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IP packet forwarding filters let the router filter packets selectively, based on their source and destination interface fields, the packet type, and the source and destination address type. The interface can be specified as an interface or interface type, and the address types can be specified as any address, network, or host. The packet type is identified by the presence of expected values in the protocol type field of the IP header and in a protocol-specific operator. Packet forwarding filters recognize the following protocol types:
The packet type can be further identified by the TCP/UDP port. You can filter only TCP packets that initiate a connection; therefore, you can restrict access to TCP services in a specific location while allowing clients in that location to access outside TCP services.
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