User's Manual

272
Figure 1.1 Port Fast
Note:
The rapid convergent spanning tree protocol, RSTP and MSTP can immediately bring an
interface to the forwarding state, and therefore there is no need to use Port Fast feature.
37.1.2 BPDU Guard
If one Port Fast receives BPDU, it may because of the false network configuration. When one Port Fast
receives BPDU, BPDU Guard will protect it passively.
In different STP modes, BPDU Guard acts differently. In SSTP/PVST mode, if a port that has the BPDU Guard
function and the Portfast function configured receives BPDU, this port will be manadatorily shut down. You
have to configure the port manually to resume this port. In RSTP/MSTP mode, if a BPDU-Guard-configured
port receives BPDU, the port will be set to the Blocking state in a period of time.
BPDU Guard characteristics can be configured independent of Port Fast. In all STP modes, the interfaces
configured with BPDU Guard will not send BPDU. But the interface can receive BPDU and process it. In
RSTP/MSTP mode, you can configure BPDU Guard on the port to ensure the device connected to the switch
will not receive BPDU.
BPDU Guard characteristics can be configured in global or interface mode. In global configuration mode, run
command spanning-tree portfast bpduguard to block all interfaces sending BPDU. Note that inappropriate use
of BPDU Guard will cause loop in complicated network.
37.1.3 BPDU Filter
With the BPDU filtering characteristic, the switch will block BPDU to send out in SSTP/PVST mode, and also
from a protection of the Port Fast.
In SSTP/PVST mode, if a Port Fast port with BPDU filter configured receives the BPDU, the characteristic
BPDU Filter and Port Fast at the port will be automatically disabled, resuming the port as a normal port. Before