Portfast and BPDU guard behavior

[nuggetinu]

Hi,

I am getting confused on what happens in these 4 instances:

1) Recieving a BPDU on a globally enabled Portfast port

2) Recieiving a BPDU when Portfast was enabled per port basis

3) Recieving a BPDU on a globally enabled Portfast port with BPDU Guard enabled
4) Recieiving a BPDU when Portfast was enabled per port basis with BPDU Guard enabled

Thanks in advance

[cofee]

1) Recieving a BPDU on a globally enabled Portfast port - Switch will immediately put that interface in fwd state.

2) Recieiving a BPDU when Portfast was enabled per port basis - same as above

3) Recieving a BPDU on a globally enabled Portfast port with BPDU Guard enabled - switch will shutdown the port in err-disabled mode.
4) Recieiving a BPDU when Portfast was enabled per port basis with BPDU Guard enabled - Switch will  shut down the port in err-disabled mode whether portfast is enabled or not. 

[nuggetinu]

I found the attached in a book and is confusing me

[cofee]

I agree with the first statement that the portfast enabled interface will go through the stp state beginning from blocking and eventually to forwarding state as long as there is no loop/

I have doubt about the 2nd statement so I will need to test it.

[cofee]

Second statement from the screenshot that you uploaded appears to be incorrect according to this test:

http://lostintransit.se/2013/08/04/busting-myths-spanning-tree-portfast-on-the-interface/

I hope you will find this useful.

[nuggetinu]

So to sum up the attached, as that part is still not clear for me, basically portfast will be disabled both in if configured globally and per port, but

1) When configured globally, portfast will be disabled and it will go into blocking phase and run the usual STP process. This is clear

2) When configured per port, portfast will be disabled but it stays in the Forwarding state, just skips the listen and learning phase, possibly creating loops temporarily. The question is, will STP run here then, and if required take action on the port if it is found to be creating loops?

Many thanks