. 15
( 19)


to WLANs and can be used for wired LAN au-
traffic into flows or classes and then providing
thentication, it is most often used in WLANs.
non-first-in, first-out (FIFO) service to the vari-
The WPA and WPA2 standards have adopted
ous queues according to their assigned weights.
five EAP types as their official authentication
In order to use dWFQ, dCEF switching must be
enabled on the interface.
early token release
dynamic address resolution
Technique used in Token Ring networks that al-
Use of an address resolution protocol to deter-
lows a station to release a new token onto the
mine and store address information on demand.
ring immediately after transmitting, instead of
waiting for the first frame to return. This fea-
dynamic random-access memory
ture can increase the total bandwidth on the
dynamic routing
Routing that adjusts automatically to network
extended binary coded decimal interchange
topology or traffic changes.
Dynamic routing is also known as adaptive
Any of a number of coded character sets devel-
oped by IBM consisting of 8-bit coded charac-
E channel ters. This character code is used by older IBM
echo channel systems and telex machines. Compare with
64-kbps ISDN circuit-switching control chan- ASCII.
nel. The E channel was defined in the 1984
332 CCNA Security Course Booklet, Version 1.0

edge card control Electronic Data Interchange for Administration,
Process on the NP of a LightStream 2020 ATM Commerce, and Transport
switch that performs per-card processing for an Data exchange standard administered by the
edge card. Such processing includes protocol United Nations to be a multi-industry EDI stan-
management (ATM connection management) dard.
and media-specific (Ethernet and FDDI) man-
agement tasks, internetworking operations such
electrically erasable programmable read-only
as packet forwarding and filtering, and network
management tasks.
EPROM that can be erased using electrical sig-
echo channel nals applied to specific pins.
See E channel.
ECMA Electronic Industries Association
European Computer Manufacturers Association Group that specifies electrical transmission
Group of European computer vendors who standards. The EIA and TIA have developed
have done substantial OSI standardization numerous well-known communications stan-
work. dards, including EIA/TIA-232 and EIA/TIA-
Enterprise Composite Network Model
Framework used by network professionals to Electronic Industries Association/Telecommu-
describe and analyze any modern enterprise nications Industry Association 232
network. It takes a complex enterprise network Common physical layer interface standard, de-
design and breaks it down into three functional veloped by EIA and TIA, that supports unbal-
areas including the Enterprise Campus, Enter- anced circuits at signal speeds of up to 64 kbps.
prise Edge, and the Service Provider Edge. Closely resembles the V.24 specification.
EIA/TIA-232 was formerly known as RS-232.
edge card
Line card on the LightStream 2020 ATM switch
that is configured to communicate with devices Electronic Industries Association/Telecommu-
outside the ATM network. Edge cards offer nications Industry Association 449
Ethernet, FDDI, frame forwarding, Frame Popular physical layer interface developed by
Relay, OC-3c, and UNI interfaces. EIA and TIA. Essentially, a faster (up to 2
Mbps) version of EIA/TIA-232 capable of
edge card control longer cable runs.
See ECC. EIA/TIA-449 was formerly known as RS-449.
edge device EIA/TIA-568
Network entity such as a LAN segment, host, Electronic Industries Association/Telecommu-
or router that connects to a LightStream 2020 nications Industry Association 568
ATM switch via an edge card. Edge devices Standard that describes the characteristics and
send and receive the data that passes through applications for various grades of UTP cabling.
the ATM network.
EDI Electronic Industries Association/Telecommu-
electronic data interchange nications Industry Association 606
The electronic communication of operational Administration standard for the telecommuni-
data such as orders and invoices between or- cations infrastructure of commercial buildings.
ganizations. It includes the following administration areas:
terminations, media, pathways, spaces, and
bounding and grounding.
Glossary 333

EIA-530 electrically erasable programmable read-
only memory
Electronic Industries Association 530
REFers to two electrical implementations of
EIA/TIA-449: RS-422 (for balanced transmis-
electromagnetic interference
sion) and RS-423 (for unbalanced transmis-
See EMI.
electromagnetic pulse
See EMP.
Enhanced Interior Gateway Routing Protocol
Advanced version of IGRP developed by Cisco. electronic data interchange
Provides superior convergence properties and See EDI.
operating efficiency, and combines the advan-
Electronic Data Interchange for
tages of link state protocols with those of dis-
Administration, Co
tance vector protocols.
Electronic Industries Association
Ethernet Interface Processor
See EIA.
Interface processor card on the Cisco 7000 se-
ries routers. The EIP provides high-speed (10-
electronic mail
Mbps) AUI ports that support Ethernet Version
See e-mail.
1 and Ethernet Version 2 or IEEE 802.3 inter-
faces, and a high-speed data path to other inter- Electronic Messaging Association
face processors. See EMA.
EIRP electrostatic discharge
Effective Isotropic Radiated Power See ESD.
EIRP is the effective power in front of the an-
tenna. The EIRP of a transmitter is the power
that the transmitter appears to have if the trans- 1) Enterprise Management Architecture. Digital
mitter were an isotropic radiator (if the antenna Equipment Corporation network management
radiated equally in all directions). By virtue of architecture, based on the OSI network man-
the gain of a radio antenna (or dish), a beam is agement model.
formed that preferentially transmits the energy 2) Electronic Messaging Association. Forum
in one direction. The EIRP is estimated by devoted to standards and policy work, educa-
adding the gain (of the antenna) and the trans- tion, and development of electronic messaging
mitter power (of the radio). systems such as electronic mail, voice mail, and
Extended Industry-Standard Architecture
32-bit bus interface used in PCs, PC-based electronic mail
servers, and some UNIX workstations and Widely used network application in which mail
servers. messages are transmitted electronically be-
tween end users over various types of networks
using various network protocols.
emulated local area network
ATM network in which an Ethernet or Token
Ring LAN is emulated using a client-server electromagnetic interference
model. ELANs are composed of an LEC, an Interference by electromagnetic signals that can
LES, a BUS, and an LECS. Multiple ELANs cause reduced data integrity and increased error
can exist simultaneously on a single ATM net- rates on transmission channels.
work. ELANs are defined by the LANE specifi-
334 CCNA Security Course Booklet, Version 1.0

