Spanning-Tree UplinkFast

[lagapidis (Lazarus Agapidis)]

Hello Mohamed

Whenever there is a topology change (a link goes down) on a switch other than the local switch, (an indirect link failure) then in such a situation, STP will reconverge in 50 seconds. This is due to the addition of the blocking timer, which is 20 seconds. Take a look at this post which refers to the blocking timer:

Spanning Tree Port States

Hello Quirik Switch ports in the blocking or alternate state still receive BPDUs from the connected switch. So for the following statement here is the explanation: So before port C on SW2 went down, when STP was converged and stable, port B had received some BPDUs from SW2. These are the “previously received BPDUs.” When the topology changed, SW2 sent new BPDUs with new information, stating that it is the root bridge. SW3 does not process these yet, until the blocking timer expires. Wh…

For a more comprehensive view of the reconvergence of STP, take a look at the following lesson:

Spanning Tree Reconvergence

I hope this has been helpful!

Laz