HP ProCurve 6400cl Series Management And Configuration Manual page 445

Switch "X"
Port X-3
VLAN Port Assignment
Port VLAN_1 VLAN_2
X-3 Untagged Tagged
Figure C-9. Example of Correct VLAN Port Assignments on a Link
1. 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.
2. 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.
Duplicate MAC Addresses Across VLANs. The switches covered by this
guide operate with multiple forwarding databases. Thus, duplicate MAC
addresses occurring on different VLANs can appear where a device having
one MAC address is a member of more than one 802.1Q VLAN, and the switch
port to which the device is linked is using VLANs (instead of STP or trunking)
to establish redundant links to another switch. If the other device sends traffic
over multiple VLANs, its MAC address will consistently appear in multiple
VLANs on the switch port to which it is linked.
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 switches covered by this guide have 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.
Link supporting VLAN_1
and VLAN_2
Troubleshooting
Unusual Network Activity
Switch "Y"
Port Y- 7
VLAN Port Assignment
Port VLAN_1 VLAN_2
Y-7 Untagged Tagged
C-25