User's Manual

271
Chapter 37 Configuring STP Optional
Characteristic
37.1 STP Optional Characteristic Introduction
The spanning tree protocol module of the switch supports seven additional characteristics (the so-called
optional characteristics). These characteristics are not configured by default. The supported condition of
various spanning tree protocol modes towards the optional characteristics are as follows:
Optional
Characteristic
Single STP PVST RSTP MSTP
Port Fast
Yes Yes No No
BPDU Guard
Yes Yes Yes Yes
BPDU Filter
Yes Yes No No
Uplink Fast
Yes Yes No No
Backbone Fast
Yes Yes No No
Root Guard
Yes Yes Yes Yes
Loop Guard
Yes Yes Yes Yes
37.1.1 Port Fast
Port Fast immediately brings an interface to the forwarding state, bypassing the listening and learning states.
In SSTP and PVST mode, you can use Port Fast on interfaces connected to the host or server, to allow those
devices to immediately connect to the network.
Port Fast is applicable for connecting ports of the host. As these ports will not receive BPDU and will not affect
the network topology, they can enter the forward state without waiting. If the Port Fast function is configured
on the interface connecting to the switch, there may cause a loop.
Port Fast Characteristics can be configured in global configuration mode or interface configuration mode.
When in global configuration mode, all interfaces will be taken as Port Fast interfaces and fast enter Forwarding
state. Thus, it is more likely to cause loop. For avoiding the network loop resulting from Port Fast function, use
BPDU Guard or BPDU Filter to protect the interface.