Glossary L

I

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. Compare to: DCC.

ICMP

Internet Control Message Protocol: Documented in RFC 792, it is a Network layer Internet protocol 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 activities, 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 prevent network loops in bridged networks.

IEEE 802.1p

802.1p specifies 3 bits in the 802.1Q header for allocation to Class of Service (CoS). This is analogous to quality of service in IP.

IEEE 802.1Q

The specification for VLAN trunking is IEEE 802.1Q, which specifies additional fields inside any LAN frame.

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 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. The first version, IGMPv1, enables hosts to subscribe to or join specified multicast groups. Enhancements were made to IGMPv2 to facilitate a host-initiated leave process, and IGMPv3 allows hosts to specify the list of hosts from whom they can receive traffic, blocking traffic from other hosts transmitting the same stream.

IGMP Join process

The process by which hosts may join a multicast session outside of the Membership Query interval.

IGMP Leave process

IGMPv1 does not have a formal leave process; a period of three query intervals must pass with no host confirmation before the interface is deactivated. IGMPv2 and IGMPv3 do allow the host to initiate the leave process immediately.

IGMP Query process

The router uses IGMP to query hosts for Membership Reports, thus managing multicast on its interfaces.

IGMP Snooping

An extension to CGMP, IGMP Snooping enables the switch to make multicast decisions directly, without the intervention of a router.

IGP

Interior Gateway Protocol: Any protocol used by the Internet to exchange routing data within an independent system. Examples include RIP, IGRP, and OSPF.

ILMI

Integrated (or Interim) Local Management Interface. A specification created by the ATM Forum, designated for the incorporation of network-management capability into the ATM UNI. Integrated Local Management Interface cells provide for automatic configuration between ATM systems. In LAN emulation, ILMI can provide sufficient information for the ATM end station to find an LECS. In addition, ILMI provides the ATM NSAP (Network Service Access Point) prefix information to the end station.

in-band

See: in-band management.

in-band management

The management of a network device 'through' the network. Examples include using Simple Network Management Protocol (SNMP) or Telnet directly via the local LAN. Compare to: out-of-band management.

in-band signaling

Configuration of a router from within the network. Examples are Telnet, Simple Network Management Protocol (SNMP), or a Network Management Station (NMS). Compare to: out-of-band signaling.

insured burst

In an ATM network, it is the largest temporarily permitted data burst exceeding the insured rate on a PVC and not tagged by the traffic policing function for being dropped if network congestion occurs. This insured burst is designated in bytes or cells. Compare to: maximum burst.

Integrated Services

Integrated Services networks use signaling protocols to establish an end- to-end path across an internetwork, with a predefined QoS applied to each traffic flow.

interarea routing

Routing between two or more logical areas. Compare to: intra-area routing. See also: area.

interface processor

Any of several processor modules used with Cisco 7000 series routers. See also: AIP, CIP, EIP, FEIP, HIP, MIP, and TRIP.

internal route processor

Route Switch Modules (RSMs) and Route Switch Feature Cards (RSFCs) are called internal route processors because the processing of layer 3 packets is internal to a switch.

Internet

The global 'network of networks,' whose popularity has exploded in the last few years. Originally a tool for collaborative academic research, it has become a medium for exchanging and distributing information of all kinds. The Internet's need to link disparate computer platforms and technologies has led to the development of uniform protocols and standards that have also found widespread use within corporate LANs. See also: TCP/IP and MBONE.

internet

Before the rise in the use of the Internet, this lowercase form was shorthand for 'internetwork' in the generic sense. Now rarely used. See also: internetwork.

