Glossary


Area Border Router ( ABR )

The router running an OSPF protocol and placed on the border of one or more OSPF areas. An ABR connects the OSPF areas to the OSPF backbone.



Access layer

In the Campus Hierarchical model , the Access layer is where the workstation connects to the network. Hubs and switches reside here, and it's also where workgroups access the network.



access list

A security feature used with the Cisco IOS to filter traffic types as part of data routing. Access lists are also used to filter traffic between different VLAN numbers .



active monitor

Active monitor is used in Token Ring and refers to the node on a Token Ring network that is responsible for management tasks , such as preventing loops and monitoring the token's activities. A network can have multiple active monitors .



address

A set of numbers, usually expressed in binary format, that are used to identify and locate a resource or device on a network.



address filter

A way of using Layer 2 MAC addresses or switching ports to filter traffic. This process allows you to filter traffic and restrict access without the use of VLANs, and is a feature of the Cisco Catalyst 3000 Series. Although it uses a process similar to access lists on the Cisco IOS, you can apply multiple address filters to the same interface.



Address Resolution Protocol ( ARP )

The protocol that is used to map an IP address to a MAC address. Described at the Internet layer of the DoD model, ARP is used to find a hardware address, given the IP address.



administrative distance

This distance is defined with a number from 0 to 225 that represents the integrity of a routing information source. This term usually refers to a particular protocol. The lower the number, the more trustworthy it is.



American National Standards Institute ( ANSI )

The organization that publishes standards for communications, programming languages, and networking.



ANDing

The process of comparing the bits of an IP address with the bits in a subnet mask to determine how a packet will be handled.



anycast address

An address used in ATM for shared multiple-end systems. An anycast address allows a frame to be sent to specific groups of hosts .



AppleTalk

A group of protocols used in Macintosh computer environments. These protocols allow a network ”or more than one network ”to operate in more than one zone.



Application layer

The layer of the OSI model that provides support for end users and for application programs using network resources.



area

Usually used in CLNS, DECnet, or OSPF networks, an area is a logical set of segments and devices that are defined as a particular group. Routers use areas to distinguish a defined group to create a single autonomous system (AS).



Asymmetric Digital Subscriber Line ( ADSL )

A service that transmits digital voice and data over existing analog phone lines.



Asynchronous Transfer Mode ( ATM )

ATM is an international standard used in high-speed transmission media such as E3, SONET, and T3 for cell relay that is common in today's corporate networks. ATM guarantees throughput, minimizes delay, and can provide scalability at speeds up to many gigabits per second.



attachment unit interface ( AUI )

IEEE 802.3 specification used between a multistation access unit (MAU) and an Ethernet network interface card (NIC). MAUs are typically associated with Token Ring networks; AUI ports are specific to Ethernet. This cable connects an AUI port on the Ethernet access card to an Ethernet 10Base2, 10Base5, or 10BaseFx transceiver.



attachment unit interface ( AUI ) connector

A 15-pin, D-type connector that is sometimes used with Ethernet connections.



attenuation

The loss of signal that is experienced as data is transmitted across network media.



autonegotiation

Allows a hub or switch and a network device to communicate their compatibilities and agree upon an optimal communication speed and/or duplex.



autonomous switching

A switching mechanism that allows Cisco routers to process packets faster by using the Ciscobus ”and not the system processor ”to switch packets.



autonomous system ( AS )

A group of networks (defined by routers) that are running the same routing protocol. Autonomous systems are subdivided by areas and must be assigned a 16-bit number to identify the area.



backbone

A high-capacity infrastructure system that provides optimal transport on a LAN. In a LAN, the data running from router to router, switch to switch, or switch to router is typically transported through a faster physical topology than the rest of the local area or virtual LAN devices. The backbone is the physical cable.



BackboneFast

A protocol used on a switch. When initiated, a root port or blocked port receives an inferior BPDU from its designated bridge, the MaxAge timer is bypassed, and the secondary or backup port immediately changes to the forwarding mode.



backplane

The primary data/control bus located on a Cisco Catalyst switch, and similar to the motherboard in a PC. The Backplane interconnects all the modules inside the switch chassis.



bandwidth

The rated throughput capacity of a given network protocol or medium.



base bandwidth

The difference between the lowest and highest frequencies that are available for network signals. The term is also used to describe the rated throughput capacity of a given network protocol or medium.



Basic Rate Interface ( BRI )

An ISDN digital communications line that consists of three independent channels: two bearer (or B) channels, each at 64Kbps; and one data (or D) channel at 16Kbps. ISDN BRI is often referred to as 2B+D .



baseline

Refers to a network's average performance that is established using the networks historical data and routine network utilizations . A network baseline allows for accurate monitoring and measurement, and serves as an effective guide to determine network changes or faults.



binary

The base 2 numbering system, characterized by its use of ones and zeros and used in digital signaling.



binding

The process of associating a protocol and a network interface card (NIC).



bit

An electronic digit used in the binary numbering system.



blocking architecture

A condition in which the total bandwidth of the ports is greater than the capacity of the switching fabric.



bridge

A device that connects and passes packets between two network segments that use the same communications protocol. Bridges operate at the Data Link layer of the OSI reference model to filter, forward, or flood an incoming frame based on the MAC address of that frame.



Bridge Protocol Data Unit ( BPDU )

A multicast frame that is generated by the switch and carries information about itself and changes in the network topology.



bridging address table

A list of MAC addresses kept by bridges and used when packets are received to determine which segment the destination address is on, before sending the packet to the next interface or dropping the packet if it is on the same segment as the sending node.



broadband

A communications strategy that uses analog signaling over multiple communications channels.



broadcast

A packet delivery system in which a copy of a packet is given to all hosts attached to the network.



broadcast domain

In a nonswitched network, all the devices that can receive a broadcast sent on the physical wire from one machine in the network. The broadcast domain is a segment that's not separated by a Layer 2 device or Layer 3 device that can filter broadcasts. On a switched network using VLANs, the broadcast domain is all the ports or collision domains that belong to the same VLAN.



broadcast storm

Occurs when broadcasts throughout the LAN become so numerous that they consume all the available bandwidth on a LAN, slowing the network to a halt.



buffer

A storage area to receive/store data while it is waiting to be processed . Buffers are mainly used by devices that receive and store data from faster processing devices, and allow the device to process the data as fast as the processing speeds allow.



bus

A path used by electrical signals to travel between the CPU and the attached hardware.



bus topology

A linear LAN architecture that uses a common cable with multipoint connections for the flow of data in a serial progression to all nodes on that network segment.



byte

A set of bits (usually eight) that operates as a unit to signify a single character.



campus

A group of buildings in a fixed geographical location, owned and controlled by an organization.



carrier access module ( CAM )

A module attaching to the ATM cell switching bus. A CAM can support two port-adapter modules to provide physical ATM line ports used by end nodes. A CAM can be placed in the Cisco Catalyst 5500 in slot 9, 10, 11, or 12; it can be placed in the LS1010 in slot 0, 1, 3, or 4.



