PLANET SGSD-1022 - Manual (Page 157)

User’s Manual of SGSD-1022 / SGSD-1022P
SGSW-2840 / SGSW-2840P
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
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
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.
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