H3C Technologies H3C S12500-X Series Switches - Manual (Page 117)

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Figure 34 Network diagram for extranet networking scheme
As shown in Figure 34 , route targets configured on PEs produce the following results:
• PE 3 can receive VPN-IPv4 routes from PE 1 and PE 2.
• PE 1 and PE 2 can receive VPN-IPv4 routes advertised by PE 3.
• Site 1 and Site 3 of VPN 1 can communicate with each other, and Site 2 of VPN 2 and Site 3 of
VPN 1 can communicate with each other.
• PE 3 advertises neither the VPN-IPv4 routes received from PE 1 to PE 2 nor the VPN-IPv4 routes
received from PE 2 to PE 1 (routes learned from an IBGP neighbor are not advertised to any other
IBGP neighbor). Therefore, Site 1 of VPN 1 and Site 2 of VPN 2 cannot communicate with each
other.
Inter-AS VPN
In an inter-AS VPN networking scenario, multiple sites of a VPN are connected to multiple ISPs in different
ASs, or to multiple ASs of an ISP.
RFC 2547bis presents the following inter-AS VPN solutions:
• VRF-to-VRF—ASBRs manage VPN routes between them through subinterfaces. This solution is also
called "inter-AS option A."
• EBGP redistribution of labeled VPN-IPv4 routes—ASBRs advertise labeled VPN-IPv4 routes to each
other through MP-EBGP. This solution is also called "inter-AS option B."
• Multihop EBGP redistribution of labeled VPN-IPv4 routes—PEs advertise labeled VPN-IPv4 routes
to each other through MP-EBGP. This solution is also called "inter-AS option C."
Inter-AS option A
In this solution, PEs of two ASs are directly connected, and each PE is also the ASBR of its AS.
The PEs acting as ASBRs are connected through multiple subinterfaces. Each of them treats the other as
a CE and advertises IPv4 routes through conventional EBGP. Within an AS, packets are forwarded as
VPN packets with two-level labels. Between ASBRs, conventional IP forwarding is used.
Ideally, each inter-AS VPN has a pair of subinterfaces to exchange VPN routing information.
CE
CE
PE 1
PE 3
Site 2
Site 1
Site 3
VPN 1
VPN 1
VPN 2
VPN 1:
Import:100:1
Export:100:1
CE
VPN 2:
Import:200:1
Export:200:1
PE 2
VPN 1:
Import:100:1,200:1
Export:100:1,200:1