Lab 94 - BGP Confederations

Prerequisites: CCNP level skills.

Topology

Pic. 1 - Topology Diagram.

Icons designed by: Andrzej Szoblik - http://www.newo.pl

Task 1
Ensure reachability between 172.16.102.0/24 and 172.16.105.0/24.

Lab Solution

Task 1

Ensure reachability between 172.16.102.0/24 and 172.16.105.0/24.

Since IBGP Split-Horizon rule forbids to advertise prefixes learned from IBGP peer to another IBGP peer, R1 does not forward 172.16.102.0/24 to R5 and 172.16.105.0/24 to R2. There are two solutions to this problem:

• Route-Reflector configuration on R1 (disabling IBGP Split-Horizon)
• Configure BGP Confederations

Note!
In order to implement BGP confederations BGP routing on R1, R3 and R4 must be reconfigured entirely.  

R2 and R5 BGP configuration remains the same (Lab 93).

R1 Configuration:

!

router bgp 65014
 no synchronization
 bgp router-id 172.16.101.1
 bgp log-neighbor-changes
 bgp confederation identifier 134
 bgp confederation peers 65003
 neighbor 10.1.13.3 remote-as 65003
 neighbor 10.1.14.4 remote-as 65014
 no auto-summary

!

R3 Configuration:

!

router bgp 65003
 no synchronization
 bgp router-id 172.16.103.3
 bgp log-neighbor-changes
 bgp confederation identifier 134
 bgp confederation peers 65014
 neighbor 10.1.13.1 remote-as 65014

 neighbor 10.1.13.1 next-hop-self
 neighbor 10.1.35.5 remote-as 50
 no auto-summary

!

R4 Configuration:

!

router bgp 65014
 no synchronization
 bgp router-id 172.16.104.4
 bgp log-neighbor-changes
 bgp confederation identifier 134
 neighbor 10.1.14.1 remote-as 65014
 neighbor 10.1.14.1 next-hop-self
 neighbor 10.1.24.2 remote-as 20
 no auto-summary

!

Notice!
The next-hop attribute behaves like in a regular EBGP-to-IBGP sessions. Confederation EBGP does NOT modify the next-hop attribute hence the next-hop-self command on R3 and R4.

Verification:

Pic. 2 - R3's BGP Table.

Pic. 3 - R4's BGP Table.

Pic. 4 - R2's BGP Table.

Notice!

The Private AS numbers are stripped off while advertising prefixes to real EBGP peers.

 Pic. 5 - Ping Test.