Information Technology Reference
In-Depth Information
Figure 10-14
MPLS VPN over a Common Transit VPN Backbone
AS 300
PE2
PE3
AS 200
AS 100
PE1
CE2
CE3
PE4
VPNa
Site 2
VPNa
Site 1
CE4
CE1
Inter-AS VPN
To achieve inter-AS VPN, you can choose from several options, depending on your design
requirements. The following options are discussed in this section:
•
Back-to-back VRF
•
Single-hop multiprotocol eBGP for VPNv4
•
Multihop multiprotocol eBGP for VPNv4
•
Non-VPN transit provider for VPNv4
Back-to-Back VRF
The simplest method to achieve inter-AS VPN is back-to-back VRF. Consider the topology
shown in Figure 10-15. Two sites, Site 1 and Site 2, are connected to two different
providers, AS 100 and AS 200, respectively. The two providers have a connection between
PE2 and PE3. The prefix 172.16.0.0/16 is advertised by CE2 in Site 2 and must be reachable
by Site 1 in a VPN across the two providers.
