思科实验3.数据链路层：生成树配置

生成树配置

基础知识
常用命令
实验流程
- 1.设计拓扑
- 2.查看交换机STP信息
- 3.配置交换机

基础知识

生成树协议（英语：Spanning Tree Protocol，STP），是一种工作在OSI网络模型中的第二层(数据链路层)的通信协议，基本应用是防止交换机冗余链路产生的环路.用于确保以太网中无环路的逻辑拓扑结构.从而避免了广播风暴,大量占用交换机的资源.
生成树协议是基于Radia Perlman在DEC工作时发明的一种算法被纳入了IEEE 802.1d中， [1] 2001年IEEE组织推出了快速生成树协议(RSTP)在网络结构发生变化时其比STP更快的收敛网络,还引进了端口角色来完善了收敛机制,被纳入在IEEE 802.1w中。----百度百科

常用命令

命令格式	含义
show spanning-tree	查看当前生成树协议信息
spanning-tree vlan 1 primary 优先权值	设置设备vlan的优先级，数字越小优先级越高，为4096的倍数
spanning-tree vlan 1 root primary	将设备调整为vlan1 的根桥

实验流程

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开始

设计拓扑

查看STP信息

配置三层交换机

1.设计拓扑

2.查看交换机STP信息

在拓扑图中，交换机所有端口均属于vlan1，在同一个广播域中，由于在物理上形成了环路，思科交换机默认是打开STP的，在STP作用下，交换机1的F0/2端口被阻塞，不能进行转发。

交换机0的STP信息

Switch>enable
Switch#show spanning-tree
VLAN0001Spanning tree enabled protocol ieeeRoot ID    Priority    32769Address     0001.4395.07D1This bridge is the rootHello Time  2 sec  Max Age 20 sec  Forward Delay 15 secBridge ID  Priority    32769  (priority 32768 sys-id-ext 1)Address     0001.4395.07D1Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 secAging Time  20Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/2            Desg FWD 19        128.2    P2p
Fa0/1            Desg FWD 19        128.1    P2pSwitch#

由此可见交换机1所连接的F0/1,F0/2端口处于转发状态。为根桥。

多层交换机的STP信息

momo#show spanning-tree
VLAN0001Spanning tree enabled protocol ieeeRoot ID    Priority    32769Address     0001.4395.07D1Cost        19Port        1(FastEthernet0/1)Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 secBridge ID  Priority    32769  (priority 32768 sys-id-ext 1)Address     00D0.5880.3C11Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 secAging Time  20Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/2            Desg FWD 19        128.2    P2p
Fa0/1            Root FWD 19        128.1    P2p

交换机1的STP信息

Switch#show spanning-tree
VLAN0001Spanning tree enabled protocol ieeeRoot ID    Priority    32769Address     0001.4395.07D1Cost        19Port        1(FastEthernet0/1)Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 secBridge ID  Priority    32769  (priority 32768 sys-id-ext 1)Address     00D0.BCDE.35D1Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 secAging Time  20Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1            Root FWD 19        128.1    P2p
Fa0/2            Altn BLK 19        128.2    P2pSwitch#

将多层交换机端口F0/1 shutdown
此时

momo#show spanning-tree
VLAN0001Spanning tree enabled protocol ieeeRoot ID    Priority    32769Address     0001.4395.07D1Cost        38Port        2(FastEthernet0/2)Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 secBridge ID  Priority    32769  (priority 32768 sys-id-ext 1)Address     00D0.5880.3C11Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 secAging Time  20Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/2            Root FWD 19        128.2    P2p

3.配置交换机

调整优先级，使得多层交换机成为根桥

momo#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
momo(config)#spanning-tree vlan 1 root primary
momo(config)#int F0/1
momo(config-if)#no shutdownmomo(config-if)#
%LINK-5-CHANGED: Interface FastEthernet0/1, changed state to up%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to upmomo(config-if)#end
momo#
%SYS-5-CONFIG_I: Configured from console by consolemomo#show spanning-tree
VLAN0001Spanning tree enabled protocol ieeeRoot ID    Priority    24577Address     00D0.5880.3C11This bridge is the rootHello Time  2 sec  Max Age 20 sec  Forward Delay 15 secBridge ID  Priority    24577  (priority 24576 sys-id-ext 1)Address     00D0.5880.3C11Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 secAging Time  20Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/2            Desg FWD 19        128.2    P2p
Fa0/1            Desg LSN 19        128.1    P2pmomo#

此时拓扑图

显然之前的交换机0根桥已经变为了多层交换机。