CCNA 1 and 2 Companion Guide, Revised (Cisco Networking Academy Program) part 103 ppsx

A standard measurement of the amount of data transferred over a network connection... ICMP Internet Control Message Protocol Network layer Internet protocol that reports errors and provi

Flash memory A special type of EEPROM that can be erased and reprogrammed in

blocks instead of one byte at a time Many modern PCs have their BIOS stored on a

Flash memory chip so that it can be updated easily if necessary Such a BIOS is

some-times called a Flash BIOS Flash memory is also popular in modems because it enables

the modem manufacturer to support new protocols as they become standardized

flooding A traffic-passing technique used by switches and bridges in which traffic

received on an interface is sent out all that device’s interfaces except the interface on

which the information was received originally

floppy disk drive Reads and writes to floppy disks

flow control A technique for ensuring that a transmitting entity does not overwhelm

a receiving entity with data When the buffers on the receiving device are full, a message

is sent to the sending device to suspend the transmission until the data in the buffers

has been processed In IBM networks, this technique is called pacing

flush timer Indicates how much time passes before a route is flushed from the routing

table The IGRP default is seven times the routing update timer

FM (frequency modulation) Modulates the frequency of the wave

fragment-free switching Switching that filters out collision fragments, which are the

majority of packet errors, before forwarding begins

frame A logical grouping of information sent as a data link layer unit over a

trans-mission medium

FTP (File Transfer Protocol) An application protocol, part of the TCP/IP protocol

stack, used for transferring files between network nodes FTP is defined in RFC 959

full duplex The capability for simultaneous data transmission between a sending

station and a receiving station

full-mesh topology Connects all devices (nodes) to each other for redundancy and

fault tolerance

GB (gigabyte) Approximately 1 billion bytes Sometimes called a “gig.” Hard drive

capacity on most PCs is typically measured in GB

GBIC (Gigabit Interface Converter) A hot-swappable input/output device that plugs

into a Gigabit Ethernet port

Gbps (gigabits per second) One billion bits per second A standard measurement of

the amount of data transferred over a network connection 10G or 10 Gigabit

Ether-net operates at 10 Gbps

ghost Fluke Networks coined this new term to mean energy (noise) detected on the cable that appears to be a frame but that lacks a valid SFD To qualify as a ghost, this

“frame” must be at least 72 octets long (including preamble); otherwise, it is classified

as a remote collision

Gigabit Ethernet Standard for a high-speed Ethernet, approved by the IEEE 802.3z standards committee in 1996

global changes to the router configuration

half duplex A capability for data transmission in only one direction at a time between a sending station and a receiving station

hard disk drive Reads and writes data on a hard disk The primary storage device in the computer

HC (horizontal cross-connect) Area where patch panels or punchdown blocks are used to connect cables from work areas to the MC The HC can be a telecommunica-tions room, a cabinet, or a floor or ceiling installation

header Control information placed before data when encapsulating that data for net-work transmission

hertz The unit of measure for the frequency of an electrical signal in the number of complete cycles per second

hierarchical topology Created similar to an extended-star topology The primary dif-ference is that it does not use a central node Instead, it uses a trunk node from which

it branches to other nodes

holddowns Prevent regular update messages from inappropriately reinstating a route that might not be up

hold-time timer Specifies the amount of time for which information about better routes is ignored The IGRP default for this variable is 3 times the update timer period plus 10 seconds

hop count A routing metric used to measure the distance between a source and a des-tination RIP uses hop count as its sole metric

hop The passage of a data packet from one network node, typically a router, to another

lan-guage 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 graphics files

hub A common connection point for devices in a network Hubs commonly connect

segments of a LAN A hub contains multiple ports When a packet arrives at one port,

it is copied to the other ports so that all the segments of the LAN can see all the packets

server or other places on the same documents Provides shortcuts to other web pages

and files

lan-guage that uses tags to indicate how a given part of a document should be interpreted

by a viewing application, such as a web browser

IC (intermediate cross-connect) The connection point between a backbone cable that

extends from the MC to the HC

ICMP (Internet Control Message Protocol) Network layer Internet protocol that

reports errors and provides other information relevant to IP packet processing It is

documented in RFC 792

IEEE (Institute of Electrical and Electronic Engineers) A professional organization

whose activities include the development of communications and network standards

IEEE LAN standards are the predominant LAN standards today

IEEE (Institute of Electrical and Electronic Engineers) IEEE is professional

organi-zation whose activities include the development of communications and network

standards IEEE LAN standards are the predominant LAN standards

IEEE 802.1X/Extensible Authentication Protocol (EAP) An alternative WLAN security

approach to WEP as specified by IEEE 802.11 IEEE 802.1X/EAP focuses on

develop-ing a framework for providdevelop-ing centralized authentication and dynamic key distribution

