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Scenario

In this scenario, Router R3 is configured to receive and filter routes from its BGP neighbor (23.1.1.2). We’ll use ACLs and route-maps to manage which routes are accepted into R3’s BGP table.

Step-by-Step Configuration

1. Configuring Access Control Lists (ACLs)

First, we create ACLs to deny specific routes and permit others.

Denying 1.1.1.0/24 and Permitting Others

R3(config)#access-list 10 deny 1.1.1.0 0.0.0.255
R3(config)#access-list 10 permit any

Denying 2.2.2.0/24 and Permitting Others

R3(config)#access-list 20 deny 2.2.2.0 0.0.0.255
R3(config)#access-list 20 permit any

2. Applying ACLs with Distribute-List

Next, we apply the first ACL using a distribute-list to filter incoming routes from the BGP neighbor.

R3(config)#router bgp 100
R3(config-router)#neighbor 23.1.1.2 distribute-list 10 in
R3(config-router)#do clear ip bgp * in

3. Verifying the BGP Routes and Running Configuration

Check the routes in the IP routing table and the current BGP configuration.

R3#show ip route
R3#show running-config | section bgp

4. Creating a Route-Map

Now, create a route-map that references the second ACL.

R3(config)#route-map cisco
R3(config-route-map)#match ip address 20
R3(config-route-map)#exit

Verify the route-map configuration.

R3#show route-map

5. Applying the Route-Map to the BGP Neighbor

Apply the route-map to the BGP neighbor to filter incoming routes.

R3(config)#router bgp 100
R3(config-router)#neighbor 23.1.1.2 route-map cisco in
R3(config-router)#end
R3#clear ip bgp * in

6. Final Verification

Check the routes in the IP routing table and the updated BGP configuration again to ensure the changes have taken effect.

R3#show ip route
R3#show running-config | section bgp

Troubleshooting Commands

Use the following commands to troubleshoot and ensure that the BGP route filtering is working correctly:

• show ip bgp – Displays the BGP routing table.
• show ip bgp neighbors – Displays detailed information about BGP neighbors.
• show ip bgp summary – Provides a summary of BGP neighbor status.
• debug ip bgp – Enables debugging of BGP events (use with caution in production environments).
• show ip access-lists – Displays the configured ACLs and their statistics.
• show ip route-map – Displays route-map information and matching criteria.

Explanation

Here is a brief explanation of the steps involved:

1. ACL Configuration: ACL 10 denies the route 1.1.1.0/24 and permits all other routes. ACL 20 denies the route 2.2.2.0/24 and permits all other routes.
2. Distribute-List: The distribute-list applies ACL 10 to filter incoming BGP routes from the neighbor 23.1.1.2.
3. Route-Map: The route-map named cisco references ACL 20 to filter routes. Applying this route-map to the BGP neighbor filters incoming routes based on the conditions specified in ACL 20.

Conclusion

Using ACLs and route-maps in BGP configurations allows for granular control over route redistribution, enhancing network performance and security. This example demonstrated how to deny specific routes and permit others using both ACLs and route-maps in a BGP environment.

By carefully planning and applying these configurations, network administrators can ensure that only desired routing information is accepted and propagated through their BGP routers, leading to more efficient and secure network operations.