chapter 6 ccna 3

chapter 6 ccna 3.Router(config)# interface type port_#.subinterface_# Router(config-subif)# encapsulation isl|dotlq VLAN_^Use the command encapsulation to specify the trunk type and the VLAN to which the subinterface belongsO The VLAN number specified must be the number of the corresponding VLAN in a switched network; in addition, the trunk connection must be configured on the switch port to which the router is connected. In this way, the switch will send the tagged frame to the router, and the router will know how to read the tag based on the specified encapsulation: the router will know which VLAN the frame came from and let the corresponding sub-interface handle it. Don't forget that not many Cisco switches currently support ISL, but all Cisco switches support 802.1Qo as indicated by the dotlq parameter.Exam Essentials Be sure to familiarize yourself with how to use the command interface to create subinterfaces. Routers and switches must use the same encapsulation: either both use 802.1Q, or both use ISL.15.5.3 Single-Arm Router Configuration ExampleTake a look at an example of how to configure a single-armed router, as shown in Figure 15.3. Assume that this is a 3800 router, the Fast Ethernet interface is the first interface in the first slot, and the switch interface to which the router is connected uses 802.1Q trunking.VLAN10 172.16.1.0/24VLAN 20 172.16.2.0/24Figure 15.3 Example of a Single-Arm RouterThe following is an example configuration for this router.Router(config)# interface fastethernet0/0 Router(config-if)# duplex full Router(config-if)# no shutdown Router(config-if)# exit Router(config )# interface fastethernet0/0.1 Router(config-subif)# encapsulation dotlq 10 Router(config-subif)# ip address 172.15.1.1 255.255.255.0 Router( config-subif)# exit Router(config)# interface fastethernet0/0.2 Router(config-subif)# encapsulation dotlq 20 Router(config-subif)# ip address 172.15.2.1 255.255.255.0 Router(config-subif)# exit