Network Terms "D"

Network Glossary and acronym's

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Daily copy backup

A specific backup type that copies only files and folders that have changed during that day. It does not mark their archive attributes.

DARPA (Department of Defense Advanced Research Projects Agency)

The agency of the U.S. Department of Defense which created the industry-standard TCP/IP suite of protocols based on packet-switching network experiments conducted in the late 1960's and 1970's.

Data definition

The process of creating a database and associated objects, such as tables, indexes, constraints, defaults, rules, procedures, triggers, and views.

Data Encryption Standard (DES)

Data Encryption Standard is a common symmetric cryptography method. It was created in 1972 and re-certified in 1993. DES has a limitation of 56-bit keys and offers little encryption security since it can be easily broken.

Data Link Control (DLC)

A non-routable protocol. Windows NT computers use DLC to connect to IBM mainframes via 3270 terminal emulators and to connect to IBM AS/400 computers via 5250 emulators. Microsoft SNA Server for Windows NT uses DLC to communicate with mainframes on a token ring network. DLC is also used with some HP print devices that are attached to the network through a built-in adapter card.

Data Link Layer (OSI model)

Layer 2 of the OSI reference model. This layer provides reliable transit of data across a physical link. The data link layer is concerned with physical addressing, network topology, line discipline, error notification, ordered delivery of frames, and flow control. The IEEE has divided this layer into two sublayers: the MAC sublayer and the LLC sublayer. Sometimes simply called link layer. Roughly corresponds to the data link control layer of the SNA model. See also application layer, MAC address, network layer, physical layer, presentation layer, session layer, and transport layer.

Data redundancy

Creating and maintaining multiple copies of the same data.

Database

A collection of information, tables, and other objects organized and presented to serve a specific purpose, such as facilitating searching, sorting, and recombining data. Databases are stored in files.

Database replication

The process by which a WINS server can resolve NetBIOS names of hosts registered with another WINS server. For example, if a host on subnet A is registered with a local WINS server, but wants to communicate with a host on subnet B where the host is registered with a different WINS server, the NetBIOS name cannot be resolved unless the two WINS servers have replicated their databases with each other.

Datagram

Another term used to describe a packet. The term is also used to describe the Internet protocol known as the User Datagram Protocol, a connectionless protocol that does not guarantee delivery of datagrams.

DCOM (Distributed Component Object Model)

A method of configuring a client/server application so that several computers can use it at the same time. DCOM uses remote procedure calls (RPCs) to allow applications to interoperate and communicate with each other.

DDE (Dynamic Data Exchange)

A system by which applications can share data and commands. Both applications must support DDE.

DDS (Digital Data Service)

Digital lines to which a computer can connect using a channel service unit/digital service unit (CSU/DSU). These kinds of lines carry 99 percent error-free digital signals at speeds ranging from 2.4 to 56 kilobits per second. DDS lines are normally leased lines rather than on-demand. An exception is Switched 56, which is a system of on-demand (dial-up) 56 Kbps DDS lines.

DEC (Digital Equipment Corporation)

A computer manufacturing company that makes RISC-based processors such as Alpha.

Default

An action that a system performs, or a characteristic that it displays unless explicitly instructed otherwise.

Default gateway

The gateway you always want to use to communicate with a host on a different network. It receives packets from the local network and transfers them to another gateway on the other network. You specify a default gateway when you configure TCP/IP.

Default route

If a default route is configured, the router will send packets via that route in cases where a dynamic route is not provided. This can be used to create sufficient reachability, especially for route between an edge and the core. Default routes also reduce the burden on network resources caused by dynamic routing.

Default subnet mask

A subnet mask that is used on TCP/IP networks that are not divided into subnets. All TCP/IP hosts require a subnet mask even if the network is a single segment.

Demand paging

A Windows process that moves data between the computer's RAM and a paging file on the hard drive.

Demilitarized Zone (DMZ)

DMZ (Demilitarized Zone) is a buffer subnet. A DMZ should only contain servers that are to be accessed by external visitors. Often it is assumed that any server placed in the DMZ will be compromised. Thus, no mission critical or sensitive systems are located in a DMZ.

A domain controller may appear in a DMZ when the DMZ is an entire isolated domain, however this is not common. User workstations are never located in a DMZ. Backup servers, unless specifically deployed for just the DMZ, are never located in a DMZ.

