Ultimate Cisco CCNA INTRO Glossary & Acronyms
From Proprofs
You are here: Home > Schools > Cisco > CCNA Certification > Wiki Home >CCNA Wiki
[edit section] Introduction & Acknowledgements
This is a ProProfs.com community member supported glossary of terms commonly used when studying for CCNA certification exam. The glosaar was originally created by cbrzana. Thanks Cbrzana for all the hard work. The glossary is maintained by entire ProProfs community. Contributions and enhancements are most welcome!
Comments and feedback thread is also available for your valuable suggestions and comments.
| Contents |
You can help and contribute to the community by expanding or improving this article (or starting new interesting articles). Click "edit this page" to get started.
[edit section] 0-9
10BASE-T The 10-Mbps baseband Ethernet specification using two pairs of twisted pair cabling (Categories 3, 4, or 5): One pair transmits data and the other receives data. 10BASE-T, which is part of the IEEE 802.3 specification, has a distance limit of approximately 100 m (328 feet) per segment.
802.1Q The IEEE standardized protocol for VLAN trunking.
[edit section] A
AAA Authentication, Authorization, and Accounting. Authentication confirms the identity of the user or device. Authorization determines what the user or device is allowed to do. Accounting records information about access attempts, including inappropriate request.
Accounting In security, the recording of access attempts.
ADSL Asymmetric digital subscriber line. One of many DSL technologies, ADSL is
designed to deliver more bandwidth downstream (from the central office to the customer
site) than upstream.
AppleTalk DDP The AppleTalk Data Delivery Protocol (DDP) is the AppleTalk
equivalent of the IP protocol. It defines a 24-bit address, with 16 bits defining the
network and 8 bits defining the node.
ARP Address Resolution Protocol. An Internet protocol used to map an IP address to a MAC address. Defined in RFC 826.
Asynchronous The lack of an imposed time ordering on a bit stream. Practically, both sides agree to the same speed, but there is no check or adjustment of the rates if they are slightly different. However, because only 1 byte per transfer is sent, slight differences in clock speed are not an issue. A start bit is used to signal the beginning of a byte.
ATM Asynchronous Transfer Mode. The international standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixed-length (53- byte) cells. Fixed-length cells allow cell processing to occur in hardware, thereby reducing transit delays. ATM is designed to take advantage of high-speed transmission media, such as E3, SONET, and T3.
Authentication In security, the verification of the identity of a person or a process.
Authorization In security, the determination of a user or devices rights in a network.
Auxiliary port A physical connector on a router that is designed to be used to allow a remote terminal, or PC with a terminal emulator, to access a router using an analog modem.
[edit section] B
Balanced hybrid A term that refers to a third general type of routing protocol algorithm, the other two being distance vector and link state. EIGRP is the only routing protocol that Cisco classifies as using a balanced hybrid algorithm.
Boolean AND A math operation performed to a pair of one-digit binary numbers. The result is another one-digit binary number. 1 AND 1 yields 1; all other combinations yield a 0.
BRIBasic Rate Interface. An ISDN interface composed of two bearer (
channels and one data (D) channel for circuit-switched communication of voice, video, and data.
Broadcast address An IP address in each subnet is considered to be the broadcast address for that subnet. It is the highest numerical value in the range of numbers for the subnet; the broadcast address cannot be assigned as an IP address to a computer. Packets sent to this address are delivered to all hosts in the subnet.
Broadcast domain A set of all devices that receive broadcast frames originating from any device within the set. Devices in the same VLAN are in the same broadcast domain.
Broadcast subnetWhen subnetting a Class A, B, or C network, two subnet numbers are "discouraged" from use; one of those two subnets is the broadcast subnet. It is the subnet number for which the subnet bits all have a value of binary 1.
Bus A common physical signal path composed of wires or other media across which signals can be sent from one part of a computer to another. Also called a highway.
[edit section] C
CDP Cisco Discovery Protocol. A media- and protocol-independent device-discovery protocol that runs on all Cisco-manufactured equipment, including routers, access servers,bridges, and switches. Using CDP, a device can advertise its existence to other devices and receive information about other devices on the same LAN or on the remote side of a WAN. Runs on all media that support SNAP headers, including LANs, Frame Relay, and ATM media.
