Alcatel-Lucent 1643 AMS User's Operation Manual page 398

Traffic provisioning
Determination of the root
For every switch a priority can be configured. The switch priority is a number between
0 (highest priority) and 61440 (lowest priority) in steps of 4096. The switch with the
highest priority will become root.
If there are two or more switches with the same highest priority, then the switch with
the lowest number for the MAC address will become root. This rule ensures that there
is always exactly one root, as MAC addresses are unique.
Priority: 28072
Determination of the root ports
Root ports are those ports that will be used to reach the root. For each switch the port
with the lowest root path cost is chosen, where the root path cost is determined by
adding the path costs to the root. In the example port 2b and 3b are root ports.
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8-46
1b
Switch 1
Root
1c
1a
LAN
Alcatel-Lucent - Proprietary
LAN
2a
Priority: 32768
Switch 2
2b
2c
Switch 3
3b
LAN
See notice on first page
Spanning tree protocol (STP)
3c
Priority: 32768
3a
365-312-807R7.2
Issue 4, May 2007