Spanning Tree Algorithm
11-14
11
The following interface attributes can be configured:
• Spanning Tree – Enables/disables STA on this interface. (Default: Enabled)
• Priority – Defines the priority used for this port in the Spanning Tree Protocol. If
the path cost for all ports on a switch are the same, the port with the highest priority
(i.e., lowest value) will be configured as an active link in the Spanning Tree. This
makes a port with higher priority less likely to be blocked if the Spanning Tree
Protocol is detecting network loops. Where more than one port is assigned the
highest priority, the port with lowest numeric identifier will be enabled.
• Default: 128
• Range: 0-240, in steps of 16
• Admin Path Cost – This parameter is used by the STA 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.)
(Range: 0 for auto-configuration, 1-65535 for the short path cost method
20
,
1-200,000,000 for the long path cost method)
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. When the short path cost
method is selected and the default path cost recommended by the IEEE 8021w
standard exceeds 65,535, the default is set to 65,535.
20. Refer to “Configuring Global Settings” on page 6 for information on setting the path cost
method.
Table 11-1 Recommended STA Path Cost Range
Port Type IEEE 802.1D-1998 IEEE 802.1w-2001
Fast Ethernet 10-60 20,000-2,000,000
Gigabit Ethernet 3-10 2,000-200,000
Table 11-2 Recommended STA Path Costs
Port Type Link Type IEEE 802.1D-1998 IEEE 802.1w-2001
Fast Ethernet Half Duplex
Full Duplex
Trunk
19
18
15
200,000
100,000
50,000
Gigabit Ethernet Full Duplex
Trunk
4
3
10,000
5,000
Table 11-3 Default STA Path Costs
Port Type Link Type IEEE 802.1w-2001
Fast Ethernet Half Duplex
Full Duplex
Trunk
200,000
100,000
50,000
Gigabit Ethernet Full Duplex
Trunk
10,000
5,000
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