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
Reviewing Dynamic Routing 105
For example, if Router B in Figure 3-7 is one unit of cost from Router A, Router B would add 1
to all costs reported by Router A when Router B runs the distance vector processes to update its
routing table. This would be maintained by the routers exchanging routing information in a timely
manner through some update mechanism.
Figure 3-7 Maintaining Routes
Routing Loops
When you are maintaining the routing information, routing loops can occur if the slow
convergence of the internetwork after a topology change causes inconsistent routing entries. The
example presented in the next few pages uses a simple network design to convey the concepts.
Later in this chapter, you look at how routing loops occur and are corrected in more complex
network designs. Figure 3-8 illustrates how each node maintains the distance from itself to each
possible destination network.
Figure 3-8 Maintaining Distance
Just before the failure of network 10.
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