Nortel Networks NN47250-500 Configuring and managing STP fast convergence features

Configuring and managing spanning tree protocol 449
Nortel WLAN—Security Switch 2300 Series Configuration Guide
To change the maximum acceptable age for root bridge hello packets on all VLANs to 15 seconds, type the following
command:
WSS# set spantree maxage 15 all
success: change accepted.
Configuring and managing 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 WSS provides the following fast convergence features to bypass the
forwarding delay:
•Port fast
• Backbone fast
• Uplink fast
Port fast convergence
Port fast convergence bypasses both the listening and learning stages and immediately places a port in the forwarding
state. You can use port fast convergence on ports that are directly connected to servers, hosts, or other MAC stations.
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 WSS 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.
Note. Do not use port fast convergence on ports connected to other bridges.
Note. If you plan to use the backbone fast convergence feature, you must enable it on all
the bridges in the spanning tree.