Network topology describes how networks fit together. Networks are connected to each other by routers. For example, the following figure shows 3 networks connected by 2 routers.
Figure 1 Basic Network Topology
The following figure shows a more complex configuration:
Figure 2 A Network Topology That Provides an Additional Path Between Networks
The topology includes a third router that directly connects Networks 1 and 3. The resulting redundancy improves reliability by maintaining connectivity even if Network 2 fails. However, the networks must use the same network protocols.