- Bronze, 100 points or more
Hi every body!
In rstp,when link moves from discarding to fowarding state is considered as topology change.
Let say we have a switch sw1 which has root port f0/1 connected to sw2, and alternate port f0/2.For some reason, sw1 did not receive any bpdu for 6 seconds and immidiately puts its alternate port in fowarding which would be considered topology change.
1)Will sw1 sends the bpdu to sw2 with proposal and tc bit set to 1 or only proposal bit=1?
thanks a lot!
thanks for your kind remarks
on failure sw2 would try to claim to be the new root bridge.
sw3 will move the alternate port to forwarding and will handshake to make it its new root port.
then the two sw2 and sw3 will make the sync on their shared link.
I think sw3 leads the convergence because it is the one that can realize the root bridge is still alive.
when sw3 presents on the shared link a BPDU proposing its port as the designated port on the segment sw2 agrees and makes its port the new root port.
a blocked like an alternate port still receives BPDUs from the designated port so recovery is fast and takes the time of two negotiations that are made by exchanging two frames each (these are flash updates they don't need to wait 2 seconds to answer).
I think the one out the previous alternate port happens first.
Hope to help
Another form of immediate transition to the forwarding state included in RSTP is similar to the Cisco UplinkFast proprietary spanning tree extension. Basically, when a bridge loses its root port, it is able to put its best alternate port directly into the forwarding mode (the appearance of a new root port is also handled by RSTP). The selection of an alternate port as the new root port generates a topology change. The 802.1w topology change mechanism clears the appropriate entries in the Content Addressable Memory (CAM) tables of the upstream bridge. This removes the need for the dummy multicast generation process of UplinkFast.
It looks like that before the new port role is negotiated with the handshake and then the TC bit is set in another BPDU.
so it should send out a BPDU with only the proposal bit set.
Hope to help