交换机是交换数据，只能识别MAC地址，而交换机可以转发数据包，能够识别IP地址，所以能够转发数据包。而三层交换机的也有路由功能，所以也能转发数据包。今天这堂课就有三层交换机实现不同vlan间通信来加以验证。

    器材：三层交换机一台，二层交换机一台。电脑三台，带水晶头双绞线若干。

    原理图：

    过程:

            1:连线，把PC1,PC2分别连到三层交换机的fa0/1,fa0/6.把PC3连到二层交换机fa0/1。再用一根线一端连到二层交换机的fa0/10，另一端连到三层交换机fa0/10.

             2:对交换机进行配置：

二层交换机的配置

Switch>en

Switch#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)#int fa0/10

Switch(config-if)#sw mode acc

Switch(config-if)#sw mode trunk

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/10, changed state to down

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/10, changed state to up

Switch(config-if)#ex

Switch(config)#vlan 10

Switch(config-vlan)#ex

Switch(config)#int fa0/1

Switch(config-if)#sw acc vlan 10

Switch(config-if)#ex

Switch(config)#host 2chensw

三层交换机的配置

Switch>en

Switch#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)#host 3chensw

3chensw(config)#vlan 10

3chensw(config-vlan)#exi

3chensw(config)#vlan 20

3chensw(config-vlan)#ex

3chensw(config)#int fa0/1

3chensw(config-if)#sw acc vlan 10

3chensw(config-if)#ex

3chensw(config)#int fa0/2

3chensw(config-if)#sw acc vlan 20

3chensw(config-if)#ex

3chensw(config)#int fa0/10

3chensw(config-if)#sw mode trunk

Command rejected: An interface whose trunk encapsulation is "Auto" can not be configured to "trunk" mode.

3chensw(config-if)#sw mode acc

3chensw(config-if)#sw mode trunk

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/10, changed state to down

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/10, changed state to up

3chensw(config-if)#int vlan 10

%LINK-5-CHANGED: Interface Vlan10, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan10, changed state to up

3chensw(config-if)#ip add 10.10.10.254 255.255.255.0

3chensw(config-if)#no shut

3chensw(config-if)#ex

3chensw(config)#int vlan 20

%LINK-5-CHANGED: Interface Vlan20, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan20, changed state to up

3chensw(config-if)#ip add 20.20.20.254 255.255.255.0

3chensw(config-if)#no shut

       3：PC1,PC2,PC3的IP分别设为：10.10.10.1，20.20.20.1，10.10.10.2.

       4：测试：用PC1分别PING PC2,PC3.

PC>ping 10.10.10.2

Pinging 10.10.10.2 with 32 bytes of data:

Reply from 10.10.10.2: bytes=32 time=32ms TTL=128

Reply from 10.10.10.2: bytes=32 time=13ms TTL=128

Reply from 10.10.10.2: bytes=32 time=18ms TTL=128

Ping statistics for 10.10.10.2:

    Packets: Sent = 3, Received = 3, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:

    Minimum = 13ms, Maximum = 32ms, Average = 21ms

PC>ping 20.20.20.1

Pinging 20.20.20.1 with 32 bytes of data:

Request timed out.

Reply from 20.20.20.1: bytes=32 time=5ms TTL=127

Reply from 20.20.20.1: bytes=32 time=3ms TTL=127

Reply from 20.20.20.1: bytes=32 time=3ms TTL=127

        验证完成，PC1,PC2间实现了 VLAN10和    VALN 20  之间的通信，以及通过设配串口fa0/10，实现在跨交换机之间通信。

          总结：两台交换机及两个vlan，配置的东西多了就有些容易混淆，导致浪费好多时间，验证本身并不复杂，只是头脑不清醒就容易差错和配错。所以要先把思路理好，理清了才动手是个好办法。

三层交换机的路由功能实现VALN间通信