Installing and Administering Internet Services

Chapter 8 247

Conﬁguring gated

Conﬁguring the RIP Protocol

RIP uses hopcount to determine the shortest path to a destination.

Hopcount is the number of routers a packet must pass through to reach

its destination. If a path is directly connected, it has the lowest hopcount

of 1. If the path passes through a single router, the hopcount increases to

2. Hopcount can increase to a maximum value of 16, which is RIP’s

“inﬁnity metric,” an indication that a network or node cannot be reached.

If gated encounters an unreachable node, it goes into “Holddown Mode.”

Holddown Mode stops a node from propagating routing information until

the other nodes it is communicating with stabilize their routing

information.

Hosts with only one LAN interface may use the RIP protocol with gated

to passively listen to routing information when there is more than one

router on the LAN. If there is only one router on the LAN (leaving only

one path off the local LAN), you may prefer to conﬁgure a static route to

that router in /etc/rc.config.d/net, or issue the route command

manually, instead of running gated.

In certain cases you may not want trafﬁc to take a certain path, because

it incurs an unacceptable cost or security risk. In these cases, gated

allows you to assign a metric to each interface. This allows you to select

or bypass a path, regardless of its length or speed.

A Simple RIP Conﬁguration

A simple conﬁguration contains RIP routers and end nodes that listen to

information exchanged by the RIP routers, as shown in Figure 8-1 below.

For the purposes of keeping this example simple, and because the

conﬁguration is similar among all end systems, only one end system’s

(node A) conﬁguration is shown here. The same is true for RIP routers

(only node B’s conﬁguration is shown here). Note that this example

shows only the syntax needed for this simple conﬁguration. A detailed

description of the full RIP protocol statement is given after this example.