MPLS - CE-PE routing : BGP

Configure BGP on R4, R5 and R6.

R4#
router bgp 65000
bgp router-id 1.1.4.4
network 1.1.4.4 mask 255.255.255.255
neighbor 1.1.14.1 remote-as 1
!

R5#
router bgp 65000
bgp router-id 1.1.5.5
network 1.1.5.5 mask 255.255.255.255
neighbor 1.1.25.2 remote-as 1
!

R6#
router bgp 65000
bgp router-id 1.1.6.6
network 1.1.6.6 mask 255.255.255.255
neighbor 1.1.36.3 remote-as 1
!

Configure BGP on R1, R2 and R3.

R1#
router bgp 1
address-family ipv4 vrf company1
neighbor 1.1.14.4 remote-as 65000          ### config eBGP with CE router
neighbor 1.1.14.4 activate                 ### activate neighbor relationship
neighbor 1.1.14.4 as-override              ### When PE router advertises networks to CE router
!                             through BGP, change AS number of CE to the AS number of MPLS VPN

R2#
router bgp 1
address-family ipv4 vrf company1
neighbor 1.1.25.5 remote-as 65000
neighbor 1.1.25.5 activate
neighbor 1.1.25.5 as-override
!

R3#
router bgp 1
address-family ipv4 vrf company1
neighbor 1.1.36.6 remote-as 65000
neighbor 1.1.36.6 activate
neighbor 1.1.36.6 as-override
!

Result:

* Why AS-OVERRIDE is required ?

As shown in the picture above, All the router ASs are 65000 which means that R4 doesn't receive advertisement from R5 and R6, and the others act the same way with R4. Therefore, no one receives advertisement from the others. To solve the problem, set the command as-override which makes to be able to replace from AS 65000 to ISP AS number by R1, R2 and R3. So that R4, R5 and R6 can receive advertisement from the others.