3Com WX2200 3CRWX220095A Switch User Manual

Configuring and Managing STP Fast Convergence Features 359
Backbone Fast
Backbone fast convergence accelerates a port’s recovery 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 bridge’s link to the root bridge
fails. The switch immediately verifies whether BPDU information stored
on a port is still valid. If not, the bridge immediately starts the listening
stage on the port.
CAUTION: The backbone fast convergence feature is not compatible
with switches that are running standard IEEE 802.1D Spanning Tree
implementations. This includes switches running Rapid Spanning Tree or
Multiple Spanning Tree.
If you plan to use the backbone fast convergence feature, you must
enable it on all the bridges in the spanning tree.
Uplink Fast
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.
Configuring Port Fast
To enable or disable port fast convergence, use the following command:
set spantree portfast port port-list {enable | disable}
To enable port fast convergence on ports 1, 3, and 5, type the following
WX1200# set spantree portfast port 1,3,5 enable
success: change accepted.