d
D Identifies a dynamically learned network from another router using the EIGRP routing protocol in a routing table. Wikipedia
daemon Program that runs as a background process. Wikipedia
Darwin Open source OS based on BSD and made by Apple. OS X and iOS get their core components from Darwin. First released November 15, 2000. Wikipedia Website
data (information) The smallest form is a bit but can be represented by byte, kilobyte (KB), megabyte (MB), gigabyte (GB), terabyte (TB), petabyte (PB), exabyte (EB), zettabyte (ZB), yottabyte (YB). Wikipedia
Data Access Layer (DAL) Wikipedia
data center Typically a data storage and processing facility run by an in-house IT department or leased offsite. Wikipedia Netacad
Data Communications Equipment (DCE) Female end of a serial connection. (used for clock rate. modem) Devices that put data on the local loop. Wikipedia
Data Deduplication Required steps: Ensure shared files and folders are not stored on the system volume. Must be NTFS; does not support ReFS.
Data Encapsulation Wikipedia YouTube
Data Encryption Standard (DES) Symmetric encryption algorithm, usually encrypted with a block cipher. The key is 64-bits long, but only 56 bits are used for encryption. Can be used by IPsec to encrypt data. Published as FIPS standard FIPS PUB 46 January 15, 1977. Wikipedia Netacad
data integrity (checksum) Maintenance of, and the assurance of the accuracy and consistency of data over its entire life-cycle, and is a critical aspect to the design, implementation and usage of any system which stores, processes, or retrieves data. The term is broad in scope and may have widely different meanings depending on the specific context – even under the same general umbrella of computing. Wikipedia
Data Link Control (DLC) Wikipedia
Data Link Layer (OSI Layer 2) Packages bits of data from the physical layer into frames. These frames are then delivered between nodes on the same network level. Wikipedia
Data Manipulation Commands (DML) Allow you to add, modify, and delete rows from tables. Basic commands are; SELECT, INSERT, UPDATE, DELETE, COMMIT, and, ROLLBACK.
Data Stream Interface (DSI) Session layer used to carry Apple Filing Protocol traffic over TCP. Wikipedia
data structure A way of organizing data. Wikipedia
Data Terminal Equipment (DTE) Male side of a serial WAN connection. Wikipedia
data type A classification identifying the type of data. (i.e. Wikipedia
Data-Link Connection Identifier (DLCI) Uniquely identify a VC (data-link) connection. PVCs and DLCIs ensure bidirectional communication from DTE to DTE. Only significant on Wikipedia
Data-Over-Cable Service Interface Specification (DOCSIS) Wikipedia
database A collection of data. Wikipedia
Database Description (DBD) One of the OSPF protocol messages.
Database management systems (DBMS) Software that interacts with end users, applications, and the database itself to capture and analyze data. The order of rows and columns is not important. Wikipedia
Database Source Name (DSN) Wikipedia
datagram Basic transfer unit in a packet-switched network.
| OSI Layer | datagam |
|---|---|
| Layer 4 | segment |
| Layer 3 | packet |
| Layer 2 | frame |
| Layer 1 | Chip (CDMA) |
date Command that displays or sets the date and time in many operating systems. Examples:
| Linux: | sudo date -s "Jul 5 08:10" | |
| Windows: | date | (Output is the same as Get-Date in PowerShell) |
DB-9 Standard end used on serial cables. Wikipedia
DC-to-DC converter Converts DC from one voltage level to another. Wikipedia
dd Vi command used to delete the current line.
ddate Shows the Discordian date. About.com
de-encapsulation Process of un-encapsulating packet. Essentially encapsulation in reverse. Layer 2 --> Layer 7. Wikipedia
Deadlock waiting for a process that never finishes. Wikipedia
Debian A Linux distribution. Wikipedia Website
Debian Almquist Shell (Dash) Light weight version of Bash. ArchWiki
Debian Package Management System Runs on dpkg Wikipedia Wikipedia
debug ip nat s=source address, a.b.c.d--->w.x.y.z=source address--->translated address, d=destination ip address, [xxxx]=ip identification number
Decent Security Website
declare Bash builtin that sets attributes for shell variables. Use - to set an attribute and + to remove it.