EMIF end of transmission
ESCON Multiple Image Facility See EOT.
Mainframe I/O software function that allows
end point
one ESCON channel to be shared among multi-
Device at which a virtual circuit or virtual path
ple logical partitions on the same mainframe.
begins or ends.
end system
electromagnetic pulse
See ES.
Caused by lightning and other high-energy phe-
nomena. Capable of coupling enough energy End System Hello
into unshielded conductors to destroy electronic
See ESH.
End System-to-Intermediate System
emulated LAN
See ES-IS.
Energy Sciences Network
emulation mode
See ESnet.
Function of an NCP that enables it to perform
activities equivalent to those performed by a Enhanced IGRP
transmission control unit. For example, with See EIGRP.
CiscoWorks, the NetView PU 2 emulates the
Enhanced Interior Gateway Routing
IBM 3274.
encapsulation See EIGRP.
The wrapping of data in a particular protocol
Enhanced Monitoring Services
header. For example, Ethernet data is wrapped
Set of analysis tools on the Catalyst 5000
in a specific Ethernet header before network
switch, consisting of an integrated RMON
transit. Also, when bridging dissimilar net-
agent and the SPAN. These tools provide traffic
works, the entire frame from one network is
monitoring, and network segment analysis and
simply placed in the header used by the data
link layer protocol of the other network.
Enterprise Composite Network Model
encapsulation bridging
Carries Ethernet frames from one router to an-
other across disparate media, such as serial and Enterprise Management Architecture
FDDI lines. Contrast with translational bridg-
See EMA.
enterprise network
Large and diverse network connecting most
Device that modifies information into the re-
major points in a company or other organiza-
quired transmission format.
tion. Differs from a WAN in that it is privately
owned and maintained.
Process by which bits are represented by volt- Enterprise Network Model
Also known as Enterprise Composite Network
Model. See ECNM.
The application of a specific algorithm to data Enterprise System Connection
so as to alter the appearance of the data making
it incomprehensible to those who are not au-
thorized to see the information. Enterprise System Connection channel
See ESCON channel.
Glossary 335

entity ESCON channel
Generally, an individual, manageable network IBM channel for attaching mainframes to pe-
device. ripherals such as storage devices, backup units,
An entity is also known as an alias. and network interfaces. This channel incorpo-
rates fiber channel technology. The ESCON
EOT channel replaces the bus and tag channel. Com-
end of transmission pare with parallel channel.
Generally, a character that signifies the end of a
ESCON Multiple Image Facility
logical group of characters or bits.
erasable programmable read-only memory
Nonvolatile memory chips that are programmed electrostatic discharge
after they are manufactured, and, if necessary, A flow or spark of electricity that originates
can be erased by some means and repro- from a static source such as a carpet and arcs
grammed. Compare with EEPROM and across a gap to another object.
equalization Extended Superframe Format
Technique used to compensate for communica- Framing type used on T1 circuits that consists
tions channel distortions. of 24 frames of 192 bits each, with the 193rd
bit providing timing and other functions. ESF is
erasable programmable read-only memory an enhanced version of SF.
error control End System Hello
Technique for detecting and correcting errors in An IS-IS hello packet type. It is part of the ES-
data transmissions. IS spec 9542; similar to IRDP in TCP/IP; used
for routers (ISs) and End Systems (ESs) to de-
error-correcting code
tect each other and form adjacencies.
Code having sufficient intelligence and incor-
porating sufficient signaling information to en- ES-IS
able the detection and correction of many errors End System-to-Intermediate System
at the receiver. ES-IS discovery protocols used for routing be-
tween end systems and intermediate systems.
error-detecting code
ES-IS is an analogous to ARP in IP. Although
Code that can detect transmission errors
not technically a routing protocol, ES-IS is
through analysis of received data based on the
commonly used with routing protocols to pro-
adherence of the data to appropriate structural
vide end-to-end data movement through an in-
ternetwork. Routing between end systems and
intermediate systems is sometimes referred to
as Level 0 routing.
end system
Any non-routing host or node. ES lives in a
particular area.
Energy Sciences Network
Data communications network managed and
funded by the U.S. Department of Energy Of-
Enterprise System Connection
fice of Energy Research (DOE/OER). Intercon-
IBM channel architecture that specifies a pair
nects the DOE to educational institutions and
of fiber-optic cables, with either LEDs or lasers
other research facilities.
as transmitters and a signaling rate of 200
336 CCNA Security Course Booklet, Version 1.0