CHAP Challenge Handshake Authentication Protocol. A security feature supported on lines using PPP encapsulation that prevents unauthorized access. CHAP does not itself prevent unauthorized access; it merely identifies the remote end. The router or access server then determines whether that user is allowed access.
CLI Command-line interface. An interface that enables the user to interact with the operating system by entering commands and optional arguments.
Clock source The device to which the other devices on the link adjust their speed when using synchronous links.
Codec Coder-decoder. An integrated circuit device that transforms analog voice signals into a digital bit stream and then transforms digital signals back into analog voice signals.
Collision domain A set of network interface cards (NICs) for which a frame sent by one NIC could result in a collision with a frame sent by any other NIC in the same collision domain.
Configuration mode Inside the Cisco IOS Software CLI, a user can move among various modes. Configuration mode enables the user to enter configuration commands but not any EXEC commands, for instance, the user can configure an IP address, but cannot show the status of any router features.
Configuration registerIn Cisco routers, a 16-bit, user-configurable value that determines how the router functions during initialization. In software, the bit position is set by specifying a hexadecimal value using configuration commands.
Console port A component of a router or switch through which commands are entered into a host.
Convergence The time required for routers to react to changes in the network, removing bad routes and adding new, better routes so that the current best routes are in all the routers routing tables.
CPE Customer premises equipment. Any equipment related to communications that is located at the customer site, as opposed to inside the telephone company's network.
CSMA/CD Carrier sense multiple access collision detect. A media-access mechanism in which devices ready to transmit data first check the channel for a carrier. If no carrier is sensed for a specific period of time, a device can transmit. If two devices transmit at once, a collision occurs and is detected by all colliding devices. This collision subsequently delays retransmissions from those devices for some random length of time.
CSU/DSU Data service unit/channel service unit. Used on digital links as an interface to the telephone company in the United States. Routers typically use a short cable from a serial interface to a DSU/CSU, which is attached to the line from the telco with a similar configuration at the other router on the other end of the link.
[edit section] D
Demarc The demarcation or separation point between carrier equipment and CPE.
Diffusing Update Algorithm (DUAL) The process by which EIGRP routers collectively calculate the routes to place into the routing tables.
Dijkstra Shortest Path First (SPF) algorithm Magic math used by link-state protocols, such as OSPF, when the routing table is calculated.
Directed broadcast addressSame thing as broadcast address.
Distance vectorThe logic behind the behavior of some interior routing protocols, such as RIP and IGRP. 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.
DNSDomain Name System. A system used on the Internet for translating names of network nodes into addresses.
DSLDigital subscriber line. Public network technology that delivers high bandwidth over conventional copper wiring at limited distances. The most common types of DSL are ADSL, HDSL, SDSL, and VDSL. Because most DSL technologies do not use the complete bandwidth of the twisted pair, there is room remaining for a voice channel.
[edit section] E
E1Similar to a T1, but used in Europe. It uses a rate of 2.048 Mbps and 32 64-kbps channels.
Enable modeInside the Cisco IOS Software CLI, a user can move among various modes. Enable mode, also called enable EXEC mode, allows the user to use the most powerful and potentially disruptive commands on a router.
EncapsulationThe wrapping of data in a particular protocol header. For example, an IP packet could be encapsulated in an Ethernet header and trailer before being sent over an Ethernet.
Encryption Applying a specific algorithm to data to alter the appearance of the data, making it incomprehensible to those who are not authorized to see the information.
Error recoveryThe process of noticing when some transmitted data was not successfully received and resending the data until it is successfully received.
Ethernet A baseband LAN specification invented by Xerox Corporation and developed jointly by Xerox, Intel, and Digital Equipment Corporation. Ethernet networks use CSMA/CD and run over a variety of cable types.
Exterior routing protocol A routing protocol designed for use between two different organizations. These typically are used between ISPs or between a company and an ISP. For example, a company would run BGP, an exterior routing protocol, between one of its routers and a router inside an ISP.
[edit section] F
FCIP Fibre Channel over IP. A protocol for sending Fibre Channel protocols over an IP network.
