Which three describe the reasons large OSPF networks use a hierarchical design? (Choose three.)
Large OSPF networks typically use a hierarchical design for several reasons. These include:
To reduce routing overhead: In a large network, there can be many OSPF routers, and each router can have a large number of links. Without a hierarchical design, every router would need to know about every link and every router in the network, which would result in a significant amount of routing overhead. By dividing the network into smaller areas, the routers in each area only need to know about the links and routers in their own area, which reduces the amount of routing overhead.
To confine network instability to single areas of the network: In a large network, network instability or failures can occur, which can lead to routing instability and a lack of connectivity. By dividing the network into smaller areas, any instability or failures are confined to the area in which they occur, and other areas of the network are not affected. This helps to ensure that the network remains stable and available.
To speed up convergence: In a large network, when a change occurs, such as a link failure, it can take some time for all the routers in the network to learn about the change and converge on a new set of routes. By dividing the network into smaller areas, the routers only need to learn about changes in their own area, which speeds up the convergence process.
To reduce the complexity of router configuration: In a large network, there can be many routers, each with a large number of links. Without a hierarchical design, the configuration of each router can be very complex. By dividing the network into smaller areas, the configuration of each router can be simplified, as it only needs to know about the links and routers in its own area.
Option C, "to lower costs by replacing routers with distribution layer switches," is not a typical reason for using a hierarchical design in OSPF networks. While distribution layer switches can be used in a hierarchical design, their use does not necessarily lower costs, as switches can be more expensive than routers.
Option D, "to decrease latency by increasing bandwidth," is also not a typical reason for using a hierarchical design in OSPF networks. While increasing bandwidth can decrease latency, a hierarchical design is not necessarily required to do so.
Therefore, the correct answers are A, B, and E.