Carrier Sense Multiple Access with Collision Avoidance ( CSMA/CA )

A media-access method comprised of collision-avoidance techniques used in Ethernet.



Carrier Sense Multiple Access with Collision Detection ( CSMA/CD )

A media-access method involving collision detection that listens to the network to see if it is in use. If the network is clear, data is transmitted. If a collision occurs, both stations retransmit their data.



Challenge Handshake Authentication Protocol ( CHAP )

Protocol used with PPP encapsulation as a security feature that identifies the remote end. After performing CHAP, the router determines whether the user is permitted access.



change control

A detailed record that documents every change made to the network.



channel

A communications path used for data transmission.



channelized T-1

A link that is separated into 23 B channels and one D channel of 64Kbps each, with the link operating at 1.544Mbps. This link can support DDR, frame relay, and X.25.



channel service unit ( CSU )

A network communications device used to connect to the digital equipment lines of the common carrier, usually over a dedicated line or Frame Relay. Used in conjunction with a data service unit (DSU) .



checksum

A mathematical method that uses a recalculation method to compare the data sent and received to determine whether the destination is receiving the correct amount of data from the source.



Cisco Connection Online ( CCO )

Cisco's Web site that offers device documentation and technical support. It also features new technology and the recent upgrades of device codes.



Cisco Discovery Protocol ( CDP )

A Cisco protocol that gathers and stores information regarding other neighboring devices on the network. It can be used in Ethernet, Token Ring, Serial, and FDDI media types. All Cisco devices including hubs support CDP.



Cisco Express Forwarding ( CEF )

Cisco's newest ASIC, which utilizes the Forwarding Information Base and an adjacency table to route Layer 2 and Layer 3 addresses with very high performance.



Cisco Group Management Protocol ( CGMP )

A Cisco protocol used by the Catalyst switch to forward multicast frames intelligently. CGMP dynamically discovers user stations participating in multicast applications and, when receiving a multicast, forwards the multicast directly to the users instead of broadcasting it throughout the network.



Class A network

A TCP/IP network that uses addresses starting between 1 and 126; IPv4 supports up to 126 Class Anetworks with 16,777,214 unique hosts each.



Class B network

A TCP/IP network that uses addresses starting between 128 and 191; IPv4 supports up to 16,384 Class B networks with 65,534 unique hosts each.



Class C network

A TCP/IP network that uses addresses starting between 192 and 223; IPv4 supports up to 2,097,152 Class C networks with 254 unique hosts each.



Class D network

A TCP/IP network that uses addresses starting between 224.0.0.0 and 239.255.255.255. Typically reserved for experimental uses and not found in production networks.



Class E network

A TCP/IP network that uses addresses starting between 240 and 254. Typically reserved for experimental uses and not found in production networks.



classless interdomain routing ( CIDR )

A technique that allows multiple addresses to be consolidated into a single entry.



Clear Header

A field (part of the 802.10 header) that copies the encrypted Protected Header for security purposes to help guarantee against tampering with the frame. Also known as the Secure Data Exchange (SDE) Protocol Data Unit .



client

A node that requests a service from another node on a network.



client/server networking

Networking architecture utilizing front-end demand nodes that request and process data stored by the back end or resource node.



collision

The result of two frames transmitting simultaneously . When these two frames collide in an Ethernet network, both frames are destroyed .



collision domain

All the interfaces on a single segment that can send data on the same physical wire. In a hub, all the interfaces that are connected to its ports are in their own collision domain. In the case of a switch, all the nodes connected to each individual port are in their own collision domain.



color blocking logic ( CBL )

A feature of the SAMBA ASIC used to enable the EARL to make forwarding decisions. It also ensures that a tagged frame coming from a particular VLAN does not exit through a port that belongs to another VLAN. CBL also assists in placing ports in one of four different modes for the Spanning Tree Protocol: blocking, learning, listening, or forwarding.



Command-Line Interface ( CLI )

Software on Cisco devices that allows you to use commands to configure and control the devices.



communication

The transfer of information among nodes on a network.



congestion

A large amount of traffic that exceeds the network's capability to process traffic in a timely manner.



connection-oriented communication

Packet transfer in which the delivery is guaranteed .



connectionless-oriented communication

Packet transfer in which the delivery is not guaranteed.



connectivity

The linking of nodes on a network so communication can take place.



Content Addressable Memory ( CAM )

A table used by a bridge to make forwarding and filtering decisions. The CAM table contains MAC addresses with port addresses leading to the physical interfaces. The CAM table uses a specialized interface that is faster than RAM to make the forwarding and filtering decisions. The CAM table updates information by examining the frames it receives from a segment and then updating the table with the source MAC address from the frame.



control plane

Functions that dictate how data actually flows through the switch fabric.



convergence

The amount of time it takes for all routers on the network to update their routing tables.



Copper Distributed Data Interface ( CDDI )

The implementation of the FDDI standard using electrical cable rather than optical cable.



core block

The end point for networks, requiring fast access and no policy implementation.



Core layer

In the Cisco hierarchical model, the backbone of the network, designed for high-speed data transmission.



cost

The number of hop counts it takes a transmission to reach a destination via a certain path. Routing protocols use cost to determine paths, with the premise being that the lower the cost, the better the path.



crosstalk

Electronic interference caused when two wires are too close to each other.



cut-through packet switching

A switching method that does not copy the entire packet into the switch buffers. Instead, the destination address is placed in buffers, the route to the destination node is determined, and the packet is quickly sent out the corresponding port. The switch begins forwarding the frame as soon as the first 13 bytes and MAC address are received. It relies on the receiving device to discard the frame if there is corruption. Cut-through packet switching maintains a low latency.



cyclic redundancy check ( CRC )

A method used to check for errors in packets that have been transferred across a network. A computation bit is added to the packet and recalculated at the destination to determine if the entire packet contents have been transferred correctly.



D channel

The D channel is a 16Kbps (BRI) or 64Kbps (PRI) ISDN channel.



DAC

A device connected to the FDDI counter-rotating rings. The DAC serves as a hub to provide passive connections to the rings for peripheral devices.



data communications equipment ( DCE )

The physical connection to the network that provides a link between a DTE and a DCE device. DCE is also used in a lab environment with DTE to simulate a WAN environment. Also defined as d ata circuit-terminating equipment .



data field

The field or section in a frame that contains the data.



data plane

Functions applied directly against the actual data being directed in and out of the switching fabric.



Data-Link Connection Identifier ( DLCI )

The identifier of virtual circuits used in Frame Relay networks.



