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User’s Manual of FGSW-2620VM / FGSW-2620PVM
79
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 ensure that the link between switch B and switch C is the blocked link.