HP procurve series 4100gl Management And Configuration Manual page 462

Troubleshooting
Unusual Network Activity
C-20
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.
MAC Address "A"; VLAN 1
Server
MAC Address "A"; VLAN 2
Figure C-4. Example of Duplicate MAC Address
VLAN 1
Switch 4108GL
(Multiple
Forwarding
VLAN 2
Database)
Problem: This switch detects
continual moves of MAC
address "A" between ports.
Switch with
Single
Forwarding
Database