利用三层交换机的路由功能实现不同VLAN之间通信（基于思科模拟器）

实验要求：

通过三层交换机实现不同vlan间的主机可以相互访问

拓扑图

配置如下

主机	PCa	PCb	PCc	PCd
VLAN	vlan 2	vlan 3	vlan 4	vlan 5
IP地址	192.168.1.1/24	192.168.2.1/24	192.168.3.1/24	192.168.4.1/24
网关	192.168.1.254	192.168.2.254	192.168.3.254	192.168.4.254

• 配置命令

SW1:

Switch>en
Switch#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)#hos
Switch(config)#hostname SW1

SW1(config)#vlan 2
SW1(config-vlan)#vlan 3

SW1(config-vlan)#int f0/1
SW1(config-if)#switchport mode access 
SW1(config-if)#switchport access vlan 2
SW1(config-if)#int vlan 2

SW1(config)#int f0/2
SW1(config-if)#switchport mode access 
SW1(config-if)#switchport access vlan 3
SW1(config-if)#int vlan 3
SW1(config-if)#
%LINK-5-CHANGED: Interface Vlan3, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan3, changed state to up

SW1(config-if)#int f0/24
SW1(config-if)#switchport mode trunk 
%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/24, changed state to down
%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/24, changed state to up

SW1(config-if)#switchport trunk allowed vlan all
SW1(config-if)#

SW3:

Switch(config)#hostname SW3
SW3(config)#vlan 4
SW3(config-vlan)#vlan 5
SW3(config-vlan)#int vlan 4
SW3(config-if)#int vlan 5

SW3(config-if)#int range f0/1-2
SW3(config-if-range)#switchport mode access 

SW3(config-if-range)#int f0/1
SW3(config-if)#switchport access vlan 4
SW3(config-if)#
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan4, changed state to up

SW3(config-if)#int f0/2
SW3(config-if)#switchport access vlan 5
SW3(config-if)#
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan5, changed state to up

SW3(config-if)#int f0/23
SW3(config-if)#switchport mode trunk 

SW3(config-if)#
%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/23, changed state to down

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/23, changed state to up

SW3(config-if)#switchport trunk allowed vlan all

SW2:

Switch>
Switch>en
Switch#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)#hostname SW2

SW2(config)#int range f0/23-24

SW2(config-if-range)#switchport mode trunk 
Command rejected: An interface whose trunk encapsulation is "Auto" can not be configured to "trunk" mode.
Command rejected: An interface whose trunk encapsulation is "Auto" can not be configured to "trunk" mode.                                       //出现问题！！

SW2(config-if-range)#switchport trunk encapsulation ?
  dot1q  Interface uses only 802.1q trunking encapsulation when trunking
  
SW2(config-if-range)#switchport trunk encapsulation dot1q   //二层端口封装802.1q协议（dot1q），也就是trunk链路的中继协议

SW2(config-if-range)#switchport mode trunk 
SW2(config-if-range)#switchport trunk allowed vlan all    //打开协议以后，成功设置为trunk模式

SW2(config)#ip routing  //启动路由转发协议，，非常重要，否则三层SW仍旧不能通信。

在SW2 上配置网关IP

SW2(config)#int vlan 2
SW2(config-if)#ip add 192.168.1.254 255.255.255.0
SW2(config-if)#int vlan 3
SW2(config-if)#ip add 192.168.2.254 255.255.255.0
SW2(config-if)#int vlan 4
SW2(config-if)#ip add 192.168.3.254 255.255.255.0
SW2(config-if)#int vlan 5
SW2(config-if)#ip add 192.168.4.254 255.255.255.0

开启vlan

SW2(config-if)#vlan 2
%LINK-5-CHANGED: Interface Vlan2, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan2, changed state to up

SW2(config-vlan)#vlan 3
%LINK-5-CHANGED: Interface Vlan3, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan3, changed state to up

SW2(config-vlan)#vlan 4
%LINK-5-CHANGED: Interface Vlan4, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan4, changed state to up

SW2(config-vlan)#vlan 5
%LINK-5-CHANGED: Interface Vlan5, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan5, changed state to up

SW2(config-vlan)#end

最后使用 PCa 来ping 其他网段内的主机

大功告成！
happy end ~

注意事项

• SW2一定要打开IP路由转发 ： SW2(config)#ip routing
• SW2在设置f0/22-23端口为trunk 模式之前，必须开启二层端口封装802.1q协议（dot1q），也就是trunk链路的中继协议

    SW2(config-if-range)#switchport trunk encapsulation dot1q   

• SW2 上面需要配置各个vlan 的网关IP