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OSPF and BGP/MPLS VPNs

Before reading this section, we recommend you be thoroughly familiar with OSPF. For detailed information about that protocol, see JUNOSe IP, IPv6, and IGP Configuration Guide.

You can use BGP/MPLS VPNs to connect OSPF domains without creating OSPF adjacencies between the domains. The BGP/MPLS VPN backbone acts as either an OSPF backbone (area 0) or an OSPF area above the backbone.

In this topology, OSPF is the routing protocol between the CE router and the PE router. This OSPF link can be configured in area 0 or any other OSPF area. However, if the customer site has any connections to area 0, then at least one OSPF router configured on a CE router must have an area 0 link to a PE site. In this case, the BGP/MPLS VPN acts as if it is in an area above the OSPF backbone area. When the PE-CE link is in a nonbackbone area, the BGP/MPLS VPN acts as an OSPF backbone.

In either case, the OSPF router configured as a PE router in the BGP/MPLS VPN is always treated as an area border router (ABR) and functions as an area 0 router so that it can distribute interarea routes to the CE router. The BGP/MPLS VPN distributes both interarea and intra-area routes between PE routers as interarea, type 3 summary routes.

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