Which Is The Objective Of The Ports Designated In Stp If The Root Port Sends Bddu Also This Has Me Very Confunsed I Look And Search On Internet And I Do Not Find That Doubt ?????
See if this helps, if you have a GNS3 lab or Cisco packet tracer, lab up 3 switch in a triangle and connect each to the next A-B B-C C-A and see how STP works
Another GNS / Packet Tracer exercise is to create a ring of 6-8 switches. The port that has the best path to the root bridge will get the root port. Then, if you disable that port or remove that connection, the spanning-tree will adjust for that switch and any others affected by the connection going down and you'll see a new layout with the other open port being set as the root port.
A root port is one that connects to the root bridge with the lowest path cost (ie it may not be directly connected to a root bridge).
Think about what a root bridge is. It's the "root" of the layer 2 network. Root bridges do not have any blocked ports, everything connects back to it and STP BPDUs emanate from there and travel outwards.
So with the rule that root bridges do not have any blocked ports, they are designated ports here. Essentially designated ports are forwarding ports that are not root ports. With a root bridge, it's not possible to have a root port to itself, therefore designated forwarding port.
I've spent a lot of time with STP a long time back and I enjoy it.