Unusual Network Activity
Note that attempting to create redundant paths through the use of VLANs will
cause problems with some switches. One symptom is that a duplicate MAC
address appears in the Port Address Table of one port, and then later appears
on another port. While the switch has multiple forwarding databases, and thus
does not have this problem, some switches with a single forwarding database
for all VLANs may produce the impression that a connected device is moving
among ports because packets with the same MAC address but different VLANs
are received on different ports. You can avoid this problem by creating
redundant paths using port trunks or spanning tree.
Figure C-5. Example of Duplicate MAC Address
MAC Address "A"; VLAN 1
MAC Address "A"; VLAN 2
by this Guide
Problem: This switch detects continual
moves of MAC address "A" between ports.