•
An Internet service provider (ISP)
•
A BGP/MPLS VPN service provider
In either case, MPLS is run in the backbone network and between the backbone and customer carrier (the
PE-CE link).
This figure illustrates an MPLS CSC L3VPN.
Figure 7: MPLS Carrier Supporting Carrier L3VPN
The figure shows two customers, A and X, connecting their remote sites through the backbone carrier. The
PE device of the backbone network connects with both customers through MPLS but under different VRFs
according to interface-VRF mapping. The MPLS label distribution protocol for PE-CE connectivity can be
either BGP or LDP, and requires them to run in a customer VRF context on the PE device.
Benefits of MPLS LDP CSC
The MPLS LDP CSC provides the following benefits to service providers who are backbone carriers and to
customer carriers.
Benefits to the Backbone Carrier
•
The backbone carrier can accommodate many customer carriers and give them access to its backbone.
The backbone carrier does not need to create and maintain separate backbones for its customer carriers.
Using one backbone network to support multiple customer carriers simplifies the backbone carrier's
VPN operations. The backbone carrier uses a consistent method for managing and maintaining the
backbone network. This is also cheaper and more efficient than maintaining separate backbones.
•
The MPLS LDP CSC feature is scalable. CSC can change the VPN to meet changing bandwidth and
connectivity needs. The feature can accommodate unplanned growth and changes. The CSC feature
enables tens of thousands of VPNs to be configured over the same network, and it allows a service
provider to offer both VPN and internet services.
•
The MPLS LDP CSC feature is a flexible solution. The backbone carrier can accommodate many types
of customer carriers. The backbone carrier can accept customer carriers who are ISPs or VPN service
providers or both. The backbone carrier can accommodate customer carriers that require security and
various bandwidths.
Cisco IOS XR MPLS Configuration Guide for the Cisco CRS Router, Release 5.1.x
22
Implementing MPLS Label Distribution Protocol
MPLS LDP Carrier Supporting Carrier for Multiple VRFs
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