extended service set
European Internet
WLAN infrastruce mode whereby two or more
See EUnet.
basic service sets are connected by a common
distribution system. An ESS generally includes European Telecommunication Standards
a common SSID to allow roaming from access Institute
point to access point without requiring client See ETSI.
Ethernet Network message indicating operational irregu-
Baseband LAN specification invented by Xerox larities in physical elements of a network or a
Corporation and developed jointly by Xerox, response to the occurrence of a significant task,
Intel, and Digital Equipment Corporation. Eth- typically the completion of a request for infor-
ernet networks use CSMA/CD and run over a mation.
variety of cable types at 10 Mbps. Ethernet is
Excess Burst
similar to the IEEE 802.3 series of standards.
See Be.
Ethernet Interface Processor
excess rate
See EIP.
Traffic in excess of the insured rate for a given
ETSI connection. Specifically, the excess rate equals
European Telecommunication Standards Insti- the maximum rate minus the insured rate. Ex-
tute cess traffic is delivered only if network re-
Organization created by the European PTTs sources are available and can be discarded
and the European Community (EC) to propose during periods of congestion. Compare with in-
telecommunications standards for Europe. sured rate and maximum rate.
EUI-64 exchange identification
Extended Universal Identifier (EUI)-64 address See XID.
This is an IPv6 address format created by tak-
ing an interface™s MAC address (which is 48
The interactive command processor of the
bits in length) and inserting another 16-bit
Cisco IOS software.
hexadecimal string (FFFE) between the OUI
(first 24 bits) and unique serial number (last 24
bits) of the MAC address. To ensure that the
The process of running a compressed data set
chosen address is from a unique Ethernet MAC
through an algorithm that restores the data set
address, the seventh bit in the high-order byte is
to its original size. Compare with companding
set to 1 (equivalent to the IEEE G/L bit) to indi-
and compression.
cate the uniqueness of the 48-bit address.
expectational acknowledgment
Type of acknowledgment scheme in which the
European Internet
acknowledgment number refers to the octet ex-
European commercial Internet service provider.
pected next.
EUnet is designed to provide electronic mail,
news, and other Internet services to European expedited delivery
markets. Option set by a specific protocol layer telling
other protocol layers (or the same protocol
European Academic Research Network
layer in another network device) to handle spe-
cific data more rapidly.
European Computer Manufacturers
explicit route
Glossary 337

In SNA, a route from a source subarea to a des- frame format, MAC mechanisms, and MTU.
tination subarea, as specified by a list of sub- Such similarities allow the use of existing
area nodes and transmission groups that 10BASE-T applications and network manage-
connect the two. ment tools on Fast Ethernet networks. Based on
an extension to the IEEE 802.3 specification.
explorer frame Compare with Ethernet.
Frame sent out by a networked device in a SRB
Fast Ethernet Interface Processor
environment to determine the optimal route to
another networked device. See FEIP.

Extended Binary Coded Decimal Fast Sequenced Transport
Interchange Code See FST.
Fast Serial Interface Processor
Extended Industry-Standard Architecture See FSIP.
fast switching
extended service set Cisco feature whereby a route cache is used to
See ESS. expedite packet switching through a router.
Contrast with slow switching.
Extended Superframe Format
See ESF. fault management
One of five categories of network management
Extended Universal Identifier (EUI)-64
defined by ISO for management of OSI net-
See EUI-64. works. Fault management attempts to ensure
that network faults are detected and controlled.
Extensible Authentication Protocol
Federal Communications Commission
exterior gateway protocol
U.S. government agency that supervises, li-
Any internetwork protocol used to exchange
censes, and controls electronic and electromag-
routing information between autonomous sys-
netic transmission standards.
failure domain
function card load
Area in which a failure has occurred in a Token
Low-level software module in the LightStream
Ring, defined by the information contained in a
2020 ATM switch that is invoked by higher-
beacon. When a station detects a serious prob-
level modules to load software from the NP to a
lem with the network (such as a cable break), it
function card.
sends a beacon frame that includes the station
reporting the failure, its NAUN, and everything FCS
in between. Beaconing in turn initiates a frame check sequence
process called autoreconfiguration. Refers to the extra characters added to a frame
for error control purposes. Used in HDLC,
fan-out unit
Frame Relay, and other data link layer protocols.
Device that allows multiple devices on a net-
work to communicate using a single network FDDI
attachment. Fiber Distributed Data Interface
LAN standard, defined by ANSI X3T9.5, speci-
Fast Ethernet
fying a 100-Mbps token-passing network using
Any of a number of 100-Mbps Ethernet specifi-
fiber-optic cable, with transmission distances of
cations. Fast Ethernet offers a speed increase
up to 2 km. FDDI uses a dual-ring architecture
ten times that of the 10BASE-T Ethernet speci-
to provide redundancy. Compare with CDDI
fication, while preserving such qualities as
and FDDI II.
338 CCNA Security Course Booklet, Version 1.0

FDDI II low-speed interface module, which offers V.35,
EIA/TIA-449, or X.21 physical interfaces.
Fiber Distributed Data Interface II
ANSI standard that enhances FDDI. FDDI II
provides isochronous transmission for connec-
IPv6 multicast address identifying all nodes on
tionless data circuits and connection-oriented
a link.
voice and video circuits. Compare with FDDI.
FDDI Interface Processor
IPv6 multicast address identifying all routers
See FIP.
on a link.
frequency-division multiplexing
IPv6 multicast address identifying all OSPF
Technique whereby information from multiple
routers on the link-local scope. It is equivalent
channels can be allocated bandwidth on a sin-
to the multicast address in OSPFv2.
gle wire based on frequency. Compare with
ATDM, statistical multiplexing, and TDM. FF02::6
IPv6 multicast address identifying all OSPF
designated routers on the link-local scope. It is
Forward Explicit Congestion Notification
equivalent to the multicast address in
Bit set by a Frame Relay network to inform
DTE receiving the frame that congestion was
experienced in the path from source to destina- FF02::9
tion. DTE receiving frames with the FECN bit IPv6 multicast address identifying all IPv6
set can request that higher-level protocols take RIPng routers on link.
flow-control action as appropriate. Compare
with BECN.
IPv6 multicast address used to create neighbor
Federal Communications Commission
solicitation messages which are sent on a local
See FCC. link when a node wants to determine the link-
layer address of another node on the same local
Federal Networking Council
link. Similar to ARP in IPv4.
See FNC.
IPv6 multicast address identifying all NTP
Fast Ethernet Interface Processor
servers in the site (site-local scope).
Interface processor on the Cisco 7000 series
routers. The FEIP supports up to two 100-Mbps Fiber Distributed Data Interface
100BASE-T ports. See FDDI.
FEP Fiber Distributed Data Interface II
front-end processor See FDDI II.
Device or board that provides network interface
fiber-optic cable
capabilities for a networked device. In SNA,
typically an IBM 3745 device. Physical medium capable of conducting modu-
lated light transmission. Compared with other
transmission media, fiber-optic cable is more
frame forwarding expensive, but is not susceptible to electromag-
Interface on the LightStream 2020 ATM switch netic interference, and is capable of higher data
that allows any traffic based on HDLC or rates.
SDLC frames to traverse the ATM network. Fiber-optic cable is also known as optical fiber.
Frame forwarding circuits are port-to-port, and
fiber-optic interrepeater link
only one PVC is allowed between a pair of
ports. Frame forwarding is supported by the See FOIRL.
Glossary 339

