However, the CME router will block DHCP requests from the Cisco IP phones (on VLAN 10) from reaching the DHCP server. Because the DHCP server is assigned to VLAN 50, DHCP requests from the PCs will be able to reach the DHCP server without a problem (because they are in the same VLAN). The primary broadcast type you need to be concerned with in this network design is DHCP requests. This command instructs the router to forward specific broadcast types to a configured IP address. In the syntax, there is one command that we have not talked about as of yet: ip helper-address. The CME router is now configured as a router-on-a-stick. Now you need to configure the CME router to perform inter-VLAN rout ing, as shown in Example 3.16.Įxample 3.16 Configuring Inter-VLAN Routing CME_Router# configure terminal CME_Router(config)# interface fa0/0 CME_Router(config-if)# no ip address CME_Router(config-if)# exit CME_Router(config)# interface fa0/0.10ĬME_Router(config-subif)# description ROUTER INTERFACE FOR VOICE VLANĬME_Router(config-subif)# encapsulation dot1q 10 CME_Router(config-subif)# ip address 172.16.1.1 255.255.255.0 CME_Router(config-subif)# ip helper-address 172.16.2.5 CME_Router(config-subif)# exit CME_Router(config)# interface fa0/0.50ĬME_Router(config-subif)# description ROUTER INTERFACE FOR DATA VLAN CME_Router(config-subif)# encapsulation dot1q 50 CME_Router(config-subif)# ip address 172.16.2.1 255.255.255.0 SwitchA(config-if)# description CONNECTION TO ROUTER-ON-A-STICK CME ROUTER SwitchA(config-if)# switchport trunk encapsulation dot1q SwitchA(config-if)# switchport mode trunk Because SwitchA is connected to the CME router, you need to configure its FastEthernet 0/20 port as a trunk interface, as shown in Example 3.15.Įxample 3.15 Configuring a Trunk to the CME Router SwitchA# configure terminal SwitchA(config)# interface fa0/20 First, start with the switch side of the configuration. In the voice and data network design shown back in Figure 3.10, the CME router will also act as a router-on-a-stick that is able to route between the voice and data VLANs. Layer 3 switching is covered in the CCNP certification track. Note The CCNA Voice exam focuses on inter-VLAN routing using separate router ports and a router-on-a-stick configuration. Because the SVIs are internal to the switch in the Layer 3 switch design, the only speed constraint becomes the backplane speed of the switch.įigure 3.13 Inter-VLAN Routing Using a Layer 3 Switch If more than one host was attempting to pass through the router at a time, the bandwidth would then divide between those hosts. Therefore, whatever was the speed of the interface connecting to the router was the maximum speed the host could reach. In the other inter-VLAN routing designs, the traffic from the hosts needed to leave the switch to reach the router. The Layer 3 switch design is superior to the previous inter-VLAN routing designs because there is virtually no bandwidth constraints for the hosts assigned to the VLAN to reach the router. For example, if you were to create interface VLAN 100, all the ports assigned to VLAN 100 would be able to reach this interface. SVIs are virtual interfaces supported on Layer 3 switches that route traffic for their assigned VLAN number.Īs soon as the SVI is created, all the users in the SVI VLAN will be able to reach the interface. To facilitate routing within the switch, you must configure switched virtual interfaces (SVIs), as shown in Figure 3.13. The concepts are the same as the previous router-on-a-stick design however, the router is now internal to the switch. This is most often called a Layer 3 or multilayer switch. This final form of inter-VLAN routing uses a router integrated into a switch.