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Glossary

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root bridge

Used with the Spanning Tree Protocol to stop network loops

from occurring. The root bridge is elected by having the lowest bridge ID.
The bridge ID is determined by the priority (32,768 by default on all bridges
and switches) and the main hardware address of the device. The root bridge
determines which of the neighboring layer 2 devices' interfaces become the
designated and nondesignated ports.

routed protocol

Routed protocols (such as IP and IPX) are used to

transmit user data through an internetwork. By contrast, routing protocols
(such as RIP, IGRP, and OSPF) are used to update routing tables between
routers.

route poisoning

Used by various DV routing protocols in order to over-

come large routing loops and offer explicit information about when a subnet
or network is not accessible (instead of merely suggesting that the network
is unreachable by not including it in updates). Typically, this is accomplished
by setting the hop count to one more than maximum. See also: poison
reverse updates.

route summarization

In various routing protocols, such as OSPF,

EIGRP, and IS-IS, the consolidation of publicized subnetwork addresses so
that a single summary route is advertised to other areas by an area border
router.

router

A network-layer mechanism, either software or hardware, using

one or more metrics to decide on the best path to use for transmission of net-
work traffic. Sending packets between networks by routers is based on the
information provided on network layers. Historically, this device has some-
times been called a gateway.

router on a stick

A term that identifies a single router interface connected

to a single distribution layer switch port. The router is an external router that
provides trunking protocol capabilities for routing between multiple
VLANs. See also: RSM, MSFC.

routing

The process of forwarding logically addressed packets from their

local subnetwork toward their ultimate destination. In large networks, the
numerous intermediary destinations a packet might travel before reaching its
destination can make routing very complex.

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