Understanding Port Fast; Understanding Bpdu Guard - Cisco 3020 - Catalyst Blade Switch Configuration Manual

Understanding Optional Spanning-Tree Features

Understanding Port Fast

Port Fast immediately brings an interface configured as an access or trunk port to the forwarding state
from a blocking state, bypassing the listening and learning states.
In Figure
can immediately connect to the network, rather than waiting for the spanning tree to converge.
Interfaces connected to a blade server should not receive bridge protocol data units (BPDUs). An
interface with Port Fast enabled goes through the normal cycle of spanning-tree status changes when the
switch is restarted.
Because the purpose of Port Fast is to minimize the time interfaces must wait for spanning-tree to
Note
converge, it is effective only when used on interfaces connected to end stations. If you enable Port Fast
on an interface connecting to another switch, you risk creating a spanning-tree loop.
You can enable this feature by using the spanning-tree portfast interface configuration or the
spanning-tree portfast default global configuration command.
Figure 15-1
Blade Servers

Understanding BPDU Guard

The BPDU guard feature can be globally enabled on the switch or can be enabled per interface, but the
feature operates with some differences.
At the global level, you enable BPDU guard on Port Fast-enabled interfaces by using the spanning-tree
portfast bpduguard default global configuration command. Spanning tree shuts down interfaces that
are in a Port Fast-operational state if any BPDU is received on those interfaces. In a valid configuration,
Port Fast-enabled interfaces do not receive BPDUs. Receiving a BPDU on a Port Fast-enabled interface
signals an invalid configuration, such as the connection of an unauthorized device, and the BPDU guard
feature puts the interface in the error-disabled state.
At the interface level, you enable BPDU guard on any interface by using the spanning-tree bpduguard
enable interface configuration command without also enabling the Port Fast feature. When the interface
receives a BPDU, it is put in the error-disabled state.
Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide
15-2
15-1, Port Fast is configured on the interfaces that are connected to blade servers. The devices
Port Fast-Enabled Interfaces
Port
Fast-enabled
ports
Chapter 15 Configuring Optional Spanning-Tree Features
Blade Switch
Blade Servers
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