It seems to be bug related to packet tracer. I assume you are trying to change port priority to modify which ports are blocked. I tried the lab you attached and it isn't behaving properly (remote switches dont see the change in priority) however I can assure you that in real equipment changing port priority will work as you were probably expecting packet tracer to
Task1: You have determined that you want the Core #2 switch to be the root switch in the spanning tree. Make the necessary changes to ensure that Core #2 is _always_ chosen as the root. (Hint: don’t use zero!). You also want Core #1 to be the designated _backup_ root bridge.
The keyword there is _always_.
On core #2
use the "spanning-tree vlan 1 root primary" command
The keyword is _backup_
On core #1
use the " spanning-tree vlan 1 root secondary"
Task 2: Adjust the necessary parameters on the distribution switches and access switches so that the primary links are used rather than the redundant links (Hint: a faster link has a lower cost!)
Use a lower cost than 19 under the port you want to be primary.
use the "spanning-tree vlan 1 cost 4"- for example to make it a Gig link
Edit: I've got to stop posting stuff online without properly checking stuff first
Here is the actual solution (attachment). It is the beginning of the next case study.
They have used the 'span vlan 1 priority XXX' command and the interface 'speed XXX' command.
It works but I think it is counter-productive to change the actual speed of the redundant link.
Chapter_3_Packet_Tracer.pka.zip 203.2 K