Data Link layer

This is Layer 2 of the OSI reference model. The Data Link layer is above the Physical layer. Data comes off the cable, through the Physical layer, and into the Data Link layer.



data service unit ( DSU )

Formats and controls data for transmission over digital lines. Used in conjunction with a channel service unit (CSU) .



data terminal equipment ( DTE )

A physical device at the user end of a user-network interface. These devices serve as a data source, a destination, or both, and include computers, protocol translators, and multiplexers. A DTE combined with a DCE also simulates a WAN environment used in a lab.



datagram

Information groupings that are transmitted as a unit at the Network layer.



debug

A CLI command that allows for detailed information or a snapshot of certain interfaces or links. This command is used in troubleshooting a problem, not for monitoring.



dedicated line

A constant connection between two points, generally used in WANs.



default gateway

Normally, a router or a multihomed computer to which packets are sent when they are destined for a host that is not on their segment of the network.



demand node

Any end user or interface that requests and accesses network resources, such as servers or printers.



demarc

An established point between the carrier equipment and the customer premise equipment (CPE).



designated bridge

A segment forwarding a frame to the root bridge with the lowest cost.



designated root bridge

The MAC address of the root bridge.



designated root cost

The cost of the shortest path to the root bridge.



designated root port

The port that is chosen as the lowest cost to the root bridge. Routing and bridging protocols use cost to determine paths, with the premise being that the lower the cost, the better the path.



designated root priority

The priority of the root bridge. All bridges have a default priority of 32,768.



destination address

The network address where the frame is being sent. In a packet, this address is encapsulated in a field of the packet so that all nodes know where the frame is being sent.



Destination Service Access Point ( DSAP )

A one-byte field in the frame that combines with the service access point (SAP) to inform the receiving host of the identity of the destination host.



dial-up line

A circuit that is established by a switched-circuit connection from the telephone company network.



dialed number identification service

The method for delivery of automatic number identification using out-of- band signaling.



diameter

A unit of measurement between the root switch and child switches, calculated from the root bridge. The root bridge counts as the first switch, and each subsequent child switch out from the root bridge is added to produce the diameter number.



dial-up networking

The connection of a remote node to a network using POTS or PSTN .



digital subscriber line ( DSL )

A public network technology that delivers high bandwidth over conventional copper wiring at limited distances.



distance-vector algorithm

An algorithm for finding the shortest path to a destination. The algorithm requires each router to update its neighbors about given hop routes.



distributed switching

An implementation in which switching decisions are made at either the local port or the line module.



Distribution layer

In the Cisco hierarchical model, this layer functions as the separation point between the Core and Access layers of the network. The devices in the Distribution layer implement the policies that define how packets are to be distributed to the groups within the network.



domain

A logical grouping of interfaces in a network or intranet to identify a controlled network of nodes that are grouped as an administrative unit.



domain name system ( DNS )

Used to identify host names that correspond to IP addresses.



dual attached stations ( DAS )

A connection that allows a device to connect to both FDDI counter-rotating rings.



dual- homed

An FDDI end station attached to two DACs for redundancy.



Dynamic Host Configuration Protocol ( DHCP )

A protocol that provides an IP address to requesting nodes on the network.



Dynamic ISL

A protocol that performs trunking negotiation and verifies that the two connected ports can become trunk links. A Dynamic ISL port can be configured in one of four modes: On, Off, Desirable, or Auto.



dynamic VLAN port

A VLAN number assigned to a certain MAC address. The node attaching to any dynamic port on the switch is a member of the VLAN assigned to the MAC address. Dynamically assigned VLANs are configured with CiscoWorks 2000 or CiscoWorks for Switched Internetworks software.



dynamic window

A mechanism that prevents the sender of data from overwhelming the receiver. The amount of data that can be buffered in a dynamic window can vary.

See also [flow control]


electromagnetic interference ( EMI )

External interference from electromagnetic signals, causing reduction of data integrity and increased error rates in a transmission medium.



Electronics Industries Association ( EIA )

The group that specifies electrical transmission standards.

See also [Telecommunications Industry Association]


emulated LAN ( ELAN )

A feature used by ATM LANE to perform the basic functionality of a VLAN in Token Ring or Ethernet environments. Like VLANs, ELANs require a route processor such as a router to route frames between ELANs.



encapsulation

A technique used by layered protocols in which a layer adds header information to the protocol data unit (PDU) from the layer above.



Encoded Address Recognition Logic ( EARL ) ASIC

An ASIC located on the Catalyst 5000 family of switches that sees all the frames that cross the bus and performs a task similar to that of the content addressable memory (CAM). The ASIC is responsible for making switching decisions based on the MAC address and the source VLAN. It's also responsible for updating the address table.



encryption

The modification of data for security purposes prior to transmission, so that it is not readable without the proper decoding method.



end-to-end VLAN

A VLAN in which users (or groups of users) who utilize a common set of security requirements are grouped independently of the physical location. The port becomes a member of the VLAN assigned to the user, or MAC address of the user's machine. This type of VLAN is beneficial for networks whose resource nodes are not centralized in one common area. Users moving around the campus network remain in the same VLAN.



Enhanced Interior Gateway Routing Protocol ( EIGRP )

A Cisco protocol containing link-state and distance-vector protocols to create a more efficient routing protocol.



Enterprise Services

Services that involve crossing the backbone to achieve access. These services are typically located on a subnet that is separate from the rest of the network devices.



EtherChannel

A connection used on the Catalyst 3000 family or Kalpana switches. It can utilize half- or full-duplex links and allows as many as seven Ethernet links to be bundled and load-balanced frame by frame to provide up to 140Mps of bandwidth.



ethernet interface processor ( EIP )

An interface processor card found in the Cisco 7000 supporting Ethernet, via 10Mbps AUI ports, allowing a path to other interfaces.



extended IP access list

An access list that allows the extended filtering of packets based on address, protocol, traffic, or port.



extended ping

This option is available in the Privileged Mode of a router, allowing a defined number of ICMP requests sent to a destination.



Fast EtherChannel

A connection used on the Catalyst 5000 family of switches that allows as many as seven Ethernet links to be bundled and load-balanced frame by frame to provide up to 800Mbps of bandwidth.



Fast Ethernet

The IEEE 802.3 specification allowing for data transfers of up to 100Mbps. See also 100BaseT .



fault tolerance

A theoretical concept defined as a resistance to failure. It is not an absolute and can be defined only in degrees.



fiber (or fibre) channel

A technology that defines full gigabit-per-second (Gps) data transfer over fiber- optic cable.



Fiber Distributed Data Interface ( FDDI )

A high-speed, data-transfer technology that is designed to extend the capabilities of existing LANs using a dual rotating-ring technology similar to Token Ring.



