Installing and Administering Internet Services

274 Chapter 8

Conﬁguring gated

Conﬁguring the OSPF Protocol

Cost

The outbound side of each router interface is associated with a

conﬁgurable cost. Lower cost interfaces are more likely to be used in

forwarding data trafﬁc. Cost values are assigned at the discretion of the

network or system administrator. While the value is arbitrary, it should

be a function of throughput or capacity of the interface: the higher the

value, the lower the throughput or capacity. Thus, the interfaces with the

highest throughput or capacity should be assigned lower cost values than

other interfaces. Interfaces from networks to routers have a cost of 0.

Figure 8-12 shows an example network where costs have been speciﬁed

for each interface.

Figure 8-12 Cost Conﬁguration Example

In Figure 8-12, there are two possible packet routes between nodes A and

D: one route goes through node B and the other route goes through node

C. The cost of each route is calculated as follows:

Node A to node B and node B to node D: 5+5 = 10

Node A to node C and node C to node D: 5+10 = 15

B C

193.2.1.33 (cost 5)

193.2.1.17 (cost 5)

193.2.1.30 (cost 10)

193.2.1.46 (cost 10)

193.2.1.35 (cost 5)

193.2.1.20 (cost 5)

LAN 1 193.2.1.32

LAN 2 193.2.1.16