User’s Manual of
| LAN 1 |
| Portcast = 19 |
A | Port 3 |
Bridge ID = 15 | |
Port 1 | Port 2 |
Portcast = 4 | Portcast = 4 |
| Portcast = 4 |
| Portcast = 4 |
|
B | Port 1 |
| C | Port 1 |
Bridge ID = 30 |
| Bridge ID = 20 | ||
Port 2 | Port 3 | Portcast = 19 | Port 2 | Port 3 |
| Portcast = 19 |
|
| Portcast = 19 |
| LAN 2 |
|
| LAN 3 |
Before Applying the STA Rules
In this example, only the default STP values are used.
| LAN 1 |
A | Port 3 |
| Root Bridge |
Port 1 | Port 2 |
| Designated Port | Designated Port |
| Root Port |
| Root Port |
|
B | Port 1 |
| C | Port 1 |
|
|
| Designated Bridge | |
Port 2 | Port 3 | Blocked | Port 2 | Port 3 |
| LAN 2 |
|
| LAN 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.
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