Announce policies are applied to outgoing advertisements to neighbors or peers in the protocol domain to determine whether to announce specific route information. Out filtering applies to RIP updates and BGP NLRI updates.
In contrast, announce policies are not applied to IS-IS or OSPF information because routing information must always be consistent across the domain. To restrict the flow of external route information in the IS-IS or OSPF protocol database, apply redistribution filters instead of announce policies.