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Glossary

routed protocol

Routed protocols (such as IP and

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

route maps

Small scripts used to manipulate rout-

ing that can contain multiple instances and multiple
conditions for each instance. Route maps are some-
what like access lists if you specify that the packet
must match an access list. In addition to having the
capability of permitting or denying the packet, you
can define what is done before the packet is for-
warded. Route maps can be used to set metrics for
route updates, set a command to its default value, and
so on.

route poisoning

Used by various DV routing proto-

cols in order to overcome 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 sum-
mary route is advertised to other areas by an area bor-
der 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 network traf-
fic. Sending packets between networks by routers is
based on the information provided on Network layers.
Historically, this device has sometimes been called a
gateway.

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.

routing domain

Any collection of end systems and

intermediate systems that operate under an identical
set of administrative rules. Every routing domain

contains one or several areas, all individually given a
certain area address.

routing metric

Any value that is used by routing

algorithms to determine whether one route is superior
to another. Metrics include such information as band-
width, delay, hop count, path cost, load, MTU, reli-
ability, and communication cost. Only the best
possible routes are stored in the routing table, while all
other information may be stored in link-state or topo-
logical databases. See also: cost.

routing protocol

Any protocol that defines algo-

rithms to be used for updating routing tables between
routers. Examples include IGRP, RIP, and OSPF.

routing table

A table kept in a router or other inter-

networking mechanism that maintains a record of
only the best possible routes to certain network desti-
nations and the metrics associated with those routes.

Route Processor: Also known as a supervisory

processor, a module on Cisco 7000 series routers that
holds the CPU, system software, and most of the mem-
ory components used in the router.

RSP

Route/Switch Processor: A processor module

combining the functions of RP and SP used in Cisco
7500 series routers. See also: RP and SP.

RTMP

Routing Table Maintenance Protocol. This

protocol is responsible for AppleTalk routing tables
and their information. This is AppleTalk's proprietary
method of maintaining route tables on AppleTalk-
enabled machines.

RTS

Request To Send: An EIA/TIA-232 control sig-

nal requesting permission to transmit data on a com-
munication line.

S reference point

ISDN reference point that works

with a T reference point to convert a 4-wire ISDN net-
work to the 2-wire ISDN network needed to commu-
nicate with the ISDN switches at the network
provider.

SAGE

Synergy Advanced Gate-Array Engine: This

chip is used for non-Ethernet applications--including
FDDI, ATM LANE, Token Ring, and the Network
Management Processor on the Supervisor engine.

www.sybex.com