Configuring Inter-AS IPv6 VPN-Option C (Solution 2)

After LDP LSPs are established for the labeled BGP routes of the public network, 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.

If an ASBR is ready to access a large number of PEs, Solution 2 is recommended because of the easy configuration.

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.

Solution 2 is described here, and solution 1 is described in Configuring Inter-AS IPv6 VPN-Option C (Solution 1).

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 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
Configuring a name for the prefix list used to filter labeled BGP routes of the public network

Establishing an EBGP Peer Relationship Between ASBRs: An EBGP peer relationship is established between ASBRs to advertise routes destined for the loopback interfaces on PEs.

Advertising the Routes of a PE in the Local AS to the Remote PE: After the routes of the loopback interface on a PE in an AS are advertised to the remote PE in another AS, the MP-EBGP peer relationship is established between PEs.

Enabling the Capability of Exchanging Labeled IPv4 Routes: To establish an inter-AS BGP LSP, you must enable ASBRs to exchange labeled IPv4 routes.

Establishing an LDP LSP for the Labeled BGP Routes of the Public Network: By enabling LDP on ASBRs to allocate labels for BGP routes, you can establish LDP LSPs for labeled BGP routes of the public network that are filtered in the IP prefix list.

Establishing an MP-EBGP Peer Relationship Between PEs: By importing extended community attributes into BGP, MP-IBGP can advertise VPNv6 routes between PEs. PEs of different ASs are generally not directly connected. To set up an EBGP connection between the PEs of different ASs, you must configure the permitted maximum number of hops between PEs.

Configuring Route Exchange Between PEs and CEs: 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 2): After configuring inter-AS IPv6 VPN OptionC (solution 2), check information about all BGP peer relationships, VPNv6 routes and IPv6 VPN routes on PEs, labels of IPv4 routes on ASBRs, and information about LDP LSP on ASBRs.