What is a route flap?

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What is a route flap?..

Route flapping is term when a router Advertise network via
one path and then other. This is basically happens due to
interface/link flapping.
Router can reach high CPU utilization in recalculation
(incase of Link state) or triggered updates (incase of
Distance vector) protocols.

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What is a route flap?..

Answer / ashfaq ahmed

Route flapping occurs when a router alternately advertises
a destination network via one route then another (or as
unavailable, and then available again) in quick sequence. A
closely related term is interface flapping where an
interface on a router has a hardware failure that will
cause the router to announce it alternately as "up"
and "down".

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withdrawn. In a network where a Link-state routing protocol
is run, route flapping will force frequent recalculation of
the topology by all participating routers. In networks with
Distance vector routing protocols flapping routes can
trigger routing updates with every state change. In both
cases, they prevent the network from 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will not be withdrawn as long as at least one of the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 this aggregate.

With regards
S.Ashfaq Ahmed.