FID0 File Transfer, Access, and Management
format indicator 0 See FTAM.
One of several formats that an SNA TH can
use. An FID0 TH is used for communication
Generally, a process or device that screens net-
between an SNA node and a non-SNA node.
work traffic for certain characteristics, such as
FID1 source address, destination address, or protocol,
format indicator 1 and determines whether to forward or discard
One of several formats that an SNA TH can that traffic based on the established criteria.
use. An FID1 TH encapsulates messages be-
tween two subarea nodes that do not support
FDDI Interface Processor
virtual and explicit routes.
Interface processor on the Cisco 7000 series
FID2 routers. The FIP supports SASs, DASs, dual
format indicator 2 homing, and optical bypass, and contains a 16-
One of several formats that an SNA TH can mips processor for high-speed (100-Mbps) in-
use. An FID2 TH is used for transferring mes- terface rates. The FIP complies with ANSI and
sages between a subarea node and a PU 2, ISO FDDI standards.
using local addresses.
FID3 Router or access server, or several routers or ac-
format indicator 3 cess servers, designated as a buffer between any
One of several formats that an SNA TH can connected public networks and a private net-
use. An FID3 TH is used for transferring mes- work. A firewall router uses access lists and
sages between a subarea node and a PU 1, other methods to ensure the security of the pri-
using local addresses. vate network.

FID4 firmware
format indicator 4 Software instructions set permanently or semi-
One of several formats that an SNA TH can permanently in ROM.
use. An FID4 TH encapsulates messages be-
First In First Out queuing
tween two subarea nodes that are capable of
See FIFO queuing.
supporting virtual and explicit routes.
fish tape
field-replaceable unit
Retractable coil of steel tape used to guide
See FRU.
cable through a wall from above or below.
FIFO queuing
First In First Out queuing
Routing problem where an advertised route be-
Classic algorithm for packet transmission. With
tween two nodes alternates (flaps) back and
FIFO, transmission occurs in the same order as
forth between two paths due to a network prob-
messages are received. Until recently, FIFO
lem that causes intermittent interface failures.
queuing is the default for all router interfaces
with the bandwidth greater then 2.048 Mbps. Flash memory
Technology developed by Intel and licensed to
file transfer
other semiconductor companies. Flash memory
Popular network application that allows files to
is nonvolatile storage that can be electrically
be moved from one network device to another.
erased and reprogrammed. Allows software im-
File Transfer Protocol ages to be stored, booted, and rewritten as nec-
See FTP. essary.
340 CCNA Security Course Booklet, Version 1.0

flash update a precursor of the 10BASE-FL specification,
which is designed to replace it.
Routing update sent asynchronously in re-
sponse to a change in the network topology.
format indicator 0
Compare with routing update.
See FID0.
fldsup account
format indicator 1
field service personnel account
See FID1.
One of the four default user accounts that are
created in the factory on each LightStream format indicator 2
2020 ATM switch. The fldsup account is for the See FID2.
use of field service personnel. Its default inter-
format indicator 3
face is the bash shell.
See FID3.
format indicator 4
Traffic passing technique used by switches and
bridges in which traffic received on an interface See FID4.
is sent out all of the interfaces of that device ex-
forward channel
cept the interface on which the information was
Communications path carrying information
originally received.
from the call initiator to the called party.
forward delay interval
Stream of data traveling between two endpoints
Amount of time an interface spends listening
across a network (for example, from one LAN
for topology change information after that in-
station to another). Multiple flows can be trans-
terface has been activated for bridging and be-
mitted on a single circuit.
fore forwarding actually begins.
flow control
forward explicit congestion notification
Technique for ensuring that a transmitting en-
tity, such as a modem, does not overwhelm a
receiving entity with data. When the buffers on forwarding
the receiving device are full, a message is sent
Process of sending a frame toward its ultimate
to the sending device to suspend the transmis-
destination by way of an internetworking device.
sion until the data in the buffers has been
processed. In IBM networks, this technique is forwarding priority
called pacing. See transmit priority.
FM Fourier transform
frequency modulation. Modulation technique in Technique used to evaluate the importance of
which signals of different frequencies represent various frequency cycles in a time series pat-
different data values. Compare with AM and tern.
four-part dotted notation
FNC See dot address.
Federal Networking Council
fractional T1
Group responsible for assessing and coordinat-
See channelized T1.
ing U.S. federal agency networking policies
and needs.
Frame Relay access device
Any network device that provides a connection
fiber-optic interrepeater link
between a LAN and a Frame Relay WAN.
Fiber-optic signaling methodology based on the
IEEE 802.3 fiber-optic specification. FOIRL is
Glossary 341

