MPLS BGP PE-CE SOO and AS-override

MPLS BGP PE-CE and AS-override

The AS override feature allows a provider edge (PE) router to change the private autonomous system (AS) number used by a customer edge (CE) device on an external BGP (EBGP) session running on a VPN routing and forwarding (VRF) access link. The private AS number is changed to the PE AS number. Another CE device connected to another PE device sees the EBGP route coming from the first site with an AS path of provider-ASN provider-ASN, instead of provider-ASN site1-ASN. This allows enterprise networks to use the same private ASN on all sites.

AS-override work in the opposite direction as to which its applied, it tells the PE the override the AS when passing the routes to the CE(Customer)
 
On R1 we see there are no routes learned for 5.5.5.0 subnet
Now lets configure AS-override on R2
R2(config-router-af)#neighbor 12.1.1.1 as-override
R2(config-router-af)#neighbor 12.1.1.1 route-map SOO in
R2(config)#route-map SOO permit 10
R2(config-route-map)#set extcommunity soo 11:55
 

  
 












R2 Config:
ip vrf CUST1
 rd 1:5
 route-target export 1:5
 route-target import 1:5
!interface Loopback0
 ip address 2.2.2.2 255.255.255.0
 ip ospf network point-to-point
!
interface FastEthernet0/0
 ip vrf forwarding CUST1
 ip address 12.1.1.2 255.255.255.0
 duplex auto
 speed auto
!
interface FastEthernet0/1
 ip address 23.1.1.2 255.255.255.0
 duplex auto
 speed auto
 mpls ip
!
router ospf 10
 log-adjacency-changes
 network 2.2.2.0 0.0.0.255 area 0
 network 23.1.1.0 0.0.0.255 area 0
!
router bgp 100
 no bgp default ipv4-unicast
 bgp log-neighbor-changes
 neighbor 4.4.4.4 remote-as 100
 neighbor 4.4.4.4 update-source Loopback0
 !
 address-family vpnv4
  neighbor 4.4.4.4 activate
  neighbor 4.4.4.4 send-community both
 exit-address-family
 !
 address-family ipv4 vrf CUST1
  neighbor 12.1.1.1 remote-as 65001
  neighbor 12.1.1.1 activate
  neighbor 12.1.1.1 as-override
  neighbor 12.1.1.1 route-map SOO in
  no synchronization
 exit-address-family
!
route-map SOO permit 10
 set extcommunity soo 11:55
R3 Config:
interface Loopback0
 ip address 3.3.3.3 255.255.255.0
!
interface FastEthernet0/0
 ip address 23.1.1.3 255.255.255.0
 duplex auto
 speed auto
 mpls ip
!
interface FastEthernet0/1
 ip address 34.1.1.3 255.255.255.0
 duplex auto
 speed auto
 mpls ip
!
router ospf 10
 log-adjacency-changes
 network 0.0.0.0 255.255.255.255 area 0
R4 Config:
ip vrf CUST1
 rd 1:5
 route-target export 1:5
 route-target import 1:5
interface Loopback0
 ip address 4.4.4.4 255.255.255.0
 ip ospf network point-to-point
!
interface FastEthernet0/0
 ip address 34.1.1.4 255.255.255.0
 duplex auto
 speed auto
 mpls ip
!
interface FastEthernet0/1
 ip vrf forwarding CUST1
 ip address 45.1.1.4 255.255.255.0
 duplex auto
 speed auto
!
router ospf 10
 log-adjacency-changes
 network 4.4.4.0 0.0.0.255 area 0
 network 34.1.1.0 0.0.0.255 area 0
!
router bgp 100
 no bgp default ipv4-unicast
 bgp log-neighbor-changes
 neighbor 2.2.2.2 remote-as 100
 neighbor 2.2.2.2 update-source Loopback0
 !
 address-family vpnv4
  neighbor 2.2.2.2 activate
  neighbor 2.2.2.2 send-community both
 exit-address-family
 !
 address-family ipv4 vrf CUST1
  neighbor 45.1.1.5 remote-as 65001
  neighbor 45.1.1.5 activate
  neighbor 45.1.1.5 as-override
  neighbor 45.1.1.5 route-map SOO in
  no synchronization
 exit-address-family
!
route-map SOO permit 10
 set extcommunity soo 11:55
R1 Config:
interface Loopback0
 ip address 1.1.1.1 255.255.255.0
!
interface FastEthernet0/0
 ip address 12.1.1.1 255.255.255.0
 duplex auto
 speed auto
!
interface FastEthernet0/1
 ip address 15.1.1.1 255.255.255.0
 duplex auto
 speed auto
!
router eigrp 10
 redistribute bgp 65001 metric 1 1 1 1 1
 passive-interface default
 no passive-interface FastEthernet0/1
 network 15.1.1.0 0.0.0.255
 auto-summary
!
router bgp 65001
 no synchronization
 bgp log-neighbor-changes
 network 1.1.1.0 mask 255.255.255.0
 neighbor 12.1.1.2 remote-as 100
 no auto-summary
R5 Config:
interface Loopback0
 ip address 5.5.5.5 255.255.255.0
!
interface FastEthernet0/0
 ip address 45.1.1.5 255.255.255.0
 duplex auto
 speed auto
!
interface FastEthernet0/1
 ip address 15.1.1.5 255.255.255.0
 duplex auto
 speed auto
!
router eigrp 10
 redistribute bgp 65001 metric 1 1 1 1 1
 passive-interface default
 no passive-interface FastEthernet0/1
 network 15.1.1.0 0.0.0.255
 auto-summary
!
router bgp 65001
 no synchronization
 bgp log-neighbor-changes
 network 5.5.5.0 mask 255.255.255.0
 neighbor 45.1.1.4 remote-as 100
 no auto-summary