Users Guide

Dell Networking OS Behavior: BPDU guard and BPDU filtering both block BPDUs, but are two separate
features.
BPDU guard:
• is used on edgeports and blocks all traffic on edgeport if it receives a BPDU.
• drops the BPDU after it reaches the RP and generates a console message.
BPDU filtering:
• disables spanning tree on an interface
• drops all BPDUs at the line card without generating a console message
Example of Blocked BPDUs
Selecting STP Root
The STP determines the root bridge, but you can assign one bridge a lower priority to increase the likelihood
that it becomes the root bridge. You can also specify that a bridge is the root or the secondary root.
To change the bridge priority or specify that a bridge is the root or secondary root, use the following
command.
• Assign a number as the bridge priority or designate it as the root or secondary root.
PROTOCOL SPANNING TREE mode
bridge-priority {priority-value | primary | secondary}
• priority-value: the range is from 0 to 65535. The lower the number assigned, the more likely this
bridge becomes the root bridge.
The primary option specifies a bridge priority of 8192.
The secondary option specifies a bridge priority of 16384.
The default is 32768.
Example of Viewing STP Root Information
To view only the root information, use the show spanning-tree root command from EXEC privilege
mode.
Dell#show spanning-tree 0 root
Root ID Priority 32768, Address 0001.e80d.2462
We are the root of the spanning tree
Root Bridge hello time 2, max age 20, forward delay 15
Dell#
STP Root Guard
Use the STP root guard feature in a Layer 2 network to avoid bridging loops. In STP, the switch in the network
with the lowest priority (as determined by STP or set with the bridge-priority command) is selected as
the root bridge. If two switches have the same priority, the switch with the lower MAC address is selected as
Spanning Tree Protocol (STP) 966