fragment FRAS
Piece of a larger packet that has been broken Frame Relay Access Support
down to smaller units. Cisco IOS software feature that allows SDLC,
Token Ring, Ethernet, and Frame Relay-at-
fragmentation tached IBM devices to connect to other IBM
Process of breaking a packet into smaller units devices across a Frame Relay network.
when transmitting over a network medium that
cannot support the original size of the packet.
Number of cycles, measured in hertz, of an al-
frame ternating current signal per unit time.
Logical grouping of information sent as a data
frequency modulation
link layer unit over a transmission medium.
Often refers to the header and trailer, used for See FM.
synchronization and error control, that surround
frequency-division multiplexing
the user data contained in the unit. The terms
See FDM.
datagram, message, packet, and segment are
also used to describe logical information group- from switch unit
ings at various layers of the OSI reference
See FSU.
model and in various technology circles.
front end
frame check sequence
Node or software program that requests serv-
See FCS.
ices of a back end.
frame forwarding
front-end processor
See FF.
See FEP.
Frame Relay
Industry-standard, switched data link layer pro-
field-replaceable unit
tocol that handles multiple virtual circuits using
Hardware component that can be removed and
HDLC encapsulation between connected de-
replaced by Cisco-certified service providers.
vices. Frame Relay is more efficient than X.25,
Typical FRUs include cards, power supplies,
the protocol for which it is generally considered
and chassis components.
a replacement.
Frame Relay Access Device
Fast Serial Interface Processor
The default serial interface processor for Cisco
7000 series routers. The FSIP provides four or
Frame Relay Access Support
eight high-speed serial ports.
Frame Relay bridging
Fast Sequenced Transport
Bridging technique, described in RFC 1490,
Connectionless, sequenced transport protocol
that uses the same spanning-tree algorithm as
that runs on top of the IP protocol. SRB traffic
other bridging functions, but allows packets to
is encapsulated inside of IP datagrams and is
be encapsulated for transmission across a
passed over an FST connection between two
Frame Relay network.
network devices (such as routers). Speeds up
frame switch data delivery, reduces overhead, and improves
See LAN switch. the response time of SRB traffic.
342 CCNA Security Course Booklet, Version 1.0

FSU equipment and DTE using BNC connectors and
operating at E1 data rates.
from switch unit
Subsystem of each line card on a LightStream
2020 ATM switch that accepts calls from the
ITU-T framing standard that defines the map-
switch card, verifies their checksums, and
ping of ATM cells into the physical medium.
passes them to the reassembly unit. The FSU
selectively drops cells if the network becomes gain
congested. The amount of increase in energy that an an-
tenna appears to add to an RF signal. There are
different methods for measuring this, depend-
File Transfer, Access, and Management
ing on the reference point chosen.
In OSI, an application layer protocol developed
for network file exchange and management be- gateway
tween diverse types of computers. In the IP community, an older term referring to
a routing device. Today, the term router is used
to describe nodes that perform this function,
File Transfer Protocol
and gateway refers to a special-purpose device
Application protocol, part of the TCP/IP proto-
that performs an application layer conversion of
col stack, used for transferring files between
information from one protocol stack to another.
network nodes. FTP is defined in RFC 959.
Compare with router.
full duplex
Gateway Discovery Protocol
Capability for simultaneous data transmission
See GDP.
between a sending station and a receiving sta-
tion. Compare with half duplex and simplex. gateway host
In SNA, a host node that contains a gateway
full mesh
Term describing a network in which devices are
organized in a mesh topology, with each net- gateway NCP
work node having either a physical circuit or a NCP that connects two or more SNA networks
virtual circuit connecting it to every other net- and performs address translation to allow cross-
work node. A full mesh provides a great deal of network session traffic.
redundancy, but because it can be prohibitively
Gateway-to-Gateway Protocol
expensive to implement, it is usually reserved
for network backbones. See GGP.

function card GDP
Line card or an NP card in a LightStream 2020 Gateway Discovery Protocol
ATM switch. Cisco protocol that allows hosts to dynamically
detect the arrival of new routers as well as de-
function card load
termine when a router goes down. Based on
See fcload. UDP.
Fuzzball generic routing encapsulation
Digital Equipment Corporation LSI-11 com- See GRE.
puter system running IP gateway software. The
Get Nearest Server
NSFnet used these systems as backbone packet
switches. See GNS.

G.703/G.704 GGP
ITU-T electrical and mechanical specifications Gateway-to-Gateway Protocol
for connections between telephone company MILNET protocol specifying how core routers
(gateways) should exchange reachability and
Glossary 343

routing information. GGP uses a distributed global unicast address
shortest-path algorithm. An IPv6 unicast address that is globally unique.
It can be routed globally with no modification.
It shares the same address format as an IPv6
global information distribution anycast address. Global unicast addresses are
Process that runs on the NP of every Light- assigned by the Internet Assigned Numbers Au-
Stream 2020 ATM switch in a network. GID thority (IANA). Compare with local unicast ad-
maintains a database and keeps nodes in the dress.
network apprised of changes in topology such
as ports, cards, and nodes being added or re- GNS
moved, and trunks going up or down. This in- Get Nearest Server
formation is supplied by the ND process. Request packet sent by a client on an IPX net-
Global information distribution is also known work to locate the nearest active server of a par-
as global information distribution daemon ticular type. An IPX network client issues a
(GIDD). GNS request to solicit either a direct response
from a connected server or a response from a
router that tells it where on the internetwork the
Global information distribution daemon. See service can be located. GNS is part of the IPX
gigabit GOSIP
In data communications, a gigabit is Government OSI Profile
1,000,000,000 (109) bits. Abbreviated Gb. U.S. government procurement specification for
OSI protocols. Through GOSIP, the govern-
gigabits per second
ment has mandated that all federal agencies
Abbreviated Gbps.
standardize on OSI and implement OSI-based
gigabyte systems as they become commercially avail-
Abbreviated GB.

