Nortel Networks NN47250-500 Changing standard spanning tree parameters

Configuring and managing spanning tree protocol 443
Nortel WLAN—Security Switch 2300 Series Configuration Guide
Changing standard spanning tree parameters
You can change the following standard STP parameters:
• Bridge priority
•Port cost
• Port priority
Bridge priority
The bridge priority determines the WSS’s eligibility to become the root bridge. You can set this parameter globally or on
individual VLANs.
The root bridge is elected based on the bridge priority of each device in the spanning tree. The device with the highest
bridge priority is elected to be the root bridge for the spanning tree. The bridge priority is a numeric value from 0
through 65,535. Lower numeric values represent higher priorities. The highest priority is 0, and the lowest priority is
65,535. The default bridge priority for all devices is 32,768.
If more than one device has the highest bridge priority (lowest numeric value), the device with the lowest MAC address
becomes the root bridge.
If the root bridge fails, STP elects a new root bridge based on the bridge priorities of the remaining bridges.
Port cost
Port cost is a numeric value that STP adds to the total cost of a path to the root bridge. When a designated bridge has
multiple equal-cost paths to the root bridge, the designated bridge uses the path with the lowest total cost. You can set
this parameter on an individual port basis, for all VLANs the port is in, or for specific VLANs.
You can specify a value from 1 through 65,535 for the port cost. The default depends on the port speed and link type.
Table 26 lists the defaults for STP port path cost.
Table 26.SNMP port path cost defaults
Port Speed Link Type Default Port Path Cost
1000 Mbps Full Duplex Aggregate Link (Port
Group) 19
1000 Mbps Full Duplex 4
100 Mbps Full Duplex Aggregate Link (Port
Group) 19
100 Mbps Full Duplex 18
100 Mbps Half Duplex 19
10 Mbps Full Duplex Aggregate Link (Port
Group) 19
10 Mbps Full Duplex 95
10 Mbps Half Duplex 100