网络拓扑结构图：
现在的趋势是IT越来越成为一种不可停顿的服务，常常对网络的可靠性要求很高。因此要求系统的核心、网络骨干不存在单点故障，主要、在部件、设备上都要求有冗余。在这种背景下，STP(spanning-tree protocol)得到了广泛的应用。STP是一个二层的链路管理，它在提供链路冗余的同时防止网络产生环路。如果上安装两块网卡，形成一个AFT(或ALB)组，一块连接主机，另一块连接备份主机，二级交换机都采用双链路分别上联到主交换机和备份主交换机，那么当主交换机失效时，工作站仍可通过备份主交换机上的备份网卡访问，服务不至于中断。
尽管STP是一种分布式算法，它要求网络中交换机的全部支持，但在实际工作中往往出现只有主干交换机支持STP协议，而二级交换机不支持STP的情况。
在去年我的同事曾经做过两个案例：
第一个，主交换机为一台cisco 4006和一台cisco 4003，二级交换机为inter 410T(不可网管交换机，不支持STP协议)。
第二个,主交换机为两台inter 480T，二级交换机为inter 460T和inter 410T。
最近，我也遇到了同样的情况。主交换机为两台3com 3300，二级交换机为四台华为2026B(替换原来的HUB，也不知道是谁推荐的，这种交换机也不支持STP协议，甚至连IP也不能配，VLAN也只能在本地划分)。甲方希望能够做到链路冗余，尽管我极力反对，反复强调网络收敛时间很长，甚至导致广播风暴的产生，但他还是决定要做。后来我知道他这样做是有道理的，机房一共两个人，一个人（领导）长期不来，另一个人显然更愿意面对外面的MM而不是机房里的设备。
步骤如下：
1.营业部网络结构中心采用两台3com 3300作为主干交换机,确认二级交换机此时都为单线上联到主交换机,备份主交换机没有连接主交换机。将主交换机的STP优先级设为0X6000，将副主交换机的STP优先级设为0X7000
Login: admin //用admin用户登录
Password:
Menu options: --------------3Com SuperStack 3 Switch 3300---------------
bridge - Administer bridging/VLANS
ethernet - Administer Ethernet ports
feature - Administer system features
ip - Administer IP
logout - Logout of the Command Line Interface
snmp - Administer SNMP
system - Administer system-level functions
Type ? for help.
-----------------------------------Switch 3300 (1)----------------------
Select menu option: bri //选择bridge菜单
Menu options: --------------3Com SuperStack 3 Switch 3300---------------
agingTime - Set the bridge address aging time
display - Display bridge information
multicastFiltering - Administer multicast filtering
port - Administer bridge ports
stpForwardDelay - Set the bridge Spanning Tree forward delay
stpHelloTime - Set the bridge Spanning Tree hello timer
stpMaxAge - Set the bridge Spanning Tree maximum age
stpPriority - Set the Spanning Tree bridge Priority
stpState - Enable/Disable Spanning Tree on a bridge
vlan - Administer VLANs
Type "q" to return to the previous menu or ? for help.
-----------------------------------Switch 3300 (1)----------------------
Select menu option (bridge): dis //选择display菜单
stpState: disabled agingTime: 1800 //现在stp协议状态是disabled
Time since topology change: 0 hrs 0 mins 0 seconds
Topology Changes: 0
Bridge Identifier: 8000 00051a5e92f8
Designated Root: 0000 000000000000
maxAge: 0 bridgeMaxAge: 20
helloTime: 0 bridgeHelloTime: 2
forwardDelay: 0 bridgeFwdDelay: 15
holdTime: 1 rootCost: 0
rootPort: No Port priority: 0x8000 //此时STP缺省优先级为32768
Menu options: --------------[1m3Com SuperStack 3 Switch 3300[0m---------------
agingTime - Set the bridge address aging time
display - Display bridge information
multicastFiltering - Administer multicast filtering
port - Administer bridge ports
stpForwardDelay - Set the bridge Spanning Tree forward delay
stpHelloTime - Set the bridge Spanning Tree hello timer
stpMaxAge - Set the bridge Spanning Tree maximum age
stpPriority - Set the Spanning Tree bridge Priority
stpState - Enable/Disable Spanning Tree on a bridge
vlan - Administer VLANs
Type "q" to return to the previous menu or ? for help.