File Transfer Protocol ( FTP )

The set of standards or protocols that allows you to transfer complete files between different computer hosts.



firewall

A device or group of devices configured with access lists and other mechanisms to stop unwanted traffic from entering a specific portion of a network.



flash memory

A type of memory that holds its contents (usually the operating system) when the power is cycled off.



flow control

A method used to control the amount of data that is transmitted within a given period of time. There are different types of flow control.

See also [dynamic window]
See also [static window]


Forwarding Engine ( FE )

A major component of ASIC; part of the ClearChannel architecture on the Cisco Catalyst Series 1900 and 2820 switches. FE is responsible for learning addresses, allocating buffer space in the shared memory space, frame queuing, forwarding decisions, and maintaining statistics.



Forwarding Information Based Switching ( FIB )

Similar to a routing table or information base, FIB is a mirror image of the routing information contained in the IP routing table. It updates this information and recalculates the next-hop information whenever the network's routing or topology changes. FIB, used with CEF ASIC , maintains a list of all known routes and eliminates the need for the route cache maintenance that is associated with fast switching or optimum switching.



fragment-free switching

A fast packet-switching method that reads the first 64 bytes of the frame to determine whether the frame is corrupted. If this first part is intact, the frame is forwarded. Also known as runtless switching .



frame

The grouping of information that is transmitted as a unit across the network at the Data Link layer.



Frame Check Sequence

This field performs a cyclic redundancy check (CRC) to ensure that all of the frame's data arrives intact.



frame filtering

This process uses a filtering table to drop frames based on a certain value contained in any one of the many fields in the data frame, such as the source or destination address. As part of normal operations, switches share filter tables. The frame's contents are compared to the filter table in the switch, thereby increasing the latency of the switch. Although frame filtering is useful for VLANs, it is not used in the Cisco Catalyst 5000 or 6000 family of switches to implement VLANs.



Frame Length

In a data frame, this field specifies the length of a frame. The maximum length for an 802.3 frame is 1,518 bytes.



Frame Relay

A switching protocol on the Data Link layer that is used across multiple virtual circuits of a common carrier, giving the user the appearance of a dedicated line.



frame tagging

A VLAN implementation method used to add VLAN information to data frames. A frame is tagged with VLAN information when it enters the switch, and the frame retains this information through the switch fabric. The tagging is removed before the frame exits the switch port with the attached destination interface. The entire process is transparent to the sending and receiving interfaces.



Frame Type

In a data frame, this field names the protocol that is being sent in the frame.



full duplex

Transmission method in which the sending and receiving (Rx and Tx) channels are separate, thus preventing collisions. Data is transmitted in two directions simultaneously on separate physical wires.



gateway

A hardware and software solution that enables communication between two dissimilar networking systems or protocols. Gateways usually operate at the upper layers of the OSI protocol stack, above the Transport layer.



Get Nearest Server ( GNS )

Used on an IPX network, NetWare-enabled devices send a request packet to locate the nearest active server of a given type. GNS is part of IPX and SAP.



gigabit ( Gb )

One billion bits or one thousand megabits.



Gigabit Ethernet

The IEEE specification for transfer rates up to one gigabit per second. See also 1000BaseX .



half duplex

A circuit designed for data transmission in both directions, but not simultaneously.



head-of-line blocking

A situation in which congestion on an outbound port limits throughput to uncongested ports. Head-of-line blocking is completely different from oversubscription , in that physical data from another source device blocks the data of the sending device.



high-level data link compression ( HDLC )

A Layer 2 serial encapsulation method that is used by PPP to transfer data over serial point-to-point links. HDLC is a bit-oriented protocol that uses frames and checksums to transfer the data.



hop

A recorded movement between two network nodes.



host

Any system on a network. In the Unix world, any device that is assigned an IP address.



host ID

A unique identifier for a client or resource on a network.



hostname

The NetBIOS name of the computer or node, given to the first element of the Internet domain name. It must be unique on your network.



Hot Standby Routing Protocol ( HSRP )

A Cisco protocol that provides redundancy. Should a link fail, another can be configured to take its place.



hub

A hardware device that connects multiple independent nodes. Also known as a concentrator or multiport repeater .



Hypertext Transfer Protocol ( HTTP )

The protocol used by Web browsers to transfer pages and files from a remote node to your computer.



input/output ( I/O )

Any operation in which data either enters a node or is sent out of a node.



Institute of Electrical and Electronics Engineers ( IEEE )

A professional organization that develops standards for networking and communications.



Integrated Local Management Interface ( ILMI )

A protocol created by the ATM forum to allow any ATM switch and ATM device to communicate using the Simple Network Management Protocol (SNMP).



Integrated Services Digital Network ( ISDN )

An internationally adopted standard for end-to-end digital communications over Public Switched Telephone Network (PSTN) that permits telephone networks to carry data, voice, and other source traffic.



intelligent hubs

Hubs that contain some management or monitoring capability.



Interior Gateway Routing Protocol ( IGRP )

A Cisco protocol using a distance-vector algorithm to calculate the best path using the factors of load, bandwidth, delay, the MTU, and reliability.



internal IPX address

A unique eight-digit number that is used to identify a server. This address is usually generated at random when the server is installed.



internal loopback address

Used for testing with TCP/IP. This address ”127.0.0.1 ”allows a test packet to reflect back into the sending adapter to determine whether it is functioning properly.



International Organization for Standardization ( ISO )

A volunteer organization, founded in 1946, which is responsible for creating international standards in many areas, including communications and computers.



Internet Control Message Protocol ( ICMP )

The Network-layer Internet protocol, documented in RFC 792, that reports errors and provides other information relevant to IP packet processing.



Internet Engineering Task Force ( IETF )

A group of research volunteers responsible for specifying the protocols used on the Internet and for specifying the architecture of the Internet.



Internet Group Management Protocol ( IGMP )

The protocol responsible for managing and reporting IP multicast group memberships.



Internet layer

In the TCP/IP architectural model, this layer is responsible for the addressing, packaging, and routing functions. Protocols operating at this layer of the model are responsible for encapsulating packets into Internet datagrams. All necessary routing algorithms are run here.



Internet Protocol ( IP )

The Network-layer protocol, documented in RFC 791, that offers a connectionless internetwork service. IP provides features for addressing, packet fragmentation and reassembly, type-of-service specification, and security.



Internet Research Task Force ( IRTF )

The research arm of the Internet Architecture Board . This group performs research in areas of Internet protocols, applications, architecture, and technology.



internetwork

A group of networks that are connected by routers or other connectivity devices so that the networks function as one network.



Internetwork Operating System ( IOS )

Cisco's proprietary operating system used in its routers and switches.



Internetwork Packet Exchange ( IPX )

The Network-layer protocol generally used by Novell's NetWare network operating system. IPX provides connectionless communication, supporting packet up to 64K in size.



Internetwork Packet Exchange/Sequenced Packet Exchange ( IPX/SPX )

This protocol is the default used in NetWare networks, and it is a combination of the IPX protocol (to provide addressing) and SPX (to provide guaranteed delivery for IPX). It's similar in nature to its counterpart , TCP/IP.



