Long time lurker, first time poster. I have a quick question and wanted to ask the audience!
I have attached a random network diagram of which I have been exploring RSTP with.
I created the diagram randomly and am manually calculating RSTP port states based on a priority change, and then a link failure, and then a link speed change to 100Mbps. The link lines are annotated with "speed / short path cost" for my reference. I am assuming that there is a single vlan (1). All links are full duplex point to point.
The priorty of Switch ..a3 has been made lower than all other Switches. The link between Switch ..a1 and ..a3 is down due to a network error (Layer 1 say..) and the link between Switch ..a2 and ..a1 has been changed to 100Mbps. With Switch ..a8 as the historic root switch before the link speed change, is the port towards ..a1 from ..a8 (on a8), a designated port, or should this be blocking? If so, would ..a1 become a root switch and the network be split in half?
I am reasonable sure that the root port on ..a1 is correct, but am open to alternative answers!
Thoughts on a postcard please!
A verify impressive first post indeed.
I didn't have 9 gigabit switches lying around, so I used a simulator. Instead of using 1000 for the links, I used 100, and then lowered the connection betwen SW1 and SW2 to 10. I also assigned the priorities of 16384 to SW3 (your root switch), and then set the others progressively higher, so that the bridge ID would be progressively worse for the higher switches.
The images are zipped and attached.