When different subnet routes in the same natural network segment are transmitted to other network segments, these routes are aggregated into one route of the same segment. This process is called route aggregation. RIP-1 packets do not carry mask information, so RIP-1 can advertise only the routes with natural masks. Because RIP-2 packets do carry mask information, RIP-2 supports subnetting.
RIP-2 route convergence can improve extensibility and efficiency and minimize the routing table of a large-scale network.
Route convergence is classified into two types as follows:
Classful aggregation based on RIP processes:
Aggregated routes are advertised with natural masks. Classful convergence summarizes the child routes to their classful address. When classful summary feature is enabled, a classful route is advertised instead of child routes on the interfaces that have IP addresses in different major network. Summary routes are advertised using the best metric of all the child routes.
For example, router 10.1.1.0/24 (metric = 2) and router 10.1.2.0/24 (metric = 3) are aggregated as an aggregated route (10.0.0.0/8 (metric = 2)) in the natural network segment. Because RIP-2 aggregation is classful, it obtains the optimal metric.
Interface-based aggregation:
A user can specify an aggregation address.
For example, router 10.1.1.0/24 (metric = 2) and router 10.1.2.0/24 (metric = 3) are aggregated as an aggregated route (10.1.0.0/16 (metric = 2)).