Inter-Switch Link ( ISL )

A special Cisco proprietary Ethernet protocol that assigns a 26-byte header to an encapsulated frame and a four-byte checksum, sometimes referred to as the FCS or the CRC .



IPCONFIG

A Windows command that displays IP information for all interfaces on the local host. This includes IP addresses, subnet masks, DNS servers, DHCP information, and some NetBIOS information.



IPSec

A protocol designed for virtual private networks (VPNs). Used to provide strong security standards for encryption and authentication.



IPX address

The unique address that identifies a node in the network.



LAN Emulation ( LANE )

A standard created by the ATM forum to govern the connections of ATM endstations to either Ethernet or Token Ring devices.



LAN Module ASIC ( LMA )

An ASIC part of the Cisco Catalyst 3000 Series switch that provides frame buffering, address learning, bus arbitration, and switching decisions for Ethernet ports.



latency

The time used to forward a packet in and out of a device. Commonly used in reference to routing and switching.



Layer 2 Forwarding Protocol ( L2F )

A dial-up VPN protocol designed to work in conjunction with PPP to support authentication standards, such as TACACS+ and RADIUS, for secure transmissions over the Internet.



Layer 2 Tunneling Protocol ( L2TP )

A dial-up VPN protocol that defines its own tunneling protocol and works with the advanced security methods of IPSec. L2TP allows PPP sessions to be tunneled across an arbitrary medium to a home gateway at an ISP or corporation.



learning bridge

A bridge that builds its own bridging address table rather than requiring you to enter information manually. Also known as a smart bridge .



line module communication processor ( LCP )

Located on each line module, the LCP is responsible for providing communications for the MCP located on the supervisor engine.



Link Accessed Procedure Balanced ( LAPB )

This is a bit-oriented, Data Link layer protocol for the X.25 protocol stack. It is a derivative of HDLC.



Link Access Procedure on the D Channel ( LAPD )

A Data Link layer protocol for ISDN that is used specifically for the D channel on ISDN. LAPD was created from LAPB for signaling requirements of ISDN.



link-state routing algorithm

An algorithm that waits for each router to broadcast its location and the cost of reaching the router and its neighbors.



local-area network ( LAN )

A group of connected computers that are located in a geographic area ”usually a building or campus ”and that share data and services.



local target logic ( LTL )

A feature of some line modules that assists the EARL in making forwarding decisions.



local VLAN

Beneficial for networks whose resources are centralized and in one geographical location. The VLAN can span one switch or many switches within the same floor or building.



logical addressing scheme

The addressing method used in providing manually assigned node addressing.



Logical Link Control ( LLC )

A sublayer of the Data Link layer of the OSI reference model that provides an interface for the Network-layer protocols and the Media Access Control (MAC) sublayer, which is also part of the Data Link layer.



loop

A continuous circle through a series of nodes in a network that a packet travels until it eventually times out. Without a protocol such as STP to detect loops, the data could continuously circle the network if no life cycle is assigned to the packet.



loopback plug

A device used for loopback testing.



loopback testing

A troubleshooting method in which the output and input wires are crossed or shorted in a manner that allows all outgoing data to be routed back into the card.



management

Fault, capacity, accounting, performance, and security control for a network.



Management Information Base ( MIB )

An MIB is a database of managed objects running on a device which gathers information from the device and sends it to a central location using SNMP management software.



master communication processor ( MCP )

A feature of the supervisor engine that takes commands from the network management processor (NCP) and forwards them to the correct line module communication processor (LCP). MCP is also responsible for testing, configuring, and controlling the local ports using LTL and CBL, and performing diagnostics on the memory, SAINT ASICs, LTL, and CBL. MCP is also responsible for downloading software to the line modules.



Media Access Control ( MAC ) address

A six-octet number that uniquely identifies a host on a network. It is a unique number that is burned into the network interface card, so it cannot be changed.



Media Access Control ( MAC ) layer

In the OSI model, the lower of the two sublayers of the Data Link layer. Defined by the IEEE as responsible for interaction with the Physical layer.



media access unit ( MAU )

The IEEE 802.3 specification that refers to a transceiver. Not to be confused with a Token Ring MAU (multistation access unit), which is sometimes abbreviated MSAU .



megabit ( Mb or Mbit )

One million bits. This term is used to rate transmission transfer speeds (not to be confused with megabyte ).



megabyte ( MB )

One million bytes. This term is usually used to refer to file size.



multicast

A single-packet transmission from one sender to a specific group of destination nodes.



multilayer switches

A switch with the ability to perform Layer 1, 2, and 3 switching and routing decisions. Newer switches can perform at layer 4 and 5.



multiprocessor

A single machine capable of supporting multiple processors.



multistation access unit ( MAU or MSAU )

A concentrator or hub used in a Token Ring network. It organizes the connected nodes into an internal ring and uses the RI (ring in) and RO (ring out) connectors to expand to other MAUs on the network.



netflow switching

A feature incorporated into the MSM, NFFC, and NFFC II that allows for transparent switching in hardware while incorporating Quality of Service (QoS) features, including security, multicast forwarding, multilayer switching, NetFlow data exporting, and packet filtering at Layer 3 and Layer 4 application ports.



NetWare Core Protocol ( NCP )

The NetWare protocol that provides a method for hosts to make calls to a NetWare server for services and network resources.



network address translation ( NAT )

An algorithm to allow translation of a network address from one network to a foreign network so it can be used on the foreign network.



network analyzer

A device, also called a protocol analyzer , that collects and analyzes data to see a particular protocol or address packet to aid in troubleshooting.



network diameter

The cabling distance between the two farthest points in the network.



network down

Describes the situation in which the clients are unable to use the network. This can be administrative, scheduled downtime for upgrades or maintenance, or it can be the result of a serious error.



Network Driver Interface Specification ( NDIS )

A Microsoft-proprietary specification or standard for a protocol-independent device driver. These drivers allow the NIC to bind multiple protocols to the same NIC, allowing the card to be used by multiple operating systems. Similar to Open Data-Link Interface (ODI) .



network ID

The part of the TCP/IP address that specifies the network portion of the IP address. It is determined by the class of the address, which is determined by the subnet mask used.



network interface card ( NIC )

The hardware component that serves as the interface, or connecting component, between your network and the node. It has a transceiver, a MAC address, and a physical connector for the network cable. Also known as a network adapter .



Network Interface layer

The bottom layer of the TCP/IP architectural model; it's responsible for sending and receiving frames.



Network layer

The third layer of the OSI reference model, where routing based on node addresses (IP or IPX addresses) occurs.



network management processor ( NMP )

A feature of the Catalyst supervisor engine that is responsible for general control and some management functions of the switch. It is responsible for executing the system's configuration changes, the CLI, and running diagnostics on boot components as well as new additional components .



