Hierarchical routing is a technique commonly used when building large networks. As a network grows, so do the resource requirements for the network’s management and control functions. In a TCP/IP network, resource consumption includes
Router memory consumed by routing tables and other routing protocol data. In an OSPF network, this other data would include the OSPF link-state database.
Router computing resources, used in calculating routing tables and other routing protocol functions. In an OSPF network, these resources include the CPU required to calculate shortest-path trees.
Link bandwidth, used in distributing routing data. In an OSPF network, this includes the bandwidth consumed by OSPF’s database synchronization ...