Government OSI Profile
gigabytes per second
Abbreviated GBps.

grade of service
Measure of telephone service quality based on
Abbreviated GHz.
the probability that a call will encounter a busy
GLBP signal during the busiest hours of the day.
Gateway Load Balancing Protocol
graphical user interface
GLBP is an improvement to HSRP and VRRP,
See GUI.
allowing automatic selection and simultaneous
use of multiple available gateways as well as
automatic failover between those gateways.
generic routing encapsulation
With GLBP, resources can be fully utilized
Tunneling protocol developed by Cisco that can
without the administrative burden of configur-
encapsulate a wide variety of protocol packet
ing multiple groups and managing multiple de-
types inside IP tunnels, creating a virtual point-
fault gateway configurations as is required with
to-point link to Cisco routers at remote points
over an IP internetwork. By connecting multi-
global information distribution protocol subnetworks in a single-protocol back-
bone environment, IP tunneling using GRE
See GID.
allows network expansion across a single-pro-
global information distribution daemon tocol backbone environment.
See GID.
344 CCNA Security Course Booklet, Version 1.0

ground H.323
Electrically neutral contact point. H.323 allows dissimilar communication devices
to communicate with each other by using a
ground loop standardized communication protocol. H.323
Arrangement that exists when a multi-path con- defines a common set of CODECs, call setup
nection exists between computers. Usually this and negotiating procedures, and basic data
occurs when computers are connected to each transport methods.
other through a ground wire and when comput-
half duplex
ers are attached to the same network using
twisted pair cable. Capability for data transmission in only one di-
rection at a time between a sending station and
ground station a receiving station. Compare with full duplex
Collection of communications equipment de- and simplex.
signed to receive signals from (and usually
hammer drill
transmit signals to) satellites.
Ground station is also known as downlink sta- Tool resembling an oversized electric drill used
tion. for drilling into masonry. As it turns the bit, it
hammers rapidly.
group address
See multicast address.
Sequence of messages exchanged between two
group delay or more network devices to ensure transmission
See distortion delay. synchronization.
guard band hardware address
Unused frequency band between two communi- See MAC address.
cations channels that provides separation of the
channels to prevent mutual interference.
Line code type used on E1 circuits.
graphical user interface
User environment that uses pictorial as well as horizontal cross-connect
textual representations of the input and output Wiring closet where the horizontal cabling con-
of applications and the hierarchical or other nects to a patch panel which is connected by
data structure in which information is stored. backbone cabling to the main distribution facil-
Conventions such as buttons, icons, and win- ity.
dows are typical, and many actions are per-
formed using a pointing device (such as a
High-Level Data Link Control
mouse). Microsoft Windows and the Apple
Bit-oriented synchronous data link layer proto-
Macintosh are prominent examples of plat-
col developed by ISO. Derived from SDLC,
forms utilizing a GUI.
HDLC specifies a data encapsulation method
gutter on synchronous serial links using frame charac-
Type of wall-mounted channel with removable ters and checksums.
cover used to support horizontal cabling. Gutter
is big enough to hold several cables.
The end point of a broadband network. All sta-
H channel tions transmit toward the headend; the headend
high-speed channel then transmits toward the destination stations.
Full-duplex ISDN primary rate channel operat-
ing at 384 Kbps. Compare with B channel, D
channel, and E channel.
Glossary 345

header plus the letters A through F to represent hexa-
decimal digits with values of 10 to 15. The
Control information placed before data when
right-most digit counts ones, the next counts
encapsulating that data for network transmis-
multiples of 16, then 162=256, etc.
sion. Compare with trailer.

hierarchical routing
header checksum
Routing based on a hierarchical addressing sys-
Field within an IP datagram that indicates the
tem. For example, IP routing algorithms use IP
integrity check on the header.
addresses, which contain network numbers,
HELLO subnet numbers, and host numbers.
Interior routing protocol used principally by
hierarchical star topology
NSFnet nodes. HELLO allows particular packet
Extended star topology where a central hub is
switches to discover minimal delay routes. Not
connected by vertical cabling to other hubs that
to be confused with the Hello protocol.
are dependent on it.
hello packet
High-Level Data Link Control
Multicast packet that is used by routers for
neighbor discovery and recovery. Hello packets
also indicate that a client is still operating and
High-Order DSP
Hello protocol
High-Performance Parallel Interface
Protocol used by OSPF systems for establish-
ing and maintaining neighbor relationships. Not
to be confused with HELLO. High-Speed Communications Interface
helper address
Address configured on an interface to which High-Speed Serial Interface
broadcasts received on that interface will be See HSSI.
See bus.
High-Energy Physics Network
Research network that originated in the United
States, but that has spread to most places in- HSSI Interface Processor
volved in high-energy physics. Well-known Interface processor on the Cisco 7000 series
sites include Argonne National Laboratory, routers. The HIP provides one HSSI port that
Brookhaven National Laboratory, Lawrence supports connections to ATM, SMDS, Frame
Berkeley Laboratory, and the Stanford Linear Relay, or private lines at speeds up to T3 or E3.
Accelerator Center (SLAC).
hertz High-Performance Parallel Interface
Measure of frequency. Synonymous with cycles High-performance interface standard defined
per second. Abbreviated Hz. by ANSI. HIPPI is typically used to connect su-
percomputers to peripherals and other devices.
heterogeneous network
Network consisting of dissimilar devices that
run dissimilar protocols and in many cases sup- Number of 32-bit words in the header.
port dissimilar functions or applications.
hexadecimal High-Order DSP
Base 16. A number representation using the
digits 0 through 9, with their usual meaning,
346 CCNA Security Course Booklet, Version 1.0

