Allied Telesis AT-S21 - Manual (Page 41)

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Menu: Bridging>Port spanning tree configuration
>Enable spanning tree for all ports
>Disable spanning tree for all ports
To enable a specific ports spanning tree, select >Enable
spanning tree for all ports , then choose the port.
The root port is chosen by a bridge as that bridge’s preferred path to
the root bridge. To prevent data loops, there must only be one root
port per bridge.
Root Priority: All of the ports are default root priority 128; the
range is 0-255. When the designated root port is disabled or
the cable connection breaks, the STP algorithm reconfigures
an alternate path to the LAN by identifying the port with the
next lowest priority number.
Port Cost: The default value is 100, and the range is 1-65535. The
spanning tree algorithm uses the cost parameter in
combination with the priority to decide which bridges provide
the lowest cost path to the root bridge for that LAN.
Higher port costs are associated with ports of lower
bandwidth, and vice versa. For example, 100 is the cost for a 10
Mbps port, 10 for a 100 Mbps port, and 1 for a 1 Gbps port.
Once the required parameters are configured, bridges can make a
determination on the best single path to a destination within a given
VLAN.
A formula determines the amount of time it takes for the topology to
reconfigure, depending upon the spanning tree values you use. Refer
to the IEEE specification for details.
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