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Comptia Networking + 008 Part 2
Glossery Defenintions C-D
192
Computer Networking
Not Applicable
04/03/2022
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Term
cable certifier
 Definition
A very powerful cable testing device used by professional installers to test the electrical characteristics of a cable and then generate a certification report, proving that cable runs pass ANSI/TIA standards.
Term
cable drop
 Definition
Location where the cable comes out of the wall at the workstation location.
Term
cable modem
 Definition
A bridge device that interconnects a cable company’s DOCSIS service to a user’s Ethernet network. In most locations, the cable modem is the demarc.
Term
cable stripper
 Definition
Device that enables the creation of UTP cables.
Term
cable tester
 Definition
A generic name for a device that tests the functionality of cables. Some common tests are for continuity, electrical shorts, crossed wires, or other electrical characteristics.
Term
cable tray
 Definition
A device for organizing cable runs in a drop ceiling.
Term
cached lookup (DNS)
 Definition
A DNS response served from a cache of previous responses.
Term
cache-only DNS server (caching-only DNS server)
 Definition
DNS server that does not have any forward lookup zones. Resolves names of systems on the Internet for the network, but is not responsible for telling other DNS servers the names of any clients.
Term
caching engine
 Definition
A server dedicated to storing cache information on a network. These servers can reduce overall network traffic dramatically.
Term
Cacti
 Definition
Network graphing program.
Term
campus area network (CAN)
 Definition
A network installed in a medium-sized space spanning multiple buildings.
Term
canonical name (CNAME) record
 Definition
A DNS record that stores a fully qualified domain name. A common use is to provide an alias for another hostname.
Term
captive portal
 Definition
A Wi-Fi network implementation used in some public facilities that directs attempts to connect to the network to an internal Web page for that facility; generally used to force terms of service on users.
Term
capture file
 Definition
A file in which the collected packets from a packet sniffer program are stored.
Term
card
 Definition
Generic term for devices designed to snap into an expansion slot.
Term
carrier-sense multiple access with collision avoidance (CSMA/CA)
 Definition
Access method used only on wireless networks. Before hosts transmit, they first listen for traffic. If the transmitting host does not hear any traffic, it will transmit its frame. It will then listen for an acknowledgment frame from the receiving host. If the transmitting host does not hear the acknowledgment, it will wait for a randomly determined period of time and try again.
Term
carrier-sense multiple access with collision detection (CSMA/CD)
 Definition
Obsolete access method that Ethernet systems used in wired LAN technologies, enabling frames of data to flow through the network and ultimately reach address locations. Hosts on CSMA/CD networks first listened to hear if there was any data on the wire. If there was none, the hosts sent out data. If a collision occurred, then both hosts waited for a randomly determined time period before retransmitting the data. Full-duplex Ethernet made CSMA/CD obsolete.
Term
Cat 3
 Definition
Category 3 wire, a standard for UTP wiring that can operate at up to 16 Mbps.
Term
Cat 5
 Definition
Category 5 wire, a standard for UTP wiring that can operate at up to 100 Mbps.
Term
Cat 5e
 Definition
Category 5e wire, a standard for UTP wiring with improved support for 100 Mbps using two pairs and support for 1000 Mbps using four pairs.
Term
Cat 6
 Definition
Category 6 wire, a standard for UTP wiring with improved support for 1000 Mbps; supports 10 Gbps up to 55 meters.
Term
Cat 6a
 Definition
Category 6a wire, a standard for UTP wiring with support for 10 Gbps up to 100 meters.
Term
Cat 7
 Definition
Category 7 wire, a standard (unrecognized by ANSI/TIA) for UTP wiring with support for 10+ Gbps at 600 MHz maximum frequency.
Term
category (Cat) rating
 Definition
A grade assigned to twisted pair cable to help network installers get the right cable for the right network technology. Cat ratings are officially rated in megahertz (MHz), indicating the highest-frequency bandwidth the cable can handle.
Term
CCMP-AES
 Definition
A 128-bit block cipher used in the IEEE 802.11i (WPA2) standard. See Advanced Encryption Standard (AES).
Term
central office
 Definition
Building that houses local exchanges and a location where individual voice circuits come together.
Term
certificate
 Definition
A digitally signed electronic document issued by a trusted third party—a certificate authority (CA)—attesting to the identity of the holder of a specific cryptographic public key.
Term
certifier
 Definition
A device that tests a cable to ensure that it can handle its rated amount of capacity.
