Dell PowerSwitch S4112F-ON EMC SmartFabric OS10 User Guide Release 10.5.1 - Page 504

Mode specific functionality Enable and disable STP Spanning Tree Protocol (STP) is enabled by default on the switches. You can disable the STP globally on the switch or at the interface level. Disabling spanning tree at an instance level causes all the port members of that instance to disable the spanning tree. This moves the port to the Forwarding / Blocking state based on the operational status of the ports. Use the spanning-tree disable command to disable the STP. Backward compatibility and interoperability Spanning tree modes are backward compatible and inter-operable with STP version. BPDU extensions STP extensions provide a means to ensure efficient network convergence by securely enforcing the active network topology. OS10 supports BPDU filtering, BPDU guard, root guard, and loop guard STP extensions. The system discards regular data traffic after a BPDU violation. BPDU filtering BPDU guard Root guard Loop guard Stops sending or receiving BPDUs from a faulty device, there by protecting the network from unexpected flooding of BPDUs. Enabling BPDU Filtering on an interface causes the system to stop sending or receiving BPDUs. Blocks the L2 bridged ports and LAG ports connected to end hosts and servers from receiving any BPDUs. When you enable BPDU guard and when the BPDU frames are being received on the interface, the bridge or LAG is placed in the blocking state. In case of a LAG, ports are either STP blocked or shutdown based on the error disable command action. The data traffic is dropped but the port continues to forward BPDUs to the CPU that are later dropped. To prevent further reception of BPDUs, configure a port to shut down using the error disable command. For more information on this command. 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 to preserve the position of the root bridge, configure the spanning-tree guard root command. This configuration places the port in an inconsistent state if the port receives superior BPDU. Root guard is enabled only on designated ports. The root guard configuration applies to all VLANs configured on the port. 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 the port stops receiving BPDUs. When the blocked port stops receiving BPDUs, it transitions to a Forwarding state causing spanning-tree loops in the network. Enable loop guard using the spanning-tree guard loop command on an interface so that it transitions to the Loop-Inconsistent state until it receives BPDUs. 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 configured on the port. NOTE: 1. Root guard and Loop guard are mutually exclusive. 2. Configuring one overwrites the other from the active configuration. 1. Enable spanning-tree BPDU filter in INTERFACE mode. spanning-tree bpdufilter enable 2. Enable STP BPDU guard in INTERFACE mode. spanning-tree bpduguard enable BPDU guard violation causes the system to perform the following actions in the port channel: 504 Layer 2