Network Management Systems ( NMS )

A complete package of hardware and software for monitoring a network and gathering information such as performance and security.



network monitor

A software-based tool that monitors a network using SNMP or ICMP to gather statistical data and to determine a baseline.



Network Time Protocol ( NTP )

A protocol that allows all network equipment to synchronize the date and time on the private or internetwork environment.



nonblocking

A condition in which the fabric contains more bandwidth than the sum total of all the ports' bandwidth combined.



nonvolatile RAM ( NVRAM )

Static memory similar to that of the flash. Memory stored in NVRAM does not get lost when the power is turned off. On a switch, the NVRAM stores the VLAN configuration, system configuration, SNMP parameters, STP configuration, and configuration of each port.



Novell Directory Services ( NDS )

The user, group, and security information database of network resources that is used in a NetWare 4.x and/or NetWare 5.x internetwork. NDS is now called eDirectory for version 6.X of NetWare.



Open Shortest Path First ( OSPF )

A link-state protocol that uses factors such as load balancing and least-cost routing to determine the shortest path.



Open Systems Interconnection ( OSI ) Model

A seven-layer model created by the ISO to standardize and explain the interactions of networking protocols.



optical time domain reflector ( OTDR )

An advanced cable tester that analyzes fiber by sending pulses .



oversubscription

A condition in which the total bandwidth of the ports is greater than the capacity of the switching fabric. Also referred to as a blocking architecture .



Packet Internet Groper ( PING )

A TCP/IP protocol-stack utility that works with the Internet Control Message Protocol to test connectivity to other systems by using an echo request and reply.



password

A set of characters that is used with a username to authenticate a user on the network and to provide the user with rights and permissions to files and resources.



permanent virtual circuit ( PVC )

A logical path established in packet-switching networks between two locations. Similar to a dedicated leased line. Also known as a permanent virtual connection in ATM terminology (but not to be confused with private virtual circuit , which is also known as a PVC ).



permissions

The authorization that is provided to users, allowing them to access objects on the network. The network administrators generally assign permissions. Slightly different from ”but often used interchangeably with ”the term rights .



physical addressing scheme

Refers to the MAC address on every network card manufactured.



Physical layer

The bottom layer (Layer 1) of the OSI reference model, where all physical connectivity is defined.



plain old telephone system ( POTS )

The current analog public telephone system. Also known as the PSTN .



plug-and-play

Architecture designed to allow hardware devices to be detected by the operating system and for the driver to be automatically loaded.



Point-To-Point Protocol ( PPP )

A common dial-up networking protocol that includes provisions for security and protocol negotiation and provides host-to-network and switch-to-switch connections for one or more user sessions. PPP is the common modem connection used for Internet dial-up.



Point-To-Point Tunneling Protocol ( PPTP )

A protocol that encapsulates private network data in IP packets. These packets are transmitted over synchronous and asynchronous circuits to hide the underlying routing and switching infrastructure of the Internet from both senders and receivers.



polling

The media-access method for transmitting data, in which a controlling device is used to contact each node to determine if it has data to send.



port adapter modules

Modules attached to the carrier access modules on the LS1010 ATM and Catalyst 5500 Series ATM bus that provide physical ATM line ports for the user stations.



Port Aggregation Protocol ( PAgP )

Manages the Fast EtherChannel bundles and aids in the automatic creation of Fast EtherChannel links.



PortFast

A protocol that forces an STP port to enter the forwarding state immediately after startup for a single workstation or server connected to a switch port.



power-on self-test ( POST )

A series of tests that automatically run on a Cisco Catalyst switch when the power is turned on. The POST tests the hardware, memory, processors, ports, and ASICs to verify that they are functioning properly.



Presentation layer

Layer 6 of the OSI reference model. Prepares information to be used by the Application layer.



primary rate interface ( PRI )

A higher-level network interface standard for use with ISDN. Defined at the rate of 1.544Mbps, it consists of a single 64Kbps D channel plus 23 (T1) or 30 (E1) B channels for voice or data.



priority queuing

A priority-based configuration that allows certain types of traffic to be routed before others based upon the level of priority configured for that type of traffic. You can configure a priority based on the particular traffic type, packet size, protocol, or interface.



proprietary

A standard or specification that is created by a manufacturer, vendor, or other private enterprise and is not always a recognized standard.



Proprietary Fat Pipe ASIC ( PFPA )

An ASIC utilized on the Catalyst 3000 Series switches that use non-10BaseT ports such as Fast Ethernet, 100VG/AnyLAN, ATM, or the Stackport of the Stack Port Matrix. The PFPA is functionally the same as the LMA.



protocol

A set of rules that govern network communications among networks, computers, peripherals, and operating systems.



protocol analyzer

A device that collects and analyzes network data traffic to aid in troubleshooting. Also called a network analyzer .



Protocol Identification

In a frame, this five-byte field identifies and communicates to the destination node the protocol that is being used in the data transmission.



protocol stack

Two or more protocols that work together (such as TCP and IP, or IPX and SPX). Also known as a protocol suite .



public switched telephone network ( PSTN )

All the telephone networks and services in the world. The same as POTS, PSTN refers to the world's collection of interconnected public telephone networks that are either commercial or government owned. PSTN is a digital network, with the exception of the connection between local exchanges and customers, which remains analog.



q.921

Resides on the D channel of ISDN as a Layer 2 protocol to provide protocol connectivity from the central office switch to the router.



q.931

Resides on ISDN as a Layer 3 protocol to provide a snapshot of messages of ISDN connections.



quality of service ( QoS )

A guarantee of a particular level of service for a connection. QoS uses queuing and other methods to guarantee that bandwidth is available for a certain protocol, application, or address. QoS is important for implementing applications such as voice and video.



queuing

A method of providing QoS by the use of buffering and priority control mechanisms to control data congestion on the network.



read/ writes

The counting of packets on the ingress (read) as well as the egress (write) from the switching fabric.



redistribution

Allowing a protocol to be integrated in a network using a different protocol.



resource node

Any interface on the network that provides a service for a demand node. Resource nodes can be such things as servers and printers. Incorrect placement of your resource nodes can have terrible effects on your network.



Remote Network Monitoring ( RMON )

An Internet Engineering Task Force (IETF) standard that defines how devices gather and share the network monitoring information that is sent to an SNMP Management Station. RMON gathers Layer 2 information concerning bandwidth use, collisions, and errors.



remote node

A node or computer that is connected to the network through a dial-up connection. Dialing in to the Internet from home is a perfect and common example of the concept.



remote services

Services in which the device that supplies the services resides on a separate subnet from the device that requests the services.



repeater

A device that regenerates and retransmits the signal on a network. Generally used to strengthen signals going long distances.



resource node

An interface on the network that provides a service for a demand node. Resource nodes can be items such as servers and printers. The incorrect placement of your resource nodes can also have terrible effects on your network.



