A flapping router is a router that transmits routing updates that first advertises a destination network via one route, then a different route. This behavior is called route flapping.



It is caused by conditions such as hardware, software and configuration errors, as well as unreliable connections -- like our dodgy wireless links, which drop out intermittantly.



Route flapping is bad, because it increases latency and processor usage on our routing machines -- often a packet in transit will be held at a router while it recalculates which route it should take.



Efforts have been made to allieviate this problem in [BGP], you can find more information at [FlapDampening].