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OSPF supports route import and export policies, controlling has the ability to redistribute routes of other routing protocols in the routing table into OSPF. In OSPF terminology, routes from other routing protocols are known as external routes and they are redistributed into OSPF as Type-5 LSAs.
When redistributing external routes, we can specify filters to control which type of routes are redistributed into OSPF otherwise it has the potential to overwhelm the OSPF process especially in large networks. It also gives the administrator the ability to stop advertising unnecessary routes through OSPF. Filtering of routes for redistribution is achieved by route maps. To create a route map, we can run the command set routing route-map <map-name>.
In the following section we will demonstrate route redistribution and the use of route map in a sample topology shown in Figure 1.
Figure 1 OSPF Route Redistribution and Route Maps
supports controlling the dissemination of routing information that is added in to the routing table with an import routing policy and advertised from the routing table with an export routing policyroute maps.
OSPF route import and export can be applied in the following scenarios:
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Figure 1. Definition of OSPF route import and export
When we refer to OSPF import and export, it is from the point of view of the routing table in RIB. This means importing route from OSPF protocol into RIB using a routing policy, and advertising route from RIB to OSPF protocol by exporting a routing policy.
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Figure 2. Definition of OSPF route import and export with VRF
Currently, only OSPF route import and export support VRF, while route import and export of other routing protocols such as RIP and BGP do not support VRF.
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