802.1W summary

BPDU FORMAT

flags
0    top change
1    proposal
2   
3    portrole
4    learning
5    forwarding
6    agreement
7    top change ACK

BPDU generate
send BPDUs every hello-time(2 by default), used for keepalive between bridges.
if hellos are not received 3 consecutive times, protocol info can be immediately aged out.

priority + extend sysetm-id
4                 12
port states

discading

learning

forwarding

port role(the blocking port role is split into)
backup port         (recieve the useful BPDUs from another bridge)
alternate port        (recieve the useful BPDUs from the same bridge)

802.1w比802.1D收斂快
1.端口狀態沒有blocking,省20s
2.quick failure detection(hello keepalive)
3.快速收斂機制
    端口快速切換
        uplinkfast快速發送BPDU,省
         backbonefast快速接收從blocking port收到的inferior BPDU.省30s.
    拓撲改變
        不同於802.1D發送TC到ROOT,然後由ROOT flooding
        802.1w由origanator直接flooding.