Fibre Channel A technology for transmitting data between computer devices at data rates from 100 MBps to 400 MBps over optical fiber or copper. Fibre Channel is optimized for connecting servers to shared storage devices and for interconnecting storage controllers and drives.
Filter Generally, a process or a device that screens network traffic for certain characteristics, such as source address, destination address, or protocol, and determines whether to forward or discard that traffic based on the established criteria.
Firewall A device or a software package that separates more secure network components from less secure components, protecting the more secure network from inappropriate access.
Flash A type of permanent memory, implemented either with a EEPROM chip or with a PC card that can be easily removed. Routers use flash instead of disk drives for storing large files, particularly the IOS.
Flow control The process of regulating the amount of data sent by a sending computer towards a receiving computer. Several flow control mechanisms exist, including TCP flow control which uses windowing.
Forward To send a frame received in one interface out another interface, toward its ultimate destination.
Four-wire circuit A line from the telco with four wires, composed of two twisted-pair wires. Each pair is used to send in one direction, so a four-wire circuit allows full-duplex communication.
Frame Relay An industry-standard, switched data link layer protocol that handles multiple virtual circuits using LAPF encapsulation between connected devices. Frame Relay is more efficient than X.25, the protocol for which it generally is considered a replacement.
Frame A logical grouping of information sent as a data link layer unit over a transmission medium. Can also be called an L2PDU.
Full mesh A term describing a network in which devices are organized in a mesh topology, with each network node having either a physical circuit or a virtual circuit connecting it to every other network node. A full mesh provides a great deal of redundancy, but because it can be prohibitively expensive to implement, it usually is reserved for network backbones.
[edit section] G
[edit section] H
Hash A mathematical formula applied to some input value for which it is difficult to recreate the input value even if you know the results of the formula. Hashes are useful for transmission of passwords because, even if intercepted, the hashed representation of a password cannot easily be used to find the original password.
HDLC High-Level Data Link Control. A bit-oriented synchronous data link layer protocol that specifies a data encapsulation method on synchronous serial links using frame characters and checksums.
Head end The upstream, transmit end of a CATV installation.
Holddown A state into which a route is placed so that routers neither advertise the route nor accept advertisements about the route for a specific length of time (the holddown period). Holddown is used to flush bad information about a route from all routers in the network. A route typically is placed in holddown when a link in that route fails.
Host address The IP address assigned to a network card on a computer.
Host A computer system on a network. Similar to a node, except that host usually implies a computer system, whereas node generally applies to any networked system, including access servers and routers.
HTML Hypertext Markup Language. A simple hypertext document-formatting language that uses tags to indicate how a given part of a document should be interpreted by a viewing application, such as a web browser.
HTTP Hypertext Transfer Protocol. The protocol used by web browsers and web servers to transfer files, such as text and graphic files.
[edit section] I
ICMP Internet Control Message Protocol. A network layer Internet protocol that reports errors and provides other information relevant to IP packet processing. Documented in RFC 792.
IEEE 802.2 An IEEE LAN protocol that specifies an implementation of the LLC sublayer of the data link layer. IEEE 802.2 handles errors, framing, flow control, and the network layer (Layer 3) service interface. Used in IEEE 802.3 and IEEE 802.5 LANs.
IEEE 802.3 An IEEE LAN protocol that specifies an implementation of the physical layer and the MAC sublayer of the data link layer. IEEE 802.3 uses CSMA/CD access at a variety of speeds over a variety of physical media.
IEEEInstitute of Electrical and Electronics Engineers. A professional organization that develops communications and network standards, among other activities.
IGRPInterior Gateway Routing Protocol. Interior Gateway Protocol (IGP) developed by Cisco to address the issues associated with routing in large networks.
Interior routing protocol A routing protocol designed for use within a single organization. For example, an entire company might choose the IGRP routing protocol, which is an interior routing protocol.
IOS Cisco operating system software that provides common functionality, scalability, and security for all Cisco products. Cisco IOS Software allows centralized, integrated, and automated installation and management of internetworks while ensuring support for a wide variety of protocols, media, services, and platforms.
IP Internet Protocol. The network layer protocol in the TCP/IP stack offering a connectionless internetwork service.
IP address A 32-bit address assigned to hosts using TCP/IP. Each address consists of a network number, an optional subnetwork number, and a host number. The network and subnetwork numbers together are used for routing, and the host number is used to address an individual host within the network or subnetwork.
