Dell PowerSwitch S4128F-ON OS10 Enterprise Edition User Guide Release 10.4.3.0 - Page 323

Root guard Loop 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, configure the spanning-tree guard root command. Root guard is enabled on ports that are 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 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. 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 configured on the port. If you disable loop guard on a port, it moves to the Listening state. If you enable BPDU filter and BPDU guard on the same port, the BPDU filter configuration takes precedence. Root guard and Loop guard are mutually exclusive. Configuring one overwrites the other from the active configuration. 1 Enable spanning-tree BPDU filter in INTERFACE mode. spanning-tree bpdufilter enable • To shut down the port channel interface, all member ports are disabled in the hardware. • 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. • To remove a physical port from a port-channel in Error Disable state, the Error Disabled state clears on this physical port. The physical port is enabled in the hardware. To clear the Error Disabled state: • Use the shutdown command on the interface. • Use the spanning-tree bpdufilter disable command to disable the BPDU guard on the interface. • Use the spanning-tree disable command to disable STP on the interface. 2 Enable STP BPDU guard in INTERFACE mode. spanning-tree bpduguard enable • To shut down the port channel interface, all member ports are disabled in the hardware. • 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. • To remove a physical port from a port-channel in Error Disable state, the Error Disabled state clears on this physical port. The physical port is enabled in the hardware. To clear the Error Disabled state: • Use the shutdown command on the interface. • Use the spanning-tree bpduguard disable command to disable the BPDU guard on the interface. • Use the spanning-tree disable command to disable STP on the interface. 3 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 filter 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- violation :disable RootGuard: enable LoopGuard disable Bpdus (MRecords) sent 134, received 138 Interface Designated Layer 2 323