IEEE 802.2 An IEEE LAN protocol that specifies an implementation of the LLC

sub-layer of the data link sub-layer IEEE 802.2 handles errors, framing, flow control, and the

network layer (Layer 3) service interface

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 Extensions to the IEEE 802.3

standard specify implementations for Fast Ethernet Physical variations of the

origi-nal IEEE 802.3 specification include 10BASE2, 10BASE5, 10BASE-F, 10BASE-T,

and 10BROAD36 Physical variations for Fast Ethernet include 100BASE-TX and

100BASE-FX

IGRP (Interior Gateway Routing Protocol) An IGP developed by Cisco to address

the problems associated with routing in large, heterogeneous networks Compare with EIGRP See also IGP, OSPF, and RIP.

impedance A measurement of the resistance of the cable to AC and is measured in ohms

insertion loss The combination of the effects of signal attenuation and impedance discontinuities on a communications link

intelligent hub Sometimes called “smart hubs.” These devices basically function as active hubs, but also include a microprocessor chip and diagnostic capabilities They are more expensive than active hubs, but are useful in troubleshooting situations

interface Connection between two systems or devices In routing terminology, a net-work connection

Interior Gateway Protocol (IGP) An Internet protocol used to exchange routing information within an autonomous system Examples of common Internet IGPs are IGRP, OSPF, and RIP

Interior Gateway Routing Protocol (IGRP) An IGP developed by Cisco to address the problems associated with routing in large, heterogeneous networks

interior router The router that is connected to the internal network The interior router accepts packets only from the application gateway The gateway controls the delivery of network-based services both to and from the internal network

interior routes Routes between subnets of a network attached to a router interface

If the network attached to a router is not subnetted, IGRP does not advertise interior routes

Internet Protocol (IP) A network layer protocol in the TCP/IP protocol suite offering

a connectionless internetwork service

Internet The largest global internetwork, connecting tens of thousands of networks worldwide and having a culture that focuses on research and standardization based on real-life use

intranet A common LAN configuration Intranets are designed to be accessed by users who have access privileges to an organization’s internal LAN

invalid timer Specifies how long a router waits in the absence of routing-update mes-sages about a specific route before declaring that route invalid The IGRP default for this variable is three times the update period

IP address A 32-bit address assigned to hosts using TCP/IP An IP address belongs to

one of five classes (A, B, C, D, or E) and is written as four octets separated by periods

(that is, dotted-decimal format) 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 A subnet mask is used to extract network and subnetwork

information from the IP address CIDR provides a new way to represent IP addresses

and subnet masks Also called an Internet address.

IP address class A 32-bit IP address is broken into a network part and a host part A

bit or bit sequence at the start of each address determines the address’s class

IP Version 6 (IPv6) The replacement for the current version of IP (Version 4) IPv6

includes support for flow ID in the packet header, which can be used to identify flows

Formerly called IPng (IP next generation)

jabber Defined several places in the 802.3 standard as being a transmission of at least