IPX Internetwork Packet Exchange. A Novell NetWare network layer (Layer 3) protocol used for transferring data from servers to workstations. IPX is similar to IP and XNS.
ISCSI IP SCSI. A protocol for sending and receiving SCSI commands over an IP network, providing file-level access to shared storage devices.
ISDN Integrated Services Digital Network. A service offered by telephone companies that permits telephone networks to carry data, voice, and other source traffic.
ISL Inter-Switch Link. The Cisco proprietary VLAN trunking protocol.
ISO International Organization for Standardization. An international organization that is responsible for a wide range of standards, including those relevant to networking. The ISO developed the OSI reference model, a popular networking reference model.
[edit section] J
[edit section] K
[edit section] L
L4PDU The data compiled by a Layer 4 protocol, including Layer 4 headers and encapsulated high-layer data, but not including lower-layer headers and trailers.
Layer 3 protocol A protocol that it has characteristics like OSI Layer 3, which defines logical addressing and routing. IP, IPX, and AppleTalk DDP are all Layer 3 protocols.
Learn The process of discovering MAC addresses, and their relative location by looking at the source MAC address of all frames received by a bridge or switch.
Link-state A type of routing protocol which sends full topology information about the network to all routers, so they all have a consistent view of the network topology and status. Link-state algorithms create a consistent view of the network and, therefore, are not prone to routing loops; however, they achieve this at the cost of relatively greater computational difficulty and more widespread traffic.
LLC Logical Link Control. The higher of the two data link layer sublayers defined by the IEEE. Synonymous with IEEE 802.2.
Local loop A line from the premises of a telephone subscriber to the telephone company .
[edit section] M
MAC Media Access Control. The lower of the two sublayers of the data link layer defined by the IEEE. Synonymous with IEEE 802.3 for Ethernet LANs.
MAC address A standardized data link layer address that is required for every device that connects to a LAN. Ethernet MAC addresses are 6 bytes long and are controlled by the IEEE. Also known as a hardware address, a MAC layer address, and a physical address.
Metric A unit of measure used by routing protocol algorithms to determine the best pathway for traffic to use to reach a particular destination.
Modem Modulator-demodulator. A device that converts digital and analog signals for the purpose of communicating over analog telephone lines. At the source, a modem converts digital signals to a form suitable for transmission over analog communication facilities. At the destination, the analog signals are returned to their digital form. Modems allow data to be transmitted over voice-grade telephone lines.
Multimode A type of fiber-optic cabling with a larger core than single-mode cabling, allowing light to enter at multiple angles. Such cabling has lower bandwidth than singlemode fiber but requires a typically cheaper light source, such as an LED.
[edit section] N
Name server A server connected to a network that resolves network names into network addresses.
Network A collection of computers, printers, routers, switches, and other devices that can communicate with each other over some transmission medium.
Network number A number that uses dotted-decimal notation like IP addresses, but the number itself represents all hosts in a single Class A, B, or C IP network.
NVRAM Nonvolatile RAM. A type of random-access memory (RAM) that retains its contents when a unit is powered off.
[edit section] O
OSI Open System Interconnection reference model. A network architectural model developed by the ISO. The model consists of seven layers, each of which specifies particular network functions, such as addressing, flow control, error control, encapsulation, and reliable message transfer. The OSI reference model is used universally as a method for teaching and understanding network functionality.
[edit section] P
Packet A logical grouping of information that includes the network layer header and encapsulated data.
PAP Password Authentication Protocol. An authentication protocol that allows Point-to-Point Protocol (PPP) peers to authenticate one another. Unlike the Challenge Handshake Authentication Protocol (CHAP), PAP passes the password and the host name or username in the clear (unencrypted).
Partial mesh A network in which devices are organized in a mesh topology, with some network nodes organized in a full mesh but others that are connected only to one or two other nodes in the network. A partial mesh does not provide the level of redundancy of a fullmesh topology but is less expensive to implement. Partial-mesh topologies generally are used in the peripheral networks that connect to a fully meshed backbone.
PCMPulse code modulation. A technique of encoding analog voice into a 64-kbps data stream by sampling with 8-bit resolution at a rate of 8000 times per second.