Term
chain of custody
 Definition
A document used to track the collection, handling, and transfer of evidence.
Term
Challenge Handshake Authentication Protocol (CHAP)
 Definition
A remote access authentication protocol. It has the serving system challenge the remote client, which must provide an encrypted password.
Term
change management
 Definition
The process of initiating, approving, funding, implementing, and documenting significant changes to the network.
Term
change management documentation
 Definition
A set of documents that defines procedures for changes to the network.
Term
change management team
 Definition
Personnel who collect change requests, evaluate the change, work with decision makers for approval, plan and implement approved changes, and document the changes.
Term
change request
 Definition
A formal or informal document suggesting a modification to some aspect of the network or computing environment.
Term
channel
 Definition
A portion of the wireless spectrum on which a particular wireless network operates. Setting wireless networks to different channels enables separation of the networks.
Term
channel bonding
 Definition
Wireless technology that enables wireless access points (WAPs) to use two channels for transmission.
Term
channel overlap
 Definition
Drawback of 2.4-GHz wireless networks where channels shared some bandwidth with other channels. This is why only three 2.4-GHz channels can be used in the United States (1, 6, and 11).
Term
Channel Service Unit/Data Service Unit (CSU/DSU)
 Definition
A piece of equipment that connects a T-carrier leased line from the telephone company to a customer’s equipment (such as a router). It performs line encoding and conditioning functions, and it often has a loopback function for testing.
Term
checksum
 Definition
A simple error-detection method that adds a numerical value to the end of each packet, enabling the receiver to detect corruption that can occur as a packet moves through the network.
Term
choose your own device (CYOD)
 Definition
Mobile deployment model where corporate employees select among a catalog of approved mobile devices. The organization retains complete control and ownership over the mobile devices, although employees can install their own apps.
Term
CIA triad
 Definition
Widely considered to be the foundation of IT security; stands for confidentiality, integrity, and availability. It is put into practice through various security methods and controls. Every security technique, practice, and mechanism put into place to protect systems and data relates in some fashion to ensuring confidentiality, integrity, and availability
Term
cipher
 Definition
A series of complex and hard-to-reverse mathematics run on a string of ones and zeroes to make a new set of seemingly meaningless ones and zeroes.
Term
cipher lock
 Definition
A door unlocking system that uses a door handle, a latch, and a sequence of mechanical push buttons.
Term
ciphertext
 Definition
The output when plaintext is run through a cipher algorithm using a key.
Term
circuit switching
 Definition
The process for connecting two phones together on one circuit.
Term
Cisco IOS
 Definition
Cisco’s proprietary operating system for routers and switches. Originally stood for Internetworking Operating System.
Term
cladding
 Definition
The part of a fiber-optic cable that makes the light reflect down the fiber.
Term
class of service (CoS)
 Definition
A prioritization value used to apply to services, ports, or whatever a quality of service (QoS) device might use.
Term
class license
 Definition
Contiguous chunk of IP addresses passed out by the Internet Assigned Numbers Authority (IANA). Classful addressing was phased out after the introduction of Classless Inter-Domain Routing and is no longer used.
Term
classful
 Definition
Obsolete IPv4 addressing scheme that relied on the original class blocks, such as Class A, Class B, and Class C.
Term
classless
 Definition
IPv4 addressing scheme that does not rely on the original class blocks, such as Class A, Class B, and Class C.
Term
Classless Inter-Domain Routing (CIDR)
 Definition
The basis of allocating and routing classless addresses, not restricting subnet masks to /8, /16, or /24, which classful addressing did. Based on variable-length subnet masking (VLSM), where subnets can be allocated according to the needs of an organization, such as /26 for a network with 254 or fewer node, or /30 for a network with only two nodes. See also subnetting.
Term
classless subnet
 Definition
A subnet that does not fall into the common categories such as Class A, Class B, and Class C.
Term
cleartext
 Definition
Readable data transmitted or stored in unencrypted form.
Term
cleartext credentials
 Definition
Any login process conducted over a network where account names, passwords, or other authentication elements are sent from the client or server in an unencrypted fashion.
Term
client
 Definition
A computer program that uses the services of another computer program; software that extracts information from a server. A Netflix or Hulu application running on a Smart TV is a client for the provider’s streaming services. Also, a machine that accesses shared resources on a server.
