For every port a path cost value can be configured. For E/FE TransLAN
®
cards, the
default value of the path cost is determined by dividing 20,000,000,000 by the
bandwidth in kbit/s. For GbE TransLAN
®
cards, the path cost is a means to influence
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 six 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.
LAN
1a
Path cost
Path cost
Path cost
Root
3a
3b
3c
1c
1b
2c
2b
2a
Switch 1
Switch 2
Switch 3
LAN
LAN
r
r
60000
10000
25000
Traffic provisioning
Spanning tree protocol (STP)
....................................................................................................................................................................................................................................
365-312-807R7.2
Issue 4, May 2007
Alcatel-Lucent - Proprietary
See notice on first page
8-47
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