PDUProtocol data unit. An OSI term to refer generically to a grouping of information by a particular layer of the OSI mode. More specifically, an LxPDU would imply the data and headers as defined by Layer x.
PingPacket Internet groper. An Internet Control Message Protocol (ICMP) echo message and its reply; ping often is used in IP networks to test the reachability of a network device.
Port number A field in a TCP or UDP header that identifies the application that either sent (source port) or should receive (destination port) the data inside the data segment.
PPPPoint-to-Point Protocol. A protocol that provides router-to-router and host-tonetwork connections over synchronous and asynchronous circuits.
Prefix notation A shorter way to write a subnet mask in which the number of binary 1s in the mask is simply written in decimal. For instance, /24 denotes the subnet mask with 24 binary 1 bits in the subnet mask. The number of bits of value binary 1 in the mask is considered to be the prefix.
PRIPrimary Rate Interface. An Integrated Services Digital Network (ISDN) interface to primary rate access. Primary rate access consists of a single 64-kbps D channel plus 23 (T1) or 30 (E1) B channels for voice or data.
Protocol Type field A field in a LAN header that identifies the type of header that follows the LAN header. Includes the DIX Ethernet Type field, the IEEE 802.2 DSAP field, and the SNAP protocol Type field.
PSTNPublic Switched Telephone Network. A general term referring to the variety of telephone networks and services in place worldwide. Sometimes called POTS.
PTT Post, telephone, and telegraph. A government agency that provides telephone services. PTTs exist in most areas outside of North America and provide both local and long-distance telephone services.
[edit section] Q
[edit section] R
RAM Random-access memory. A type of volatile memory that can be read and written by a microprocessor.
RFC Request For Comments. A document used as the primary means for communicating information about the TCP/IP protocols. Some RFCs are designated by the Internet Architecture Board (IAB) as Internet standards, and others are informational. RFCs are available online from numerous sources, including www.rfc-editor.org/.
RIP Routing Information Protocol. An Interior Gateway Protocol (IGP) supplied with UNIX Berkeley Standard Distribution (BSD) systems. RIP is the most common IGP in the Internet and uses hop count as a routing metric.
RJ-45 A popular type of cabling connector used for Ethernet cabling. It is similar to the RJ-11 connector used for telephone wiring in homes in the United States. RJ-45 allows the connection of eight wires.
ROMRead-only memory. A type of nonvolatile memory that can be read but not written by the microprocessor.
Routed protocol A protocol that can be routed by a router. A router must be capable of interpreting the logical internetwork as specified by that routed protocol. Examples of routed protocols include AppleTalk, DECnet, and IP.
Routing protocol A protocol that accomplishes routing through the implementation of a specific routing algorithm. Examples of routing protocols include the Interior Gateway Routing Protocol (IGRP), the Open Shortest Path First (OSPF) protocol, and the Routing Information Protocol (RIP).
[edit section] S
Segment A term used in the TCP specification to describe a single transport layer unit of information. Can instead be called an L4PDU.
Segmentation The process of breaking a large piece of data from an application into pieces appropriate in size to be sent through the network.
Single-mode A type of fiber-optic cabling with a narrow core that allows light to enter only at a single angle. Such cabling has a higher bandwidth than multimode fiber but requires a light source with a narrow spectral width (such as a laser).
Socket A software structure operating as a communications endpoint within a network device.
SONETSynchronous Optical Network. A standard format for transporting a wide range of digital telecommunications services over optical fiber. SONET is characterized by standard line rates, optical interfaces, and signal formats. SONET is a high-speed (up to 2.5 Gbps) synchronous network specification developed by Bellcore and designed to run on optical fiber. STS-1 is the basic building block of SONET. It was approved as an international standard in 1988.
Star A method of connecting devices in which endpoints on a network are connected to a common central switch by point-to-point links.
Storage router A device that sits between an IP network and storage devices, translating between disk IO protocols as they pass through non-IP and IP networks.
STP Shielded twisted pair. A two-pair wiring medium used in a variety of network implementations. Shielded twisted-pair cabling has a layer of shielded insulation to reduce electromagnetic interference (EMI). Can also refer to Spanning Tree Protocol, which is used to prevent bridging/switching loops.
