一、实验目标

• 理解生成树协议工作原理；

• 掌握快速生成树协议RSTP基本配置方法；

二、实验背景

学校为了开展计算机教学和网络办公，建立了一个计算机教室和一个校办公区，这两处的计算机网络通过两台交换机互相连接组成内部校园网，为了提高网络的可靠性，作为网络管理员，你要用2条链路将交换机互连，现要求在交换机上做适当的配置，使网络避免环路。

三、技术原理

生成树协议(spanning-tree)，作用是在交换网络中提供冗余备份链路，并且解决交换网络中的环路问题；

生成树协议是利用SPA算法，在存在交换环路的网络中生成一个没有环路的树形网络。运用该算法将交换网络的冗余备份链路从逻辑上断开，当主链路出现故障时，能够自动的切换到备份链路，保证数据的正常转发；

生成树协议版本：STP、RSTP(快速生成树)、MSTP(多生成树协议)；

生成树协议的特点是收敛时间长，从主要链路出现故障到切换至备份链路需要50秒的时间；

快速生成树协议在生成树协议的基础上增加了两种端口角色：替换端口和备份端口，分别做为根端口和指定端口的冗余端口。当根端口或指定端口出现故障时，冗余端口不需要经过50秒的收敛时间，可以直接切换到替换端口或备份端口，从而实现RSTP协议小于1秒的快速收敛。

四、实验步骤

实验拓扑

默认情况下STP协议启用的，通过两台交换机之间传送BPDU协议数据单元，选出根交换机、根端口等，以便确定端口的转发状态。上图中标记为橙色的端口处于block堵塞状态。

设置RSTP

查看交换机 show spanning-tree 状态，了解根交换机和根端口情况；

通过更改交换机生成树的优先级spanning-tree vlan * priority 4096 可以变化根交换机的角色；

S1:

Switch>en
Switch#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)#hostname S1
S1(config)#end
S1#
%SYS-5-CONFIG_I: Configured from console by consoleS1#show spanning-tree                                    //查看交换机spanning-tree 状态
VLAN0001Spanning tree enabled protocol ieeeRoot ID    Priority    32769Address     0060.5C36.5620Cost        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     0060.7078.8BDEHello Time  2 sec  Max Age 20 sec  Forward Delay 15 secAging Time  20Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/10           Desg FWD 19        128.10   P2p
Fa0/1            Root FWD 19        128.1    P2p
Fa0/2            Altn BLK 19        128.2    P2pS1#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
S1(config)#interface fa0/10
S1(config-if)#switchport access vlan 10                            //将fa0/10划分到vlan 10
% Access VLAN does not exist. Creating vlan 10
S1(config-if)#exit
S1(config)#interface range fa0/1 - 2                               //设置fa0/1,fa0/2端口状态为trunk模式
S1(config-if-range)#switchport mode trunk %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to down%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to up%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/2, changed state to down%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/2, changed state to upS1(config-if-range)#exit
S1(config)#spanning-tree mode ?                                    //设置spanning-tree 为RSTP模式pvst        Per-Vlan spanning tree moderapid-pvst  Per-Vlan rapid spanning tree mode
S1(config)#spanning-tree mode rapid-pvst
S1(config)#

S2:

Switch>en
Switch#show spanning-tree
VLAN0001Spanning tree enabled protocol ieeeRoot ID    Priority    32769Address     0060.5C36.5620             This bridge is the root                                //根交换机Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 secBridge ID  Priority    32769  (priority 32768 sys-id-ext 1)Address     0060.5C36.5620Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 secAging Time  20Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1            Desg FWD 19        128.1    P2p
Fa0/2            Desg FWD 19        128.2    P2p
Fa0/10           Desg FWD 19        128.10   P2pSwitch#
%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to down%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to up%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/2, changed state to down%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/2, changed state to upSwitch#
Switch#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)#hostname S2
S2(config)#interface fa0/10
S2(config-if)#switchport access vlan 10
% Access VLAN does not exist. Creating vlan 10
S2(config-if)#exit
S2(config)#interface range fa0/1 - 2
S2(config-if-range)#switchport mode trunk
S2(config-if-range)#exit
S2(config)#spanning-tree mode rapid-pvst
S2(config)#

五、测试

当主链路处于down状态时，能够自动的切换到备份链路，保证数据的正常转发。

在S2上shutdown 掉 fa0/1

Switch#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)#int
Switch(config)#interface fa0/1
Switch(config-if)#shu
Switch(config-if)#shutdown                                         //shutdown fa0/1端口Switch(config-if)#
%LINK-5-CHANGED: Interface FastEthernet0/1, changed state to administratively down%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to downSwitch#show spanning-tree
VLAN0001Spanning tree enabled protocol rstpRoot ID    Priority    32769Address     0001.63E2.4A7AThis 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     0001.63E2.4A7AHello Time  2 sec  Max Age 20 sec  Forward Delay 15 secAging Time  20Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1            Desg FWD 19        128.1    P2p
Fa0/2            Desg FWD 19        128.2    P2pVLAN0010Spanning tree enabled protocol rstpRoot ID    Priority    32778Address     0001.63E2.4A7AThis bridge is the rootHello Time  2 sec  Max Age 20 sec  Forward Delay 15 secBridge ID  Priority    32778  (priority 32768 sys-id-ext 10)Address     0001.63E2.4A7AHello Time  2 sec  Max Age 20 sec  Forward Delay 15 secAging Time  20Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1            Desg FWD 19        128.1    P2p
Fa0/2            Desg FWD 19        128.2    P2p
Fa0/10           Desg FWD 19        128.10   P2pSwitch#

PC1:

PC>ipconfigIP Address......................: 192.168.1.2
Subnet Mask.....................: 255.255.255.0
Default Gateway.................: 192.168.1.1PC>ping -t 192.168.1.3Pinging 192.168.1.3 with 32 bytes of data:Reply from 192.168.1.3: bytes=32 time=78ms TTL=128
Reply from 192.168.1.3: bytes=32 time=94ms TTL=128
Reply from 192.168.1.3: bytes=32 time=78ms TTL=128
Reply from 192.168.1.3: bytes=32 time=78ms TTL=128
Reply from 192.168.1.3: bytes=32 time=78ms TTL=128
Reply from 192.168.1.3: bytes=32 time=94ms TTL=128
Reply from 192.168.1.3: bytes=32 time=93ms TTL=128
Reply from 192.168.1.3: bytes=32 time=93ms TTL=128
Reply from 192.168.1.3: bytes=32 time=62ms TTL=128
Reply from 192.168.1.3: bytes=32 time=94ms TTL=128
Reply from 192.168.1.3: bytes=32 time=79ms TTL=128
Reply from 192.168.1.3: bytes=32 time=94ms TTL=128
......

测试效果:

转至：http://www.cnblogs.com/mchina/archive/2012/07/15/2591973.html