DEF CON (aka: DEFCON) One of the world's largest security/hacker conventions. First held June 9, 1993. Website Wikipedia
DEF CON 26 Caesar's Palace & Flamingo, Las Vegas August 9-12, 2018. Website Wikipedia
DEF CON 27 August 8-11, 2019 at Paris, Ballys, & Planet Hollywood, Las Vegas. Website
DEF CON 28 SAFE MODE August 6-9, 2020 online. Website
DEF CON 29 Aug. 5-8, 2021 Website
DEF CON 30 Aug. 11-14, 2022 Website
DEF CON China 2 On Hold - Dates TBD. 751D Park in Beijing, China. Website
default gateway The IP address of a router that is the exit or "door" to another network. Typically this address is the first or last useable host address for that subnet. Wikipedia
default route Where packets go when it does not match a route in the routing table. 0.0.0.0/0 for IPv4, ::/0 for IPv6. Wikipedia Cisco
default static route a static route with 0.0.0.0/0 as the destination address. All IP packets that do no have a learned static route will be sent here. This is known a Gateway of Last Resort when configured.
default-information originate Propagates a default static route in router updates.
del Command that deletes one or more files. Use rm in UNIX. Wikipedia
delay (aka: latency) Network quality issue measuring the time required for a packet to travel from the source to the destination. Wikipedia
Dell Private computer company. Founded February 1, 1984. Website Wikipedia Support
Dell EMC (formerly EMC Corporation) Founded in 1979. Website Wikipedia
Dell PowerEdge (PE) Dell's server product line. Website Wikipedia
Dell Remote Access Controller (DRAC) Out-of-band management platform on certain Dell servers. The platform may be provided on a separate expansion card, or integrated into the main board; when integrated, the platform is referred to as iDRAC. Wikipedia
Dell Technologies Parent company of Dell created after the merger of Dell Inc. and EMC Corporation. Founded September 7, 2016. Website Wikipedia
delta Δ Change. Wikipedia
demarcation point (DMARC) Separates customer from service provider equipment. Wikipedia
demidecode die.net
Demilitarized Zone (DMZ) Section of a network containing servers that must connect to an external network, such as the internet. Wikipedia Netacad
Denial of Service (DoS) A DoS attack works by continuously sending packets of unexpected size or unexpected data. This results in interruption of service to users. Wikipedia Netacad
Dennis Ritchie Developed the C programming language with help from Ken Thompson in 1973. Wikipedia
Dense Wavelength-Division Multiplexing (DWDM) Uses optical (fiber) to transmit data over a WAN connection. Multiplies the amount of bandwidth for a single strand fiber. Enables bidirectional communications. 10Gbps multiplexed signal. Multiplex more than 80 channels or wavelengths on single fiber. Supports SONET and SDH. Wikipedia
dependent Value of an attribute that is determined by another attribute.
Deployment Image Servicing and Management (DISM) MSDN
DESCHALL First group to publicly crack the Data Encryption Standard (DES). Announced June 18, 1997. Wikipedia This Day in Tech History
designated port All non-root ports permitted to forward traffic. Selected per trunk.
Designated Router (DR) uses multicast address 224.0.0.5 for updates.
Desktop Management Interface (DMI) Wikipedia
Desktop Services Store (.DS_Store) A hidden file created by Finder in OS X. Wikipedia
desktop.ini Wikipedia
Destination IP Address Contains a 32-bit binary value that represents the destination IP address of the packet.
destination MAC address Part of an Ethernet frame.
Destination network The address of a remote network and how that network was learned in a routing table.
detective controls (during the event) Identify and characterize an incident in progress e.g. by sounding the intruder alarm and alerting the security guards or police. Wikipedia
determination The role of a key. (A determines B)
Development and Operations (DevOps) Wikipedia
DFS Namespace Website Wikipedia
DFS Replication Website Wikipedia
DHCP snooping Wikipedia
Diagnostics and Recovery Toolset (DaRT) Helps diagnose an offline copy of Windows Wikipedia
Dialed Number Identification Service (DNIS) Wikipedia
dialup A private WAN infrastructure. Limited to speeds less than 56Kbps due to the PSTN.
