Allied Telesis AT-8550 - Manual (Page 96)

Spanning Tree Protocol Domains
6-2
Spanning Tree Protocol Domains
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.
Caution
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 an 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.
Caution
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.