NSAP address field that is used for subdividing hot swapping
the domain into areas. This is roughly equiva- See OIR and POS.
lent to a subnet in IP.
hot wire
holddown Ungrounded lead wire that connects the trans-
State into which a route is placed so that routers former and electrical devices or appliances via
will neither advertise the route nor accept ad- an electrical outlet and power plug.
vertisements about the route for a specific
length of time (the holddown period). Hold-
High-Speed Communications Interface
down is used to flush bad information about a
Single-port interface, developed by Cisco, pro-
route from all routers in the network. A route is
viding full-duplex synchronous serial commu-
typically placed in holddown when a link in
nications capability at speeds up to 52 Mbps.
that route fails.
Hot Standby Router Protocol
Conformity of a product or specification to in-
Provides high network availability and trans-
ternational standards, such as ITU-T, CSA,
parent network topology changes. HSRP cre-
TUV, UL, or VCCI. Enables portability across
ates a Hot Standby router group with a lead
company and international boundaries.
router that services all packets sent to the Hot
hop Standby address. The lead router is monitored
Term describing the passage of a data packet by other routers in the group, and if it fails, one
between two network nodes (for example, be- of these standby routers inherits the lead posi-
tween two routers). tion and the Hot Standby group address.

hop count HSSI
Routing metric used to measure the distance High-Speed Serial Interface
between a source and a destination. RIP uses Network standard for high-speed (up to 52
hop count as its sole metric. Mbps) serial connections over WAN links.

horizontal cross connect HSSI Interface Processor
See HCC. See HIP.

host HTML
Computer system on a network. Similar to the hypertext markup language
term node except that host usually implies a Simple hypertext document formatting lan-
computer system, whereas node generally ap- guage that uses tags to indicate how a given
plies to any networked system, including access part of a document should be interpreted by a
servers and routers. viewing application, such as a WWW browser.
See also hypertext and WWW browser.
host address
See host number. hub
1) Generally, a term used to describe a device
host node
that serves as the center of a star-topology net-
SNA subarea node that contains an SSCP. work.
2) Hardware or software device that contains
host number
multiple independent but connected modules of
Part of an IP address that designates which
network and internetwork equipment. Hubs can
node on the subnetwork is being addressed.
be active (where they repeat signals sent
A host number is also known as a host address.
through them) or passive (where they do not re-
Hot Standby Router Protocol peat, but merely split, signals sent through
Glossary 347

3) In Ethernet and IEEE 802.3, an Ethernet ICC
multiport repeater, sometimes referred to as a intermediate cross connect
concentrator. IDF that connects the horizontal cross-connect
to the main cross-connect. See HCC and MCC.
hybrid network
Internetwork made up of more than one type of ICMP
network technology, including LANs and Internet Control Message Protocol
WANs. Network layer Internet protocol that reports er-
rors and provides other information relevant to
IP packet processing. Documented in RFC 792.
Electronically-stored text that allows direct ac-
cess to other texts by way of encoded links. Hy- ICMP Router Discovery Protocol
pertext documents can be created using HTML, See IRDP.
and often integrate images, sound, and other
Identification, Flags, Frag Offset
media that are commonly viewed using a
Field within an IP datagram that provides frag-
WWW browser.
mentation of datagrams to allow differing
hypertext markup language MTUs in the internet.
Identity Based Network Services
Abbreviation for input/output.
IAB intermediate distribution facility
Internet Architecture Board Secondary communications room for a building
Board of internetwork researchers who discuss using a star networking topology. The IDF is
issues pertinent to Internet architecture. Re- dependent on the MDF.
sponsible for appointing a variety of Internet-
related groups such as the IANA, IESG, and
initial domain identifier
IRSG. The IAB is appointed by the trustees of
NSAP address field that identifies the domain.
the ISOC.
International Data Number. See X.121.
Internet Assigned Numbers Authority
Organization operated under the auspices of the
ISOC as a part of the IAB. IANA delegates au-
interdomain part
thority for IP address-space allocation and do-
NSAP address field that consists of the AFI and
main-name assignment to the NIC and other
IDI together. This is roughly equivalent to a
organizations. IANA also maintains a database
classful IP network, in decimal format.
of assigned protocol identifiers used in the
TCP/IP stack, including autonomous system IDPR
numbers. Interdomain Policy Routing
Interdomain routing protocol that dynamically
exchanges policies between autonomous sys-
Identity Based Network Services
tems. IDPR encapsulates interautonomous sys-
Integrated solution combining several Cisco
tem traffic and routes it according to the
products that offer authentication, access con-
policies of each autonomous system along the
trol, and user policies to secure network con-
path. IDPR is currently an IETF proposal.
nectivity and resources.
348 CCNA Security Course Booklet, Version 1.0

