BGP Best Practice / Private-AS vs. Public-AS in the MPLS Core

[Michel Bou Sleiman]

Dears,

We have recently aquired a large network with ASR9K as Internet Gateways and non-Cisco devices in the MPLS Core.

We would liike to know which is the best recommended solution to use Private MP-BGP AS in the MPLS Core or extend the IGW Public AS, knowing  that the IGW will be in a VRF and not the global routing table. Moreover, the clients of the MPLS Core have their own BGP Public AS and would need to connect to the MPLS Core to obtain internet services from the IGW.

(Cust1)------EBGP------[VRF_Cust_1](MPLS CORE AS_2)[VRF_IGW]------EBGP-----(IGW AS_1) in the case of having a private BGP AS in the core

(Cust1)------EBGP------[VRF_Cust_1](MPLS CORE AS_1)[VRF_IGW]------iBGP-----(IGW AS_1) in the case of having same public BGP AS in the core

Waiting for your feedback and thoughts.

Thanks,

Michel.

[xthuijs]

Michel,

if your mpls core is also used for internet transit, then it is best to be a public AS.

if not, then you can leave it be and remove the private AS at your border routers.

If oyu are connecting multiple MPLS networks together to link L2 or L3 VPN services, I think it is easiest to have it all one AS, otherwise you end up with complex designs such as Carrier supporting Carrier (CSC) or Inter-AS option A (vrf lite), B (using vpnv4 at the inter AS gateay) or C (using vpnv4 at the interAS gateway with route reflectors in each AS peering with each other).

regards

xander

Xander Thuijs CCIE #6775
Principal Engineer 
ASR9000, CRS, NCS6000 & IOS-XR