Department of Defense Advanced Research Projects Agency (DARPA)

The agency of the U.S. Department of Defense which created the industry-standard TCP/IP suite of protocols based on packet-switching network experiments conducted in the late 1960's and 1970's.

DES (Data Encryption Standard)

Designated Router (DR)

A Designated Router (DR) is a router in a PIM-Sparse Mode tree that initiates the Join/Prune message cascade upstream in response to the IGMP membership information that is received from IGMP hosts.

Destination replication partner

A replication partner that receives updates from a source replication partner. Also called a target replication partner.

Device driver

A software component that allows a hardware device to communicate with the operating system of a computer.

DFS (Distributed File System)

A file management system that lets users and administrators create a virtual file structure such that a folder or hierarchy of folders appear to contain a collection of files that are, if fact, located on multiple computers or drives connected at various physical locations on the network. A Dfs directory tree helps users to browse through, search for, and access data on the network.

DHCP (Dynamic Host Configuration Protocol)

A protocol that dynamically assigns IP addresses to each computer on a network.

DHCP discover

A message that makes a request for an IP lease. The message contains the client's hardware address and computer name, so that DHCP servers know which client sent the request.

DHCP Manager

A Microsoft utility used to manage DHCP servers.

DHCP offer

All DHCP servers that have valid IP addressing information available send a DHCP offer to the client when the client makes a request.

DHCP request

The client will initialize TCP/IP and broadcasts a request for the location of a DHCP server and IP addressing information.

DHCP scope

The ability to set a start and end range for the assignment of IP addresses using DHCP. Addresses can also be excluded from the available addresses as well. The scope is set using the DHCP Console.

Dial-up Networking

A software program that allows a client computer to connect to an external or remote network via modem. It is the client version of RAS. Examples of dial-up networking include connecting from home to a computer at work over the phone lines or connecting with an internet service provider by modem.

Differential backup

A backup process that copies to tape only those files that have not been marked by previous backups. A differential backup does not mark the files after backing them up.

Diffuse Mode (Scatter Mode)

One mode that an infrared device operates in is diffuse mode (also called scatter mode), which operates by broadcasting a large beam of light rather than a narrow beam. It does not require line-of-sight connections.

Diffusing Update Algorithm Link-state (DUAL)

Diffusing Update Algorithm Link-state (DUAL) technology makes decisions concerning EIGRP routing computations and guarantees freedom from routing loops. DUAL tracks all routes advertised by neighbors, and uses metrics (also called cost) to select the best path and a second best path to reach a destination.

Dig

Dig is the Linux preferred tool for testing name resolution. Dig resolves (looks up) the IP address of a host name. Displays other name resolution-related information such as the DNS server used for the lookup request.

Digital certificates

Encoded computer information that provides verification of the identity of a client or server. These certificates include encoded information that identifies a particular person, company, or computer, and are often used to distribute public encryption keys to recipients.

Digital Data Service (DDS)

Digital envelope

A method of hiding the content of a message from anyone but the recipient. The sender uses the recipient's public key to encrypt the contents of the message. The recipient uses her own private key to decrypt and read the message.

Digital Equipment Corporation (DEC)

A computer manufacturing company that makes RISC-based processors such as Alpha.

Digital Network Architecture (DNA)

In the mid-1970s, Digital Equipment Corporation developed a protocol suite known as Digital Network Architecture (DNA). It is also known as DECnet. The Physical and Data Link layers of DNA were the predecessors of the Ethernet IEEE 802.3 standard.

Digital signature

A method of verifying the sender of a message, but does not encrypt the message itself. The sender uses his own private key to encrypt a digital signature attached to a message. The recipient uses the sender's public key to decrypt the signature and verify the sender's identity.

Digital Subscriber Line (DSL)

DSL or Digital Subscriber Line is a form of high-speed dial-up connection used to connect remote systems to the Internet. DSL operates over existing copper phone lines and is an economical choice for homes and small businesses.

Digital Volt Meter (DVM)

An electrical device that you can use to diagnose cable problems. A DVM can determine if there is a break or short in the cable by testing the resistance (measured in ohms) of the network cable.

Direct Memory Access (DMA)

Direct Memory Access (DMA) channels are conduits used by high-speed devices to communicate directly with RAM, bypassing the CPU.

Directory replication

Directory replication is the process of sharing directory information between servers inside and between sites.

