3Com 2500 manual Static Routes, Dynamic Routes Using RIP

4-6 CHAPTER 4: ROUTING WITH IP TECHNOLOGY

Routing Table

Destination IP Address	Subnet Mask	Metric	Gateway	Interface
158.101.1.1	255.255.255.0	1	158.101.1.2	1
158.101.2.1	255.255.255.0	1	158.101.2.2	2
158.101.3.1	255.255.255.0	1	158.101.3.2	3
default route	255.255.255.0	1	158.101.1.2	1

Figure 4-5 Example of a Routing Table in the LANplex Routing Model

Routing table information is generated and updated in either of the following ways:

■Statically — You manually enter routes, which do not change until you change them (that is, they will not time out).

■Dynamically — The router uses a routing protocol, such as RIP, to exchange information. Routes are recalculated at regular intervals.

Static Routes

A static route is one that you manually configure in the routing table. Static routes are useful in environments where no routing protocol is used or where you want to override some of the routes generated with a routing protocol. Because static routes do not automatically change in response to network topology changes, you should manually configure only a small number of reasonably stable routes.

Dynamic Routes Using RIP

Automated methods of configuring routes help you keep up with a changing network environment, allowing routes to be reconfigured quickly and reliably. Interior Gateway Protocols (IGP), which operate within networks, provide this automated method. The LANplex system uses the Routing Information Protocol (RIP), one of the most widely used IGPs, to configure its routing tables dynamically.

RIP operates in terms of active and passive devices. The active devices, usually routers, broadcast their RIP messages to all devices in a network or subnet; they update their own routing tables when they receive a RIP message. The passive devices, usually hosts, listen for RIP messages and update their routing tables; they do not send RIP messages.