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Glossary

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generally placed in holddown when one of its
links fails.

hop

The movement of a packet between any two

network nodes. See also: hop count.

hop count

A routing metric that calculates the dis-

tance between a source and a destination. RIP employs
hop count as its sole metric. See also: hop and RIP.

host address

Logical address configured by an

administrator or server on a device. Logically identi-
fies this device on an internetwork.

HSCI

High-Speed Communication Interface: Devel-

oped by Cisco, a single-port interface that provides
full-duplex synchronous serial communications capa-
bility at speeds up to 52Mbps.

HSRP

Hot Standby Router Protocol: A protocol that

provides high network availability and provides
nearly instantaneous hardware fail-over without
administrator intervention. It generates a Hot Standby
router group, including a lead router that lends its ser-
vices to any packet being transferred to the Hot
Standby address. If the lead router fails, it will be
replaced by any of the other routers--the standby
routers--that monitor it.

HSSI

High-Speed Serial Interface: A network stan-

dard physical connector for high-speed serial linking
over a WAN at speeds of up to 52Mbps.

hubs

Physical-layer devices that are really just mul-

tiple port repeaters. When an electronic digital signal
is received on a port, the signal is reamplified or regen-
erated and forwarded out all segments except the seg-
ment from which the signal was received.

ICD

International Code Designator: Adapted from

the subnetwork model of addressing, this assigns the
mapping of Network layer addresses to ATM
addresses. HSSI is one of two ATM formats for
addressing created by the ATM Forum to be utilized
with private networks. See also: DCC.

ICMP

Internet Control Message Protocol: Docu-

mented in RFC 792, it is a Network layer Internet pro-

tocol for the purpose of reporting errors and providing
information pertinent to IP packet procedures.

IEEE

Institute of Electrical and Electronics Engineers:

A professional organization that, among other activi-
ties, defines standards in a number of fields within
computing and electronics, including networking and
communications. IEEE standards are the predominant
LAN standards used today throughout the industry.
Many protocols are commonly known by the reference
number of the corresponding IEEE standard.

IEEE 802.1

The IEEE committee specification that

defines the bridging group. The specification for STP
(Spanning-Tree Protocol) is IEEE 802.1d. The STP
uses SPA (spanning-tree algorithm) to find and pre-
vent network loops in bridged networks. The specifi-
cation for VLAN trunking is IEEE 802.1q.

IEEE 802.3

The IEEE committee specification that

defines the Ethernet group, specifically the original
10Mbps standard. Ethernet is a LAN protocol that
specifies Physical layer and MAC sublayer media
access. IEEE 802.3 uses CSMA/CD to provide access
for many devices on the same network. FastEthernet is
defined as 802.3u, and Gigabit Ethernet is defined as
802.3q. See also: CSMA/CD.

IEEE 802.5

IEEE committee specification that

defines Token Ring media access.

IGMP

Internet Group Management Protocol:

Employed by IP hosts, the protocol that reports their
multicast group memberships to an adjacent multicast
router.

ignore

A Cisco IOS command, which can be caused

in three ways: the hardware buffer fills up and it sig-
nals to the transmitting interface to throttle down, the
interface is receiving frames faster than the SP can pull
them off, and when the CxBus is so busy that the inter-
face processor is unable to copy the packet from the
hardware buffer to the SP buffers.

IGP

Interior Gateway Protocol: Any protocol used

by the Internet to exchange routing data within an
independent system. Examples include RIP, IGRP,
and OSPF.

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