HP ProCurve series 2500 Management And Configuration Manual page 342

Troubleshooting
Unusual Network Activity
1.
2.
Duplicate MAC Addresses Across VLANs. Duplicate MAC addresses on
different VLANs are not supported and can cause VLAN operating problems.
There are no explicit events or statistics to indicate the presence of duplicate
MAC addresses in a VLAN environment. However, one symptom that may
occur is that a duplicate MAC address can appear in the Port Address Table
of one port, and then later appear on another port. (This can also occur in a
LAN where there are redundant paths between nodes and Spanning Tree is
turned off.) For more information, refer to "VLAN Restrictions" on page 9-75.
11-10
If VLAN_1 (VID=1) is configured as "Untagged" on port 3 on switch "X",
then it must also be configured as "Untagged" on port 7 on switch "Y".
Make sure that the VLAN ID (VID) is the same on both switches.
Similarly, if VLAN_2 (VID=2) is configured as "Tagged on the link port on
switch "A", then it must also be configured as "Tagged" on the link port
on switch "B". Make sure that the VLAN ID (VID) is the same on both
switches.