Prerequisites: CCNP level skills.
Topology
Task 1
Configure BGP on all routers according to the topology diagram. Advertise all loopbacks using 'network' statement. Check the next-hop behavior on LAN link connecting R1, R2 and R4.
Lab Solution
Task 1
Configure BGP on all routers according to the topology diagram. Advertise all loopbacks using 'network' statement. Check the next-hop behavior on LAN link connecting R1, R2 and R4.
R1 Configuration:
!
router bgp 13
no synchronization
bgp router-id 1.1.1.1
bgp log-neighbor-changes
network 172.16.101.0 mask 255.255.255.0
neighbor 10.1.13.3 remote-as 13
neighbor 10.1.13.3 next-hop-self
neighbor 10.1.124.4 remote-as 40
no auto-summary
no synchronization
bgp router-id 1.1.1.1
bgp log-neighbor-changes
network 172.16.101.0 mask 255.255.255.0
neighbor 10.1.13.3 remote-as 13
neighbor 10.1.13.3 next-hop-self
neighbor 10.1.124.4 remote-as 40
no auto-summary
!
R2 Configuration:
!
router bgp 20
no synchronization
bgp router-id 2.2.2.2
bgp log-neighbor-changes
network 172.16.102.0 mask 255.255.255.0
neighbor 10.1.124.4 remote-as 40
no auto-summary
no synchronization
bgp router-id 2.2.2.2
bgp log-neighbor-changes
network 172.16.102.0 mask 255.255.255.0
neighbor 10.1.124.4 remote-as 40
no auto-summary
!
R3 Configuration:
!
router bgp 13
no synchronization
bgp router-id 3.3.3.3
bgp log-neighbor-changes
network 172.16.103.0 mask 255.255.255.0
neighbor 10.1.13.1 remote-as 13
neighbor 10.1.13.1 next-hop-self
neighbor 10.1.35.5 remote-as 50
no auto-summary
no synchronization
bgp router-id 3.3.3.3
bgp log-neighbor-changes
network 172.16.103.0 mask 255.255.255.0
neighbor 10.1.13.1 remote-as 13
neighbor 10.1.13.1 next-hop-self
neighbor 10.1.35.5 remote-as 50
no auto-summary
!
R4 Configuration:
!
router bgp 40
no synchronization
bgp router-id 4.4.4.4
bgp log-neighbor-changes
network 172.16.104.0 mask 255.255.255.0
network 172.16.144.0 mask 255.255.255.0
neighbor 10.1.124.1 remote-as 13
neighbor 10.1.124.2 remote-as 20
no auto-summary
no synchronization
bgp router-id 4.4.4.4
bgp log-neighbor-changes
network 172.16.104.0 mask 255.255.255.0
network 172.16.144.0 mask 255.255.255.0
neighbor 10.1.124.1 remote-as 13
neighbor 10.1.124.2 remote-as 20
no auto-summary
!
R5 Configuration:
!
router bgp 50
no synchronization
bgp router-id 5.5.5.5
bgp log-neighbor-changes
network 172.16.105.0 mask 255.255.255.0
neighbor 10.1.35.3 remote-as 13
no auto-summary
no synchronization
bgp router-id 5.5.5.5
bgp log-neighbor-changes
network 172.16.105.0 mask 255.255.255.0
neighbor 10.1.35.3 remote-as 13
no auto-summary
!
Verification:
Pic. 2 - R5' BGP Table.
Pic. 3 - R1's BGP Prefix from AS 20.
Even though R1 receives the prefix over EBGP session the next-hop address is R2's address rather than R4's. This is the default behavior on Broadcast and NBMA networks. Pay a special attention to NBMA since the circuits may not be fully meshed and the reachability to the next-hop address may be a problem.
Pic. 4 - Prefix Details.
Next-Hop Attribute: 10.1.124.2
Advertising Router: 10.1.124.4
Advertising Router ID: 4.4.4.4