Configuring Inter-AS IPv6 VPN Option B

In the scenario where the backbone network spans two ASs, ASBRs need to advertise VPNv6 routes through MP-EBGP.

Usage Scenario

If an ASBR can manage VPN routes but there are not enough interfaces for all inter-AS VPNs, inter-AS VPN Option B can be used. Inter-AS VPN Option B requires ASBRs to help to maintain and advertise VPNv6 routes and you need not create VPN instances on the ASBRs.

On the network shown in Figure 1, the interfaces connected between ASBRs do not need to be bound to the VPN. A single-hop MP-EBGP peer relationship is set up between the ASBRs to transmit all inter-AS VPN routing information.

Figure 1 Schematic diagram for inter-AS IPv6 VPN Option B

Pre-configuration Tasks

Before configuring inter-AS VPN Option B, complete the following tasks:

Configure an IGP for the MPLS backbone network of each AS to ensure IP connectivity of the backbone network within an AS.
Configure the basic MPLS functions for the MPLS backbone network of each AS and establish an LDP LSP or TE tunnel between MP-IBGP peers.
Configure a VPN instance on the PE connected to the CE and binding interfaces to the VPN instance.
Configure an IPv6 address for the interface connecting the CE to the PE.

Configuring MP-IBGP Between a PE and an ASBR in the Same AS: By importing extended community attributes to BGP, MP-IBGP can advertise VPNv6 routes between the PE and the ASBR.

Configuring MP-EBGP Between ASBRs in Different ASs: After the MP-EBGP peer relationship is established between ASBRs, an ASBR can advertise the VPNv6 routes of its AS to the other ASBR.

Controlling the Learning and Advertising of VPN Routes on ASBR: An ASBR can either save partial VPNv6 routes by filtering VPN targets through a routing policy or save all VPNv6 routes.

(Optional) Configuring One-Label-per-Next-Hop Label Distribution on an ASBR: To conserve label resources on an ASBR, configure one-label-per-next-hop label allocation on the ASBR. One-label-per-next-hop label allocation on ASBRs and one-label-per-instance label distribution on PEs must be used together.

Configuring Route Exchange Between a CE and a PE: BGP, the static route (including the default route), or IGP can run between a CE and a PE. You can choose any of them as required.

Verifying the Configuration of Inter-AS IPv6 VPN Option B: After configuring inter-AS IPv6 VPN Option B, you can view the status of all BGP peer relationships and VPNv6 routing information on PEs or ASBRs.