IDRP layer. IEEE 802.12 uses the demand priority
media-access scheme at 100 Mbps over a vari-
IS-IS Interdomain Routing Protocol
ety of physical media.
OSI protocol that specifies how routers com-
municate with routers in different domains.
IEEE 802.1x
IEC IEEE standard specifying authentication proto-
cols, such as EAP.
International Electrotechnical Commission
Industry group that writes and distributes stan-
IEEE 802.2
dards for electrical products and components.
IEEE LAN protocol that specifies an imple-
IEEE mentation of the LLC sublayer of the data link
layer. IEEE 802.2 handles errors, framing, flow
Institute of Electrical and Electronics Engineers
control, and the network layer (Layer 3) service
Professional organization whose activities in-
interface. Used in IEEE 802.3 and IEEE 802.5
clude the development of communications and
network standards. IEEE LAN standards are
the predominant LAN standards today.
IEEE 802.3
IEEE 802.1 IEEE LAN protocol that specifies an imple-
mentation of the physical layer and the MAC
IEEE specification that describes an algorithm
sublayer of the data link layer. IEEE 802.3 uses
that prevents bridging loops by creating a span-
CSMA/CD access at a variety of speeds over a
ning tree. The algorithm was invented by Digi-
variety of physical media. Extensions to the
tal Equipment Corporation. The Digital
IEEE 802.3 standard specify implementations
algorithm and the IEEE 802.1 algorithm are not
for Fast Ethernet. Physical variations of the
exactly the same, nor are they compatible.
original IEEE 802.3 specification include
IEEE 802.11 10BASE2, 10BASE5, 10BASE-F, 10BASE-T,
IEEE specification developed to eliminate the and 10Broad36. Physical variations for Fast
problems inherent with proprietary WLAN Ethernet include 100BASE-T, 100BASE-T4,
technologies. It began with a 1 Mbps standard and 100BASE-X.
and has evolved into several other standards, in-
IEEE 802.3i
cluding 802.11a, 802.11b, and 802.11g.
Physical variation of the original IEEE 802.3
IEEE 802.11a specification that calls for using Ethernet type
IEEE WLAN standard for 54 Mbps at 5 GHz. signaling over twisted pair networking media.
The standard sets the signaling speed at 10
IEEE 802.11b
megabits per second using a baseband signaling
IEEE WLAN standard for 11 Mbps at 2.4 GHz.
scheme transmitted over twisted pair cable em-
ploying a star or extended star topology.
IEEE 802.11g
IEEE WLAN standard for 54 Mbps at 2.4 GHz.
IEEE 802.4
IEEE LAN protocol that specifies an imple-
IEEE 802.11h
mentation of the physical layer and the MAC
IEEE specification that radios must comply
sublayer of the data link layer. IEEE 802.4 uses
with in order to use the 11 channels for the
token-passing access over a bus topology and is
802.11a standard. IEEE 802.11h includes the
based on the token bus LAN architecture.
TPC and DFS features.
IEEE 802.5
IEEE 802.11i
IEEE LAN protocol that specifies an imple-
IEEE 802.11 specification for WPA.
mentation of the physical layer and MAC sub-
IEEE 802.12 layer of the data link layer. IEEE 802.5 uses
IEEE LAN standard that specifies the physical token passing access at 4 or 16 Mbps over STP
layer and the MAC sublayer of the data link cabling and is similar to IBM Token Ring.
Glossary 349

IEEE 802.6 IIN
IEEE MAN specification based on DQDB tech- Intelligent Information Network
nology. IEEE 802.6 supports data rates of 1.5 to Network that seamlessly supports new IP
155 Mbps. strategies, including service-oriented architec-
ture (SOA), Web services and virtualization. It
IESG is implemented using SONA. Compare with
Internet Engineering Steering Group SONA.
Organization, appointed by the IAB, that man-
ages the operation of the IETF.
Incumbent Local Exchange Carrier
IETF Traditional telephone company. In the U.S., the
Internet Engineering Task Force Regional Bell Operation Companies (RBOCs)
Task force consisting of over 80 working that were formed after the divestiture of AT and
groups responsible for developing Internet stan- T and the Independent Operating Companies
dards. The IETF operates under the auspices of (IOCs) that usually are located in more rural
ISOC. areas or single cities are ILECs. In other areas
of the world, ILECs are the Post, Telephone,
and Telegraphs (PTTs), government-managed
International Federation for Information Pro-
Research organization that performs OSI pre- ILMI
standardization work. Among other accom- Interim Local Management Interface
plishments, IFIP formalized the original MHS Specification developed by the ATM Forum for
model. incorporating network-management capabilities
into the ATM UNI.
Internet Group Management Protocol IMP
Used by IP hosts to report their multicast group Interface message processor
memberships to an adjacent multicast router. Former name for ARPANET packet switches.
An IMP is now known as a packet-switch node
Interior Gateway Protocol
Internet protocol used to exchange routing in- in-band signaling
formation within an autonomous system. Ex- Transmission within a frequency range nor-
amples of common Internet IGPs include IGRP, mally used for information transmission. Com-
OSPF, and RIP. pare with out-of-band signaling.
IGRP Industry-Standard Architecture
Interior Gateway Routing Protocol See ISA.
IGP developed by Cisco to address the prob-
lems associated with routing in large, heteroge-
neous networks. Compare with Enhanced Electromagnetic waves whose frequency range
IGRP. is above that of microwaves, but below that of
the visible spectrum. LAN systems based on
IIH this technology represent an emerging technol-
Intermediate System-to-Intermediate System ogy.
Used by routers to detect neighbors and form
adjacencies. In addition to the IIH, which is an Infrastructure mode indicates a WLAN topol-
IS-IS PDU, there is an ISH and an ESH, which ogy where clients connect through an access
are ES-IS PDUs. point.
350 CCNA Security Course Booklet, Version 1.0

initial domain identifier more efficient than two separate implementa-
tions. Compare with IS-IS.
See IDI.
Integrated IS-IS was formerly known as Dual
initial domain part IS-IS.
See IDP.
Integrated Services Digital Network
Internet Network Operations Center
Intelligent Information Network
BBN group that in the early days of the Internet
See IIN.
monitored and controlled the Internet core gate-
ways (routers). INOC no longer exists in this
interarea routing
Term used to describe routing between two or
input/output more logical areas. Compare with intra-area
See I/O.

interdomain ID
Institute of Electrical and Electronics
Engineers See IDI.
interdomain part
insulator See IDP.
Any material with a high resistance to electrical
Interdomain Policy Routing
current. See conductor.
insured burst
The largest burst of data above the insured rate
1) Connection between two systems or devices.
that will be temporarily allowed on a PVC and
2) In routing terminology, a network connec-
not tagged by the traffic policing function for
dropping in the case of network congestion.
3) In telephony, a shared boundary defined by
The insured burst is specified in bytes or cells.
common physical interconnection characteris-
Compare with maximum burst.
tics, signal characteristics, and meanings of in-
insured rate terchanged signals.
The long-term data throughput, in bits or cells 4) The boundary between adjacent layers of the
per second, that an ATM network commits to OSI model.
support under normal network conditions. The
interface message processor
insured rate is 100 percent allocated; the entire
See IMP.
amount is deducted from the total trunk band-
width along the path of the circuit. Compare interface module
with excess rate and maximum rate.
Combination of a line card and an access card


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