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If an IS-IS import policy is applied that results in a reject terminating action for a non-external route, then the reject action is ignored and the route is accepted anyway. By default, such a route is now installed in the routing table with a priority of low. This behavior prevents traffic black holes, that is, silently discarded traffic, by ensuring consistent routing. However, you can use the the reject policy option to reject routes based on the prefix or the configured tag.Example: Configuring a Routing Policy to Prioritize IS-IS Routes
Are import policies allowed? Why is that? Besides the use case of prioritizing the routes is there any other use case? For now, I see the import policy similar to OSPF import on externals with the difference that it filters not only externals but the internals and external ISIS routes. Many Thanks!Alin