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Spanning Tree Algorithm Configuration
22-20
22
• Default: 128
• Range: 0-240, in steps of 16
• Admin MST Path Cost – This parameter is used by the MSTP to determine the
best path between devices. Therefore, lower values should be assigned to ports
attached to faster media, and higher values assigned to ports with slower media.
(Path cost takes precedence over port priority.) Note that when the Path Cost
Method is set to short (page 3-63), the maximum path cost is 65,535.
By default, the system automatically detects the speed and duplex mode used on
each port, and configures the path cost according to the values shown below. Path
cost “0” is used to indicate auto-configuration mode.
• Range –
-Ethernet: 200,000-20,000,000
-Fast Ethernet: 20,000-2,000,000
-Gigabit Ethernet: 2,000-200,000
• Default –
-Ethernet – Half duplex: 2,000,000; full duplex: 1,000,000; trunk: 500,000
-Fast Ethernet – Half duplex: 200,000; full duplex: 100,000; trunk: 50,000
-Gigabit Ethernet – Full duplex: 10,000; trunk: 5,000
Web – Click Spanning Tree, MSTP, Port Configuration or Trunk Configuration. Enter
the priority and path cost for an interface, and click Apply.
Figure 22-7 MSTP Port Configuration
CLI – This example sets the MSTP attributes for port 4.
Console(config)#interface ethernet 1/4 45-1
Console(config-if)#spanning-tree mst port-priority 0 51-17
Console(config-if)#spanning-tree mst cost 50 51-16
Console(config-if)