Routing Protocol Support for Import and Export Policies
When applying routing policies to routing protocols, you must know whether each protocol supports import and export policies and the level at which you can apply these policies. Protocol Support for Import and Export Policies summarizes the import and export policy support for each routing protocol. Protocols That Can Be Imported to and Exported from the Routing Table also lists explicitly configured routes, which for the purposes of this table are considered a pseudoprotocol. Explicitly configured routes include aggregate and generated routes.
You can apply an import policy to aggregate and generated routes, but you cannot apply an export policy to these routes. These routes cannot be exported from the routing table to the pseudoprotocol, because this protocol is not a real routing protocol. However, aggregate and generated routes can be exported from the routing table to routing protocols.
You cannot apply import policies to the link-state protocols IS-IS and OSPF. As link-state protocols, IS-IS and OSPF exchange routes between systems within an AS. All routers and systems within an AS must share the same link-state database, which includes routes to reachable prefixes and the metrics associated with the prefixes. If an import policy is configured and applied to IS-IS or OSPF, some routes might not be learned or advertised, or the metrics for learned routes might be altered, which would make a consistent link-state database impossible.
For BGP only, you can also apply import and export policies at group and peer levels as well as at the global level. A peer import or export policy overrides a group import or export policy. A group import or export policy overrides a global import or export policy.
For example, if you define an import policy for an individual peer at the peer level and also define an import policy for the group to which it belongs, the import policy defined for the peer level only is invoked. The group import policy is not used for that peer, but it is applied to other peers in that group.
For RIP and RIPng only, you can apply import policies at the global and neighbor levels and export policies at a group level. For more information about RIP and RIPng, see the Junos Routing Protocols Configuration Guide.
For information about the routing protocols from which the routing table can import routes and to which routing protocols the routing table can export routes, see Protocols That Can Be Imported to and Exported from the Routing Table. For information about the default routing policies for each routing protocol, see Default Import and Export Policies for Protocols.
