o
O In a routing table, 'O' indicates a route that was learned dynamically by OSPF. Learned by type 1 and 2 LSAs. Cisco
O E1 External routes to an AS. Learned by type 5 LSAs Cisco
O E2 External routes to an AS. Learned by type 5 LSAs Cisco
O I Cisco
O IA OSPF Interarea (originated from another area) summary LSAs. Learned from type 3 or type 4 LSAs. Cisco
O(1) scheduler Old process scheduler in Linux. Wikipedia
object Resources (e.g., printers) or security principals Wikipedia
object (obj) A value in memory. Contains attributes and methods. Wikipedia
Object Group-Based ACL Csico
Object Identifier (OID) Csico YouTube
Object Linking and Embedding (OLE) Microsoft protocol. Wikipedia
Object Management Group (OMG) Developed the UML standards. Wikipedia
Object-Oriented Programming (OOP) Program consists of objects that contain attributes and methods. Wikipedia
Objective-C Object-oriented programming language. Released in 1983. Wikipedia
octal (oct) Base-8 number system. Wikipedia
octet Four octets make up an ip address. Each octet has 8 binary bits. For example in 192.168.1.000000001, the 4th or last octet (00000001) is represented in binary. Wikipedia
Odyssey Codename for an unreleased version of Windows. Wikipedia
Offensive Security Certified Professional (OSCP) Website Wikipedia
Office 97 Released November 19, 1996. Wikipedia
ohm (Ω) (R) Unit of resistance. Named after Georg Ohm. Wikipedia
OK Computer Third studio album from Radiohead. Released May 21, 1997. Wikipedia
Omega 24th and last letter of the Greek alphabet. Wikipedia
One M9 Smartphone from HTC. Released April 10, 2015. Website Wikipedia
One-time pad Wikipedia
one-time password (OTP) Wikipedia
one-to-many One record matches many records in a second table. Wikipedia
OneCore The 'core' of Windows that is shared across devices.
OneDrive Microsoft's cloud storage solution. Previously known as SkyDrive. Wikipedia Website
OnePlus Chinese smartphone manufacturer. Founded December 16, 2013. Website Wikipedia
OnePlus 2 Released July 28, 2015. Website Wikipedia
OnePlus 5T (OP5T) Smartphone from OnePlus. First released November 21, 2017. Website Wikipedia
OnePlus One Released April 23, 2014. Website Wikipedia
OnePlus X Released October 29, 2015. Website Wikipedia
Online Certificate Status Protocol (OCSP) Used to obtain the revocation status of digital certificates in public keys. Alternative to Certificate Revocation Lists (CRL) that enables clients to request and receive the electronic status of digital certificates automatically in real-time. Described in RFC 6960 June 2013. Wikipedia RFC 6960
Open Computing Language (OpenCL) Wikipedia
Open Database Connectivity (ODBC)
Open Shortest Path First (OSPF) (IGP, link-state, classless protocol) Efficient trigger updates. Fast convergence. Easily scalable. Wikipedia
Open Shortest Path First version 3 (OSPFv3) UIGP, link-state, classless protocol. uses Dijkstra's algorithm to make IPv6 routes. Very much like it's IPv4 counterpart, OSPF.
Open Systems Interconnection model (OSI model)
| layer 1 | physical |
| layer 2 | data link |
| layer 3 | network |
| layer 4 | transport |
| layer 5 | session |
| layer 6 | presentation |
| layer 7 | application |
Open Web Interface for .NET (OWIN) Standard for an interface between .NET web applications and web servers. Website Wikipedia
OpenBSD UNIX like OS based off BSD. Forked from NetBSD in 1995. Website Wikipedia
OpenPGP Most widely used email encryption standard in the world. Created by Phil Zimmermann in 1991. Website
OpenSSH An open source version of SSH typically used on Linux systems. Wikipedia Website
open|filtered Nmap port state. Nmap places ports in this state when it is unable to determine whether a port is open or filtered. This occurs for scan types in which open ports give no response. Nmap
ordered pair (x,y) Wolfram MathWorld Wikipedia
Overclock3D.net Technology discussion forum. Founded March 9, 2005. Website
OnePlus 3 Announced June 14, 2016. Website Wikipedia
open port Nmap port state that allows access to applications. An application is actively accepting TCP connections, UDP datagrams or SCTP associations on this port. Finding these is often the primary goal of port scanning. Nmap
OpenStack Open source cloud platform. Wikipedia Website YouTube
OpenVAS (Open Vulnerability Assessment System, originally known as GNessUs) Open Source vulnerability scanner and manager forked from Nessus. Functions much like a database server, performing complex queries while the client interfaces with the server to simplify reporting and configuration. Began under the name of GNessUs as a fork of Nessus October 2005. Website Wikipedia
OpenVMS First released October 25, 1977. Website Wikipedia
Opera Web browser developed by Opera Software. First released April 1995. Website Wikipedia
Operand Arguments that are effected by the operator. Wikipedia
Operating System (OS) Interface for the user that manages resources of the system. Wikipedia YouTube
Operator Function to be performed on the operand. //operator ( operand ) Wikipedia
Opteron Processor line made by AMD. First processor to support the 64-bit version of the x86 instruction set; AMD64 or x86-64. First released April 22, 2003. Wikipedia
Optical Carrier 3 (OC3) 155.52 Mbps bandwidth leased line. Wikipedia
Optical Character Recognition (OCR) Recognize text from a scanned image or document.
