4.0.0, shown in Figure 3-9, all routers had consistent
knowledge and correct routing tables. The network is said to have converged. For this example,
A
Process to
Update This
Routing
Table
B
Process to
Update This
Routing
Table
Topology
Change
Causes
Routing
Table
Update
Router A Sends
Out This Updated
Routing Table
After the
Next Period
Expires
A C B E0
S0
S0
10.1.0.0 10.4.0.0 10.2.0.0
S0
S1 E0
10.3.0.0
Routing Table
10.1.0.0
10.2.0.0
10.3.0.0
10.4.0.0
E0
S0
S0
S0
0
0
1
2
Routing Table
10.2.0.0
10.3.0.0
10.4.0.0
10.1.0.0
S0
S1
S1
S0
0
0
1
1
Routing Table
10.3.0.0
10.4.0.0
10.2.0.0
10.1.0.0
S0
E0
S0
S0
0
0
1
2
106 Chapter 3: Medium-Sized Routed Network Construction
the cost function is hop count, so the cost of each link is 1. Router C is directly connected to
network 10.4.0.0, with a distance of 0. The path of Router A to network 10.4.0.0 is through Router
B, with a hop count of 2.
Figure 3-9 Slow Convergence Produces Inconsistent Routing
When network 10.4.0.0 fails, Router C detects the failure and stops routing packets out its E0
interface. However, Routers A and B have not yet received noti?¬?cation of the failure.
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