BGP Overview
Configuring BGP
page 3-16
OmniSwitch AOS Release 7 Advanced Routing Configuration Guide
March 2011
Route Dampening
Route dampening is a mechanism for controlling route instability. If a route (or path) is frequently adver-
tised and withdrawn, it can expend router resources. Route dampening categorizes a route as either
behaved
or
ill-behaved
. A well behaved route shows a high degree of stability over an extended period of
time, while an ill-behaved route shows a high degree of instability over a short period of time. This insta-
bility is also known as
flapping
.
Route dampening can suppress (not activate) an ill-behaved route until it has achieved a certain degree of
stability. Route suppression is based on the number of times a route flaps over a period of time.
Note.
This mechanism does not apply to IPv6 prefixes.
The following diagram illustrates this concept:
Routes 1, 2, and 3 are entering AS 100, but Route 2 (because it is flapping) has exceeded the dampening
threshold. It is therefore not propagated into the AS.
The dampening threshold and suppression time of a route is determined by various factors discussed in
“Controlling Route Flapping Through Route Dampening” on page 3-36
.
CIDR Route Notation
Although CIDR is supported by the router, CIDR route notation is not supported on the CLI command
line. For example, in order to enter the route “198.16.10.0/24” you must input “198.16.10.0
255.255.255.0”. Some show commands, such as
ip bgp policy prefix-list
, do use CIDR notation to
indicate route prefixes.
Route 1
Route 3
Route 2
(flapping)
Route 1
Route 3
AS 100