Intel 480T, User Manual

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C H A P T E R 7 Spanning Tree* Protocol (STP)
Spanning Tree 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 Protocol 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.
STPD Status for GVRP-Added Ports
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