Directory Service Agent (DSA)

A process that runs on a domain controller and provides access to the Active Directory database.

Directory Services Restore Mode

A special safe mode you use to restore the system state data on a domain controller.

Direct-Sequence Spread Spectrum (DSSS)

A type of signaling method, used by a wireless networking architecture, where the transmitter breaks data into pieces and sends the pieces across multiple frequencies in a defined range. DSSS is more susceptible to interference and less secure then other forms of signaling, such as Frequency Hopping Spread Spectrum (FHSS).

DirectX APIs

A low-level API that provides fast response to user input. Microsoft designed DirectX specifically to run graphically-intensive computer games. DirectX components are Microsoft DirectDraw, Microsoft DirectPlay, and Microsoft DirectSound.

Disk partition

Also called a partition. A portion of the free space on a hard disk that you format with a file system. Partitions can be either primary or extended.

Distance Vector Multicast Routing Protocol (DVMRP)

Distance Vector Multicast Routing Protocol (DVMRP) is a protocol that shares information between routers to transport IP Multicast packets among networks.

Distance vector routing protocol

Class of routing algorithms that iterate on the number of hops in a route to find a shortest-path spanning tree. Distance vector routing algorithms call for each router to send its entire routing table in each update, but only to its neighbors. Distance vector routing algorithms can be prone to routing loops, but are computationally simpler than link state routing algorithms. Also called Bellman-Ford routing algorithm. See also link state routing algorithm.

Distribute list

A distribute list is a type of access list that is applied to routing updates. Unlike normal access lists, distribute lists can control routing updates no matter their origin.

Distributed applications

Applications that split processing tasks between a client (front-end) and a server (back-end).

Distributed Component Object Model (DCOM)

Distributed File System (DFS)

Distributed Management Interface (DMI)

The Distributed Management Interface (DMI) is a standard for organizing information about desktop, notebook, and server computers. DMI is part of the System Management BIOS (SMBIOS) specification which allows data about a system to be stored in the individual system's BIOS. Management software interfaces with the BIOS on a monitored system to gather this information and assemble it into an administrator-specified format such as a report or a database.

Distributed Parity

Distributed parity is a method of data protection used in a RAID 5 configuration. Duplicate data (parity) is placed on multiple disks (distributed) to protect against data loss in the event of a storage disk failure.

Distributed processing

A technique of using both the client and server's processors to complete a task. The client or "front end" accepts input and runs simple calculations, while the server or "back end" handles processes that require more processing power.

Distribution group

A distribution group is a universal group that has been mail-enabled, such as a security group. A distribution group can be used to send an e-mail to a large number of people in an Exchange organization, such as entire departments or groups.

Distribution list

A distribution list contains addresses for individual users, public folders, and other distribution lists. They allow each member to receive a copy of a message sent to the entire list. Applications use distribution lists.

Distribution tree

A distribution tree shows the source of multicast information and the path that multicast traffic use across the network infrastructure.

DLC (Data Link Control)

DMA (Direct Memory Access)

Direct Memory Access (DMA) channels are conduits used by high-speed devices to communicate directly with RAM, bypassing the CPU.

DMI (Distributed Management Interface)

DMZ (Demilitarized Zone)

DNA (Digital Network Architecture)

DNS (Domain Name Server)

A server that maintains a database of IP address/computer name mappings. A DNS server can run on Windows NT, Unix, or NetWare (5). The DNS has the responsibility to resolve fully qualified domain names and other host names to IP addresses. In DNS, the clients are called resolvers and the servers are called name servers.

DNS (Domain Name System)

A hierarchical client/server-based database management system that translates computer names into IP addresses. DNS maps to the application layer and uses UDP and TCP as the underlying protocols. Clients, known as resolvers, contact name servers for the IP address they are seeking.

DNS Domain

A domain that defines different levels of authority in a hierarchical structure. The highest level is called the root domain. The other levels of domains are currently defined as com, edu, org, net, gov, mil, num, and arpa. Second level domains are any domains defined by companies such as Microsoft.com or Novell.com.

DNS Service Discovery (DNS-SD)

A service location feature used in Zeroconf networking implementation. DNS-SD allows IP hosts to automatically find available services, such as file servers, printers, and routers. DNS-SD is a Mac OS related feature.

