Spanning Tree Protocol-state

[snarayanaraju]

Hi Experts,

I have a conceptual doubt in Spanning Tree Protocol logic.

I have 3 Switches R0, R1 & R2 connected in Triangular fashion. R0-R1-R2-R0 as shown in diagram attached. R0 is Root Bridge being the Lowest Bridge ID

I am seeing that R2 Port connected to R1 port is blocked as a normal behavior of STP. I assume STP chosen R1 ports as Designated Port because it has Lowest Bridge ID (Since both R1 & R2 has equal cost path to R0).

I am trying to change the Blocked port in R2 so that it will become FWD port and R1 port will become BLK port. So, I entered command “spanning -tree cost 5” in R1.

But I am not seeing this cost get reflected in any of the switches. I even tried to change the Spanning tree cost of R0's Fa0/0 and Fa0/1 Port to 100 for testing. It is also not getting advertised to R1 & R2.

I am confused with my understanding. Can anyone please help me, what does this command “spanning -tree cost “ does and how to make R2 switch's all the ports to become FWD state.

Thanks in advance for helping me

Sairam

[Peter Paluch]

Hello Jon,

Great explanation and thank you for covering up my rather bad post :)

Thank you very much for your kind words - and also for your rating. Your post was not bad at all. In fact, when I started writing my rather lengthy reply, I did not see your answer yet. You must have submitted it before I finished writing mine. I just felt that Sairam was trying to understand something in STP that in my own opinion is often misunderstood so I engaged in that lengthy explanation so I could be sure that we and Sairam are on the same "wavelength".

Oh and congrats on the gold star.

Thank you very much again! To receive such commendation from a vet like you is particularly valuable for me. Nevertheless, I can not compare to your rating level... :-) I am just trying to follow the best :)

Best regards,

Peter