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收敛快
1.端口状态没有blocking,省20s
2.quick failure detection(hello keepalive)
3.快速收敛机制
    端口快速切换
        uplinkfast快速发送BPDU,省
         backbonefast快速接收从blocking port收到的inferior BPDU.省30s.
    拓扑改变
        不同于802.1D发送TC到ROOT,然后由ROOT flooding
        802.1w由origanator直接flooding.

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