Redistribution imports routes from one protocol to another. Redistribution sends route updates for a protocol-based route through another protocol. For example, if OSPF routes exist in a router and they must travel through a BGP network, then configure redistribution of OSPF routes through BGP. This configuration sends OSPF routes to a router that uses BGP.
You can redistribute routes
on an interface basis
on a global basis between protocols on a single VRF instance (intraVRF)
between the same or different protocols on different VRF instances (interVRF)
To configure interface-based redistribution, configure a route policy, and then apply it to the interface. Configure the match parameter to the protocol from which to learn routes.
Use the ip ospf redistribute command to accomplish the (intraVRF) redistribution of routes through OSPF, so that OSPF redistribution occurs globally on all OSPF-enabled interfaces. This redistribution does not require a route policy, but you can use one for more control.
Note
The route policies treat permit and deny rules differently for inbound and outbound traffic.
For an in-policy (RIP, BGP) or an accept policy (OSPF) using a route-map, if a particular route is not explicitly denied in the accept policy or in-policy with the route-map, then the route is implicitly allowed.
For an out-policy (RIP, BGP) or a redistribute policy (RIP, OSPF, BGP) using a route-map, even if a particular route is not explicitly allowed in the redistribution policy or out-policy with the route-map, then the route is implicitly denied.
In order to permit or deny only explicit routes, configure a policy with additional sequences, where, the last sequence permits all routes that are not explicitly permitted or denied.
DvR Controllers redistribute routes (direct routes, static routes and the default route) into the DvR domain. You can configure redistribution of DvR host routes into OSPF.