Reverse Address Resolution Protocol ( RARP )

The protocol that allows a MAC address to be mapped or correlated to identify the IP address of the device. Opposite of ARP.



rights

Authorization provided to users, allowing them to perform certain tasks. The network administrators generally assign rights. Slightly different from ”but often used interchangeably with ”the term permissions .



ring in ( RI )

A connector used in an IBM Token Ring network on a multistation access unit (MSAU) to expand to other MSAUs on the network. Counterpart to the RO (ring out), the RI connector on the MSAU connects to the media to accept the token from the ring.



ring topology

A network structure that is physically and logically organized in a ring formation with devices connected to the ring.



ring out ( RO )

A connector used in an IBM Token Ring network on a multistation access unit (MSAU) to expand to other MSAUs on the network. A counterpart to the RI (ring in), the RO connector on the MAU connects to the media to send the token out to the ring.



root bridge

The bridge or switch that is most centrally located in the network and provides the shortest path to other links on the network. Unlike other bridges, the root bridge always forwards frames out over all of its ports.



root timers

The timers received from the root bridge.



Routing Information Field ( RIF )

A field on Source Route Bridge Token Ring frames that contains information regarding the rings and bridges that the frame must travel to the destination interface.



Routing Information Protocol ( RIP )

Protocol that uses hop counts as a routing metric to control the direction and flow of packets between routers and switches on an internetwork.



runtless switching

A switching method in which the switch reads the first 64 bytes to verify that there is no corruption of the packet. If the packet is corrupted, a preset maximum of errors changes the switching type from cut-through switching to store-and-forward switching. Also known as fragment-free switching .



Security Association Identifier ( SAID )

One of the three values that make up a Clear Header on the FDDI frame type. It is used for security for the Clear Header, which contains a SAID, LSAP, and the Management Defined Field (MDF).



Sequenced Packet Exchange ( SPX )

Protocol used in conjunction with IPX when connection-oriented delivery is required. It is used mainly in NetWare network environments.



server

A resource node that fulfills service requests for demand nodes. Usually referred to by the type of service it performs, such as file server, email server, or print server.



service access point ( SAP )

A field in a frame that instructs the receiving host which protocol the frame is intended for.



Service Advertising Protocol ( SAP )

NetWare protocol used on an IPX network. SAP maintains server information tables, listing each service that has been advertised to it, and provides this information to any nodes attempting to locate a service.



Service Advertising Protocol agent ( SAP agent )

Router or other node on an IPX network that maintains a server information table. Such a table lists each service that has been advertised to it and provides this information to any nodes that are attempting to locate a service.



Service Profile Identifier ( SPID )

This number is assigned by the service provider and network administrators and identifies a BRI port and services provided to the number. Although ISDN uses SPIDS in North America to access the service provider, it is optional in other areas.



Session

The dialog that exists between two computers.



Session layer

This fifth layer of the OSI reference model establishes, manages, and terminates sessions between applications on different nodes.



shared systems

The infrastructure component routed directly into the backbone of an internetwork for optimal systems access. Provides connectivity to servers and other shared systems.



shielded twisted pair ( STP )

Twisted-pair network cable that uses shielding to insulate the cable from electromagnetic interference.



Simple Network Management Protocol ( SNMP )

A protocol used in TCP/IP networks to provide network devices with a method to monitor and control network devices. It is used to manage configurations, statistics collection, performance, and security, and to report network management information to a management console that is a member of the same community.



Simple Network Management Protocol ( SNMP ) trap

An SNMP protocol utility that sends out an alarm in an identified community, notifying its members that some network activity differs from the established threshold, as defined by the administrator.



single attached station ( SAS )

A FDDI device that has a single connection to a single DAC.



socket

A logical interprocess communications mechanism through which a program communicates with another program or with a network.



socket identifier

An eight-bit number that is used to identify the socket. Developers and designers of services and protocols usually assign socket identifiers. Also known as a socket number .



source address

The address of the host who sent the frame. The source address is contained in the frame so that the destination node knows who sent the data.



source route bridging ( SRB )

A type of bridging that is used to segment Token Ring networks. Requires all rings and bridges to have a unique number.



source route switching ( SRS )

A type of bridging that combines SRB and SRT. Developed to allow more physical rings on the network. It allows for increasing bandwidth needs while preserving the benefits of SRB.



source route translational bridging ( SR/TLB )

A type of bridging that bridges a Token Ring segment to another physical media type such as Ethernet or FDDI. It is transparent to the source and destination interfaces.



source route transparent bridging ( SRT )

A type of bridging that combines SRB and TB. Using SRT, the bridge places a RIF into a frame traveling from the TB to the SRB side. It then strips the RIF when the frame travels from the SRB port to the TB port.



Source Service Access Point ( SSAP )

A one-byte field in the frame that combines with the SAP to tell the receiving host the identity of the source or sending host.



Spanning Tree Algorithm ( STA )

Defined by IEEE 802.1 as part of the Spanning Tree Protocol to eliminate loops in an internetwork with multiple paths. The Spanning Tree Algorithm is responsible for performing Spanning Tree Protocol topology recalculations when a switch is powered up and when a topology change occurs.



Spanning Tree Protocol ( STP )

Defined by IEEE 802.1, STP was developed to eliminate the loops caused by the multiple paths in an internetwork. STP communicates topology changes from switch to switch with the use of bridge protocol data units (BPDUs).

See also [color blocking logic]


split-horizon

Routing mechanism that inquires about routes to prevent information from using the same interface through which the information was received, therefore preventing a loop.



standard IP access list

An access list that only filters based on the source address.



star topology

A logical network topology with end points that join at a common area using point-to-point links.



static IP addresses

IP addresses that are assigned to each network device individually. Often referred to as hard-coded .



static VLAN port

A port on a switch manually assigned a VLAN number. Any node or interface connected to the port automatically becomes a member of the assigned VLAN.



static window

A mechanism used in flow control to prevents a data sender from overwhelming the receiver. Only a set amount of data can be buffered in a static window.

See also [flow control]


station IPX address

A 12-digit number that is used to uniquely identify each device on an IPX network.



storage area network

A subnetwork of storage devices, usually found on high-speed networks and shared by all servers on the network.



store-and-forward

A fast packet-switching method that produces a higher latency than other switching methods, because the switch waits for the entire packet to arrive before checking the CRC. It then forwards or discards the packet.



subinterface

A virtual interface that can be configured on an interface.



subnet mask

A 32-bit address that is used to mask or screen a portion of the IP address to differentiate the part of the address that designates the network from the part that designates the host.



subnetting

The process of dividing your assigned IP address range into smaller clusters of hosts.



switch

A Layer 2 networking device that forwards frames based on destination addresses.



switch block

Switching devices located in wiring closets, requiring high-speed uplinks and redundancy.



switched port analyzer ( SPAN )

A port at which traffic from another port or group of ports is attached to a protocol analyzer or probe device. The SPAN aids in the diagnoses of problems that are related to traffic patterns on the network.



switched virtual circuit

A virtual circuit that is established dynamically on demand to form a dedicated link and is then broken when transmission is complete. Also known as a switched virtual connection in ATM terminology.



switching fabric

A term used to describe the " highway " that the data travels to get from the input port on a switch to the output port.



