On large networks, the RIPng routing table of each device contains a large number of routes, which consumes lots of system resources. In addition, if a specific link connected to a device within an IP address range frequently alternates between Up and Down, route flapping occurs.
To address these problems, RIPng route summarization was introduced. With RIPng route summarization, a device summarizes routes destined for different subnets of a network segment into one route destined for one network segment and then advertises the summary route to other network segments. RIPng route summarization reduces the number of routes in the routing table, minimizes system resource consumption, and prevents route flapping.
RIPng route summarization is interface-based. After RIPng route summarization is enabled on an interface, the interface summarizes routes based on the longest matching rule and then advertises the summary route. The smallest metric among the specific routes for the summarization is used as the metric of the summary route.
For example, an interface has two routes: 11:11:11::24 with metric 2 and 11:11:12::34 with metric 3. After RIPng route summarization is enabled on the interface, the interface summarizes the two routes into the route 11::0/16 with metric 2 and then advertises it.