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Guscht
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MSTP - Wiki confuses me

Tue Sep 06, 2022 11:55 pm

Hi,

I am trying now for 2 hours to understand the MSTP wiki:
https://wiki.mikrotik.com/wiki/Manual:S ... e_Protocol

Can somebody please explain the follwing:
In this case for VLAN 10,20 to reach the third device from the first device it would choose between ether1 and ether2, one port will be blocked and set as an alternate port, ether1 will have path cost as 5+9=14 and ether2 will have path cost as 10, ether2 will be elected as the root port for MSTI1 on the third device. In case for VLAN 30,40 to reach the first device from the third device, ether1 will have path cost as 5+9=14 and ether2 will have path cost as 15, ether1 will be elected as the root port for MSTI2 on the third device.

How do they calculate 14? VLAN 10,20 = Instance1
They refer to Port 2 and 3, but in the drawing Port 3 is not part of the region?!

Use the following commands on R1_3, R2_3, R3_3:
/interface bridge port mst-override
add identifier=1 interface=ether2 internal-path-cost=5
add identifier=1 interface=ether3 internal-path-cost=9

And why does ether2 has a path cost of 10? I could understand 5, but where do the other 5 come from?
and ether2 will have path cost as 10

And the next point:
Use the following commands on R1_3, R2_3, R3_3:

/interface bridge port
set [find where interface=ether3] internal-path-cost=25
Again, why Port3? This port is not part of the region?! WHY 3 😢😢😢😢

And why 25? The default value is 10, why should a cost value of 25 force the traffic going through this port and not the port of the green line?


And at least:
Use the following commands on R3_3:

/interface bridge port
set [find where interface=ether2] path-cost=30
set [find where interface=ether3] path-cost=40
set [find where interface=ether4] path-cost=20

Use the following commands on R1_3 and R2_3:

/interface bridge port
set [find where interface=ether2] path-cost=20
set [find where interface=ether3] path-cost=30
Why never configuring Port 1?

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