optical disc (OD) (disc) Formats include CD, DVD, Blu-ray, etc. Standard physical size is 12cm (4.7 inches). First recorded historical use of an optical disc was in 1884 when Alexander Graham Bell, Chichester Bell and Charles Sumner Tainter recorded sound on a glass disc using a beam of light. Wikipedia
Optical Disk Drive (ODD) (aka: optical drive) Reads and writes optical media such as DVD or Blu-Ray. Sometimes referred to by the highest media they can read. (i.e. CD drive, DVD drive, Wikipedia
Optical Mark Reader (OMR) (Scantron reader)
Optical Time Domain Reflectometer (OTDR) Tool that enables you to locate a break in fiber-optic cable. Wikipedia
option (aka: flag or switch) Special kind of argument that modifies another argument. Generaly preceded by - or -- Wikipedia
Optiplex 7020 Desktop from Dell. Website Wikipedia
Optiplex GX620 Desktop from Dell. Website Wikipedia
Organic Light Emitting Diode Display (OLED) Wikipedia
Organization for the Advancement of Structured Information Standards (OASIS) Wikipedia Website
Organizational Unit (OU) Container of objects within a domain. Wikipedia TechNet YouTube (Microsoft MCSA/MCSE Learning Channel)
Organizationally Unique Identifier (OUI) The first 3 octets of a MAC address. Wikipedia MAC Address Lookup
Orthogonal Frequency-Division Multiplexing (OFDM) Method of encoding digital data on multiple carrier frequencies. Uses a relatively slow modulation rate for symbols with high data rates. Simultaneous transmission of data over 52 data streams. Supports Supported by 802.11a, 802.11g, and 802.11n. Wikipedia
OS X Recovery Hold down "Command-R" to while the computer is starting up enter. Apple Support Macworld
OS/2 Wikipedia
Osborne 1 First commercially successful portable microcomputer. Released April 3, 1981. Wikipedia Technologizer
Osborne Computer Corporation (OCC) Founded by Adam Osborne in 1980. Wikipedia
Osborne Executive Successor to the Osborne 1. Announced in 1982. Released April 18, 1983. Wikipedia This Day in Tech History
OSPF area A group of routers that share the same link-state information in their link-state databases. Wikipedia
OSPF message types Used to discover routers and exchange routing information. Packets: Hello, DBD, LSR, LSU, LSAck. Transmitted over IP Wikipedia
OSPF network types
| Point-to-point: | Two routers connected over a common link with no other routers on that link. | ||
| Broadcast Multi-access: | Multiple routers connected over Ethernet. | ||
| NBMA: | Multiple routers connected in a network such as frame relay that does not allow broadcasts. | ||
| Point-to-multipoint: | Multiple routers interconnected in a hub-and-spoke topology over a NBMA network. (Branch sites connecting to one central cite.) | ||
| Virtual Links: | Special OSPF network used to connect distant OSPF areas to the backbone area. |
OSPF priority Can be a number 1-255. (255 is the highest and is most likely to become a DR.) The DR or BDR is chosen by the highest priority value. A priority of 0 does not become a DR/BDR.DR/BDR. Wikipedia
OSPF route calculation In an OSPF network, all routers calculate the best path to destination within their own area, then the internetwork, and then to external destination networks. Wikipedia
OSPF states
| Down state: | No Hello packets are received. | ||
| Init state: | Hello packets received. | ||
| Two-way state: | DR and BDR election. | ||
| ExStart state: | Negotiate master / slave and DBD packet sequence number. | ||
| Exchange state: | Exchange of DBD packets | ||
| Loading state: | Additional information is sent. | ||
| Full state: | Routers converged. |
Out-of-Band (OOB) Management Uses a direct connection for initial configuration through either a console or AUX cable. Requires terminal emulation software. Can also be used for general maintenance. Wikipedia Netacad
outgoing interface The exit interface used when forwarding packets to a destination network.
output Wikipedia
overhead Extra bandwidth or computational power needed on top of a task. Wikipedia