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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. Normally, this setting is not required.
Command examples
1.
(config)# spanning-tree mst transmission-limit 5
Sets the maximum number of BPDUs to be sent per hello-time to 5 for Multiple
Spanning Tree.
(3) Setting the maximum number of hops
You can set the maximum number of hops for BPDUs sent from the root bridge. The BPDU
counter is incremented whenever a switch is passed, and BPDUs exceeding the maximum
number of hops are disabled and ignored.
For ports connected to Single Spanning Tree switches, the maximum enabled time
(max-age) parameter is used instead of the maximum number of hops (max-hops). The
counter for the number of hops is a valid parameter between Multiple Spanning Tree
switches.
Points to note
The maximum number of hops can be increased to have BPDUs reach many
switches. If no value is set, 20 is used for the maximum number of hops.
Command examples
1.
(config)# spanning-tree mst max-hops 10
Sets the maximum number of hops for BPDUs on Multiple Spanning Tree to 10.
(4) Setting maximum enabled times for BPDUs
For Multiple Spanning Tree, the maximum enabled time (
for ports connected to Single Spanning Tree switches. It does not need to be set for
configurations in which Multiple Spanning Tree is run for switches across the entire
topology.
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 mst max-age 25
Sets the maximum enabled time for Multiple Spanning Tree BPDUs to 25 seconds.
19 Spanning Tree Protocol
max-age
) is a valid parameter only
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