RSTP proposal agreement process
Ok i havent time to test this so i decided to ask here, i wish others who are studying ccie would do the same as its a good way to share info.
1) Connecting two switches back to back, the ports default to designated discard state, in this state they transmit bpdu's with the proposal bit set in the bpdu.They will
stay in this state until a bpdu is received from a neighboring switch.Ok if this is the case , that means if you connect and end device you must ensure to enable portfast
otherwise the port will always stay in a discard state and never pass traffic.
2) I have a hub and spoke arrangement, Switch A is the hub connecting to two spokes B and C. The proposal agreement session is complete and both B and C saw A as the root so placed there nonEdge ports in discarding state and the ports conected to A in forwarding state.Now i connect B and C together, both ports start in designated discarding state, send bpdu's with the proposal bit set, B has the lower sender BID so it has the superior bpdu, so as the synch process goes this should block all nonEdge ports, so the port to A i.e. the root port would be blocked.C would then do the proposal agreement between itself and A, A would win and C would block its port to B.As you can see a vicious circle.So whats the exact steps? Is the root port blocked during the synch process or not?
1) Connecting two switches back to back, the ports default to designated discard state, in this state they transmit bpdu's with the proposal bit set in the bpdu.They will
stay in this state until a bpdu is received from a neighboring switch.Ok if this is the case , that means if you connect and end device you must ensure to enable portfast
otherwise the port will always stay in a discard state and never pass traffic.
2) I have a hub and spoke arrangement, Switch A is the hub connecting to two spokes B and C. The proposal agreement session is complete and both B and C saw A as the root so placed there nonEdge ports in discarding state and the ports conected to A in forwarding state.Now i connect B and C together, both ports start in designated discarding state, send bpdu's with the proposal bit set, B has the lower sender BID so it has the superior bpdu, so as the synch process goes this should block all nonEdge ports, so the port to A i.e. the root port would be blocked.C would then do the proposal agreement between itself and A, A would win and C would block its port to B.As you can see a vicious circle.So whats the exact steps? Is the root port blocked during the synch process or not?
Networking, sometimes i love it, mostly i hate it.Its all about the $$$$
Comments
It surprises me that you never seem to be able to answer any tech queries, anyway i'll just have to sim it up later.
Anyway like everything else this is gonna break my heart for the next few days until it jumps out and hits me.
Stay tuned..
So both B and C have root ports to A. As soon as i connect B and C together they must exchange BPDUs with the proposal bit set.
SwitchB has the lower bridge id so its port maintains the designated state, SwitchC will see the superior bpdus comming from B and change its port to the alternate state as it already has a direct path to root.
Switch B will continue to send proposals but it never gets an answer from C as C is not in discard state.No rapid transition will occur so the port on SwitchB will have to wait the standard 2 x forwarding.