Term
client/server
 Definition
A relationship in which a client obtains services from a server on behalf of a user. In classic terms, a network architecture (topology) where one computer shares resources (the server) and other computers on the network access those resources (clients).
Term
client/server application
 Definition
An application located on a client that makes use of services provided by a server. This server can be external or located on the client system.
Term
client/server network
 Definition
A network that has dedicated server machines and client machines.
Term
client-to-site VPN
 Definition
A type of VPN connection where a single computer logs into a remote network and becomes, for all intents and purposes, a member of that network.
Term
clock strata
 Definition
Tiers of NTP time sources layered according to relative accuracy. A number indicates the accuracy of each tier (called a stratum), counting up from the most-accurate Stratum 0.
Term
closed-circuit television (CCTV)
 Definition
self-contained, closed system in which video cameras feed their signal to specific, dedicated monitors and storage devices.
Term
cloud computing
 Definition
The cloud is like a cafeteria of computing and networking resources that are managed by someone else and enhanced by layers of powerful services and software. Cloud computing is the act of using these resources and services.
Term
cloud/server-based anti-malware
 Definition
Anti-malware software that offloads a significant amount of processing from individual hosts to local or cloud-based servers.
Term
clustering
 Definition
Multiple pieces of interconnected equipment, such as servers, that appear to the network as a single (logical) device. Clustering provides redundancy and fault tolerance.
Term
coarse wavelength division multiplexing (CWDM)
 Definition
An optical multiplexing technology in which a few signals of different optical wavelength could be combined to travel a fairly short distance.
Term
coaxial cable
 Definition
A type of cable that contains a central conductor wire surrounded by an insulating material, which in turn is surrounded by a braided metal shield. It is called coaxial because the center wire and the braided metal shield share a common axis or centerline.
Term
code-division multiple access (CDMA)
 Definition
Early cellular telephone technology that used spread-spectrum transmission. Obsolete.
Term
cold site
 Definition
A location that consists of a building, facilities, desks, and everything that a business needs except computers.
Term
collision
 Definition
The result of two nodes transmitting at the same time on a multiple access network such as a wireless network. Both frames may be lost or partial frames may result.
Term
collision domain
 Definition
A set of connected hosts that all share one medium to transmit and receive. The shared medium can result in a collision if two hosts transmit at the same time. Characteristic of early, half-duplex, non-switched Ethernet.
Term
co-location
 Definition
A process in which an organization places its own server hardware in a public, third-party data center. Also written without the hyphen as colocation.
Term
command
 Definition
A request, typed from a terminal or embedded in a file, to perform an operation or to execute a particular program.
Term
community cloud
 Definition
A private cloud paid for and used by more than one organization with similar goals or needs (such as medical providers who all need to comply with the same patient privacy laws).
Term
compatibility issue
 Definition
When different pieces of hardware or software don’t work together correctly.
Term
compatibility requirements
 Definition
With respect to network installations and upgrades, requirements that deal with how well the new technology integrates with older or existing technologies.
Term
computer forensics
 Definition
The science of gathering, preserving, examining, and presenting evidence stored on a computer or any form of digital media that is presentable in a court of law.
Term
concentrator
 Definition
A device that brings together at a common center connections to a particular kind of network (such as Ethernet) and implements that network internally.
Term
configuration management
 Definition
A set of documents, policies, and procedures designed to help an organization maintain and update its network in a logical, orderly fashion.
Term
configuration management documentation
 Definition
Documents that define the configuration of a network. These would include wiring diagrams, network diagrams, baselines, and policy/procedure/configuration documentation.
Term
configurations
 Definition
The settings stored in devices that define how they are to operate.
Term
connection
 Definition
Generically, a link that enables two computers to communicate.
Term
connectionless
 Definition
A type of communication characterized by sending packets that are not acknowledged by the destination host. Connectionless protocols are generally faster than connection-oriented protocols. UDP is the quintessential connectionless protocol in the TCP/IP suite.
Term
connection-oriented
 Definition
Network communication between two hosts that includes negotiation between the hosts to establish a communication session. Data segments are then transferred between hosts, with each segment being acknowledged before a subsequent segment can be sent. Orderly closure of the communication is conducted at the end of the data transfer or in the event of a communication failure. TCP is the only connection-oriented protocol in the TCP/IP suite.
Term
console port
 Definition
Connection jack in a switch or router used exclusively to connect a computer that will manage the device.
