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Incoming routing information filters limit the routing information accepted by a router from its neighboring routers.
When incoming routing information filters are enabled on a router, the router accepts only the allowed routes from each neighboring router, thereby hiding specified routes from some routers and from certain parts of the network. However, incoming routing information filters cannot be used to filter out directly connected networks.
A typical incoming routing information filter consists of the destination network of the route and the interface through which advertisements of the route are expected to be received.
Incoming routing information filters keep the filtering router from adding certain routes to its routing table when it receives the information from its neighbors. The filtering router cannot forward a packet to a filtered route even if it receives a packet destined for it. In this way, incoming routing information filters provide a higher level of security than that provided by outgoing routing information filters.
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