Route summarization, also called route aggregation, is a method of minimizing the number of routing tables in an IP (Internet Protocol) network. It works by consolidating selected multiple routes into a single route advertisement, in contrast to flat routing in which every routing table contains a unique entry for each route.
To implement route summarization in IP Version 4 (IPv4), Classless Inter-Domain Routing (CIDR) must be used. All IP addresses in the route advertisement must share identical high-order bits. The length of the prefix must not exceed 32 bits.
Route summarization offers several important advantages over flat routing. Route summarization can minimize the latency in a complex network, especially when many routers are involved. Because of the reduced number of routing entries, the overhead for routing protocols is minimized. Network stability can be improved by reducing or eliminating unnecessary routing updates after part of the network undergoes a change in topology. Route summarization also greatly reduces processor workloads, memory requirements and bandwidth demand.
See also: supernetting