BGP is used to transmit routing information. BGP accepts only the wanted routes which can be filtered or applied routing policy flexibly, and modifies route attributes to direct network traffic properly.
BGP is used to transmit routing information between ASs. Route reception directly affects traffic forwarding.
The BGP device may receive routes to the same destination from different BGP peers. To control traffic forwarding paths, the router needs to filter the received BGP routes.
The router may be attacked and receive a large number of routes from its BGP peers, consuming lots of resources of the router. Therefore, the administrator must limit the resources to be consumed based on networking planning and router capacities, no matter whether too many BGP routes caused by malicious attacks or incorrect configurations.
Filters can be used to filter routes to be received by BGP. BGP can filter the routes received from all peers or peer groups or only the routes received from a specific peer or peer group. If multiple filter policies are configured, BGP accepts only routes that match all the filter policies.