h
H.264 Video codec. (AKA: MPEG-4 AVC) Wikipedia
H.323 ITU-T standard for A/V transmission through packets. Wikipedia
half duplex Only one device can talk at a time, similar to Nextel push-to-talk. Hubs should only be half duplex.
Halftone Wikipedia
Hard Disk Drive (HDD) Usually shortened to hard drive, it uses a spinning platter to store information. Divided into tracks, sectors, clusters, and cylinders.
hardware-assisted virtualization Intel VT-x or AMD-V Wikipedia
Harvard Mark II Wikipedia
hash (aka: message digest) Function that can be used to map data of arbitrary size to data of fixed size. Essentially, a number generated from a string of text. A given input will always generate the same output (deterministic algorithm). In networking, it ensures messages did not change in transit. Similar to a Cycle Redundancy Check (CRC), only stronger. Hard to reverse (one-way hash) but is not encryption. Typically 128 bit or longer output. Examples include MD5 and SHA. Wikipedia Netacad
Hash-Based Message Authentication Code (HMAC) (aka: Keyed-Hash Message Authentication Code [KHMAC]) Data integrity algorithm guaranteeing the integrity of a message. Adds a secret key to the hash function. Wikipedia
Haskell programming language Wikipedia
Haswell Microarchitecture codename from Intel. Announced June 4, 2013. Wikipedia
HAVING clause The HAVING clause is used to restrict the output of a GROUP BY query by applying a conditional criteria to the grouped rows.
head Command that displays the beginning of a file. Tail shows the end. Linux 101 Hacks YouTube
Headend Where signals are first received in a cable network. Data is then distributed downstream to the cable network. Similar to a CO in a telephone network.
heartbeats Packets sent between NLB cluster nodes. Website Wikipedia
Heartbleed OpenSSL bug. Wikipedia
hello packet One of the OSPF protocol messages.
help Command that provides Help information. Examples include;
| ? |
| /? |
| -help |
| --help |
| Get-Help |
henry (H) 1 volt-second per ampere. Symbolized by 'L' WikiHow
here string Multi-line string. Wikipedia
hertz (Hz) SI unit of frequency. One cycle per second. Wikipedia
Heterogeneous System Architecture (HSA) Not-for-profit group whose goal is to make it easy to program for parallel computing. Website
Heuristically Programmed Algorithmic (HAL) 9000 computer Wikipedia Wikipedia
Hewlett Packard (HP) Tech company based in Palo Alto, California. Founded January 1, 1939. Website Wikipedia
hexadecimal (hex) Base-16 number system. Used in IPv6 and MAC addresses. 4 hexadecimal units = 16 binary units. Usually represented in text by the value preceded by 0x. Wikipedia
hextet Unofficial term for every 16 bit segment in an IPv6 address Wikipedia
Hierarchical Network Design Access layer, Distribution layer, and Core layer. Wikipedia
High Efficiency Video Coding (HEVC) (aka: H.265 or MPEG-H Part 2) Video compression standard. Formally published by the ITU-T on June 7, 2013. Wikipedia
High Performance File System (HPFS) Wikipedia
High-Level Data Link Control (HDLC) (frame header) Supports only single protocol environments. Wikipedia
High-Speed Serial Interface (HSSI) developed by Cisco Wikipedia
HMAC Header { Authentication Header | TCP header | data | IP address } Wikipedia
horizontal cross-connect Where horizontal cabling connects to a patch panel or punch block. Wikipedia
Huawei Founded in 1987. Wikipedia
hub Basic network connectivity device that repeats any signal it receives on one port to all other ports. Operates at OSI layer 1. Succeeded by switches. As of 2011, connecting network segments by repeaters or hubs is deprecated by IEEE 802.3. Wikipedia
hub-and-spoke topology Has a WAN link from each remote site when interconnecting multiple sites (for example, multiple corporate locations). Similar to the star topology.
HyperText Markup Language 5 (HTML 5) First released as a standard October 28, 2014. Wikipedia
HAF X Computer case made by Cooler Master. Released May 2010. Website YouTube (Cooler Master)
Hierarchical File System (HFS) Wikipedia
High-speed WAN Interface Card (HWIC) Cisco
HMAC-Message Digest 5 (HMAC-MD5) (Legacy) 128-bit shared-secret key and hash.