dialup modem Wikipedia
Diameter protocol Wikipedia
die Part of an integrated circuit. Wikipedia
dielectric Insulating material used in capacitors. Wikipedia
Difference of Cubes Factoring: A3 - B3 = (A - B)(A2 + AB + B2) Khan Academy
difference of squares x2+y2 = (a+b)(a-b)
Differentiated Services (DiffServ) (aka: soft QoS) Prioritized model to QoS. Marks packets according to the type of service they desire. Most modern QoS configurations are based on the DiffServ approach. Wikipedia
Differentiated Services Code Point (DSCP) (formerly: Type of Service (ToS) field) QoS marking that uses the first 6 bits in the DS Byte of an of an IPv4 packet header. Wikipedia (Differentiated Services) Wikipedia (IPv4 Header) Wikipedia (Quality of Service)
Diffie–Hellman key Exchange (DHE) (aka: Diffie-Hellman (DH)) Key negotiation and agreement protocol used in public key cryptography. Asymmetric algorithm used to create shared keys. Does not provide encryption but is used to establish the secret key between two parties. First published by Whitfield Diffie and Martin Hellman in 1976.
| DH1 | (Legacy) 768 bit key. |
| DH2 | (Legacy) 1024 bit key |
| DH5 | (Legacy) 1536 bit key |
| DH7 | |
| DH14 | 2048 bit key |
| DH15 | 3072 bit key |
| DH16 | 4096 bit key |
| DH19 | supports Elliptical Curve Cryptography |
| DH20 | supports Elliptical Curve Cryptography |
| DH24 | supports Elliptical Curve Cryptography |
Diffusing Update Algorithm (DUAL) Algorithm used by IGRP and EIGRP. Generates loop-free and backup paths. Developed by Dr. J.J. Garcia-Luna-Achieves at SRI International. Wikipedia
digest Fixed length output "thumbprint" for the data being hashed. Wikipedia
Digital Attack Map Top daily DDoS attacks worldwide. Website
digital certificate (aka: public key certificate) Includes the public key, digital signature, and verification from a third party. Wikipedia YouTube (itfreetraining)
digital certificates Exchanged to authenticate peers
Digital Equipment Corporation (DEC) Developed the PDP line of computers. Created the first firewall in 1988. Later acquired by Compaq. Wikipedia
Digital Linear Tape (DLT) (formerly: CompacTape) Magnetic tape data storage technology. Maximum capacity of 800GB or 160GB in the value line. Developed by Digital Equipment Corporation (DEC) in 1984. Wikipedia
Digital Millennium Copyright Act (DMAC)
Digital Rights Management (DRM)
Digital Serial Interface (DSI) Protocol for controlling lighting in buildings. Wikipedia
Digital Signal 0 (DS0) Dedicated line (not shared) at 64Kbps. 24 bundled is a DS1 line or T1 line. Wikipedia
Disable-ADAccount PowerShell cmdlet used to disable an Active Directory account. TechNet
dism.exe /online /cleanup-image /restorehealth Command that will attempt to repair your corrupted file from a trusted online source (Windows Update). Requires administrative privileges. Tom's Hardware
Double Data Rate Synchronous DRAM (DDR SDRAM) Wikipedia
Drupal Free, open-source CMS framework written in PHP. First released May 18, 2000. Website Wikipedia
Digital Signal 0 (DS0) Adapter Cisco
Digital Signal 1 (DS1) (T1 line) 1.544Mbps bandwidth Wikipedia T1Rex
Digital Signal 3 (DS3) 44.736Mbps Wikipedia
digital signature (aka: hash) Mathematical method used to check the authenticity and integrity of a message, digital document, or software. Gives a recipient reason to believe that the data was created by a known sender (authentication), that the sender cannot deny having sent the data (non-repudiation), and that the data was not altered in transit (integrity). Used when connecting to a secure website. Can be used as an alternative to HMAC. Wikipedia
Digital Signature Algorithm (DSA) (authentication) Federal Information Processing Standard (FIPS) for digital signatures, based on the mathematical concept of modular exponentiation and the discrete logarithm problem. DSA is a variant of the Schnorr and ElGamal signature schemes. DSA signature generation is faster than DSA signature verification. Attributed to David W. Kravitz. Filed under U.S. Patent 5,231,668 July 26, 1991. Adopted by the U.S. government in 1993 with FIPS 186. Wikipedia
Digital Signature Standard (DSS)
Digital Subscriber Line (DSL) A type of broadband internet connection media that uses phone lines. (WAN)
Digital Subscriber Line Access Multiplexer (DSLAM) Wikipedia
Digital Versatile Disc (DVD) Typically 4.7 GB to 8.5 GB.
