Step 3: Isolate Filtering and Port Security Problems

Generally speaking, any analysis of the forwarding process should consider any security features that might discard some frames or packets. For example, both routers and switches can be configured with access control lists (ACL) that examine the packets and frames being sent or received on an interface, with the router or switch discarding those packets/frames.

The CCNA exams do not include coverage of switch ACLs, but the exams do cover a switch feature called port security. As covered in Cisco CCENT/CCNA ICND1 100-101 Official Cert Guide, Chapter 8, the port security feature can be used to cause the switch to discard some frames sent into and out of an interface. Port security has three basic ...

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