PLANET WGSW-5242 - Manual (Page 73)

User’s Manual of WGSW-5242
73
switch as the root bridge using the Priority setting, or influencing STP to choose a particular port to block using the Port Priority
and Port Cost settings is, however, relatively straight forward.
Bridge ID = 15
Port 3
Port 1 Port 2
A
Bridge ID = 20
Port 1
Port 2 Port 3
C
Bridge ID = 30
Port 1
Port 2 Port 3
B
LAN 1
LAN 2 LAN 3
Portcast = 19
Portcast = 19 Portcast = 19
Portcast = 4
Portcast = 4
Portcast = 19
Portcast = 4
Portcast = 4
Figure 4-5-2
Before Applying the STA Rules
In this example, only the default STP values are used.
Root Bridge
Port 3
Port 1 Port 2
A
Designated Bridge
Port 1
Port 2 Port 3
C
Port 1
Port 2 Port 3
B
LAN 1
LAN 2 LAN 3
Designated Port
Root Port Root Port
Designated Port
Blocked
Figure 4-5-3
After Applying the STA Rules
The switch with the lowest Bridge ID (switch C) was elected the root bridge, and the ports were selected to give a high port cost
between switches B and C. The two (optional) Gigabit ports (default port cost = 4) on switch A are connected to one (optional)
Gigabit port on both switch B and C. The redundant link between switch B and C is deliberately chosen as a 100 Mbps Fast
Ethernet link (default port cost = 19). Gigabit ports could be used, but the port cost should be increased from the default to