C
HAPTER
8
| Spanning Tree Algorithm
Configuring Interface Settings for STA
– 215 –
◆ 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. Note that path cost takes precedence over
port priority. (Range: 0 for auto-configuration, 1-65535 for the short
path cost method
5
, 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.
◆ Admin Link Type – The link type attached to this interface.
■
Point-to-Point – A connection to exactly one other bridge.
■
Shared – A connection to two or more bridges.
■
Auto – The switch automatically determines if the interface is
attached to a point-to-point link or to shared media. (This is the
default setting.)
5. Refer to "Configuring Global Settings for STA" on page 207 for information on setting the
path cost method.
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
Table 12: Default STA Path Costs
Port Type Short Path Cost
(IEEE 802.1D-1998)
Long Path Cost
(802.1D-2004)
Ethernet 65,535 1,000,000
Fast Ethernet 65,535 100,000
Gigabit Ethernet 10,000 10,000
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