System information

Configuring BGP
12-37
Using an AS Path Access List
The commands in the following example configure Router Los Angeles using an AS
path access list. Filter List 1 assigns a weight attribute of 1000 to updates received
from neighbors from AS 100. Access List 1 permits any update whose AS-path
attribute begins with 100 (specified by “^”). The same is true for Access List 2
regarding AS 300. Filter List 2 assigns a weight attribute of 500 to updates received
from AS 300.
Example
MOT(config)#router bgp 400
MOT(config-bgp)#neighbor 3.3.3.1 remote-as 100
MOT(config-bgp)#neighbor 3.3.3.1 filter-list 1 weight 1000
MOT(config-bgp)#neighbor 4.4.4.1 remote-as 300
MOT(config-bgp)#neighbor 4.4.4.1 filter-list 2 weight 500
MOT(config-bgp)#exit
MOT(config)#ip as-path access-list 1 permit ^100
MOT(config)#ip as-path access-list 2 permit ^300
Adjusting BGP Timers
BGP supports the following two commands that set the frequency of keepalive and
holdtime timers:
• timers bgp — globally sets the keepalive timers for BGP
• neighbor timers — sets the keepalive timers for a BGP peer or peer group
Keepalive messages are exchanged between BGP peers or peer groups to monitor the
health of the link between them. If a BGP peer does not receive a keepalive message,
it waits for a configured holdtime before the ailing BGP peer is declared dead by its
waiting peer.
To configure the keepalive frequency and holdtime interval globally for BGP, use the
timers bgp command in Router BGP Configuration mode, as shown below:
MOT(config-bgp)#timers bgp <keepalive> <holdtime>
where:
keepalive – is the frequency in seconds, that the BSR sends keepalive messages to
its peers; default is 60 seconds.