Cisco WS-C6506 Software Manual page 189

Chapter 7 Configuring Spanning Tree
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 the nondefault parameter values that are permitted by 802.1D. See
Table 7-6
Table 7-6
Parameter
Network Diameter (dia)
Hello Time
Forward Delay Timer
Maximum Age Timer
Note You can set the switch ports in PortFast mode for improved convergence. PortFast mode affects only the
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 learning before
reaching the forwarding state. For information about PortFast, see the
Works" section on page 9-2
BackboneFast, and Loop Guard."
To configure the spanning tree parameters to improve convergence, perform this task in privileged mode:
Task
Step 1
Configure the hello time for a VLAN or an
MISTP instance.
Step 2 Verify the configuration.
Step 3 Configure the forward delay time for a
VLAN or an MISTP instance.
Step 4 Verify the configuration.
Step 5
Configure the maximum aging time for a
VLAN or an MISTP instance.
Step 6 Verify the configuration.
This example shows how to configure the spanning-tree hello time, Forward Delay Timer, and Maximum
Age Timer to 2, 4, and 4 seconds:
Console> (enable) set spantree hello 2 100
Spantree 100 hello time set to 7 seconds.
Console> (enable)
Console> (enable) set spantree fwddelay 4 100
Spantree 100 forward delay set to 21 seconds.
Console> (enable)
Console> (enable) set spantree maxage 6 100
OL-8978-04
for the nondefault parameters for a reconvergence of 14 seconds.
Nondefault Parameters
in Chapter 9, "Configuring Spanning-Tree PortFast, UplinkFast,
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
Time
2
2 seconds
4 seconds
6 seconds
Command
set spantree hello interval [vlan] mistp-instance
[instances]
show spantree [vlan | mistp-instance instances]
set spantree fwddelay delay [vlan] mistp-instance
[instances]
show spantree [mod/port] mistp-instance [instances]
[active]
set spantree maxage agingtime [vlans] mistp-instance
instances
show spantree [mod/port] mistp-instance [instances]
[active]
Configuring a Root Switch
"Understanding How PortFast
7-47