Synchronous Data Link Control ( SDLC )

A bit-oriented serial protocol for the Data Link layer of SNA. SDLC created the basics for HDLC and LAPB protocols.



synchronous transmission

A digital signal transmission method that uses a precise clocking method and a predefined number of bits sent at a constant rate.



syslog

Messages sent to a remote machine regarding the switch system configuration, such as software and configuration changes.



T1

Digital WAN carrier facility that transmits DS-1-formatted data at rates of up to 1.544Mbps through the telephone switching network, using AMI or B8ZS coding.



T3

Digital WAN carrier facility that transmits DS-3 formatted data at rates of up to 44.763Mbps.



TACACS+

A security feature that uses an MD5-encrypted algorithm to enforce strict authentication controls. It requires both a user name and a password, thus allowing administrators to better track network usage and changes based on user accounts.



TCP/IP
See [Transmission Control Protocol/Internet Protocol]
Telecommunications Industry Association ( TIA )

An organization that develops standards with the EIA (Electronics Industries Association) for telecommunications technologies.



Telnet

Standard terminal-emulation protocol in the TCP/IP protocol used to perform terminal emulation over TCP/IP via remote terminal connections, enabling users to log in to remote systems and use their resources as if the users were locally on that system.



thicknet coax

Thick cable (approximately 0.375 inches in diameter) most commonly found in the backbone of a coaxial network.



thinnet coax

Cable thinner than thicknet (approximately 0.25 inches in diameter), commonly used in older bus topologies to connect the nodes to the network.



time domain reflectors ( TDRs )

An advanced cable tester that can isolate a cable fault within a few feet of the actual problem on the wire.



time-to-live ( TTL )

Indicator of how long a packet remains alive on the network.



token

A frame that provides controlling information. In a Token Ring network, the node that possesses the token is the one that is allowed to transmit next.



Token Ring

An IBM proprietary, token-passing, LAN topology defined by the IEEE 802.5 standard. Token Ring operates at either 4Mbps or 16Mbps in a star topology.



topology

The shape or layout of a physical network and the flow of data through the network.



trace

Also referred to as traceroute . A command used to send ECMO ECHO messaged to track the path of a packet from a source to a destination.



Transmission Control Protocol ( TCP )

Part of the TCP/IP protocol stack. A connection-oriented, reliable, data-transmission communication service that operates at the OSI Transport layer.



Transmission Control Protocol/Internet Protocol ( TCP/IP )

The suite of protocols combining TCP and IP, developed to support the construction of worldwide internetworks.

See also [Transmission Control Protocol]
See also [Internet Protocol]


Transmission Control Protocol/Internet Protocol ( TCP/IP ) socket

A socket , or connection to an endpoint, that is used in TCP/IP communication transmissions.



transmit

The process of sending data using light, electronic, or electric signals. In networking, this is usually done in the form of digital signals that are composed of bits.



Transparent Bridging ( TB )

A bridging type that uses the MAC address to make forwarding and filtering decisions transparent to the sender and receiver interfaces. Used in Ethernet.



Transport layer

Layer 4 of the OSI reference model. Controls the flow of information.



Trivial File Transfer Protocol ( TFTP )

A simplified version of FTP that allows files to be transferred over a network from one computer to another. Also used to install the Cisco IOS on an IOS-based switch, router, or GSR.



troubleshooting model

A series of guidelines to be used as an aid in the troubleshooting process to resolve network issues.



trunk link

A special type of VLAN connections. Unlike a user port, trunk links expect the device at the other end of the connection to understand the inserted frame tags. Standard Ethernet and Token Ring cards do not understand frame tags.



twisted pair

A type of cable that uses multiple twisted pairs of copper wire.



unicast

A frame in which the destination MAC address specifies the single computer of destination. Summarized as direct network traffic between two individual nodes.



unshielded twisted pair ( UTP )

A type of cable that uses multiple twisted pairs of copper wire in a casing that does not provide much protection from EMI. UTP is rated in five categories and is the most common cable in Ethernet networks.



UplinkFast

Provides a protocol to aid in fast convergence after an STP topology change and achieves load balancing between redundant links.



User Datagram Protocol ( UDP )

Operating at the Transport layer of the OSI model, this communications protocol provides connectionless and unreliable communications services. It requires a transmission protocol such as IP to guide it to the destination host.



virtual LAN ( VLAN )

Allows a network administrator to divide a bridged network into several broadcast domains. Each VLAN is considered its own separate subnet, and Layer 3 routing is still required to route between VLANs. VLANs can be based on the port identifier of the switch, the MAC address, Layer 3 addressing, directory information, or application information. VLANs can be implemented on different media types such as Ethernet, FDDI, Token Ring, or ATM. The benefits of VLANs are limited broadcast domains, added security, and redundancy.



virtual private network ( VPN )

A network that uses a public network (such as the Internet) as a backbone to connect two or more private networks. VPN provides users with the equivalent of a private network in terms of security.



VLAN Trunking Protocol ( VTP )

A protocol used to enhance and configure the extension of broadcast domains across multiple switches. VTP dynamically reports the addition of VLANs throughout the switched network, thus creating a consistent switched network.



VLAN Trunking Protocol ( VTP ) pruning

A protocol used to reduce the number of switches participating in VTP by removing switches from the database that do not have certain VLANs assigned to numbered ports. If VTP pruning were not enabled on a trunk port, all VLAN traffic would travel through the trunk links to all the switches whether they had destination ports or not.



wide-area network ( WAN )

This data communications network serves users across a broad geographical area. WANs often use transmission devices such as modems and channel service units/data service units (CSU/DSU) to carry signals over leased lines or common carrier lines.



window flow control

A flow-control method in which the receiving host buffers the data it receives and holds it in the buffer until it can be processed. After it is processed, an acknowledgment is sent to the sender.



WINIPCFG

A Windows 95 or 98 command utility that brings up a graphical user interface (GUI) to display DHCP-obtained IP information settings. This utility allows you to release, renew, or view the DHCP settings for the local hosts adapters.





CCNP CIT Exam Cram 2 (642-831)
CCNP CIT Exam Cram 2 (Exam Cram 642-831)
ISBN: 0789730219
EAN: 2147483647
Year: 2003
Pages: 213
Authors: Sean Odom

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