Hi Rene/Laz
I am a bit confused as to what a switch inserts into its root path cost field for sending on to the next switch. Is it not the cost of its shortest path to the root bridge? In the first topology we have:
- SW3 receives BPDUs on its 10 Mbit interface (cost 100) and on its 1000 Mbit interface (cost 4). It will use its 1000 Mbit interface as its root port (shortest path to the root bridge is 19+19+4=42).
- SW3 will forward BPDUs to SW4. The root path cost field will be 100.
SW3’s shortest path is through SW4 itself, with a cost of 42, but we are saying here that it will send a root path cost of 100 to SW4, which is the cost corresponding to the 10Mbit connection, the physically most direct route to the root.
Can you clarify?
Thanks,
Phil