Netgear RH348 User Manual download pdf (Page 24)

Reference Guide for the Model RT328 and Model RH348 ISDN Routers

1-6 Introduction

Basic Router Concepts

In general, the cost of providing network bandwidth is proportional to the data speed and the

distance over which the network extends. Large amounts of bandwidth are provided easily and

relatively inexpensively in a local area network (ofﬁce, department, and similar situations).

However, providing the same high data speeds between two local networks that are physically

distant may be prohibitively expensive. Because of this expense, high-speed local area networks

(LANs) are usually interconnected by slower-speed links to form a wide area network (WAN).

In order to make the best use of the slower WAN links, a mechanism must be in place at each

location for selecting data meant only for another location and sending it by the best available link.

The function of selecting and forwarding this data is performed by a router.

What is a Router?

A router is a device that forwards trafﬁc between networks based on network layer information in

the data and on routing tables maintained by the router. In these routing tables, a router builds up a

logical picture of the overall network by gathering and exchanging information with other routers

in the network. Using this information, it chooses the best path for forwarding network trafﬁc.

Routers vary in performance and scale, number of routing protocols supported, and types of

physical WAN connections supported. The Model RT328/RH348 router is a small ofﬁce router

that routes the IP protocol over a dial-up ISDN connection.

Routing Information Protocol

One of the protocols used by a router to build and maintain a picture of the network is the Routing

Information Protocol (RIP). RIP is a distance vector protocol, meaning that all the decisions about

which path to use are based upon a logical distance between source and destination networks. This

distance is measured in “hops,” meaning the number of relaying routers in the path between the

source LAN router and the router of the destination LAN. For example, the LAN of router A is

considered to be 1 hop away. If router A can reach the network of router B by a direct WAN link to

the network of router B, the network of router B is two hops away. If another network must be

reached by calling router B and having router B forward the data, that network is n hops away,

where n is the number of routers traversed by the data to get to the network farthest away. When

there are multiple paths to a network, the path with the fewest number of hops is chosen and is

regarded as the best path, and all other information about how to get to that network is discarded.

Intro.fm Page 6 Tuesday, October 10, 2000 3:15 PM

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Netgear RH348 User Manual Page 24