Connectivity Guide

Spanning-tree extensions
STP extensions ensure ecient network convergence by securely enforcing the active network topology. OS10 supports BPDU ltering,
BPDU guard, loop guard, and root guard STP extensions.
BPDU ltering Protects the network from unexpected ooding of BPDUs from an erroneous device. Enabling BPDU Filtering
instructs the hardware to drop BPDUs and prevents ooding from reaching the CPU. BPDU ltering is enabled by
default on Edge ports. All BPDUs received on the Edge port drop. If you explicitly congure BPDU ltering on a
port, that port drops all BPDUs it receives.
BPDU guard Blocks the L2 bridged ports and LAG ports connected to end hosts and servers from receiving any BPDUs. When
you enable BPDU guard, it places a bridge or LAG port in an Error_Disable or Blocking state if the port receives any
BPDU frames. In a LAG, all member ports, including new members are placed in an Blocking state. The network
trac drops but the port continues to forward BPDUs to the CPU that are later dropped. To prevent further
reception of BPDUs, congure a port to shut down using the
shutdown command. The port can only resume
operation from the Shutdown state after manual intervention.
Root guard Avoids bridging loops and preserves the root bridge position during network transitions. STP selects the root bridge
with the lowest priority value. During network transitions, another bridge with a lower priority may attempt to
become the root bridge and cause unpredictable network behavior. To avoid such an attempt and preserve the
position of the root bridge, congure the spanning-tree guard root command. Root guard is enabled on
ports that are designated ports. The root guard conguration applies to all VLANs congured on the port.
Loop guard Prevents L2 forwarding loops caused by a cable or interface hardware failure. When a hardware failure occurs, a
participating spanning tree link becomes unidirectional and a port stops receiving BPDUs. When a blocked port
stops receiving BPDUs, it transitions to a Forwarding state causing spanning tree loops in the network. You can
enable loop guard on a port that transitions to the Loop-Inconsistent state until it receives BPDUs using the
spanning-tree guard loop command. After BPDUs are received, the port moves out of the Loop-
Inconsistent or blocking state and transitions to an appropriate state determined by STP. Enabling loop guard on a
per port basis enables it on all VLANs congured on the port. If you disable loop guard on a port, it is moved to the
Listening state.
If you enable BPDU Filter and BPDU Guard on the same port, the BPDU Filter conguration takes precedence. Root Guard and Loop Guard
are mutually exclusive. Conguring one overwrites the other from the active conguration.
• Enable spanning-tree BPDU lter in INTERFACE mode. Use the spanning-tree bpdufilter disable command to disable the
BPDU lter on the interface.
spanning-tree bpdufilter enable
• Enable spanning-tree BPDU guard in INTERFACE mode.
spanning-tree bpduguard enable
– Use the shutdown command to shut down the port channel interface, all member ports that are disabled in the hardware.
– Use the spanning-tree bpduguard disable command to add a physical port to a port-channel already in the Error Disable
state, the new member port is also disabled in the hardware.
• Set the guard types to avoid loops in INTERFACE mode.
spanning-tree guard {loop | root | none}
– loop — Set the guard type to loop.
– none — Set the guard type to none.
– root — Set the guard type to root.
BPDU lter
OS10(conf-if-eth1/1/4)# spanning-tree bpdufilter enable
OS10(conf-if-eth1/1/4)# do show spanning-tree interface ethernet 1/1/4
ethernet1/1/4 of vlan1 is designated Blocking
Edge port:no (default) port guard :none (default)
Link type is point-to-point (auto)
Boundary: NO bpdu filter : Enable bpdu guard : bpduguard shutdown-on-
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Layer 2