Routing policies are grouped together in the vRouter configuration under the policy node. This policy node simply serves as a container for policy statements; it's the actual policy statements that define the rules that will be applied to routing updates.
Once a policy has been defined, in order for it to take affect, it needs to be applied to a specific routing protocol. A policy can be applied as either an import policy or an export policy to routing protocols like RIP, OSPF, and BGP. In the case of BGP, policies can be applied per peer. Only one import and one export policy can be applied to a protocol (or a BGP peer).
A policy that has been applied as an import policy to a routing protocol is used to evaluate routing updates received through the routing protocol to which the policy is applied. For example, if a user configures an import policy for the BGP protocol, all BGP announcements received by the vRouter is compared against the import policy first, prior to being added to the BGP and routing tables.
A policy that has been applied as an export policy to a routing protocol is used to evaluate routing updates that are transmitted by the routing protocol to which the policy is applied. For example, if a user configures an export policy for BGP, all BGP updates originated by the vRouter will be compared against the export policy statement prior to the routing updates being sent to any BGP peers.
In addition to controlling routing updates transmitted by a routing protocol, export policies are also used to provide route redistribution. For example, if a user wants to redistribute routes learned through OSPF into BGP, the user would configure a policy statement identifying the OSPF routes of interest, and then the user would apply this policy statement as an export policy for OSPF.