Term
content filter
 Definition
An advanced networking device that implements content filtering, enabling administrators to filter traffic based on specific signatures or keywords (such as profane language).
Term
content switch
 Definition
Advanced networking device that works at least at Layer 7 (Application layer) and hides servers behind a single IP address.
Term
contingency planning
 Definition
The process of creating documents—a contingency plan—that set out how to limit damage and recover quickly from an incident.
Term
continuity
 Definition
The physical connection of wires in a network.
Term
continuity tester
 Definition
Inexpensive network tester that can only test for continuity on a line.
Term
convergence
 Definition
Point at which the routing tables for all routers in a network are updated.
Term
core (fiber-optics)
 Definition
The central glass of the fiber-optic cable that carries the light signal.
Term
core layer
 Definition
One tier of a three-tiered architecture commonly used in data centers. The core layer ties together all the switches at the distribution layer and interconnects with external networks such as the Internet.
Term
corporate-owned business only (COBO)
 Definition
Deployment model where the corporation owns all the mobile devices issued to employees. Employees have a whitelist of preapproved applications they can install.
Term
corporate-owned personally enabled (COPE)
 Definition
Deployment model that is very similar to COBO, in that the organization issues mobile devices. With COPE, however, employees are presented with a whitelist of preapproved applications that they may install.
Term
cost (routing metric)
 Definition
A metric for the desirability of a particular route. Can incorporate factors that affect performance such as bandwidth.
Term
counter
 Definition
A predefined event that is monitored and recorded to a log file. Logs store information about the performance of some particular aspect of a system. Different programs refer to the monitored aspect with different terms. Performance Monitor calls them counters; syslog calls them facilities.
Term
CRC (cyclic redundancy check)
 Definition
A mathematical method used to check for errors in long streams of transmitted data with high accuracy. The CRC is found in the Frame Check Sequence (FCS).
Term
crimper
 Definition
Also called a crimping tool, the tool used to secure a crimp (or an RJ-45 connector) onto the end of a cable.
Term
crossover cable
 Definition
specially terminated UTP cable used to interconnect routers or switches, or to connect network cards without a switch. Crossover cables reverse the sending and receiving wire pairs from one end to the other.
Term
crosstalk
 Definition
Electrical signal interference between two cables that are in close proximity to each other.
Term
crypto-malware
 Definition
Malicious software that uses some form of encryption to lock a user out of a system.
Term
CSMA/CA (carrier-sense multiple access with collision avoidance)
 Definition
Access method used only on wireless networks. Before hosts transmit, they first listen for traffic. If the transmitting host does not hear any traffic, it will transmit its frame. It will then listen for an acknowledgment frame from the receiving host. If the transmitting host does not hear the acknowledgment, it will wait for a randomly determined period of time and try again.
Term
CSMA/CD (carrier-sense multiple access with collision detection)
 Definition
Obsolete access method that Ethernet systems used in wired LAN technologies, enabling frames of data to flow through the network and ultimately reach address locations. Hosts on CSMA/CD networks first listened to hear if there was any data on the wire. If there was none, the hosts sent out data. If a collision occurred, then both hosts waited for a randomly determined time period before retransmitting the data. Full-duplex Ethernet made CSMA/CD obsolete.
Term
CSU/DSU (Channel Service Unit/Data Service Unit)
 Definition
A piece of equipment that connects a T-carrier leased line from the telephone company to a customer’s equipment (such as a router). It performs line encoding and conditioning functions, and it often has a loopback function for testing.
Term
customer-premises equipment (CPE)
 Definition
The primary distribution box and customer-owned/managed equipment that exists on the customer side of the demarc.
Term
cyclic redundancy check (CRC)
 Definition
A mathematical method used to check for errors in long streams of transmitted data with high accuracy. The CRC is found in the Frame Check Sequence (FCS).
Term
data backup
 Definition
The process of creating extra copies of data to be used in case the primary data source fails.
Term
data center
 Definition
A dedicated space—a building or part of a building—housing a networked group of servers that provides data storage, Web hosting, application hosting, cloud services, and more.
Term
Data Link layer
 Definition
identifies devices on the Physical layer. MAC addresses are part of the Data Link layer. Switches operate at the Data Link layer.
Term
Data Over Cable Service Interface Specification (DOCSIS)
 Definition
The standard protocol used by cable modem networks to facilitate data transfer.
Term
datagram
 Definition
A connectionless transfer unit created with User Datagram Protocol designed for quick transfers over a packet-switched network.
