3Com corebuilder 3500 Implementation Manual page 409

When you define an export policy, you can configure the router to accept
or reject routes. An accept export policy configures the router to place the
specified route in external link state advertisements for propagation over
the network. The routes are advertised with the cost and the external
metric type defined by the policy. A reject export policy prevents the
router from placing the specified route in external link state
advertisements, thereby prohibiting propagation of the route over the
network.
Figure 73 illustrates the export policy process.
Figure 73 Export Policy Process
Reject
You define these criteria as part of an export policy:
The method by which the route was learned by the router. Possible
origins include directly connected interfaces and static routes, as well
as RIP routes imported by autonomous system boundary routers.
When you define an export policy against a directly connected
interface, you can specify one or all of the physical router interfaces
that are directly connected to the network against which you want the
export policy to be applied. For example, if you define an export policy
that rejects a direct interface, the router does not advertise the
specified interface over the network.
OSPF Routing Policies
IP Network
OSPF
Link State Database
Accept
Export Policy
Outgoing traffic (self-originated)
Routing
Table
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