Prerequisites: CCNP level skills.
Note!
Configuration from Lab 123 must be used in this lab.
Topology
Task 1
After merging the three ASes (Lab 123/124), the administrator of AS 50 noticed that prefixes arriving on R5 carry the AS 123 in the AS_PATH attribute. Before AS 50 configure their R5 router to peer with AS 123, the administrator asked you to remove AS 123 from the AS_PATH attribute.
Solution
Task 1
After merging the three ASes (Lab 123/124), the administrator of AS 50 noticed that prefixes arriving on R5 carry the AS 123 in the AS_PATH attribute. Before AS 50 configure their R5 router to peer with AS 123, the administrator asked you to remove AS 123 from the AS_PATH attribute.
Pic. 2 - Current BGP Table on R5.
!
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 replace-as
no auto-summary
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 replace-as
no auto-summary
!
Pic. 3 - R5's BGP Table.
The option 'no-prepend' removes the local-as numbers (look at lab 124). The option 'replace-as' strips off the original AS number when updates are sent to the BGP neighbor configured to use the local-as number.
