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Anupam Datta
Beginner

Inter-AS design with two ASBR

Hi,

I was trying to prepare an Inter-AS design, where planning to connect ISP PE routers through a L3 switch. All ISP PE and ASBR switch runs LDP & MP-EBGP. I am little confuse here whether it would work or not, bcause all document says to connect ISP PE's through another ASBR  but MP-EBGP peering between PE's dirrectly. Where as in my scnario MP-EBGP runs between PE-ASBR switch as below. Can anybody help me to understand if this will work or not .

          EBGP                      MP-iBGP                    MP-iBGP                                 MP-EBGP                               MP-EBGP                  MP-iBGP                   MP-iBGP                       EBGP

                                                                                                                                LDP                                        LDP

CE1----------ISP1-PE1------------ISP1-RR------------------ISP1-PE2--------------------ASBR-SW----------------ISP2-P2-----------ISP2-RR-------------ISP2-PE1--------CE2

1 REPLY 1
Akash Agrawal
Cisco Employee

Hi Anupam,

Inter-as VPN can provisioned either via MP-eBGP between ASBR routers or MP-eBGP between RR/PE routers.

There are 3 flavour of Inter-AS VPN

1. Option-A -- Back to back VRF

2. Option-B -- MP-eBGP between ASBR routers

3. Option-C -- MP-eBGP between RR/PE routers and ipv4 eBGP + label between ASBR routers.

You are trying to implement Option-B that is possible. For Option-B also you have two sub-options

a. redistribute link connecting ABSR into IGP.

b. Next-hop self on ASBR router while advertising over ibgp session

Please go through below doc for that

http://www.cisco.com/en/US/tech/tk436/tk428/technologies_configuration_example09186a0080094472.shtml

http://www.cisco.com/en/US/docs/ios/mpls/configuration/guide/mp_vpn_connect_asbr.html

Details about Inter-AS VPN configuration you can get in below book very well

MPLS Configuration on Cisco IOS Software, by Lancy Lobo, -  CCIE No. 4690, Umesh Lakshma

http://www.amazon.com/Configuration-Software-paperback-Networking-Technology/dp/1587142503