| DVD | 4.7 GB |
| DVD DL | 8.5 GB |
| DVD DS | 9.4 GB |
| DVD DS, DL | 17 GB |
| DVD-RAM | 4.7 GB |
| MiniDVD | 1.46 GB |
| MiniDVD DL | 2.66 GB |
Digital Video Broadcasting (DVB) Wikipedia
Digital Video Broadcasting-Common Interface (DVB-CI) Wikipedia
Digital Visual Interface (DVI)
| DVI-I | (integrated, combines digital and analog in the same connector; digital may be single or dual link) |
| DVI-D | (digital only, single link or dual link) |
| DVI-A | (analog only) |
Developed April 1999. Wikipedia
digital-to-analog converter (DAC) Wikipedia
Dijkstra's algorithm Used in OSPF.
DIN connector Wikipedia
dir Command that displays a list of files and subdirectories in a directory. Use ls in UNIX-based systems or Windows through PowerShell. Wikipedia TechNet
Direct Current (DC) Current goes only one direction. Favored by Thomas Edison. Wikipedia
Direct Media Interface (DMI) Wikipedia
Direct Memory Access (DMA) Wikipedia
Direct Memory Access (DMA) attack
Direct Memory Interface (DMI) Website Wikipedia
Direct X Diagnostic Tool (dxdiag) Program that displays information about DirectX. (version,
Direct-Sequence Spread Spectrum (DSSS) Spread spectrum modulation technique used to reduce overall signal interference. Modulates data over an entire range of frequencies using a series of symbols called chips which are shorter in duration than a bit. Chips are transmitted at a higher than normall rate and include random data making it difficult to eavesdrop. Supported by 802.11b and 802.11g. Wikipedia
DirectAccess Automatically establishes a secure bi-directional IPSec connection. Introduced with Windows 7 and Windows Server 2008 R2. Website Wikipedia
directed broadcast Broadcaster sent to all hosts on a specific network such as non-local network. Routers do not forward these by default.
directly connected static route Static route that uses only the exit interface.
directory Another name for a folder. Holds other files or dirctories. Represented by eitehr / (Linux) or \ (Windows).
Directory Services Restore Mode (DSRM) Used in a domain controller to take Active Directory offline. Wikipedia
Directory System Agent (DSA) The directory service component that runs as Ntdsa.dll on each domain controller, providing the interfaces through which services and processes gain access to the directory database. TechNet
Dirty Change on Write (Dirty COW) (aka: CVE-2016-5195) Linux kernel vulnerability. Linux.com Red Hat
disk spinning platters (Hard drives)
disk array Wikipedia
Disk Operating System (DOS) Wikipedia
DISKCOMP Compares the contents of two floppy disks.
DISKCOPY Copies the contents of one floppy disk to another.
DISKPART DOS command used to manage disk partitions. TechNet
DisplayPort (DP) Digital display interface developed by a consortium of PC and chip manufacturers and standardized by the Video Electronics Standards Association (VESA). Version, 1.0 approved by VESA on May 3, 2006. Wikipedia
Distance Vector Routing Protocol Router only know what is next to them. Does not have an actual map of the whole network.
Distinguished Name (DN) (aka: LDAP Distinguished Name (DN)) Unique database name for every Active Directory (AD) object. Made up of Relative Distinguished Name (RDN). Wikipedia YouTube (Microsoft MCSA/MCSE Learning Channel)
Distributed Component Object Model (DCOM) Website Wikipedia
Distributed Coordination Function (DCF) Used with CSMA/CA on WLANs to prevent collisions with random back off timers. Wikipedia
Distributed Denial of Service (DDoS) A DDoS attack is similar to a DoS attack but originates from multiple sources. Wikipedia Network
Distributed File System (DFS) Wikipedia
Distribution Layer Forwards traffic between local networks using Layer 3 devices with ACLs and QoS. Netacad
Distribution System (DS) The bridge between 2 BSSs
Django High-level web development framework written in Python. First released July 21, 2005. Website Wikipedia
DNS caching How long a DNS server will hold a record before checking for updates. Usually determined by TTL.
