Configuring Inter-AS IPv6 VPN-Option C (Solution 1)

EBGP connections in multi-hop mode are established between PEs of different ASs to exchange VPNv6 routes.

Applicable Environment

If the MPLS backbone network carrying VPN-IPv6 routes crosses multiple ASs, the inter-AS VPN is needed.

If each AS has a large amount of VPN-IPv6 routes to be exchanged, the VPN-Option C can be adopted to prevent the ASBR becoming a bottleneck of the network. Two solutions can be adopted to realize inter-AS VPN-Option C:

Solution 1: After learning the labeled BGP routes of the public network in the remote AS from the remote ASBR, the local ASBR allocates labels for these routes and advertises these routes to the IBGP peer that supports the label switching capability. A complete LSP is set up as a result.
Solution 2: The IBGP peer relationship between the PE and ASBR is not needed. In this solution, an ASBR learns the labeled public BGP routes of the remote AS from the peer ASBR. Then these labeled public BGP routes are imported to IGP to trigger the establishment of an LDP LSP. This process can establish a complete LDP LSP between the two PEs.

In inter-AS IPv6 VPN-Option C, do not enable LDP between ASBRs. If LDP is enabled on the interfaces between ASBRs, LDP sessions are then established between the ASBRs. In this case, the ASBRs establish an egress LSP and send Mapping messages to the upstream ASBR. After receiving Mapping messages, the upstream ASBR establishes a transit LSP. When there are high-volume BGP routes, enabling LDP on the interfaces between ASBRs leads to the occupation of a large number of LDP labels.

Pre-configuration Tasks

Before configuring inter-AS IPv6 VPN-Option C, complete the following tasks:

Configuring IGP for MPLS backbone networks in each AS to realize IP connectivity of the backbones in one AS
Configuring basic MPLS capability for the MPLS backbone network
Configuring MPLS LDP and establishing LSP between a PE and an ASBR in the same AS
Configuring the IBGP peer relationship between the PE and the ASBR of the same AS
Configuring a VPN Instance on the PE devices connected to the CE devices and Binding Interfaces to a VPN Instance
Configuring the IPv6 addresses of the CE interfaces through which the CE accesses the PE

Enabling Exchange of the IPv4 Routes with Labels: In inter-AS IPv6 VPN Option C, an inter-AS BGP LSP needs to be established on the backbone network, and BGP peers on the backbone network can exchange labeled IPv4 routes with each other.

Configuring a Route-Policy to Control Label Distribution: You need to configure a route-policy to control label allocation for the inter-AS BGP LSP. If labeled IPv4 routes are advertised to the PE of the local AS, you need to re-allocate the MPLS label to these routes. If routes sent by the PE of the local AS are advertised to the peer ASBR, you need to allocate the MPLS label to these routes.

Establishing the MP-EBGP Peer Between PEs: With extended community attributes added to BGP, MP-IBGP can advertise VPNv4 routes between PEs. PEs of different ASs are indirectly connected in most cases. Therefore, to set up the EBGP connections between them, you need to configure the permitted maximum hops between the PEs and ensure that the PEs are reachable.

Configuring Route Exchange Between the PE and CE: The routing protocol between a PE and a CE can be BGP4+, static route, RIPng, OSPFv3, or IS-ISv6.

Verifying the Configuration of Inter-AS IPv6 VPN-Option C (Solution 1): After inter-AS IPv6 VPN Option C is configured, you can view information about all BGP peer relationships, VPNv6 routing information and IPv6 VPN routing information on the PE, and information about labeled IPv4 routes on the ASBR.