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Spanning Tree Protocol
The spanning tree protocol (STP) is a bridge-to-bridge link management protocol
that provides path redundancy while preventing undesirable loops. To provide path
redundancy, spanning tree protocol defines a tree that spans all switches and
bridges in the extended network. If one of the network segments in the tree becomes
inaccessible, STP reconfigures itself to reestablish the links. To prevent loops, STP
selects just one switch port as the designated path to the root, assigning it the
Forwarding, or active state. It assigns all other ports the blocking, or standby, state.
A port in the blocking state does not forward any transmitted frames in any
direction.
Note: In the VLAN STP configuration menu, for the selection of port priority/port
path cost, select only the ports which are part of the current VLAN. Do not
configure ports in other VLANs.
The path cost indicates the relative speed of the segment: The higher the speed of
the segment, the lower the path cost. Switches and bridges in the network attempt
to determine the path to the route with the lowest path cost. IEEE 802.1D
recommends that you assign path costs using the following formula:
Path cost = 1000 / LAN speed in Mbps
If two ports to the root have the same path cost, the STP device selects the one with
the highest priority (lowest value), an arbitrary value that you assign. To block
traffic on a particular segment, assign it low port priority (high value)
If more ports have the same priority value assigned, the lowest port number will be
selected.
IEEE 802.1D Spanning Tree Protocol (STP)
When the IEEE 802.1D Spanning Tree Protocol is active, a port within that domain
will require several seconds to make the transition from the blocking state to the
forwarding state, when the port is initially activated (e.g. joins an existing ring or
activates a dedicated link.) Some client or server applications may attempt to
establish session activity during this time, resulting in error messages indicating a
connection failure. These applications should be configured to wait at least 30
seconds after the LAN link is active, before attempting to establish session activity.
This delay can be reduced by modifying the 802.1D Spanning Tree Protocol default
parameters.
If STP is enabled on a dedicated port, and a station is attached to it, it takes at least
30 seconds for the port to transition Down
Forwarding.
CrossFire 8730 Switch Reference Guide, DOC-7047 v. 1.1
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