DNS poisoning (DNS spoofing) Attack that introduces erroneous or malicious entries into a DNS server’s zone file or a server’s hostname-to-IP address cache, intending to misdirect DNS resolution requests. Wikipedia
DNS query Request for name resolution. Wikipedia
DNS Server Maps name-to-IP addresses for internal hosts. Forwards name resolution requests between servers. Stores resource records used to resolve names which contain the name, address, and type of record. Some types are: A (an end device address), NS (an authoritative name server), CNAME, MX (Mail Exchange).
DNS zone transfer Can be either AXFR (full transfer) or IXFR (incremental transfer) Wikipedia
doc .doc Proprietary filename extension for a Microsoft Word document. Wikipedia
Docker Allows you to package an application with all of its dependencies into a standardized unit for software development. Website
DockerCon 2018 June 12-24 in San Francisco, California. Website
Document Object Model (DOM) Wikipedia
docx A Microsoft Word document. Wikipedia
dollar sign underscore $_ Object being passed through the pipeline.
domain Collection of user accounts, computers, printers, and other objects managed in a database. Wikipedia
domain Used to organize and describe an attribute's set of possible values in data modeling.
Domain Component (DC) TechNet YouTube (Microsoft MCSA/MCSE Learning Channel)
Domain Controller (DC) A Windows server used to control user permissions. Sometimes referred to as an Active Directory Server. Wikipedia
domain name Uniquely identifies parts of the internet such as a website. Easier to remember than an IP address. Wikipedia
Domain Name System (DNS) (aka: Domain Name Service) (UDP port 53) Translates domain names such as google.com into IP addresses. Originaly published in RFC 882 and RFC 883 November 1983. Wikipedia RFC 882 RFC 883 Cisco (Configuring DNS on Cisco Routers)
Don't Fragment (DF) A router will attempt to fragment a packet that is too big, unless the packet has its don't fragment (DF) bit set. If a packet does exceed an interface's MTU and has its DF bit set, the router drops the packet.
Doom First-person shooter. First released December 10, 1993 to MS-DOS and Mac OS. Wikipedia
doping Adding impurity atoms to a semiconducting material. Can be p-type or n-type. Wikipedia
dormant cyber pathogen What Michael Ramos, the San Bernardino County district attorney, claims was on a terrorist's iPhone. Used in a hearing for the San Bernardino iPhone case on March 22, 2016. Ars Technica
DOSKEY Edits command lines, recalls Windows commands, and creates macros.
Double Data Rate version three Synchronous DRAM (DDR3 SDRAM) Release in 2007. Wikipedia
Double Data Rate version two Synchronous DRAM (DDR2 SDRAM) Release in 2003. Wikipedia
double-precision (IEEE 754) Wikipedia
dpkg (Debian package) A command that can be used to install and remove packages in a Debian based OS. It can also be used to view the currently installed packages. Wikipedia
dpkg-reconfigure tzdata Reconfigure the date and timezone on a Debian-based Linux distribution. Example:
sudo dpkg-reconfigure tzdata |
Dreamcast Video game console made by Sega. Released in Japan November 27, 1998. Released in North America September 9, 1999. Wikipedia
driver Allows the OS to communicate with specific hardware.
driverless cars Approved by the California Department of Motor Vehicles (DMV) February 26, 2018. Regulations in effect as of April 2, 2018. Ars Technica DMV
DRIVER_IRQL_NOT_LESS_OR_EQUAL (d1) An attempt was made to access a pageable (or completely invalid) address at an interrupt request level (IRQL) that is too high. This is usually caused by drivers using improper addresses. Windows Debugging Tools
Droid Razr First released November 11, 2011. Wikipedia
Dropbox File hosting service. Release June 2007. Website Wikipedia
DROTHER A router that is not a DR or a BDR in an OSPF Cisco
Dual In-line Memory Module (DIMM) Type of memory module that typically comes with 168, 184, 240, or 288 pins. Larger than a SIMM slot.
