This is a normal behavior and has nothing to do with RSTP. After the Root Ports have been selected, Dist1 and ASW need to decide who will be the designated bridge on the segment between them.
Dist1 hears the root with a path cost of 3 because Po1 cost is 3. ASW hears the root with a cost of 2 because of T1/2.
Dist1 will send a BPDU towards ASW with root path cost 3. ASW has cost 2 on T1/2 so it will send a BPDU to Dist1 with a root path cost 2.
Therefore ASW assumes a designated role because it is sending a lower (better) root path cost BPDU to the segment than Dist1 (cost 2 versus 3) and ASW T1/1 will be designated and Dist1 T6/3 will be alternate blocking.
The lower link cost means a better path to the root. When you change the cost of Po1 to 1, Dist1 will advertise a better root path cost than ASW and it will be a designated bridge on the segment between them. IOS by default also applies a lower (better) cost to port channels as their bandwidth is higher than the single link.
This is actually a pretty cool feature, i didn't even know it existed until I was looking for a solution to advertise a subnet (prefix in BGP talk), only if a certain condition existed. This is exactly what conditional advertisements does
j ai une question j ai achete un routeur cisco 887VA-k9 , je le configuré avec la configuration ci- dessous
si je le lier avec mon pc portable sur l un de ses ports directement ça marche toute est bien ( la connexion internet + m...
Attached policy provides CLI access to the Cisco 4G router over text messaging. Two files are in the attached .tar file:
2. PDF with instructions on how to load and use the .tcl file.