Flat WAN Topologies
A wide-area network (WAN) for a small company can consist of a few sites connected in a loop. Each site has a WAN router that connects to two other adjacent sites via point-to-point links, as shown at the top of Figure 5-2. As long as the WAN is small (a few sites), routing protocols can converge quickly, and communication with any other site can recover when a link fails. (As long as only one link fails, communication recovers. When more than one link fails, some sites are isolated from others.)
Figure 5-2. A Flat Loop Topology (top) and a Hierarchical Redundant Topology (Bottom)
Figure 5-2. A Flat Loop Topology (top) and a Hierarchical Redundant Topology (Bottom)
A flat loop topology is generally not recommended for networks with many sites, however. A loop topology can mean that there are many hops between routers on opposite sides of the loop, resulting in significant delay and a higher probability of failure. If your analysis of traffic flow indicates that routers on opposite sides of a loop topology exchange a lot of traffic, you should recommend a hierarchical topology instead of a loop. To avoid any single point of failure, redundant routers or switches can be placed at upper layers of the hierarchy, as shown at the bottom of Figure 5-2.
The flat loop topology shown at the top of Figure 5-2 meets goals for low cost and reasonably good availability. The hierarchical redundant topology shown at the bottom of Figure 5-2 meets goals for scalability, high availability, and low delay.
Continue reading here: Flat LAN Topologies
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