User guide

8-2 E
XTREME
W
ARE
S
OFTWARE
U
SER
G
UIDE
S
PANNING
T
REE
P
ROTOCOL
(STP)
S
PANNING
T
REE
D
OMAINS
The switch can be partitioned into multiple virtual bridges. Each virtual bridge can run
an independent Spanning Tree instance. Each Spanning Tree instance is called a
Spanning Tree Domain (STPD). Each STPD has its own Root Bridge and active path. Once
the STPD is created, one or more VLANs can be assigned to it.
A port can belong to only one STPD. If a port is a member of multiple VLANs, then all
those VLANs must belong to the same STPD.
The key points to remember when configuring VLANs and STP are the following:
• Each VLAN forms an independent broadcast domain.
• STP blocks paths to create a loop-free environment.
• When STP blocks a path, no data can be transmitted or received on the blocked port.
• Within any given STPD, all VLANs belonging to it use the same spanning tree.
Care must be taken to ensure that multiple STPD instances within a single
switch do not see each other in the same broadcast domain. This could happen
if, for example, another external bridge is used to connect VLANs belonging to
separate STPDs.
If you delete a STPD, the VLANs that were members of that STPD are also deleted. You
must remove all VLANs associated with the STP before deleting the STPD.
If no VLANs are configured to use the protocol filter
any
on a particular port,
STP BPDUs are not flooded within a VLAN when STP is turned off. If you need
STP to operate on this type of port, enable STP on the associated VLAN, so
that it can participate.
On the BlackDiamond switch, in order to support more than 255 ports (as limited
by the 802.1D specification), both the cost and port ID fields in the BPDU are
used to uniquely identify each port.
STPD S
TATUS FOR
GVRP-A
DDED
P
ORTS
If a port is added to a VLAN by GVRP, the newly added port reflects the SPTD
membership and status of the VLAN to which it is added. For example, if VLAN Red is
a member of STPD s0, and s0 is enabled, then all ports added to VLAN Red by GVRP
have s0 enabled on those ports, as well. The command for disabling STP on a port basis
has no permanent affect on ports controlled by GVRP.