OSPF adds routes to the VRF’s forwarding table at the PE router side with routes learned
from the CE router.
Distributing Routes Between PE Routers
The OSPF routes in the VRF forwarding table are OSPF IPv4 routes, but BGP/MPLS VPNs
distribute VPN-IPv4 routes by means of MP-BGP. You must configure the VRF to
redistribute the OSPF routes into MP-BGP. MP-BGP converts each imported OSPF route
to a VPN-IPv4 route, applies export policy to the route, and then propagates the route
to a remote PE site by means of the MPLS/VPN backbone. At the destination PE router,
MP-BGP places each route in the appropriate VRF forwarding table based on the import
policy for each VRF and the route target associated with the route.
Preserving OSPF Routing Information Across the MPLS/VPN Backbone
MP-BGP attaches two new extended community attributes to the routes redistributed
from OSPF:
•
OSPF domain identifier extended community attribute
•
OSPF route type extended community attribute
MP-BGP uses these attributes and the MED to preserve OSPF routing information across
the BGP/MPLS VPN backbone.
OSPF Domain Identifier Attribute
The OSPF domain identifier attribute uniquely identifies the OSPF domain from which a
route was redistributed into MP-BGP.
You must configure an OSPF domain ID for the VRFs on the PE router with the domain-id
command. All VRFs that belong to a given OSPF domain must be configured with the
same domain ID. If not configured, the domain ID defaults to zero. If you configure a value
of zero, MP-BGP does not attach an OSPF domain identifier attribute.
If the OSPF domain ID for the destination PE router differs from the originating PE router,
MP-BGP redistributes the route into OSPF as an OSPF type 5 external route.
OSPF Route Type Attribute
The route type attribute carries the OSPF area ID and LSA type, as indicated in Table 93
on page 480:
Table 93: Route Types and Route Origins
Origin of RouteType of Route
Type 1 LSA1 – intra-area route
Type 2 LSA2 – intra-area route
Type 3 LSA3 – interarea summary route
Type 5 LSA5 – external route (area ID = 0)
Copyright © 2010, Juniper Networks, Inc.480
JunosE 11.2.x BGP and MPLS Configuration Guide
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