Specifications

Switching 8-35
Software Release 2.7.3
C613-03098-00 REV A
Multiple Spanning Trees and STP Interaction
with VLANs
In a legacy network that has no VLANs configured, and has STP enabled,
switches in the LAN run a distributed Spanning Tree Algorithm to create a
single Spanning Tree.
In a network of switches with VLANs configured, all VLANs belong to a
default Spanning Tree called default. Multiple Spanning Trees can be created
with each Spanning Tree encompassing multiple VLANs. Spanning Tree
Protocol entities, called STPs here, operate independently of each other; each
STP has its own root bridge and active path. Once an STP is created, one or
more VLANs can be assigned to it. In operation, additional STPs in the switch
place no significant burden on the CPU.
Table 8-7: Spanning Tree port states
State Meaning
DISABLED STP operations are disabled on the port. The port does not
participate in frame relay or the operation of the Spanning
Tree Algorithm and Protocol. The port can still switch if its
switch state is enabled.
BLOCKING The port does not participate in frame relay. The forwarding
process discards received frames and does not submit
forwarded frames for transmission. This is the “standby”
mode.
LISTENING The port is enabled for receiving frames only. The port is
preparing to participate in frame relay. The forwarding
process discards received frames and does not submit
forwarded frames for transmission.
LEARNING The port is enabled for receiving frames only, and the
Learning Process can add new source address information
to the Forwarding Database.
FORWARDING The normal state for a switch port. The forwarding process
and the Spanning Tree entity are enabled for transmit and
receive operations on the port.
Table 8-8: Rapid Spanning Tree port states
State Meaning
DISABLED STP operations are disabled on the port.
DISCARDING The port does not participate in frame relay. The forwarding
process discards received frames and does not submit
forwarded frames for transmission.
LEARNING The port is enabled for receiving frames only, and the
learning process can add new source address information
to the forwarding database. The port does not forward any
frames.
FORWARDING The normal state for a switch port. The forwarding process
and the Spanning Tree entity are enabled for transmit and
receive operations on the port.