Cisco ME 3400 - Page 679

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Cisco ME 3400 Ethernet Access Switch Command Reference
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Chapter 2 Cisco ME 3400 Ethernet Access Switch Cisco IOS Commands
spanning-tree portfast (global configuration)
Note Exercise caution when enabling STP on a customer-facing ENI.
You can enable these features when the switch is operating in the per-VLAN spanning-tree plus
(PVST+), the rapid-PVST+, or the multiple spanning-tree (MST) mode.
Use the spanning-tree portfast bpdufilter default global configuration command to globally enable
BPDU filtering on STP ports that are Port Fast-enabled. The STP ports still send a few BPDUs at link-up
before the switch begins to filter outbound BPDUs. You should globally enable BPDU filtering on a
switch so that hosts connected to switch STP ports do not receive BPDUs. If a BPDU is received on a
Port Fast-enabled STP port, the interface loses its Port Fast-operational status and BPDU filtering is
disabled.
You can override the spanning-tree portfast bpdufilter default global configuration command on an
STP port by using the spanning-tree bdpufilter interface configuration command.
Caution Enabling BPDU filtering on an STP port is the same as disabling spanning tree on it and can result in
spanning-tree loops.
Use the spanning-tree portfast bpduguard default global configuration command to globally enable
BPDU guard on STP ports that are in a Port Fast-operational state. In a valid configuration, Port
Fast-enabled STP ports do not receive BPDUs. Receiving a BPDU on a Port Fast-enabled STP port
signals an invalid configuration, such as the connection of an unauthorized device, and the BPDU guard
feature puts the STP port in the error-disabled state. The BPDU guard feature provides a secure response
to invalid configurations because you must manually put the STP port back in service. Use the BPDU
guard feature in a service-provider network to prevent an access port from participating in the spanning
tree.
You can override the spanning-tree portfast bpduguard default global configuration command by
using the spanning-tree bdpuguard interface configuration command on an STP port.
Use the spanning-tree portfast default global configuration command to globally enable the Port Fast
feature on all nontrunking STP ports. Configure Port Fast only on STP ports that connect to end stations;
otherwise, an accidental topology loop could cause a data packet loop and disrupt switch and network
operation. A Port Fast-enabled STP port moves directly to the spanning-tree forwarding state when
linkup occurs without waiting for the standard forward-delay time.
You can override the spanning-tree portfast default global configuration command by using the
spanning-tree portfast interface configuration command on an STP port. You can use the no
spanning-tree portfast default global configuration command to disable Port Fast on all STP ports
unless they are individually configured with the spanning-tree portfast interface configuration
command.
Examples This example shows how to globally enable the BPDU filtering feature:
Switch(config)# spanning-tree portfast bpdufilter default
This example shows how to globally enable the BPDU guard feature:
Switch(config)# spanning-tree portfast bpduguard default
This example shows how to globally enable the Port Fast feature on all nontrunking interfaces:
Switch(config)# spanning-tree portfast default