Cisco IE 4000, Software Configuration Manual

Page: 873 / 1066

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Configuring IP Unicast Routing
Configuring BGP
router bgp 5
neighbor 172.16.70.24 route-reflector-client
Configuring Route Dampening
Route flap dampening minimizes the propagation of flapping routes across an internetwork. A route is considered to be
flapping when it is repeatedly available, then unavailable, then available, then unavailable, and so on. When route
dampening is enabled, a numeric
penalty value is assigned to a route when it flaps. When a route’s accumulated penalties
reach a configurable limit, BGP suppresses advertisements of the route, even if the route is running. The reuse limit is a
configurable value that is compared with the penalty. If the penalty is less than the reuse limit, a suppressed route that
is up is advertised again.
Dampening is not applied to routes that are learned by IBGP. This policy prevents the IBGP peers from having a higher
penalty for routes external to the AS.
BEFORE YOU BEGIN
Enable BGP routing as described in the Enabling BGP Routing, page 850 .
DETAILED STEPS
To disable flap dampening, use the no bgp dampening router configuration command without keywords. To set
dampening factors back to the default values, use the no bgp dampening router configuration command with values.
EXAMPLE
In the following example, BGP dampening is applied to prefixes filtered through the route-map named BLUE:
Switch(config)# ip prefix-list RED permit 10.0.0.0/8
Switch(config)# !
Switch(config)# route-map BLUE
Switch(config-route-map)# match ip address ip prefix-list RED
Switch(config-route-map)# exit
Command Purpose
1. configure terminal Enter global configuration mode.
2. router bgp autonomous-system Enter BGP router configuration mode.
3. bgp dampening Enable BGP route dampening.
4. bgp dampening half-life reuse suppress
max-suppress [ route-map map ]
(Optional) Change the default values of route
dampening factors.
5. end Return to privileged EXEC mode.
6. show ip bgp flap-statistics [{ regexp
regexp } | { filter-list list } | { address mask
[ longer-prefix ]}]
(Optional) Monitor the flaps of all paths that are flapping.
The statistics are deleted when the route is not
suppressed and is stable.
7. show ip bgp dampened-paths (Optional) Display the dampened routes, including the
time remaining before they are suppressed.
8. clear ip bgp flap-statistics [{ regexp
regexp } | { filter-list list } | { address mask
[ longer-prefix ]}
(Optional) Clear BGP flap statistics to make it less likely
that a route will be dampened.
9. clear ip bgp dampening (Optional) Clear route dampening information, and
unsuppress the suppressed routes.
10. copy running-config startup-config (Optional) Save your entries in the configuration file.