| 100-pin DIMM | printer SDRAM |
| 168-pin DIMM | SDR SDRAM (less frequently for FPM/EDO DRAM in workstations/servers, may be 3.3 or 5 V) |
| 184-pin DIMM | DDR SDRAM |
| 200-pin DIMM | FPM/EDO DRAM in some Sun workstations and servers |
| 240-pin DIMM | DDR2 SDRAM, DDR3 SDRAM and FB-DIMM DRAM |
| 278-pin DIMM | HP high density SDRAM |
| 288-pin DIMM | DDR4 SDRAM |
Dual In-Line Package (DIP) Wikipedia
dual stack Allows IPv4 and IPv6 to coexist on the same network.
Dual-Tone Multi-Frequency signaling (DTMF) Wikipedia
duck typing Wikipedia
Duo Video chat app from Google. Announced May 18, 2016. Available for Android and iOS August 16, 2016. Website Wikipedia CNET
duplex settings half duplex and full duplex
Duplicate Address Detection (DAD) Checks for duplicate IPv6 unicast addresses.
DVD Double Layer (DVD DL) 8.55 GB
| DVD-R DL | 8,543,666,176 Bytes |
| DVD+R DL | 8,547,991,552 Bytes |
DVD Double Sided (DVD DS) 9.4 GB
| DVD-R DS, DVD-RW DS | 9,414,639,616 Bytes |
| DVD+R DS, DVD+RW DS | 9,400,745,984 Bytes |
DVD Double Sided, Double-Layer (DVD DS, DL) (aka: dual-layer) 17.09 GB
| DVD-R DS, DL | 17,087,332,352 Bytes |
| DVD+R DS, DL | 17,095,983,104 Bytes |
DVD+R Single Sided, Single Layer DVD recordable (DVD+R) and DVD rewritable (DVD+RW) discs have a 4.7 GB capacity.
| DVD+R, DVD+RW | 4,700,372,992 Bytes |
DVD-R Single Sided, Single Layer DVD recordable (DVD-R) and DVD rewritable (DVD-RW) discs have a 4.7 GB capacity.
| DVD-R, DVD-RW | 4,707,319,808 Bytes |
dvorak An alternative English keyboard layout to QWERTY that is designed to be more efficient. Wikipedia
Dynamic ACL Cisco
Dynamic Domain Name Service (DDNS) Automatically updates the name server in a domain name system. Wikipedia
Dynamic Host Configuration Protocol (DHCP) (RFC 2131) Used to assign an IP address, subnet mask, default gateway, and DNS server address to a host. When a host connects to the network it will broadcast a DHCPDISCOVER message. A DHCP server send a DHCPOFFER back to the host which contains the IP address and subnet mask to be assigned as well as the IP address of the DNS server and default gateway. If multiple offers were received, it will chose one with DHCPREQUEST. The server will send back a DHCPACK to acknowledge the lease is set.
| DHCPDISCOVER-->DHCPOFFER-->DHCPREQUEST-->DHCPACK |
Dynamic Host Configuration Protocol version 6 (DHCPv6) A method for automatically assigning IPv6 global unicast addresses. Similar to DHCP for IPv4. Can be used along with SLAAC.
Dynamic Memory Feature in Microsoft Hyper-V that let virtual machines use more physical memory than assigned. Introduced in Windows Server 2008 R2 Service Pack 1 (SP1). TechNet
Dynamic Multipoint VPN (DMVPN) Wikipedia Cisco (DMVPN) Cisco (Configure DMVPN using GRE over IPSec between Multiple Routers) YouTube (Keith Barker)
Dynamic NAT (DNAT) (aka: many-to-many) Many inside local user (a network) are mapped to a pool of inside global addresses.
Dynamic programming language Type of high-level programming language. Wikipedia
Dynamic Random Access Memory (DRAM) Type of RAM that stores each bit of data in a separate capacitor within an integrated circuit. Wikipedia
dynamic routing protocol (EIGRP, RIPv2
Dynamic Trunking Protocol (DTP) Cisco proprietary. Wikipedia
Dynamic-Link Library (DLL) Microsoft's implementation of a shared library. Wikipedia