NT. Basic disks can also contain volume, striped, mirror, or RAID-5 sets that were created using Windows NT 4.0 or earlier. As long as a compatible file format is used, basic disks can be accessed by MS-DOS, Windows 95, Windows 98, and all versions of Windows NT.

basic input/output system (BIOS)

The set of essential software routines that tests hardware at startup, is involved with starting the operating system, and supports the transfer of data among hardware devices. The BIOS is stored in read-only memory (ROM) so that it can be executed when the computer is turned on. Although critical to performance, the BIOS is usually invisible to computer users.

basic volume

A volume on a basic disk. Basic volumes include primary partitions, logical drives within extended partitions, as well as volume, striped, mirror, or RAID-5 sets that were created using Windows NT 4.0 or earlier. Only basic disks can contain basic volumes. Basic and dynamic volumes cannot exist on the same disk.

Berkeley Internet Name Domain (BIND)

An implementation of the Domain Name System (DNS) written and ported to most available versions of the UNIX operating system. The Internet Software Consortium maintains the BIND software. See also BIND boot file.

binary

A base-2 number system in which values are expressed as combinations of two digits, 0 and 1.

BIND

See Berkeley Internet Name Domain.

BIND boot file

Configuration file used by Domain Name System (DNS) servers running under versions of the Berkeley Internet Name Domain (BIND) software implementation. The BIND boot file is a text file, Named.boot, where individual lines in the file list boot directives used to start a service when the DNS server is started. By default, Microsoft DNS servers use DNS service parameters stored in the Windows 2000 registry, but allow the use of a BIND boot file as an alternative for reading boot configuration settings. See also BIND; registry boot.

bindery

A database in Novell NetWare 2.x and 3.x that contains organizational and security information about users and groups.

binding

A process by which software components and layers are linked together. When a network component is installed, the binding relationships and dependencies for the components are established. Binding allows components to communicate with each other.

BINL service

See Boot Information Negotiation Layer service.

BINLSVC

See Boot Information Negotiation Layer Service.

BIOS

See basic input/output system.

BIOS parameter block (BPB)

A series of fields containing data on disk size, geometry variables, and the physical parameters of the volume. The BPB is located within the boot sector.

bit

The smallest unit of information handled by a computer. One bit expresses a 1 or a 0 in a binary numeral, or a true or false logical condition. A group of 8 bits makes up a byte, which can represent many types of information, such as a letter of the alphabet, a decimal digit, or other character. Bit is also called binary digit.

bit stuffing

A technique used by PPP on synchronous links, such as T-Carrier, ISDN, or other digital links, to prevent the occurrence of the Flag character within the PPP frame.

bit-wise logical AND

A mathematical operation that compares equal numbers of bits using the logical AND comparison. If both bits being compared are 1, the result is 1. Otherwise, the result is 0.

bits per second (bps)

The number of bits transmitted every second, used as a measure of the speed at which a device, such as a modem, can transfer data. A character is made up of 8 bits. In asynchronous communication, each character is preceded by a start bit and terminates with a stop bit. So for each character, 10 bits are transmitted. If a modem communicates at 2,400 bits per second (bps), then 240 characters are sent every second.

black hole

A condition of an internetwork where packets are lost without an indication of the error.

block policy option

An option that prevents Group Policy objects specified in higher-level Active Directory containers from applying to a computer or user.

bonding

The combining of ISDN B channels through hardware support.

boot

To start or reset a computer. When first turned on or reset, the computer executes the software that loads and starts the computer's operating system, which prepares it for use.

Boot Information Negotiation Layer (BINL) service

A service that runs on Windows 2000 Server that acts on client boot requests. For example, by using Remote Installation Service the BINL service listens for and answers DHCP (PXE) requests. It also services Client Installation Wizard requests. BINL directs the client to the files needed to start the installation process. This service also checks Active Directory to verify credentials, determine whether a client needs service, and whether to create a new or reset an existing computer account on behalf of the client.

boot partition

The volume that contains the operating system and its support files. The boot partition can be (but does not have to be) the same as the system partition. Both a primary partition and a logical drive in an extended partition can be used as a boot partition.

boot sector

A critical disk structure for starting your computer located at sector 1 of each volume or floppy disk. It contains executable code and data that is required by the code, including information used by the file system to access the volume. The boot sector is created when you format the volume.

bootable CD

An automated installation method that runs Setup from a CD-ROM. This method is useful for computers at remote sites with slow links and no local IT department. See also automated installation.

bootstrap protocol (BOOTP)

A set of rules or standards to enable computers to connect with one another, used primarily on TCP/IP networks to configure workstations without using media disks. RFCs 951 and 1542 define this protocol. DHCP is a boot configuration protocol that uses this protocol.

Border Gateway Protocol (BGP)

A routing protocol designed for use between autonomous systems. See also autonomous system.

bottleneck

A condition, usually involving a hardware resource, that causes the entire system to perform poorly.

BounceKeys

A keyboard filter that assists users whose fingers bounce on the keys when pressing or releasing them.

bound trap

In programming, a problem in which a set of conditions exceeds a permitted range of values that causes the microprocessor to stop what it is doing and handle the situation in a separate routine.

boundary layer

A common interface between two software components that is standardized to allow other components to connect to this interface.

