Tuesday, May 3, 2011

Lab 121 - BGP Conditional Route Advertisement

Prerequisites: CCNP level skills.

Note!
Topology from Lab 118.

Topology

Pic. 1 - Topology Diagram.
Icons designed by: Andrzej Szoblik - http://www.newo.pl

Task 1
Configure R3 so that it advertises the default route only to R1. This default route should be advertised only if the interface between R3 and R5 is up.

Solution

NOTICE!
R3 should have default route configured in order to advertise it using bgp (for instance:
ip route 0.0.0.0 0.0.0.0 null0

Task 1
Configure R3 so that it advertises the default route only to R1. This default route should be advertised only if the interface between R3 and R5 is up.

Pic. 2 - R3 Has no Default Route Before Applying Configuration.
R3 Configuration:
!
 ip route 0.0.0.0 0.0.0.0 null0
!
ip prefix-list R3_R5_LINK seq 5 permit 10.1.35.0/24
!
route-map DEFAULT_ROUTE permit 10
 match ip address prefix-list R3_R5_LINK
!
router bgp 30
 no synchronization
 bgp router-id 172.16.103.3
 bgp log-neighbor-changes
 network 172.16.103.0 mask 255.255.255.0
 neighbor 10.1.13.1 remote-as 10
 neighbor 10.1.13.1 default-originate route-map DEFAULT_ROUTE
 neighbor 10.1.23.2 remote-as 20
 neighbor 10.1.35.5 remote-as 50
 no auto-summary
!

Verification:
Pic. 3 - R1's BGP Table.

 Pic. 4 - R2's BGP Table.

Notice!
Only R1 receives the default route.

Now, shutting down the E0/0 on R3

Pic. 5 - Link between R3 and R5 is Down.

Pic. 6 - R1 Loses the Default Route.