交换知识点(STP)

交换知识点整理（部分）

一.交换机的作用

1.MAC地址学习

2.帧的转发，过滤

3.防环

PC上查看MAC地址命令：

PC>ipconfig /all

FastEthernet0 Connection:(default port)

Physical Address................: 0001.9782.7064

交换机查看MAC地址表命令：

Switch#sh mac-address-table

Mac Address Table

-------------------------------------------

Vlan Mac Address Type Ports

---- ----------- -------- -----

1 0001.9782.7064 DYNAMIC Fa0/2

1 0001.9792.b97c DYNAMIC Fa0/1

二.冗余网络带来的问题

1.广播风暴

2.重复帧

3.MAC地址表不稳定

三.解决冗余网络问题的方案：生成树协议Spanning Tree Protocol（STP）

1.生成树

桥ID(比小)：①priority（默认32768）②MAC地址

CISCO默认使用每VLAN生成树（PVST）

桥ID(比小)：①priority（默认32768）+扩展系统ID（VLAN ID）②MAC地址2.根桥ROOT BRIDGE

发送最优BPDU,管理STP

3.根端口RP

到达ROOT BRIDGE路径，代价比小

接收BPDU

每台非根桥上有且仅有一个RP

p.s.代价与连接速率的对照关系：

10Gbps→2

1Gbps→4

100Mbps→19

10Mbps→100

4.指派端口DP

转发BPDU

5.非指派端口

BLOCKING阻塞：不能够转发数据

6.STP端口状态：

阻塞（BLOCKING）→侦听(LISTENING)→学习(LEARNING)→转发(FORWARDING) 利用神器PT来研究STP生成树的工作方式

Switch0#sh spanning-tree

VLAN0001

Spanning tree enabled protocol ieee

Root ID Priority 32769

Address 0060.3E34.0392

Cost 19

Port 20(FastEthernet0/20)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)

Address 00E0.A304.3AEB

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 20

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/20 Root FWD 19 128.20 P2p

Fa0/10 Altn BLK 19 128.10 P2p

Switch1#sh spanning-tree

VLAN0001

Spanning tree enabled protocol ieee

Root ID Priority 32769

Address 0060.3E34.0392

Cost 19

Port 5(FastEthernet0/5)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)

Address 00E0.8FBE.7940

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 20

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/10 Desg FWD 19 128.10 P2p

Fa0/5 Root FWD 19 128.5 P2p

Switch2#sh spanning-tree

VLAN0001

Spanning tree enabled protocol ieee

Root ID Priority 32769

Address 0060.3E34.0392

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)

Address 0060.3E34.0392

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 20

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/20 Desg FWD 19 128.20 P2p

Fa0/5 Desg FWD 19 128.5 P2p

抢根：

方法一：设置优先级

Switch0(config)#spanning-tree vlan 1 priority ?

<0-61440> bridge priority in increments of 4096

Switch0(config)#spanning-tree vlan 1 priority 0

Switch0#sh sp

VLAN0001

Spanning tree enabled protocol ieee

Root ID Priority 1

Address 00E0.A304.3AEB

This bridge is the root

方法二：设置主备角色