Control Points

All policies provide two points at which you can control routing information or packets through the router (see Figure 4). These control points allow you to control the following:

• Routing information before and after it is placed in the routing table.
• Data packets before and after a forwarding table lookup.
• Local packets before and after they are received by the Routing Engine. (Figure 4 appears to depict only one control point but because of the bidirectional flow of the local packets, two control points actually exist.)

Figure 4: Policy Control Points

Because there are two control points, you can configure policies that control the routing information or data packets before and after their interaction with their respective tables, and policies that control local packets before and after their interaction with the Routing Engine. Import routing policies control the routing information that is placed in the routing tables, whereas export routing policies control the routing information that is advertised from the routing tables. Input firewall filters control packets that are received on a router interface, whereas output firewall filters control packets that are transmitted from a router interface.

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