Brocade BigIron RX Series Configuration Guide - Manual (Page 919)

BigIron RX Series Configuration Guide 841
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Originating the default route
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The <suppress> parameter specifies how high a route’s penalty can become 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 four times the half-life setting. Thus, if you use the
default half-life of 15 minutes, the maximum suppression time is 60 minutes.
The following example shows how to change the dampening parameters.
BigIron RX(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. If you
want to leave some parameters unchanged, enter their default values.
Originating the default route
By default, the device does not originate and advertise a default route using BGP4. A BGP4 default
route is the IP address 0.0.0.0 and the route prefix 0 or network mask 0.0.0.0. For example,
0.0.0.0/0 is a default route.
NOTE
The device checks for the existence of an IGP route for 0.0.0.0/0 in the IP route table before creating
a local BGP route for 0.0.0.0/0.
To enable the router to originate and advertise a default BGP4 route, enter the following command.
BigIron RX(config-bgp)# default-information-originate
Syntax: [no] default-information-originate
Changing the default local preference
When the router uses the BGP4 algorithm to select a route to send to the IP route table, one of the
parameters the algorithm uses is the local preference. Local preference is an attribute that
indicates a degree of preference for a route relative to other routes. BGP4 neighbors can send the
local preference value as an attribute of a route in an UPDATE message.
Local preference applies only to routes within the local AS. BGP4 routers can exchange local
preference information with neighbors who also are in the local AS, but BGP4 routers do not
exchange local preference information with neighbors in remote ASs.
The default local preference is 100. For routes learned from EBGP neighbors, the default local
preference is assigned to learned routes. For routes learned from IBGP neighbors, the local
preference value is not changed for the route.
When the BGP4 algorithm compares routes on the basis of local preferences, the route with the
higher local preference is chosen.