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max-age ≥ 2 x (hello-time + 1). When a parameter is changed, parameters must be
adjusted on all switches comprising the Spanning Tree Protocol.
(1) Setting BPDU sending intervals
A short BPDU sending interval makes topology changes easier to detect. A longer interval
requires more time to detect a topology change, but can reduce BPDU traffic and the load
on the Spanning Tree program for the Switch.
Points to note
When no value is set, BPDUs are sent at two-second intervals. Normally, this setting
is not required.
Command examples
1.
(config)# spanning-tree vlan 10 hello-time 3
Sets the PVST+ BPDU sending interval to three seconds for VLAN 10.
Notes
A short BPDU sending interval makes topology changes easier to detect, but might
increase load on the Spanning Tree program due to an increase in BPDU traffic. If
setting this parameter shorter than the default value (two seconds) causes timeout
messages to be output and the topology to change frequently, change it back to the
default value.
(2) Setting the maximum number of BPDUs to be sent
To prevent an increase in CPU load for a Spanning Tree Protocol, the maximum number of
BPDUs to be sent per hello-time (BPDU sending interval) can be chosen. If topology
changes frequently occur, a large quantity of BPDUs are sent to report and gather topology
changes, possibly increasing BPDU traffic and CPU load. This can be controlled by limiting
the maximum number of BPDUs to be sent.
Points to note
If no value is set, operation is performed with a maximum number of BPDUs per
hello-time (BPDU sending interval) of 3. The configuration for this parameter only
takes effect for Rapid PVST+, and is fixed at 3 for PVST+. Normally, this setting is
not required.
Command examples
1.
(config)# spanning-tree vlan 10 transmission-limit 5
Sets the maximum number of BPDUs to be sent per hello-time to 5 for VLAN 10
Rapid PVST+.
(3) Setting maximum enabled times for BPDUs
You can set the maximum enabled time for BPDUs sent from the root bridge. The BPDU
counter is incremented whenever a switch is passed, and BPDUs exceeding the maximum
enabled time are disabled and ignored.
Points to note
The maximum enabled time can be increased to have BPDUs reach many switches.
If no value is set, 20 is used for the maximum enabled time.
Command examples
1.
(config)# spanning-tree vlan 10 max-age 25
Sets the maximum enabled time for BPDUs to 25 seconds on the PVST+ for VLAN
10.
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