Internet protocol

Any protocol belonging to the TCP/IP protocol stack. See also: TCP/IP.

internetwork

Any group of private networks interconnected by routers and other mechanisms, typically operating as a single entity.

internetworking

Broadly, anything associated with the general task of linking networks to each other. The term encompasses technologies, procedures, and products. When you connect networks to a router, you are creating an internetwork.

inter-VLAN routing

Cisco has created the proprietary protocol Inter-Switch Link (ISL) to allow routing between VLANs with only one Ethernet interface. To run ISL, you need to have two VLAN-capable FastEthernet or Gigabit Ethernet devices, such as a Cisco 5000 switch and a 7000 series router.

intra-area routing

Routing that occurs within a logical area. Compare to: interarea routing.

intruder detection

A system that operates by monitoring the data flow for characteristics consistent with security threats. In this manner, an intruder can be monitored or blocked from access. One trigger for an intruder detection system is multiple ping packets from a single resource in a brief period of time.

Inverse ARP

Inverse Address Resolution Protocol: A technique by which dynamic mappings are constructed in a network, enabling a device such as a router to locate the logical network address and associate it with a permanent virtual circuit (PVC). Commonly used in Frame Relay to determine the far-end node's TCP/IP address by sending the Inverse ARP request to the local DLCI.

IOS

Cisco's famous fully-inclusive Internetwork Operating System.

IP

Internet Protocol: Defined in RFC 791, it is a Network layer protocol that is part of the TCP/IP stack and allows connectionless service. IP furnishes an array of features for addressing, type-of-service specification, fragmentation and reassembly, and security.

IP address

Often called an 'Internet address,' this is an address uniquely identifying any device (host) on the Internet (or any TCP/IP network). Each address consists of four octets (32 bits), represented as decimal numbers separated by periods (a format known as 'dotted- decimal'). Every address is made up of a network number, an optional subnetwork number, and a host number. The network and subnetwork numbers together are used for routing, while the host number addresses an individual host within the network or subnetwork. The network and subnetwork information is extracted from the IP address by using the subnet mask. There are five classes of IP addresses (A-E), which allocate different numbers of bits to the network, subnetwork, and host portions of the address. See also: CIDR, IP, and subnet mask.

IPCP

IP Control Program: The protocol used to establish and configure IP over PPP. See also: IP and PPP.

IP multicast

A technique for routing that enables IP traffic to be reproduced from one source to several endpoints or from multiple sources to many destinations. Instead of transmitting only one packet to each individual point of destination, one packet is sent to a multicast group specified by only one IP endpoint address for the group.

IPX

Internetwork Packet Exchange: Network layer protocol (layer 3) used in Novell NetWare networks for transferring information from servers to workstations. Similar to IP and XNS.

IPXCP

IPX Control Program: The protocol used to establish and configure IPX over PPP. See also: IPX and PPP.

IPX spoofing

Provides IPX RIP/SAP traffic without requiring a connection to the opposing network. This allows a per-minute tariffed link, such as ISDN or analog phone, to support IPX without requiring the link to remain active.

IPXWAN

Protocol used for new WAN links to provide and negotiate line options on the link by using IPX. After the link is up and the options have been agreed upon by the two end-to-end links, normal IPX transmission begins.

IRDP

ICMP Router Discovery Protocol: Enables hosts to use the Internet Control Message Protocol (ICMP) to find a new path when the primary router becomes unavailable. IRDP is an extension to the ICMP protocol and not a dynamic routing protocol. This ICMP extension allows routers to advertise default routes to end stations.

ISDN

Integrated Services Digital Network: Offered as a service by telephone companies, a communication protocol that allows telephone networks to carry data, voice, and other digital traffic. See also: BISDN, BRI, and PRI.

ISL routing

Inter-Switch Link routing is a Cisco proprietary method of frame tagging in a switched internetwork. Frame tagging is a way to identify the VLAN membership of a frame as it traverses a switched internetwork.

isochronous transmission

Asynchronous data transfer over a synchronous data link, requiring a constant bit rate for reliable transport. Contrast with: asynchronous transmission and synchronous transmission.

ITU-T

International Telecommunication Union Telecommunication Standardization Sector: A group of engineers who develop worldwide standards for telecommunications technologies.