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Dedicated ASBR for Inter-AS MPLS


What are the advantages of having a dedicated ASBR for Inter-AS MPLS? At present I am using a PE as ASBR and it is shared for all types of customers. I am using Option-A for inter-AS.




Re: Dedicated ASBR for Inter-AS MPLS

HI Prakash, [Pls RATE if HELPS]

Separate autonomous systems from different service providers can communicate by exchanging IPv4 NLRI in the form of VPN-IPv4 addresses.

The ASBRs use eBGP to exchange that information. Then an Interior Gateway Protocol (IGP) distributes the network layer information for VPN-IPv4 prefixes throughout each VPN and each autonomous system.

Routing information uses the following protocols:

• Within an autonomous system, routing information is shared using an IGP.

• Between autonomous systems, routing information is shared using an eBGP. An eBGP allows a service provider to set up an interdomain routing system that guarantees the loop-free exchange of routing information between separate autonomous systems.

The primary function of an eBGP is to exchange network reachability information between autonomous systems, including information about the list of autonomous system routes.

The autonomous systems use EGBP border edge routers to distribute the routes, which include label switching information. Each border edge router rewrites the next hop and MPLS labels.

Hope I am Informative.


Best Regards,

Guru Prasad R

Hall of Fame Super Silver

Re: Dedicated ASBR for Inter-AS MPLS

Hello Prakashi,

in addition to Guru's post some considerations:

an ASBR for inter-AS MPLS VPN is challenged on the signalling plane more then in the forwarding plane.

They need to build wide CEF tables for MPLS forwarding and for example this can create problems on some linecards on a GSR.

If the amount of traffic is low a device like a C7200 VXR with NPE G1 or NPE-G2 that have 1 GB RAM can act as ASBR and it is cheaper then an engine 5 linecard on the GSR (12000).

As Guru explained in its post the ASBR has to join the LSPs in two domains for all VPNs from this comes the high memory usage.

Hope to help


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