DNS-SD (DNS Service Discovery)

Domain

A logical grouping of computers and users. In a domain, all users have access to a central directory database that stores security and user account information for the domain.

Domain Admins

A built-in global group that is added automatically to the Administrators local group, making all members of Domain Admins group domain administrators.

Domain controller

Windows 2000 domain controllers contain copies of the Active Directory database. They provide a centralized approach to administration and account maintenance.

Domain Dfs

A configuration of Dfs in which Active Directory stores the information about the virtual file structure. Advantages include fault-tolerance.

Domain Guests

A built-in global group in which the Guest user account is a member.

Domain Name

A domain name locates entities (for example, websites) on the Internet. Domain names are managed within a domain name system (DNS), which is a hierarchy that is made up of the following components:

. (dot) domain (also called the root domain)
Top Level Domains (TLDs) such as .com, .edu, .gov
Additional domains such as yahoo.com, microsoft.com, etc.

Domain Name Server (DNS)

Domain Name System (DNS)

Domain partition

An Active Directory partition that stores objects, attribute, and attribute values for a particular domain. Each domain in Active Directory has its own domain partition.

Domain user accounts

User name and password information stored in the Active Directory database on the domain controllers.

Domain Users

Any user account created in a Windows domain is a domain user. Domain Users is a global group.

DOS

See MS-DOS.

DR (Designated Router)

A Designated Router (DR) is a router in a PIM-Sparse Mode tree that initiates the Join/Prune message cascade upstream in response to the IGMP membership information that is received from IGMP hosts.

Drive mapping

A specific letter used to map a drive or volume on a workstation or server.

DROTHER

Any other router that is not a DR or a BDR is called a DROTHER. This is simply a term used to describe a non-DR or non-BDR router. It is not technically an OSPF router role.

DSA (Directory Service Agent)

A process that runs on a domain controller and provides access to the Active Directory database.

DSL (Digital Subscriber Line)

DSSS (Direct-Sequence Spread Spectrum)

DUAL (Diffusing Update Algorithm Link-state)

Dual Ring

A dual ring is an enhanced version of the ring networking topology. A dual ring network includes two rings; the primary and secondary rings, which increase performance and fault tolerance. A break in one ring in a dual ring configuration has no effect on communications. A decrease in bandwidth might result, but data can be sent on the other ring.

Dual Stack

A method used to allow concurrent support for both IPv4 and IPv6 within the same network.

Dual-boot

The ability to boot a computer with either one of two operating systems. Both operating systems must be loaded on the computer. At bootup a menu prompts the user to load the operating system the computer should use.

Duplex (Simplex)

Simplex and duplex are methods of communication transmission. Simplex is the one-way transmission of a signal across a medium. Duplex is the two-way transmission of a signals across a medium. There are two types of duplex transmission; half-duplex and full-duplex. Half-duplex allows transmission of signals, one party at a time. Full-duplex allows transmission and reception of signals to occur concurrently.

DVM (Digital Volt Meter)

An electrical device that you can use to diagnose cable problems. A DVM can determine if there is a break or short in the cable by testing the resistance (measured in ohms) of the network cable.

DVMRP (Distance Vector Multicast Routing Protocol)

Distance Vector Multicast Routing Protocol (DVMRP) is a protocol that shares information between routers to transport IP Multicast packets among networks.

Dynamic Data Exchange (DDE)

A system by which applications can share data and commands. Both applications must support DDE.

Dynamic disk

A disk device managed by Windows 2000 Disk Management. Dynamic disks do not contain partitions or logical drives. They can contain only dynamic volumes created with Disk Management. They cannot be accessed by earlier version of Windows or by MS-DOS.

Dynamic distribution group

A dynamic distribution group is an Exchange distribution group whose membership is defined by the results of a query which is executed every time a message is sent to the group. This is optimal for environments in which people move groups or buildings often and e-mail groups need to be able to accommodate changes as they occur.

Dynamic Host Configuration Protocol (DHCP)

A protocol that dynamically assigns IP addresses to each computer on a network.

Dynamic routing

Dynamic routing is an addressing method that senses changes in the network topology and responds accordingly without administrator involvement. Dynamic routers:

Propagate changes and shifts in the network topology to each router in the network, causing the routing tables on each router to always be up to date.
Are responsible for all networks to which they are connected.
Employ additional processes or services to exchange routing information between routers.