Spanning Tree Algorithm
10-14
10
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.) 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.
• 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.)
• Admin Edge Port (Fast Forwarding) – You can enable this option if an interface is
attached to a LAN segment that is at the end of a bridged LAN or to an end node.
Since end nodes cannot cause forwarding loops, they can pass directly through to
the spanning tree forwarding state. Specifying Edge Ports provides quicker
convergence for devices such as workstations or servers, retains the current
Table 10-4 Recommended STA Path Cost Range
Port Type
Short Path Cost
*
(IEEE 802.1D-1998)
* Use the STA Configuration screen (page 10-6) to set the path cost method.
Long Path Cost
*
(802.1D-2004)
Gigabit Ethernet 2,000-65,535 2,000-200,000
10G Ethernet 200-20,000 200-20,000
Table 10-5 Default STA Path Costs
Port Type
Short Path Cost
*
(IEEE 802.1D-1998)
* Use the STA Configuration screen (page 10-6) to set the path cost method.
Long Path Cost
*
(802.1D-2004)
Gigabit Ethernet 10,000 10,000
10G Ethernet 1,000 1,000
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