You may think you can prevent the dating of Jack and Rose through dispatching them to different branches in same city, while they could meet during lunch break.

In our last story, we have set PC 1 to VLAN 10, and PC2 to VLAN 20. Then how to achieve the communication between them? The answer is through the routing function. There are two equipment can support this function, one is one-armed router, the other one is layer 3 switch.

We provide the example of one-armed router to achieve this communication.

1. Configure the sub-interface on the router and wrapper 802.1q.

Router>               //Begin

Router>en           //Enter privilege mode

Router#conf t      //Enter global mode

Router(config)#int f0/0   //Create and enter port f0/0

Router(config-if)#no shutdown     //Open port

Router(config-if)#int f0/0.1           //Create and enter the sub-interface

Router(config-subif)#description vlan10     //Describe the sub-interface

Router(config-subif)#encapsulation dot1q 10     //Wrapper 802.1q on sub-interface, and set VID as 10

Router(config-subif)#ip add 192.168.10.1 255.255.255.0    //Configure the IP address for the sub-interface as 192.168.10.1

Router(config-subif)#no shutdown        //Open port

Router(config-subif)#exit    //Return to user mode

Router(config)#int f0/2      //Create and enter port f0/2

Router(config-subif)#description vlan20       //Describe the sub-interface

Router(config-subif)#encapsulation dot1q 20   //Wrapper 802.1q on sub-interface, and set VID as 20

Router(config-subif)#ip add 192.168.20.1 255.255.255.0   //Configure the IP address for the sub-interface as 192.168.20.1

Router(config-subif)#no shutdown   //Open port

Router(config-subif)#end

2. Dividing VLAN on the switch

Switch>     //Begin

Switch>en     //Enter privilege mode

Switch#conf t       //Enter global mode

Switch(config)#vlan 10     //Create vlan10

Switch(config-vlan)#vlan 20    //Create vlan20

Switch(config-vlan)#exit

Switch(config)#int f0/2     //Create port f0/2

Switch(config-if)#switchport acc vlan 10  //Set port f0/2 into vlan10

Switch(config-if)#exit  //Return to user mode

Switch(config)#int f0/3     //Create port f0/3

Switch(config-if)#switchport acc vlan 20    //Set port f0/3 into vlan20

Switch(config-if)#end  //End

3. Define Trunk on the switch

Switch>

Switch>en

Switch#conf t

Switch(config)#int f0/1    //Create port f0/1

Switch(config-if)#switchport mode trunk   //If the switch realizes the communication between vlans through the router, it needs to configure the ports connected to the switch into trunk mode, and only the trunk line can make the VLAN pass through.

Switch(config-if)#exit  //Return to user mode

Rose and Jack often meet at noon, so often they are late for work in the afternoon, as time goes by, their work efficiency drops, and now all colleagues around know.

The boss is angry, and decide to dispatch Jack to another brunch in other city. This is like we add a switch into the system, and connect PC1 to this switch, as following:

Now, the PC1 and PC 2 can not communicate with each other.

To be continued.