20,000 to 50,000 bit-times in duration However, most diagnostic tools report jabber

whenever a detected transmission exceeds the maximum legal frame size—which is

considerably smaller than 20,000 to 50,000 bit-times

KB (kilobyte) Approximately 1000 bytes (1024 bytes exactly)

kbps (kilobits per second) One thousand bits per second A standard measurement of

the amount of data transferred over a network connection

kBps (kilobytes per second) One thousand bytes per second A standard measurement

of the amount of data transferred over a network connection

keepalive Message sent by one network device to inform another network device

that the virtual circuit between the two is still active

latency Delay between the time when a device receives a frame and the time when

that frame is forwarded out the destination port

light-emitting diode (LED) Semiconductor device that emits light produced by

con-verting electrical energy Status lights on hardware devices are typically LEDs

link-state advertisements (LSAs) Small packets of routing information that are sent

between routers

link-state routing protocol A routing algorithm in which each router broadcasts or multicasts information regarding the cost of reaching each of its neighbors to all nodes

in the internetwork Link-state algorithms create a consistent view of the network and are therefore not prone to routing loops However, they achieve this at the cost of rela-tively greater computational difficulty and more widespread traffic than do distance vector routing algorithms

LLC (Logical Link Control) The higher of the two data link layer sublayers defined

by the IEEE The LLC sublayer handles error control, flow control, framing, and MAC-sublayer addressing The most prevalent LLC protocol is IEEE 802.2, which includes both connectionless and connection-oriented variants

load sharing When dynamic routing protocols direct traffic from the same session over different paths in a network for better performance

local-area network (LAN) A high-speed, low-error data network covering a relatively small geographic area (up to a few thousand meters) LANs connect workstations, peripherals, terminals, and other devices in a single building or another geographically limited area

logarithms Equals the exponent that a given number has to be raised to in order to generate a certain value

logical connection Uses standards called protocols

long frame A frame that is longer than the maximum legal size and that takes into consideration whether the frame was tagged

MAC (Media Access Control The lower of the two sublayers of the data link layer defined by the IEEE The MAC sublayer handles access to shared media, such as whether

token passing or contention will be used See also LLC.

MAC address A standardized data link layer address that is required for every device that connects to a LAN Other devices in the network use these addresses to locate specific devices in the network and to create and update routing tables and data struc-tures MAC addresses are 6 bytes long and are controlled by the IEEE Also called a hardware address, MAC-layer address, or physical address

Manchester encoding Digital encoding scheme, used by IEEE 802.3 and Ethernet, in which a mid[nd]bit-time transition is used for clocking; a 1 is denoted by a high level during the first half of the bit time

Mb (megabit) Approximately 1 million bits

MB (megabyte) Approximately 1 million bytes (1,048,576 bytes exactly) A megabyte

is sometimes called a “meg.” The amount of RAM in most PCs is typically measured

in MB Large files are typically some number of MB in size

Mbps (megabits per second) One million bits per second A standard measurement

of the amount of data transferred over a network connection Basic Ethernet operates

at 10 Mbps

MBps (megabytes per second) One million bytes per second A standard measurement

of the amount of data transferred over a network connection

MC (main cross-connect) The cross-connect that normally is located in the primary

telecommunications room or the equipment room

Media Access Control (MAC) A hardware address that uniquely identifies each node

of a network This address controls data communication for the host on the network

Media Access Control (MAC) address A standardized data link layer address that is

required for every port of devices that connect to a LAN Other devices in the network

use these addresses to locate specific ports in the network and to create and update

routing tables and data structures MAC addresses are 6 bytes long and are controlled

by the IEEE

media Media is the plural of medium Media refers to various physical environments

through which transmission signals pass Common network media include

twisted-pair, coaxial, fiber-optic cable, and the atmosphere (through which microwave, laser,

and infrared transmission occurs)

metric An algorithm that generates a number for each path through the network

Typically, the smaller the metric number is, the better the path is

metropolitan-area network (MAN) A network that spans a metropolitan area

Gen-erally, a MAN spans a larger geographic area than a LAN but a smaller geographic

area than a WAN

microprocessor A silicon chip that contains a CPU

microsegmentation Allows the creation of private or dedicated segments—one host

per segment Each host receives instant access to the full bandwidth and does not have

to compete for available bandwidth with other hosts

modal dispersion When multiple modes of light propagating through fiber travel

different distances, depending on their entry angles, which causes them to arrive at the

destination (receiving end of the cable) at slightly different times

modem Device that converts digital and analog signals At the source, a modem con-verts 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 The term modem is also

used to describe various digital devices such as CSU/DSUs and ISDN terminal adapters

