Chapter 7
| Spanning Tree Algorithm
Configuring Interface Settings for STA
– 191 –
◆ 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
4
, 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.)
◆ Root Guard – STA allows a bridge with a lower bridge identifier (or same
identifier and lower MAC address) to take over as the root bridge at any time.
Root Guard can be used to ensure that the root bridge is not formed at a
suboptimal location. Root Guard should be enabled on any designated port
connected to low-speed bridges which could potentially overload a slower link
by taking over as the root port and forming a new spanning tree topology. It
could also
be used to form a border around part of the network where the root
bridge is allowed. (Default: Disabled)
4. Refer to “Configuring Global Settings for STA” on page 183 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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