Brocade Virtual ADX Switch and Router Guide (Supporting ADX v03.1.00) - Manual (Page 234)

220 Brocade Virtual ADX Switch and Router Guide
53-1003246-01
Configuring route flap dampening
8
Memory limit error
SYSLOG: <11Jan 1 00:00:00 mu1, BGP: From Peer 192.168.1.2 received Long AS_PAT
H= AS_CONFED_SET(4) 1 2 3 AS_CONFED_SEQUENCE(3) 4 AS_SET(1) 5 6 7 AS_SEQ(2) 8 9
attribute length (9) Exceeded internal memory limit
NOTE
The router generates a log message one time every two minutes. Because of this rate limit, it is
possible that some errors might not appear in the log. In this case, you can use the debug ip bgp
events command to view errors pertaining to the maxas-limit value and the actual AS path attributes
received.
Configuring route flap dampening
Route flap dampening reduces the amount of route state changes propagated by BGP4 due to
unstable routes. This in turn reduces processing requirements.
To enable route flap dampening using the default values, enter the following command.
Virtual ADX(config-bgp)# dampening
Syntax: [no] dampening [half-life reuse suppress max-suppress-time]
The half-life parameter specifies the number of minutes after which the penalty for a route
becomes half its value. The route penalty allows routes that have remained stable for a period
despite earlier instability to eventually become eligible for use again. The decay rate of the penalty
is proportional to the value of the penalty. After the half-life expires, the penalty decays to half its
value. A dampened route that is no longer unstable can eventually again become eligible for use.
You can configure the half-life to be from 1 - 45 minutes. The default is 15 minutes.
The reuse parameter specifies how low a penalty for a route must be before the route becomes
eligible for use again, after being suppressed. You can set the reuse threshold to a value from 1 –
20000. The default is 750 (0.75, or three-fourths, of the penalty assessed for a one flap).
The suppress parameter specifies how high the penalty for a route can be before the device
suppresses the route. You can set the suppression threshold to a value from 1 – 20000. The
default is 2000 (more than two flaps).
The max-suppress-time parameter specifies the maximum number of minutes that a route can be
suppressed regardless of how unstable it is. You can set the maximum suppression time to a value
from 1 – 255 minutes. The default is 40 minutes.
This example shows how to change the dampening parameters.
Virtual ADX(config-bgp)# dampening 20 200 2500 40
This command changes the half-life to 20 minutes, the reuse threshold to 200, the suppression
threshold to 2500, and the maximum number of minutes a route can be dampened to 40.
NOTE
To change any of the parameters, you must specify all the parameters with the command. To want
to leave any parameters unchanged, enter their default values.