Term
datagram TLS (DTLS) VPN
 Definition
A virtual private network solution that optimizes connections for delay-sensitive applications, such as voice and video. A DTLS VPN uses TLS to provide encryption for enhanced security.
Term
dead spot
 Definition
A place that should be covered by the network signal but where devices get no signal.
Term
deauthentication (deauth) attack
 Definition
A form of DoS attack that targets 802.11 Wi-Fi networks specifically by sending out a frame that kicks a wireless client off its current WAP connection. A rogue WAP nearby presents a stronger signal, which the client will prefer. The rogue WAP connects the client to the Internet and then proceeds to intercept communications to and from that client.
Term
decapsulation
 Definition
The process of stripping all the extra header information from a packet as the data moves up a protocol stack.
Term
decibel (dB)
 Definition
A measurement of the quality of a signal.
Term
dedicated circuit
 Definition
A circuit that runs from a breaker box to specific outlets.
Term
dedicated line
 Definition
A telephone line that is an always open, or connected, circuit. Dedicated telephone lines usually do not have telephone numbers.
Term
dedicated server
 Definition
A machine that does not use any client functions, only server functions.
Term
default
 Definition
A software function or operation that occurs automatically unless the user specifies something else.
Term
default gateway
 Definition
In a TCP/IP network, a router that accepts traffic for all routes unknown to a client or another router. In SOHO networks, this is usually the only router in the network and provides the interface to the ISP’s network.
Term
defense in depth
 Definition
Using multiple layers of security to protect against threats to the network.
Term
demarc
 Definition
A device that marks the dividing line of responsibility for the functioning of a network between internal users and upstream service providers. Also, demarcation point.
Term
demarc extension
 Definition
Any cabling that runs from the network interface to whatever box is used by the customer as a demarc.
Term
demilitarized zone (DMZ)
 Definition
A lightly protected or unprotected subnet positioned between an outer firewall and an organization’s highly protected internal network. Screened subnets are used mainly to host public servers (such as Web servers).
Term
demultiplexer
 Definition
Device that can extract and distribute individual streams of data that have been combined to travel along a single shared network cable.
Term
denial of service (DoS)
 Definition
An attack that floods a networked resource with so many requests that it becomes overwhelmed and ceases functioning. DoS prevents users from gaining normal use of a resource.
Term
dense wavelength division multiplexing (DWDM)
 Definition
An optical multiplexing technology in which a large number of optical signals of different optical wavelength could be combined to travel over relatively long fiber cables.
Term
designated router (DR)
 Definition
The main router in an OSPF network that relays information to all other routers in the area.
Term
desktop as a service (DaaS)
 Definition
A cloud computing service that enables a user or organization to virtualize user workstations and manage them as flexibly as other cloud resources.
Term
destination (header field)
 Definition
A field common to many packet-switched network protocols. Contains the address of the intended recipient (in the address format—such as a MAC or IP address—appropriate for the protocol).
Term
destination port
 Definition
A fixed, predetermined number that identifies which process the data in a TCP segment or UDP datagram is intended for. The destination port number is contained in the destination field of segments and datagrams.
Term
device driver
 Definition
A subprogram to control communications between the computer and some peripheral hardware.
Term
device ID
 Definition
The last six digits of a MAC address, identifying the manufacturer’s unique serial number for that NIC.
Term
DHCP four-way handshake (DORA)
 Definition
DHCP process in which a client gets a lease for an IPv4 address—Discover, Offer, Request, and Acknowledgment.
Term
DHCP lease
 Definition
Created by the DHCP server to allow a system requesting DHCP IP information to use that information for a certain amount of time.
Term
DHCP relay
 Definition
A router feature that, when enabled, accepts DHCP broadcasts from clients and then sends them via unicast addresses directly to the DHCP server. In common terms, DHCP communications can cross from one network to another through a router that has DHCP relay configured. Also known as a DHCP relay agent.
Term
DHCP scope
 Definition
The pool of IP addresses that a DHCP server may allocate to clients requesting IP addresses or other IP information like DNS server addresses.
Term
DHCP snooping
 Definition
Switch process that monitors DHCP traffic, filtering out DHCP messages from untrusted sources. Typically used to block attacks that use a rogue DHCP server.
