3Com WX4400 Reference Manual page 222

222 C 6: C
HAPTER ONFIGURING
WX S P
YSTEM ARAMETERS
Port fast convergence bypasses both the listening and learning stages and
immediately places a port in the forwarding state. Use port fast
convergence on network ports that are directly connected to servers,
hosts, or other MAC stations.
Do not use port fast convergence on ports connected to other bridges.
9 Click OK.
Enabling STP Fast Convergence Features
The standard STP timers delay traffic forwarding briefly after a topology
change. The time a port takes to change from the listening state to the
learning state or from the learning state to the forwarding state is called
the forwarding delay. In some configurations, this delay is unnecessary.
The WX switch provides the following fast convergence features to
bypass the forwarding delay:
Backbone fast convergence—Backbone fast convergence accelerates
the recovery of a port following the failure of an indirect link.
Normally, when a forwarding link fails, a bridge that is not directly
connected to the link does not detect the link change until the
maximum age timer expires. Backbone fast convergence enables the
WX switch to listen for bridge protocol data units (BPDUs) sent by a
designated bridge when the designated link of a bridge to the root
bridge fails, and immediately verifies whether BPDU information
stored on a port is still valid. If the BPDU information on the port is no
longer valid, the bridge immediately starts the listening stage on the
port.
If you plan to use the backbone fast convergence feature, enable it on all
of the bridges in the spanning tree.
Uplink fast convergence—Uplink fast convergence enables a WX
switch that has redundant links to the network core to immediately
change the state of a backup link to forwarding if the primary link to
the root fails. Uplink fast convergence bypasses the listening and
learning states to immediately enter the forwarding state.
The uplink fast convergence feature is applicable to bridges that are
acting as access switches to the network core (distribution layer) but are
not in the core themselves. Do not enable the feature on WX switches
that are in the network core.