# Distribution of OSPF Routes from PE Router to CE Router Overview

At the remote PE site, MP-BGP converts the OSPF routes to BGP VPN-IPv4 routes and sends them across the BGP/MPLS VPN backbone. At the destination PE router, MP-BGP must redistribute the BGP VPN-IPv4 routes back into OSPF IPv4 routes. The PE OSPF router becomes the originator of the routes, which are either type 5 external routes or type 3 internal routes. The PE router can announce the OSPF routes to the appropriate CE router through its directly connected PE-CE OSPF link.

If the route has a route type of inter or intra, it is redistributed as a type 3 summary interarea route and the destination PE router generates a type 3 LSA for it.

A route is redistributed as an external route if the route:

- Originates in an OSPF domain that is different from that of the destination PE router.
- Has a route type of 5 or 7, both of which indicate an external route.

In the first case, the PE router advertises the route as an external type 2 route. In the second case, the PE router advertises the route as an external type 2 route if the least-significant bit is set in the option byte in the route type extended community attribute; otherwise the PE router advertises the route as external type 1 route.