Subnet broadcast address Same thing as broadcast address.
Subnet mask A 32-bit address mask used indicate the bits of an IP address that are being used for the subnet part of the address. Sometimes referred to simply as the mask.
Subnet Subnets are subdivisions of a Class A, B, or C network, as configured by a network administrator. Subnets allow a single Class A, B, or C network to be used instead of multiple networks, and still allow for a large number of groups of IP addresses, as is required for efficient IP routing.
Subnetting The process of subdividing a Class A, B, or C network and into smaller portions called subnets.
Switch A network device that filters, forwards, and floods frames based on the destination address of each frame. The switch operates at the data link layer of the Open System Interconnections (OSI) reference model.
Synchronous The imposition of time ordering on a bit stream. Practically, a device will try to use the same speed as another device on the other end of a serial link. However, by examining transitions between voltage states on the link, the device can notice slight variations in the speed on each end and can adjust its speed accordingly.
[edit section] T
T1 A line from the telco that allows transmission of data at 1.544 Mbps.
TCP Transmission Control Protocol. A connection-oriented transport layer TCP/IP protocol that provides reliable data transmission.
TCP/IP Transmission Control Protocol/Internet Protocol. A common name for the suite of protocols developed by the U.S. Department of Defense in the 1970s to support the construction of worldwide internetworks. TCP and IP are the two best-known protocols in the suite.
Telco A common abbreviation for telephone company.
Telnet The standard terminal emulation protocol in the TCP/IP protocol stack. Telnet is used for remote terminal connection, enabling users to log in to remote systems and use resources as if they were connected to a local system. Telnet is defined in RFC 854.
Trace Short for traceroute. A program available on many systems that traces the path that a packet takes to a destination. It is used mostly to debug routing problems between hosts. A traceroute protocol also is defined in RFC 1393.
Transparent bridge A device that forwards frames between LAN segments based on the destination MAC address. Transparent bridging is so named because the presence of bridges is transparent to network end nodes.
Trunking Also called VLAN trunking. A method (using either Cisco's ISL protocol or the IEEE 802.1q protocol) to support multiple VLANs that have members on more than one switch.
Twisted pair Transmission medium consisting of two insulated wires arranged in a regular spiral pattern. The wires can be shielded or unshielded. Twisted pair is common in telephony applications and in data networks.
[edit section] U
UDP User Datagram Protocol. Connectionless transport layer protocol in the TCP/IP protocol stack. UDP is a simple protocol that exchanges datagrams without acknowledgments or guaranteed delivery.
Update timer A timer used by a router to indicate when to send the next routing update.
User mode A mode of the user interface to a router or switch in which the user can type only nondisruptive EXEC commands, generally just to look at the current status, but not to change any operational settings.
UTP Unshielded twisted pair. A four-pair wire medium used in a variety of networks. UTP does not require the fixed spacing between connections that is necessary with coaxial-type connections. Five types of UTP cabling are commonly used: Category 1 through Category 5 cabling.
[edit section] V
VLAN A group of devices on one or more LANs that are configured (using management software) so that they can communicate as if they were attached to the same wire, when, in fact, they are located on a number of different LAN segments. Because VLANs are based on logical instead of physical connections, they are extremely flexible.
VoIP Voice over IP. The capability to carry voice over an IP-based Internet. VoIP enables a router to carry voice traffic (for example, telephone calls and faxes) over an IP network.
[edit section] W
Well-known port A port number reserved for use by a particular application. The use of well-known ports allows a client to send a TCP or UDP segment to a server, to the correct destination port for that application.
Windowing The term window represents the number of bytes that can be sent without receiving an acknowledgment. Windowing is the dynamic raising and lowering of the window to control the flow of data in a network.
WWW World Wide Web. A large client/server network of Internet servers providing hypertext and other services (based on HTML and HTTP) to terminals running client applications, such as a browser.
[edit section] X
[edit section] Y
[edit section] Z
Zero subnet When subnetting a Class A, B, or C network, two subnet numbers are "discouraged" from use; the zero subnet is one of these two subnets. It is the subnet number for which the subnet bits all have a value of binary 0.
Top 5 Contributors to this article
|
|||||
