problem in spanning-tree

[chpmotry]

Hello everyone. I have a network with the topology shown in the figure below.

In black oval shape (layer3 switch) The port f0/1 is main port and port f0/2 is backup link to connecting to c3750-12s(root bridge)  with switch c3750-12s because in black oval shape the port f0/1 is fiber optic port and port f0/2 is a ethernet port .

I want the switch that I showed with a black oval (layer3 switch) in the figure to select port f0/2 as an alternate port in spanning-tree vlan 2. All six switches participating in spanning-tree pass vlan 2 through their communication ports. Whatever I do, one of the switch ports that I showed with a blue-gray oval is selected as an alternate port.

[paul driver]

Hello
isnt that port (fa0/3) an access port so it wont become an alternate port for any vlan as its the only port connecting to that host , plus it looks that its in vlan 3 anyway?

[chpmotry]

I am so Sorry @paul driver

I corrected my question . Please review it again

[Joshqun Ismayilov]

@chpmotry  what is the question? )) why Fa0/2 is blocking ? 

Thanks !

[chpmotry]

I am so Sorry @Joshqun Ismayilov 

I corrected my question . Please review it again

[Joshqun Ismayilov]

Hello, 

In this case, you only need to increase the port cost for Fa0/2. (you can do it under interface config)

Thanks!

[chpmotry]

I once changed the priority of port 2 to 16 and noticed that the alternate open port was the same as port 2 from the adjacent Layer 2 switch.
Then, I increased the cost of port 2 from the Layer 3 switch in the black oval and again, the result was the same.

[MHM Cisco World]

f0/3 can not be BLK 
but 

f0/2 can be BLK is you config it cost higher than 16 

MHM

[chpmotry]

I am so sorry @MHM Cisco World 

I corrected my question . Please review it again

[MHM Cisco World]

Dont worry' I already know what yoh try and I answer you' 

Config stp cost to be more than 16 in link of f0/2

MHM

[chpmotry]

Thank you @MHM Cisco World 

is it necessary to doing other things such as set spanning-tree priority vlan 2 in all six switches in topology?

I once changed the priority of port 2 to 16 and noticed that the alternate open port was the same as port 2 from the adjacent Layer 2 switch.

Then, I increased the cost of port 2 from the Layer 3 switch in the black oval and again, the result was the same.

[Martin L]

BLK port is STP port on trunking link to other switch and must be on the same vlan x.  so, fa0/3 port which looks like an access port cannot blocking unless u add another link to PC or convert it to trunking port

Regards, ML
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[chpmotry]

I am so Sorry @Martin L .

I corrected my question . Please review it again.