Users Guide

OS10(conf-router-neighbor)# exit
OS10(conf-router-bgp-65501)# end
OS10# show running-configuration bgp
!
router bgp 65501
confederation identifier 100
confederation peers 65502 65503 65504
!
neighbor 1.1.1.2
remote-as 65502
no shutdown
!
neighbor 2.1.1.2
remote-as 65503
no shutdown
!
neighbor 3.1.1.2
remote-as 65504
no shutdown
Route dampening
When EBGP routes become unavailable, they “flap” and the router issues both WITHDRAWN and UPDATE notices. A flap occurs
when a route is withdrawn, readvertised after being withdrawn, or has an attribute change.
The constant router reaction to the WITHDRAWN and UPDATE notices causes instability in the BGP process. To minimize this
instability, configure penalties (a numeric value) for routes that flap. When that penalty value reaches a configured limit, the
route is not advertised, even if the route is up, the penalty value is 1024.
As time passes and the route does not flap, the penalty value decrements or decays. If the route flaps again, it is assigned
another penalty. The penalty value is cumulative and adds underwithdraw, readvertise, or attribute change.
When dampening applies to a route, its path is described by:
History entry
Entry that stores information about a downed route.
Dampened path Path that is no longer advertised.
Penalized path Path that is assigned a penalty.
1. Enable route dampening in ROUTER-BGP mode.
dampening [half-life | reuse | max-suppress-time]
● half-life — Number of minutes after which the penalty decreases (1 to 45, default 15). After the router assigns a
penalty of 1024 to a route, the penalty decreases by half after the half-life period expires.
● reuse — Number compares to the flapping route’s penalty value. If the penalty value is less than the reuse value, the
flapping route again advertises or is no longer suppressed (1 to 20000, default 750). Withdrawn routes are deleted from
the history state.
● suppress — Number compares to the flapping route’s penalty value. If the penalty value is greater than the suppress
value, the flapping route no longer advertises and is suppressed (1 to 20000, default 2000).
● max-suppress-time — Maximum number of minutes a route is suppressed (1 to 255, default is four times the
half-life value or 60 minutes).
2. View all flap statistics or for specific routes meeting the criteria in EXEC mode.
show ip bgp flap-statistics [ip-address [mask]]
● ip-address [mask]— Enter the IP address and mask.
● filter-list as-path-name — Enter the name of an AS-PATH ACL.
● regexp regular-expression — Enter a regular express to match on.
When you change the best path selection method, path selections for the existing paths remain unchanged until you reset it by
using the clear ip bgp command in EXEC mode.
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