Lab 124 - BGP Local-AS No-prepend - Learn Cisco

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Lab 124 - BGP Local-AS No-prepend

Prerequisites: CCNP level skills.

Note!
Configuration from Lab 123 must be used in this lab.

Topology

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

Task 1
After merging the three ASes (Lab 123), prefixes advertised by AS 40 and AS 50 prepend local-as AS numbers. Configure routers in such a way that the local-AS numbers no longer get propagated within AS 123 and to other autonomous systems.

Solution

Task 1
After merging the three ASes (Lab 123), prefixes advertised by AS 40 and AS 50 prepend local-as AS numbers. Configure routers in such a way that the local-AS numbers no longer get propagated within AS 123 and to other autonomous systems.

Pic. 2 - R3's Local-AS on R1.

Pic. 3 - R3's Local-AS on R3.

Notice!
R3 is DIRECTLY connected to AS 50 (R5) and also shows AS 30 (local-as) in the AS_PATH

Pic. 4 - R3's Local-AS on R4.

Notice!
Only one prefix is shown as an example. On R3 you can use:
show ip bgp regexp _40$.
AS 10 and AS 20 also show in the AS_PATH attribute.

R1 Configuration:
!
router bgp 123
 no synchronization
 bgp router-id 172.16.101.1
 bgp log-neighbor-changes
 network 172.16.101.0 mask 255.255.255.0
 neighbor 10.1.13.3 remote-as 123
 neighbor 10.1.13.3 next-hop-self
 neighbor 10.1.14.4 remote-as 40
 neighbor 10.1.14.4 local-as 10 no-prepend
 no auto-summary
!

R2 Configuration:
!
router bgp 123
 no synchronization
 bgp router-id 172.16.102.2
 bgp log-neighbor-changes
 network 172.16.102.0 mask 255.255.255.0
 neighbor 10.1.23.3 remote-as 123
 neighbor 10.1.23.3 next-hop-self
 neighbor 10.1.24.4 remote-as 40
 neighbor 10.1.24.4 local-as 20 no-prepend
 no auto-summary
!

R3 Configuration:
!
router bgp 123
 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 123
 neighbor 10.1.13.1 route-reflector-client
 neighbor 10.1.13.1 next-hop-self
 neighbor 10.1.23.2 remote-as 123
 neighbor 10.1.23.2 route-reflector-client
 neighbor 10.1.23.2 next-hop-self
 neighbor 10.1.35.5 remote-as 50
 neighbor 10.1.35.5 local-as 30 no-prepend
 no auto-summary
!

Verification:
Pic. 5 - R1 Has No AS 30 in AS_PATH.

Pic. 6 - R4 Has No AS 30 in AS_PATH.

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