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Understanding Interprovider VPNs
Interprovider and carrier-of-carriers VPNs provide solutions for situations in which the customer of a VPN service provider might be another service provider rather than an end customer. The customer service provider depends on the virtual private network (VPN) service provider (SP) to deliver a VPN transport service between the customer service provider’s points of presence (POPs) or regional networks.
For interprovider VPNs, the customer sites belong to different ASs. You need to configure external BGP (EBGP) to exchange the customer’s external routes. There are several different methods for enabling interprovider VPNs based on RFC 4364, BGP/MPLS IP Virtual Private Networks (VPNs):
- Interprovider Layer 3 VPN Option A—Interprovider VRF-to-VRF connections at the AS boundary routers (ASBR) (not very scalable).
- Interprovider Layer 3 VPN Option B—Interprovider EBGP redistribution of labeled VPN-IPv4 routes from AS to neighboring AS (somewhat scalable).
- Interprovider Layer 3 VPN Option C—Interprovider multihop EBGP redistribution of labeled VPN-IPv4 routes between source and destination ASs, with EBGP redistribution of labeled IPv4 routes from AS to neighboring AS (very scalable).
