Table of Contents
Advertisement
19 Spanning Tree Protocol
Notes
When link aggregation is used, the default value for the path costs of a channel
group is not the total of all ports in the channel group, but the speed of a single port.
(3) Setting port priority for each instance
The port priority is set to determine which port is used when a Spanning Tree Protocol is
used to make connections between two switches redundant, and the path costs are the
same value for both.
Normally, we recommend that you use link aggregation as functionality to make
connections between two switches redundant, but use this functionality when a Spanning
Tree Protocol is needed for redundancy because the partner connected switch does not
support link aggregation.
Points to note
For port priorities, a lower value indicates a higher priority. When redundancy is used
between two switches, the path whose switch is closer to the root bridge and whose
port has a higher priority is used as the communication path. If this parameter is not
set, the port with the lower port number is prioritized.
Command examples
1.
(config)# interface fastethernet 0/1
(config-if)# spanning-tree port-priority 64
(config-if)# exit
Sets the port priority for port 0/1 to 64.
2.
(config)# interface fastethernet 0/1
(config-if)# spanning-tree mst 20 port-priority 144
(config-if)# exit
Sets the port priority of port 0/1 for instance 20 to 144. For port 0/1, only instance 20
has a port priority of 144, with other instances running at 64.
19.10.4 Configuring Multiple Spanning Tree parameters
Each parameter must be set to satisfy the following relationship: 2
max-age ≥ 2
adjusted across the entire topology.
(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 mst hello-time 3
Sets the BPDU sending interval for Multiple Spanning Tree to three seconds.
Notes
A short BPDU sending interval makes topology changes easier to detect, but might
334
x
(hello-time + 1). When a parameter is changed, parameters must be
(forward-time - 1) ≥
x
Advertisement
Table of Contents
