Editing Route flapping (section)

==Condition==
Route flapping is caused by pathological conditions (hardware errors, software errors, configuration errors, intermittent errors in communications links, unreliable connections, etc.) within the network which cause certain reachability information to be repeatedly advertised and withdrawn. For example, [[link flap]] occurs when an interface on a router has a hardware failure that causes the router to announce it alternately as ''up'' and ''down''.

In networks with [[link-state routing protocol]]s, route flapping will force frequent recalculation of the topology by all participating routers. In networks with [[distance-vector routing protocol]]s, route flapping can trigger routing updates with every state change. In both cases, it prevents the network from [[Convergence (routing)|converging]].

Route flapping can be contained to a smaller area of the network if [[route aggregation]] is used. As an aggregate route will not be withdrawn as long as at least one of the aggregated subnets is still valid, a flapping route that is part of an aggregate will not disturb the routers that receive the aggregate.<ref>{{cite book
  | title = CCNP 1 Advanced Routing Companion Guide
  | publisher = [[Cisco Press]]
  | location = Indianapolis
  | date = 2004
  | page = [https://archive.org/details/ccnp1advancedrou02edunse/page/50 50]
  | isbn = 1-58713-135-8
  | url = https://archive.org/details/ccnp1advancedrou02edunse/page/50
  }}
</ref>