Term
DHCPv6
 Definition
IPv6 version of DHCP. A stateful DHCPv6 server works similarly to an IPv4 DHCP server, while a stateless DHCPv6 server provides configuration information and lets the host pick its own address via stateless address autoconfiguration (SLAAC).
Term
differential backup
 Definition
Similar to an incremental backup in that it backs up the files that have been changed since the last backup. This type of backup does not change the state of the archive bit.
Term
differentiated services (DiffServ)
 Definition
The underlying architecture that makes quality of service (QoS) work.
Term
dig (domain information groper)
 Definition
Command-line tool in non-Windows systems used to diagnose DNS problems.
Term
digital signature
 Definition
A hash of a message which has been encrypted and attached to the message. The hash is encrypted with the signer’s private key. The recipient can decrypt the hash with the signer’s public key and use the hash to confirm the message was not altered. This both verifies a sender’s identity and the integrity of the message.
Term
digital subscriber line (DSL)
 Definition
A high-speed Internet connection technology that uses a regular telephone line for connectivity. DSL comes in several varieties, including asymmetric (ADSL) and symmetric (SDSL), and many speeds. Typical home-user DSL connections are ADSL with a download speed of up to 9 Mbps and an upload speed of up to 1 Kbps.
Term
dipole antenna
 Definition
The standard straight-wire antenna that provides most omnidirectional function.
Term
direct current (DC)
 Definition
A type of electric circuit where the flow of electrons is in a complete circle.
Term
directional antenna
 Definition
An antenna that focuses its signal more toward a specific direction; as compared to an omnidirectional antenna that radiates its signal in all directions equally.
Term
direct-sequence spread-spectrum (DSSS)
 Definition
A spread-spectrum broadcasting method defined in the 802.11 standard that sends data out on different frequencies at the same time.
Term
disaster recovery
 Definition
The means and methods to recover primary infrastructure from a disaster. Disaster recovery starts with a plan and includes data backups.
Term
discretionary access control (DAC)
 Definition
Authorization method based on the idea that there is an owner of a resource who may at his or her discretion assign access to that resource. DAC is considered much more flexible than mandatory access control (MAC).
Term
disk mirroring
 Definition
Process by which data is written simultaneously to two or more disk drives. Read and write speed is decreased but redundancy, in case of catastrophe, is increased. Also known as RAID level 1.
Term
disk striping
 Definition
Process by which data is spread among multiple (at least two) drives. It increases speed for both reads and writes of data, but provides no fault tolerance. Also known as RAID level 0.
Term
disk striping with parity
 Definition
Process by which data is spread among multiple (at least three) drives, with parity information as well to provide fault tolerance. The most commonly implemented type is RAID 5, where the data and parity information is spread across three or more drives.
Term
dispersion
 Definition
Diffusion over distance of light propagating down fiber cable.
Term
distance vector
 Definition
Set of routing protocols that calculates the total cost to get to a particular network ID and compares that cost to the total cost of all the other routes to get to that same network ID.
Term
distributed control system (DCS)
 Definition
A small controller added directly to a machine used to distribute the computing load.
Term
Distributed Coordination Function (DCF)
 Definition
One of two methods of collision avoidance defined by the 802.11 standard and the only one currently implemented. DCF specifies strict rules for sending data onto the network media. See also Point Coordination Function (PCF).
Term
distributed denial of service (DDoS)
 Definition
Multicomputer assault on a network resource that attempts, with sheer overwhelming quantity of requests, to prevent regular users from receiving services from the resource. Can also be used to crash systems. DDoS attacks are usually executed using botnets consisting of compromised systems referred to as zombies.
Term
distributed switching
 Definition
The centralized installation, configuration, and handling of every switch in a virtualized network.
Term
distribution layer
 Definition
One tier of a three-tiered architecture commonly used in data centers. The distribution layer interconnects racks of servers and other rack-mounted gear through top-of-rack switching. Modern data center design leverages advances in virtualization and software-defined networking (SDN) to replace the distribution layer common in the three-tiered network design with a virtualized mesh network.
Term
DNS cache poisoning (DNS poisoning)
 Definition
an attack that adds or changes information in a DNS server’s cache to point hostnames to incorrect IP addresses, under the attacker’s control. When a client requests an IP address from this DNS server for a Web site, the poisoned server hands out an IP address of an attacker machine, not the legitimate site. When the client subsequently visits the attacker site, they become vulnerable to a number of threats including malware.