-----------------------------------[1mprimary3300 (1)[0m----------------------
Select menu option (bridge): stpsta //选择stpState菜单
Enter new value (disable, enable)[disable]: en //enable STP协议
Select menu option (bridge): dis //display状态
stpState: enabled agingTime: 1800
Time since topology change: 0 hrs 0 mins 6 seconds
Topology Changes: 0
Bridge Identifier: 8000 00051a612eb8
Designated Root: 8000 00051a612eb8
maxAge: 20 bridgeMaxAge: 20
helloTime: 2 bridgeHelloTime: 2
forwardDelay: 15 bridgeFwdDelay: 15
holdTime: 1 rootCost: 0
rootPort: No Port priority: 0x8000
Select menu option (bridge): stppri //选择stpPriority菜单
Enter new hexadecimal value (0x0-0xffff) [0x8000]: 0x6000 //将优先值设为十六进制的6000,这将导致该交换机成为根交换机
Select menu option (bridge): stpfor //选择stpForwardDelay菜单
Enter new value in seconds (4-30) [15]: 9 //想改变ForwardDelay值为9，但不成功
Failed to Set value due to dependencies
//forward值是一个端口从它的spanning-tree协议的学习和聆听状态转到转发状态所等待的秒数。
此举主要是考虑参照CISCO的手册，此时网络直径为3，即任意两终端结点之间的最大跳数，执行spanning-tree vlan 1 root primary diameter 3将导致以下3条语句的出现，这是自动优化的结果
spanning-tree vlan 1 priority 24576
spanning-tree vlan 1 forward-time 9
spanning-tree vlan 1 max-age 12
Select menu option (bridge): stpmax //选择stpMaxAge菜单
Enter new value (6-40) [20]: 12
//maximum-aging time值是交换机在拓扑变化时在接收spanning-tree配置信息之前所等待的秒数。
Select menu option (bridge): dis //display状态
stpState: enabled agingTime: 1800
Time since topology change: 0 hrs 4 mins 8 seconds
Topology Changes: 0
Bridge Identifier: 6000 00051a612eb8
Designated Root: 6000 00051a612eb8
maxAge: 12 bridgeMaxAge: 12
helloTime: 2 bridgeHelloTime: 2
forwardDelay: 15 bridgeFwdDelay: 15
holdTime: 1 rootCost: 0
rootPort: No Port priority: 0x6000
-----------------------------------[1mprimary3300 (1)[0m----------------------
Select menu option (bridge): stpmax //为了稳妥起见，maxujum-aging time还是用缺省的20
Enter new value (6-40) [12]: 20
Select menu option (bridge): dis //再display状态
stpState: enabled agingTime: 1800
Time since topology change: 0 hrs 6 mins 2 seconds
Topology Changes: 0
Bridge Identifier: 6000 00051a612eb8
Designated Root: 6000 00051a612eb8
maxAge: 20 bridgeMaxAge: 20
helloTime: 2 bridgeHelloTime: 2
forwardDelay: 15 bridgeFwdDelay: 15
holdTime: 1 rootCost: 0
rootPort: No Port priority: 0x6000
-------------------------------------------------------------------------
elect menu option (bridge): dis //将备份主交换机也按照上述步骤设置STP优先级为ox7000
stpState: enabled agingTime: 1800
Time since topology change: 0 hrs 0 mins 42 seconds
Topology Changes: 0
Bridge Identifier: 7000 00051a5e92f8
Designated Root: 7000 00051a5e92f8
maxAge: 20 bridgeMaxAge: 20
helloTime: 2 bridgeHelloTime: 2
forwardDelay: 15 bridgeFwdDelay: 15
holdTime: 1 rootCost: 0
rootPort: No Port priority: 0x7000
---------------------------------------------------------------------------
2.连接冗余链路，调
【责编:admin】
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