A problem condition that can occur with dynamic routers on large internetworks. When a router is flapping (called a “flapping router”), it broadcasts routing table updates that alternate between two different routes to a host.
For example, the flapping router might indicate during the first broadcast that route A is the best route to a given host, indicate during the second broadcast that route B is the best route, indicate during the following broadcast that route A is best, and so on.
Flapping routers thus generate unnecessary routing traffic over the network. This generally happens when a router is unnecessarily configured to load-balance between paths with equal hop counts. To determine whether a router is flapping, use a network packet sniffer.
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Route flapping occurs when a router interface alternates rapidly between the up and down states and it can cripple a router with excessive updates and recalculations.However, the summarization configuration prevents the RTC route flapping from affecting any other routhers.
While the RTC may be kept busy dealing with its own route flap, RTZ, and all upstream routers, are unaware of any downstream problem.
Summarization effectively insulates the other routers from the problem of route flapping.
Two examples are routing loops and route flapping. Routing loops can cause packets to circle in the network without ever reaching their destination. Route flapping can cause routers to change their minds frequently and lead to a lot of unnecessary routing announcements.