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BGP: Configuring Prefix Filters
Page 24 | Use Route Maps and Other Filters to Filter and Alter BGP and OSPF Routes
Filter out a range of different prefix lengths
This example filters out routes to 45.0.0.0 with prefix lengths in the range 5-8, accepts routes
to 52.0.0.0/8, and implicitly filters out all other BGP routes.
awplus(config-router)#
neighbor 45.45.45.46 prefix-list list1 in
4. Shut down the neighbor, and then bring it up again.
awplus(config-router)#
neighbor 45.45.45.46 shutdown
awplus(config-router)#
neighbor 45.45.45.46 no shutdown
5. Check that the IP route table now contains one of the routes learnt from that
neighbor, but not the other.
awplus(config-router)#
do show ip route
Codes: C - connected, S - static, R - RIP, B - BGP
O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
* - candidate default
B 45.0.0.0/8 [20/0] via 45.45.45.46, vlan1, 00:00:06
C 45.45.45.0/24 is directly connected, vlan1
C 64.0.0.0/4 is directly connected, vlan64
1. Remove the existing prefix list entry.
awplus(config)#
no ip prefix-list list1 permit 45.0.0.0/8
2. Add the following prefix list entries.
awplus(config)#
ip prefix-list list1 deny 45.0.0.0/4 ge 5 le 8
awplus(config)#
ip prefix-list list1 permit 52.0.0.0/8
3. Set that prefix list as the prefix list filter for neighbor 45.45.45.46
awplus(config)#
router bgp 34567
awplus(config)#
neighbor 45.45.45.46 prefix-list list2 in
4. Shut down the neighbor, and then bring it up again.
awplus(config-router)#
neighbor 45.45.45.46 shutdown
awplus(config-router)#
neighbor 45.45.45.46 no shutdown