Spanning-Tree Reconvergence

Hello Christian!

Hmm, not quite. At least not based on your diagram. You should think about it this way.

In order to determine which port between SW2 and SW4 is designated, you should imagine placing an imaginary device on the link between the two switches like so:

You then measure the cost from H1 to the root bridge via each of the two possible paths like so:

When you measure the cost from H1 to each of the two switches, use half of the cost between the two. So the costs are:

  • H1 → SW2 → SW1 = 2+4 = 6 (green line)
  • H1 → SW4 → SW3 → SW1 = 2+4+4=10 (red line)

So since the path via SW2 is shorter, the port on switch 2 becomes designated.

Therefore it is the port on SW4 that becomes blocked. Does that make sense?

I hope this has been helpful!