3Com SuperStack II 3000 TX User Manual page 121

Using the Switch C-5
You are trying to manage the Switch over a
network which has STP, and you are losing con-
tact with the management agent intermittently.
®
As shown in Figure C-1, there is a SuperStack II
Switch unit (Switch A) between your management
workstation and the Switch 3000 TX (Switch B). You
have configured more than one VLAN on both
Switch units, and there is a parallel STP path for
each VLAN between the Switch units.
When Switch B transmits BPDUs across a VLAN
other than VLAN 1, Switch A learns the MAC
address of Switch B through the port on that
VLAN. The management agent of Switch B is only
accessible through VLAN 1, and so your manage-
ment workstation cannot communicate with Switch
B until it transmits BPDUs across VLAN 1. When that
occurs, Switch A learns the MAC address of Switch
B through the port on VLAN 1.
To avoid this situation, we recommend that you
connect the two SuperStack II Switch units using a
Virtual LAN Trunk (VLT). For more information
about VLTs, refer to "Connecting Common VLANs
Between Switch Units" on page 5-3.
Figure C-1 Network configuration that results in loss of contact