Packet filtering helps control packet movement through the network, as shown in Figure B-8. Such control can help limit network traffic and restrict network use by certain users or devices. To permit packets to cross or deny packets from crossing specified router interfaces, Cisco provides access lists. An IP access list is a sequential collection of permit and deny conditions that apply to IP addresses or upper-layer IP protocols.
Figure B-8 Access Lists Control Packet Movement Through a Network
Transmission of Packets on an Interface
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