Administrator Guide

Layer 2 Switching Commands 788
spanning-tree vlan max-age
Use the spanning-tree vlan max-age command to configure the spanning tree
maximum age time for a set of VLANs. Use the no form of the command to
return the maximum age timer to the default value.
Syntax
spanning-tree vlan vlan-list max-age 6-40
no spanning-tree vlan vlan-list > max-age
• max-age — The maximum age time before a bridge port saves its
configuration information.
Default Configuration
The default maximum aging time is 20 seconds.
Command Modes
Global Configuration Mode
User Guidelines
Set this value to a lower number to accelerate discovery of topology changes.
The network operator must take into account the end to end BPDU
propagation delay and message age overestimate for their specific topology
when configuring this value.
The default setting of 20 seconds is suitable for a network of diameter 7, lost
message value of 3, transit delay of 1, hello interval of 2 seconds, overestimate
per bridge of 1 second, and a BPDU delay of 1 second. For a network of
diameter 4, a setting of 16 seconds is appropriate if all other timers remain at
their default values. IEEE 802.1Q notes that RSTP and MSTP treat the
common spanning tree message age field as a hop count. Section 13.37
Performance discusses appropriate and recommended values and further
refers the network operator to the discussion in IEEE 802.1D section 17.14.
In particular, operators should make themselves of the requirement that
bridges must enforce the following constraint:
2 × (
Bridge_Forward_Delay – 1.0 seconds ) >= Bridge_Max_Age >= 2 ×
(
Bridge_Hello_Time + 1.0 seconds )
2CSNXXX_SWUM204.book Page 788 Monday, January 25, 2016 1:25 PM