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Glossary

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ring topology

A network logical topology comprising a series of repeaters

that form one closed loop by connecting unidirectional transmission links.
Individual stations on the network are connected to the network at a
repeater. Physically, ring topologies are generally organized in a closed-loop
star. Compare with: bus topology and star topology.

RJ connector

registered jack connector: Used with twisted-pair wiring to

connect the copper wire to network interface cards, switches, and hubs.

RIP

Routing Information Protocol: The most commonly used interior

gateway protocol in the Internet. RIP employs hop count as a routing metric.
See also: Enhanced IGRP, IGP, OSPF, and hop count.

robbed-bit signaling

Used in Primary Rate Interface clocking mechanisms.

rolled cable

Type of Ethernet cable that is used to connect a PC's COM

port to a router or switch console port.

ROM

read-only memory: Chip used in computers to help boot the device.

Cisco routers use a ROM chip to load the bootstrap, which runs a power-on
self test, and then find and load the IOS in flash memory by default.

root bridge

Used with 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 proto-
cols (such as RIP, IGRP, and OSPF) are used to update routing tables
between routers.

route flap

A route that is being announced in an up/down fashion.

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.

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