3Com 3CRWXR10095A, 3CRWX120695A WXR100 manual Enabling STP Fast Convergence Features

Viewing and Configuring VLANs 213

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 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, 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 If the BPDU information on the port is no longer valid, the bridge immediately starts the listening stage on the port.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, you must enable it on all 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.

To enable fast convergence features:

1Access the VLAN table:

a Select the Configuration tool bar option.

b In the Organizer panel, click the plus sign next to the WX switch. c Click the plus sign next to System.

d Select VLANs.