Spanning Tree

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配置

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PVST+

switch(config)# spanning-tree mode stp

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RSTP

switch(config)# spanning-tree mode rapid-pvst

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MSTP

switch(config)# spanning-tree mst

switch(config)# spanning-tree mst configuration

switch(config-mst)# name Region1

switch(config-mst)# revision 1

switch(config-mst)# instance 1 vlan 11-13

switch(config-mst)# instance 2 vlan 21-23

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Spanning Tree 選舉

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選Root Switch (Switches)

1. Bridge ID 小

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Switch選一個Root Port (Switch ports)

1. 去Root的cost 少
2. 對接的Switch的Bridge ID 小
3. 對接的Port 的 Port ID 小

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Link選一個Designated Port (Link ports)

1. Root Switch的所有Ports都是Designated Port
2. 去Root的cost少
3. Ports的Switch的Bridge ID 小
4. 剩下的Ports都是non-Designated Port

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RSTP Mode限定: 選Alternate/Backup Port (Link ports)

1. non-Designated Port的Switch的Bridge ID比對面的Switch大, 就是Alternate Port
2. 相反, 則是Backup Port

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Port State

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PVST+ Port State	BPDU	Function	Forwarding Delay
Disabled	–	–	–
Blocking	Rx	–	–
Listening	Rx & Tx	Election	15s
Learning	Rx & Tx	Root Port / Designated Port	15s
Forwarding	Rx & Tx	Rx & Tx Frame

RSTP Port State	BPDU	Function	Forwarding Delay
Disabled	–	–	–
–	–	–	–
–	–	–	–
Learning	Rx & Tx	Root Port / Designated Port	15s
Forwarding	Rx & Tx	Rx & Tx Frame

Cost

100Mb: 19

155Mb: 14

1000Mb: 4

10000: 2