IP event dampening
introduces a configurable exponential delay mechanism to suppress the effects
of excessive interface flapping events on routing protocols and routing tables
in the network. This feature allows the network operator to configure a router
to automatically identify and selectively dampen a local interface that is
flapping, removing it from the network until it becomes stable again. Thus, the
network becomes more stable, with a faster convergence time.
parameters should be considered only when the link type does not offer fast
enough link failure detection. The standard default values for the hello
interval and hello multiplier are 10 seconds and 3 seconds. Therefore, the
multiplier times the interval will give a default hold-time of 30 seconds.
Although a slower
hello interval saves bandwidth and CPU usage, there are some situations when a
faster hello interval is preferred. In the case of a large configuration that
uses Traffic Engineering (TE) tunnels, if the TE tunnel uses ISIS as the
Interior Gateway Protocol (IGP), and the IP routing process is restarted at the
router at the ingress point of the network (headend), then all the TE tunnels
get resignaled with the default hello interval. A faster hello interval
prevents this resignaling. To configure a faster hello interval, you need to
decrease the ISIS hello interval manually using the
point-to-point adjacency over a broadcast media can improve convergence times
of a customer’s network because it prevents the system from electing a
designated router (DR), prevents flooding from using CSNPs for database
synchronization, and simplifies shortest path first (SPF) computations.