Bourne shell

A UNIX command processor developed by Steven Bourne.

branch

A segment of a logical tree structure, representing a folder and any folders that it contains.

bridgehead server

In Active Directory replication, a single server in each site that is designated to perform site-to-site replication. Bridgehead servers are designated automatically by the KCC, or they can be assigned manually by an administrator. Bridgehead servers ensure that most replication occurs within sites rather than between sites.

bridgehead server

A server that receives and forwards e-mail traffic at each end of a connection agreement, similar to the task a gateway performs.

broadcast

An address that is destined for all hosts on a particular network segment. See also broadcast network.

broadcast and unknown server (BUS)

A multicast service on an emulated local area network (ELAN) that forwards broadcast, multicast, and initial unicast data traffic sent by a LAN emulation client. See also emulated local area network (ELAN).

broadcast datagram

An IP datagram sent to all hosts on the subnet. See also datagram.

broadcast message

A network message sent from a single computer that is distributed to all other devices on the same segment of the network as the sending computer.

broadcast name resolution

A mechanism defined in RFC 1001/1002 that uses broadcasts to resolve names to IP addresses through a process of registration, resolution, and name release. See also broadcast datagram; Request for Comments (RFC).

broadcast network

A network that supports more than two attached nodes and has the ability to address a single physical message to all of the attached nodes (broadcast). Ethernet is an example of a broadcast network.

browse list

Any list of items that can be browsed, such as a list of servers on a network, or a list of printers displayed in the Add Printer wizard.

browser

A client tool for navigating and accessing information on the Internet or an intranet. In the context of Windows networking, "browser" can also mean the Computer Browser service, a service that maintains an up-to-date list of computers on a network or part of a network and provides the list to applications when requested. When a user attempts to connect to a resource in a domain, the domain's browser is contacted to provide a list of available resources.

brute force attack

See key search attack.

buffer

An area of memory used for intermediate storage of data until it can be used.

buffer overflow attack

An attack in which an attacker exploits a weakness in a program or service to force a buffer overflow condition and then cause malicious code (provided by the attacker) to run in the computer's memory. Through a successful buffer overflow attack, an attacker can take control of the computer with the rights and permissions of the system and the logged--on user.

bulk encryption

A process in which large amounts of data, such as files, e-mail messages, or online communications sessions, are encrypted for confidentiality. It is usually done with a symmetric key algorithm. See also encryption; symmetric key encryption.

BUS

See broadcast and unknown server.

bus

A communication line used for data transfer among the components of a computer system. A bus is essentially a highway that allows different parts of the system to share data.

C

C shell

A UNIX command processor whose programming constructs are similar to those of the C language.

C2 level of security

U.S. government security level that designates a system that has controls capable of enforcing access limitations on an individual basis. In a C2 system, the owner of a system resource has the right to decide who can access it, and the operating system can detect when data is accessed and by whom.

cable modem

A modem that provides broadband Internet access in the range of 10 to 30 Mbps.

cache

For DNS and WINS, a local information store of resource records for recently resolved names of remote hosts. Typically, the cache is built dynamically as the computer queries and resolves names; it helps optimize the time required to resolve queried names. See also cache file; naming service; resource record.

cache file

A file used by the Domain Name System (DNS) server to preload its names cache when service is started. Also known as the "root hints" file because resource records stored in this file are used by the DNS service to help locate root servers that provide referral to authoritative servers for remote names. For Windows DNS servers, the cache file is named Cache.dns and is located in the %systemroot%\System32\Dns folder. See also authoritative; cache; systemroot.

cache hints file

see cache file.

caching

A special pool in memory in which recently-used data values are temporarily held for quicker subsequent accesses. For DNS, the ability of DNS servers to store information about the domain namespace learned during the processing and resolution of name queries. In Windows 2000, caching is also available through the DNS client service (resolver) as a way for DNS clients to keep a cache of name information learned during recent queries. See also caching resolver.

caching resolver

For Windows 2000, a client-side Domain Name System (DNS) name resolution service that performs caching of recently learned DNS domain name information. The caching resolver service provides system-wide access to DNS-aware programs for resource records obtained from DNS servers during the processing of name queries. Data placed in the cache is used for a limited period of time and aged according to the active Time To Live (TTL) value. You can set the TTL either individually for each resource record (RR) or default to the minimum TTL set in the start of authority RR for the zone. See also cache; caching; expire interval; minimum TTL; resolver; resource record; Time To Live (TTL).

caching-only server

A DNS name server that only performs queries, caches the answers, and returns the results. It is not authoritative for any names and does not contain any zones. It only stores data that it has cached while resolving queries. See also caching; name server; zone.

Call Manager

A software component that establishes, maintains and terminates a connection between two computers.

Callback Control Protocol (CBCP)

The Network Control Protocol for negotiating the use of callback over PPP links.

capture buffer

The maximum size of the capture file. When the capture file reaches the maximum size, the oldest frames are removed to make room for newer frames (FIFO queue).