Alcatel-Lucent 1643 AMS Applications And Planning Manual page 192

Ethernet Overview
For every port a path cost value can be configured. For E/FE TransLAN
default value of the path cost is determined by dividing 20,000,000,000 by the
bandwidth in kbit/s. For GbE TransLAN
the active network topology.
Determination of the designated and blocked ports
The designated port is the one port that is going to be used for a certain LAN. In the
example, there are 6 LANs.
The designated ports for LAN 1, LAN 2 and LAN 3 are the ports 1a, 2a and 3a
respectively, because these LANs have only one connection to a switch. If there are
more connections to a switch, then the port with the lowest root path cost is chosen.
Thus the designated ports for LAN 4, LAN 5 and LAN 6 are the ports 1b, 1c and 3c
respectively.
....................................................................................................................................................................................................................................
11-16
Path cost
60000
1b
Switch 1
Root 1c
1a
LAN
Alcatel-Lucent - Proprietary
LAN
2a
Switch 2
r
Path cost
2c 2b
25000
Switch 3
r
10000 3b
Path cost
LAN
®
cards, the path cost is a means to influence
See notice on first page
Spanning tree protocol (STP)
3c
3a
®
cards, the
365-312-801R7.2
Issue 3, May 2007