Configuring Inter-AS VPN Option A
In inter-AS VPN Option A, an ASBR takes the peer ASBR as its CE and advertises VPNv4 routes to the peer ASBR through EBGP.
Context
If the MPLS backbone network bearing the VPN routes is across multiple ASs, configure the Inter-AS VPNs.
The Inter-AS VPN Option A is convenient to implement and is suitable when the amount of the VPNs and the VPN routes on the PE is small.
In VPN-Option A, the Autonomous System Boundary Routers (ASBRs) must support the VPN instances and can manage VPN routes. In addition, the ASBRs must reserve special interfaces including sub-interfaces and physical interfaces for each inter-AS VPN. Option A, therefore, requires high performance of the ASBRs. No inter-AS configuration is needed on the ASBRs.
Inter-AS VPN Option A is easy to deploy. When the amount of the VPNs and the VPN routes on the PE is small, this solution can be adopted.
Procedure
- Perform Configuring Basic BGP/MPLS IP VPN on each AS.
- Configure ASBR by considering the peer ASBR as its CE.
- Configure VPN instances for the PE and the
ASBR separately.
The VPN instance for PE is used to access CE; that for ASBR is used to access its peer ASBR.
In inter-AS VPN Option A mode, for the same VPN, the VPN targets of ASBR and the PE VPN instance must be matched in an AS. This is not required for the PEs in different ASs.