Web Management Guide-R04

Chapter 7 | Spanning Tree Algorithm
Configuring Interface Settings for STA
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◆ 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. Note that path cost takes precedence over port priority. (Range: 0 for
auto-configuration, 1-65535 for the short path cost method
11
, 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.
Administrative path cost cannot be used to directly determine the root port on
a switch. Connections to other devices use IEEE 802.1Q-2005 to determine the
root port as in the following example.
Figure 125: Determining the Root Port
For BPDU messages received by i1 on SW3, the path cost is 0.
For BPDU messages received by i2 on SW3, the path cost is that of i1 on SW2.
11. Refer to “Configuring Global Settings for STA” on page 217 for information on setting the
path cost method. The range displayed on the STA interface configuration page shows the
maximum value for path cost. However, note that the switch still enforces the rules for path
cost based on the specified path cost method (long or short).
Table 11: Recommended STA Path Cost Range
Port Type IEEE 802.1D-1998 IEEE 802.1w-2001
Ethernet 50-600 200,000-20,000,000
Fast Ethernet 10-60 20,000-2,000,000
Gigabit Ethernet 3-10 2,000-200,000
10G Ethernet 1-5 200-20,000
Table 12: Default STA Path Costs
Port Type Short Path Cost
(IEEE 802.1D-1998)
Long Path Cost
(IEEE 802.1D-2004)
Ethernet 65,535 1,000,000
Fast Ethernet 65,535 100,000
Gigabit Ethernet 10,000 10,000
10G Ethernet 1,000 1,000