Term
DNS caching
 Definition
A feature of DNS servers that temporarily stores information about previous DNS lookups to speed up future requests.
Term
DNS domain
 Definition
A specific branch of the DNS name space. Top-level DNS domains include .com, .gov, and .edu.
Term
DNS forwarding
 Definition
DNS server configuration that sends (forwards) DNS requests to another DNS server.
Term
DNS record
 Definition
A piece of data, such as an IP address, attached to a name in the DNS tree. Each record type helps different aspects of DNS do their job. For example: A records store the IP address of a domain, NS records store the name server for a given DNS entry, and MX records direct e-mail to specific e-mail servers.
Term
DNS resolver cache
 Definition
A cache used by Windows DNS clients to keep track of DNS information.
Term
DNS root servers
 Definition
Servers at the top of the hierarchy of DNS servers running the Internet. There are only 13 root servers.
Term
DNS server
 Definition
Software that responds to DNS queries, often running on a system dedicated to this purpose.
Term
DNS tree
 Definition
A hierarchy of DNS domains and individual computer names organized into a tree-like structure, the top of which is the root.
Term
document
 Definition
A medium and the data recorded on it for human use; for example, a report sheet or book. By extension, any record that has permanence and that can be read by a human or a machine.
Term
documentation
 Definition
A collection of organized documents or the information recorded in documents. Also, instructional material specifying the inputs, operations, and outputs of a computer program or system.
Term
domain
 Definition
A term used to describe a grouping of users, computers, and/or networks. In Microsoft networking, a domain is a group of computers and users that shares a common account database and a common security policy. For the Internet, a domain is a group of computers that shares a common element in their DNS hierarchical name.
Term
domain controller
 Definition
A Microsoft Windows Server system specifically configured to store user and server account information for its domain. Often abbreviated as “DC.” Windows domain controllers store all account and security information in the Active Directory domain service.
Term
domain information groper (dig)
 Definition
Command-line tool in non-Windows systems used to diagnose DNS problems.
Term
Domain Name System (DNS)
 Definition
A TCP/IP name resolution system that resolves hostnames to IP addresses, IP addresses to hostnames, and other bindings, like DNS servers and mail servers for a domain.
Term
domain users and groups
 Definition
Users and groups that are defined across an entire network domain.
Term
door access controls
 Definition
Methodology to grant permission or to deny passage through a doorway, whether computer-controlled, human-controlled, token-oriented, or by other means.
Term
dotted decimal notation
 Definition
Shorthand method for discussing and configuring binary IP addresses using a base 10 numbering system.
Term
drive mirroring
 Definition
The process of writing identical data to two hard drives on the same controller at the same time to provide data redundancy.
Term
DSL Access Multiplexer (DSLAM)
 Definition
A device located in a telephone company’s central office that connects multiple customers to the Internet.
Term
DSL modem
 Definition
A device that enables customers to connect to the Internet using a DSL connection. A DSL modem isn’t really a modem—it’s more like an ISDN terminal adapter—but the term stuck, and even the manufacturers of the devices now call them DSL modems.
Term
dual stack
 Definition
Networking device, such as a router or PC, that runs both IPv4 and IPv6.
Term
dynamic addressing
 Definition
A way for a computer to receive IP information automatically from a server program. See also Dynamic Host Configuration Protocol (DHCP).
Term
Dynamic ARP Inspection (DAI)
 Definition
Uses information collected by DHCP snooping to spot and ignore suspicious ARPs to prevent ARP cache poisoning and other malevolent efforts.
Term
Dynamic DNS (DDNS)
 Definition
A protocol that enables DNS servers to get automatic updates of IP addresses of computers in their forward lookup zones, mainly by talking to the local DHCP server.
Term
Dynamic Host Configuration Protocol (DHCP)
 Definition
A protocol that enables a DHCP server to set TCP/IP settings automatically for a DHCP client.
Term
dynamic multipoint VPN (DMVPN)
 Definition
A virtual private network solution optimized for connections between multiple locations directly.
Term
dynamic NAT (DNAT)
 Definition
Type of network address translation (NAT) in which many computers can share a pool of routable IP addresses that number fewer than the computers.
Term
dynamic port numbers
 Definition
Port numbers 49152–65535, recommended by IANA to be used as ephemeral port numbers.
Term
dynamic routing
 Definition
Process by which routers in an internetwork automatically exchange information with other routers. Requires a dynamic routing protocol, such as OSPF or EIGRP.
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