The router-on-a-stick method requires you to create a subinterface for each VLAN to be routed.ДЄ subinterface is created using the interface interface_id.subinterface_id global configuration mode command. *Mar 1 00:23:52.137: %LINEPROTO-5-UPDOWN: Line protocol on InterfaceДЇastEthernet0/1, changed state to up R1 Subinterface Configuration (4.2.4) Example 4-5 S2 Configuration S2(config)# vlan 10 The configuration for S2 is similar to S1, as shown in Example 4-5. S2 VLAN and Trunking Configuration (4.2.3) *Mar 1 00:23:44.511: %LINEPROTO-5-UPDOWN: Line protocol on Interface *Mar 1 00:23:43.093: %LINEPROTO-5-UPDOWN: Line protocol on Interface Example 4-4 Configure Trunking Ports S1(config)# interface fa0/1

Finally, ports Fa0/1 connecting to S2 and Fa05 connecting to R1 are configured as trunk ports, as shown in Example 4-4. Example 4-3 Configure Access Ports S1(config)# interface fa0/6 Assume PC1 has been configured with the correct IP address and default gateway. Next, port Fa0/6 connecting to PC1 is configured as an access port in VLAN 10, as shown in Example 4-3. Example 4-2 Create the Management Interface S1(config)# interface vlan 99 Next, the management interface is created on VLAN 99 along with the default gateway of R1, as shown in Example 4-2. Example 4-1 Create and Name VLANs S1(config)# vlan 10 VLANs are created only after you exit out of VLAN subconfiguration mode. First, the VLANs are created and named, as shown in Example 4-1. 15 and 13 in the configuration are the VLAN idвЂ™s to which the subinterface Fast Ethernet 0/0.1 and 0/0.Step 1. The 802.1q restricts the frames which do not have any tags on them. 802.1q has VLAN identifier tag that gives the information about which VLAN does the frame belongs. The trunk ports make use of trunk protocols like ISL and dot1q or IEEE 802.1q to transmit the VLAN information between two switches. Trunk ports allow the VLAN data to pass from one switch to another switch. IEEE 802.1q is simply represented as dot1q.

Dot1q encapsulation technique is used when VLANвЂ™s are configured. Encapsulation is the process of adding control data when it passes through the layered network.

The Fast Ethernet 0/0.1 and Fast Ethernet 0/0.2 indicates two logical interfaces derived from physical interface fast Ethernet 0/0. The configuration of subinterface is same as that of configuring a physical interface.Д¬ISCO-ROUTER(config)# interface FastEthernet 0/0.1Д¬ISCO-ROUTER(config-if)# encapsulation dot1q 15Д¬ISCO-ROUTER(config-if)# ip address 12.31.14.15 255.0.0.0Д¬ISCO-ROUTER(config)# interface FastEthernet 0/0.2Д¬ISCO-ROUTER(config-if)# encapsulation dot1q 13Д¬ISCO-ROUTER(config-if)# ip address 132.26.26.1 255.255.0.0 Once the port is active, we can divide the port logically. The above list of commands makes an inactive Fast Ethernet port active. Hence, Fast Ethernet 0/0 must be made active before dividing the Fast Ethernet interface logically.Д¬ISCO-ROUTER(config)# interface FastEthernet 0/0 Let us consider an example where we create two sub interfaces or logical interfaces on Fast Ethernet 0/0 port of the router. Before configuring a sub interface, the physical interface that is going to be divided must be turned active or on. The configuration of a sub interface is same as that of configuring physical interface. Sub interfaces are used when Virtual Local Area Network (VLAN) is created in the network and inter-VLAN routing is enabled using a router on a stick method. A physical interface can be divided into multiple sub interfaces. Instead of having another router or additional interface cards, it is very easy to divide physical interface into two parts logically.ДЄ sub interface is the logical division of physical interface. Imagine a scenario where we have a router with a single interface and the same interface has to connect to two different IP networks. The interface is the point of communication between two devices.

Subinterfaces router on a stick