HMAC-Secure Hash Algorithm 1 (HMAC-SHA-1) 160-bit secret key and hash.
hold time The amount of time a neighbor should wait before considering the advertising router to be down. Used in EIGRP.
holddown timer Wikipedia
HoloLens Holographic headset made by Microsoft. Website
HOME ~ Environment variable for the home directory in Bash. Use echo $HOME or echo ~ to display.
Homebrew Computer Club Early computer hobbyist group in Menlo Park, California. Met from March 1975 to December 1986. First meeting held on March 5, 1975. Wikipedia
HomeGroup Allows Windwos users to share files across computers on a home network. Introduced with Windows 7 Website Wikipedia Netacad
Honeypot-based detection Decoy setup on the network to make a hacker think they get away with infecting a system or stealing information. Wikipedia
hop The jump from one outgoing interface on a router to another outgoing interface.
Hop Limit The amount of hops a packet can take before it is dropped.
Horizontal cabling Inside Wiring (IW) or plenum that connects the telecommunication room to individual outlets in the wall or floor. Wikipedia
horsepower (HP) (1 hp = 550 ft-lb/s, 1 hp = 746w) Average horse can do 550 foot-pounds of work per second.
host An end device with a configured IP address.
Host Bus Adapter (HBA) Connects a computer to network and storage devices. Wikipedia
hostname The network name of a host. Can be show in the CLI of Windows and UNIX-Like operating systems by entering hostname. Wikipedia
Hosts file A text file used by an OS to map IP addresses. Windows filepath: "%WinDir%\System32\Drivers\Etc\Hosts" Wikipedia Microsoft Support
Hot Standby Router Protocol (HSRP) Cisco proprietary protocol. Wikipedia RFC 2281 Cisco
hot swap Allows a piece of hardware to be removed without powering down the device. Wikipedia
HP Compaq dc5800 Small Form Factor PC Desktop computer from HP. Released Q4 2008. Website Wikipedia
HP Integrated Lights-Out (iLO) Out-of-band management used with HP servers. Website Wikipedia
hping Command-line TCP/IP packet assembler/analyzer. Tool used by security testers to bypass filtering devices by injecting modified IP packets. Developed by Salvatore Sanfilippo. Website Wikipedia sectools.org
href HTML tag attribute. Specifies a URL. W3Schools
HTC Taiwanese consumer electronics company headquartered in Xindian District, New Taipei City, Taiwan. Founded May 15, 1997. Website Wikipedia
HTML attachment File often sent by email that can contain malicious code and can be downloaded and executed on a client’s computer. When a user clicks the attachment, it opens a browser session and could open a malicious web site. Netcraft
HTTP Strict Transport Security (HSTS) Protects HTTPS traffic. Wikipedia
HTTP version 2 (HTTP/2) Published as RFC 7540 May 14, 2015. Wikipedia RFC 7540 IETF
Hybrid Fiber-Coaxial (HFC) Part of the link to the service provider uses fiber while the other part (usually the last mile) uses coaxial cable. Wikipedia
Hyper-V Native hypervisor that runs in Windows. Wikipedia
Hypertext Markup Language (HTML) Common language that most web pages are coded with in conjunction with CSS. Other programs may use HTML to display information including emails. Wikipedia Khan Academy
Hypertext Transfer Protocol (HTTP) (port 80) Transfers webpages that make up the World Wide Web (WWW). When a request for a webpage is made to a web server, HTTP specifies the message types used for communication. The three common message types are GET, POST, and PUT. Introduced under RFC 2068 in January 1997. Wikipedia RFC 2068 RFC 2616 RFC 7540
Hypertext Transfer Protocol Secure (HTTPS) (port 443) A more secure form of HTTP that encrypts data with either Transport Layer Security (TLS) or Secure Sockets Layer (SSL) protocols. Wikipedia EFF
Hypervisor Two types;
| type 1 hypervisor | Runs directly (bare-metal) on hardware in place of an OS to run guest hosts. |
| type 2 hypervisor | Runs on top of the host OS. |
hypotenuse Longest side of a right-angled triangle. Wikipedia Khan Academy