STP block Question

[rafael2gc]

Hi,

There is any way to bring the block to the port fa0/24 of switch2.

I´ve tried manipulating port cost and port priority without sucess and now i´m not sure that this is really possible.

thanks

Rafaelgc

[Peter Paluch · Accepted solution]

Hi,

In your topology with the Sw1 being the root switch, it is not possible. The Fa0/24 port on Sw2 would be blocked only if it received better BPDUs than it generates itself. However, that is not possible - the Sw2 is closer to the root switch than Sw3, and thus, the root path cost advertised by Sw2 is necessarily lower than the cost advertised by Sw3. Because the root path cost is the second tie breaker (the first one being the root bridge ID), it will immediately decide that the Sw2 has the better port on the link, and it will remain unblocked.

Best regards,

Peter

[rafael2gc]

Hi Peter,

Thanks a lot to take time to awnser my question.

I suspected that was not possible.

Best Regards

Rafaelgc

[francisco_1]

How is the L2 topology setup?

Changing the port priority should move the port in to forwarding state.  Lowest value on the upstream is utilized to pick the root port. Default port priroty is 128 & port # -

Example

int fa0/1

spanning-tree port priority 16

Francisco.