Configuring A Root Switch To Improve Convergence - Cisco WS-X6066-SLB-APC - Content Switching Module Software Manual

Chapter 8 Configuring Spanning Tree
To configure a switch as the secondary root switch for an instance, perform this task in privileged mode:
Task
Configure a switch as the secondary root switch
for an instance.
This example shows how to configure the secondary root for an instance:
Console> (enable) set spantree root secondary mistp-instance 2-4 dia 4
Instances 2-4 bridge priority set to 8192
VLInstances 2-4 bridge max aging time set to 14 seconds.
Instances 2-4 bridge hello time set to 2 seconds.
Instances 2-4 bridge forward delay set to 9 seconds.
Switch is now the root switch for active Instances 1-6.
Console> (enable)

Configuring a Root Switch to Improve Convergence

By lowering the values for the Hello Time, Forward Delay Timer, and Maximum Age Timer parameters
on the root switch, you can reduce the convergence time. For information on configuring these timers,
see the
Reducing the timer parameters values is possible only if your network has LAN links of 10 Mbps or
Note
faster. In a network with links of 10 Mbps or faster, the network diameter can reach the maximum
value of 7. With WAN connections, you cannot reduce the parameters.
When a link failure occurs in a bridged network, the network reconfiguration is not immediate.
Reconfiguring the default parameters (specified by IEEE 802.1D) for the Hello Time, Forward Delay
Timer, and Maximum Age Timer requires a 50-second delay. This reconfiguration time depends on the
network diameter, which is the maximum number of bridges between any two end stations.
To speed up convergence, use nondefault parameter values permitted by the 802.1D standard. See
Table 8-5
Table 8-5
Parameter
Network Diameter (dia)
Hello Time
Forward Delay Timer
Maximum Age Timer
You can set switch ports in PortFast mode for improved convergence. PortFast mode affects only the
Note
transition from disable (link down) to enable (link up) by moving the port immediately to the
forwarding state. If a port in the PortFast mode begins blocking, it then goes through listening and
78-13315-02
"Configuring Spanning Tree Timers" section on page
for the nondefault parameters for a reconvergence of 14 seconds.
Nondefault Parameters
Catalyst 6000 Family Software Configuration Guide—Releases 6.3 and 6.4
Command
set spantree root [secondary] mistp-instance
instance [dia network_diameter]
[hello hello_time]
8-35.
Time
2
2 seconds
4 seconds
6 seconds
Configuring a Root Switch
8-33