Specifications

CHAPTER 3

Spanning Tree

Configure this command on all switches in the network:

(config)# spanning-tree backbonefast

BPDU Guard

BPDU Guard prevents loops if another switch is attached to a Portfast port. When BPDU Guard is enabled on an inter-

face, it is put into an error-disabled state (basically, shut down) if a BPDU is received on the interface. It can be enabled

at either global config mode—in which case it affects all Portfast interfaces—or at interface mode. Portfast does not need

to be enabled for it to be configured at a specific interface. The following configuration example shows BPDU guard

being enabled and verified.

(config)# spanning-tree portfast bpduguard default

(config-if)# spanning-tree bpduguard enable

# show spanning-tree summary totals

BPDU Filtering

BPDU filtering is another way of preventing loops in the network. It also can be enabled either globally or at the interface

and functions differently at each. In global config, if a Portfast interface receives any BPDUs, it is taken out of Portfast

status. At interface config mode, it prevents the port from sending or receiving BPDUs. The commands are:

(config)# spanning-tree portfast bpdufilter default

(config-if)# spanning-tree bpdufilter enable

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CCNP SWITCH 642-813 Quick Reference by Denise Donohue