MSDS (material safety data sheet) A document that contains information on the use, storage, and handling of a hazardous material It provides detailed information on the potential health effects of exposure and how to work safely with the material

par-ticular interface can handle

multicast Single packets copied by the network and sent to a specific subset of net-work addresses

multicast address A unique network address that directs packets that have that desti-nation address to predefined groups of IP addresses

multimeter A testing tool used to ensure that no voltage is on the telecommunica-tions line Most of these devices can measure AC/DC voltage, current, resistance, diode, continuity, and transistor

multimode Multimode is a type of fiber-optic cable that transmits more than one light path

MUTOA (multiuser telecommunications outlet assembly) A device that holds multi-ple outlets for use in work areas where modular furniture is used Computers and tele-phones are plugged directly into the MUTOA

narrowband interference Noise that only affects small ranges of frequencies

NEC National Electrical Code

protocol used by network operating systems such as LAN Manager, LAN Server, Windows for Workgroups, and Windows NT NetBEUI formalizes the transport frame and adds functions NetBEUI implements the OSI LLC2 protocol

network access layer The layer that is concerned with all the issues that an IP packet requires to make a physical link to the network medium

network interface card (NIC) A printed circuit board that fits into the expansion slot

of a bus on a computer motherboard Also can be a peripheral device

network layer Layer 3 of the OSI reference model This layer provides connectivity

and path selection between two end systems The network layer is the layer at which

routing occurs

NEXT (near-end crosstalk) Computed as the ratio in voltage amplitude between the

test signal and the crosstalk signal when measured from the same end of the link

NFPA National Fire Protection Association

noise As related to communications, noise refers to undesirable signals Noise can

originate from natural and technological sources and is added to the data signals in

communications systems

nonvolatile RAM (NVRAM) RAM that retains its contents when a unit is powered off

NRZ (nonreturn to zero) Signals that maintain constant voltage levels with no signal

transitions (no return to a 0V level) during a bit interval

NRZI (nonreturn to zero inverted) Signal that maintains constant voltage levels with

no signal transitions (no return to a 0V level) It interprets the presence of data at the

beginning of a bit interval as a signal transition and interprets the absence of data as

no transition

unit is powered off

octet 8 bits In networking, the term octet often is used (rather than byte) because

some machine architectures employ bytes that are not 8 bits long

Open System Interconnection (OSI) reference model A network architectural model

developed by the ISO This model consists of seven layers, each of which specifies

par-ticular 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

oscilloscope An important electronic device used to view electrical signals such as

voltage waves and pulses

OSHA Occupational Safety and Health Administration

OUI (organizationally unique identifier) Three octets assigned by the IEEE in a

block of 48-bit LAN addresses

packet A logical grouping of information that includes a header containing control information and (usually) user data Packets most often refer to network-layer units of

data The terms datagram, frame, message, and segment also describe logical

informa-tion groupings at various layers of the OSI reference model and in various technology circles

packet-switched services Routes small units of data called packets through a network based on the destination address contained within each packet

parallel port An interface that can transfer more than 1 bit simultaneously It is used

to connect external devices, such as printers

partial-mesh topology At least one device maintains multiple connections to others without being fully meshed A partial-mesh topology still provides redundancy by having several alternative routes

patch cable A cable with a connector on each end, used to transfer signals from one piece of network equipment to another

patch cord A length of cable used to connect links at the cross-connect

patch panel A device used to interconnect data networking or voice systems to the physical cable network The rear of the patch panel has network cables that are punched down The front of the patch panel has a factory-terminated interface of some type

peer-to-peer communication A form of communication in which each layer of the OSI model at the source must communicate with its peer layer at the destination

peer-to-peer network Networked computers act as equal partners, or peers, to each other As peers, each computer can take on the client function or the server function

organi-zation that has developed a standard for small credit card-sized devices called PCM-CIA cards (or PC cards) Originally designed to add memory to portable computers, the PCMCIA standard has been expanded several times and is now suitable for many types of devices

physical connection A connection to a network that is made by connecting a special-ized expansion card, such as a modem or NIC, from a PC with a cable to a network

physical layer Layer 1 of the OSI reference model The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, main-taining, and deactivating the physical link between end systems

ping (Packet Internet Groper) ICMP echo message and its reply Often used in IP networks to test the reachability of a network device