Spanning Tree Protocol
Determining the path for forwarding BPDUs
When determining which port to use for forwarding and which port to block, the switch uses information in the BPDU, including each bridge priority ID. A technique based on the lowest root cost is then computed to determine the most efficient path for forwarding.
Bridge priority
The bridge priority parameter controls which bridge on the network is the STP root bridge. To make one switch the root bridge, configure the bridge priority lower than all other switches and bridges on your network. The lower the value, the higher the bridge priority. The bridge priority is configured using the following command:
/cfg/l2/stp x/brg/priorPort priority
The port priority helps determine which bridge port becomes the designated port. In a network topology that has multiple bridge ports connected to a single segment, the port with the lowest port priority becomes the designated port for the segment. The port priority is configured using the following command:
/cfg/l2/stp y/port x/priorPort path cost
The port path cost assigns lower values to
By default, all switch ports have the path cost set to 2. To use dynamic path cost, based on link speed, set the path cost to 0 (zero). For example, if the path cost is set to zero:
•A 10 Gbps link receives a path cost of 2•A 100 Mbps link receives a path cost of 19Configure the port path cost using the following command:/cfg/l2/stp y/port x/costSpanning Tree Group configuration guidelinesThis section provides important information on configuring Spanning Tree Groups (STGs).
Default Spanning Tree configuration
In the default configuration, a single STG with the ID of 1 includes all ports on the switch. It is called the default STG. All other STGs (except the default STG) are empty, and VLANs must be added by the user.
You cannot assign ports directly to an STG. Add the ports to a VLAN, and add the VLAN to the STG. STGs
An STG cannot be deleted, only disabled. If you disable the STG while it still contains VLAN members, Spanning Tree will be off on all ports belonging to that VLAN.
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