It does not apply to hosts, so once it reaches its destination, that VLAN ID is sent as untagged, or untagged, that is, it is presented as a normal Ethernet frame. This protocol works only between network devices: routers and switches. Basically it is the protocol that allows each Ethernet frame that is generated from the hosts (computers) to have a VLAN ID, that is, an identifier that indicates which VLAN that frame has to go to. This refers to the IEEE 802.1Q communication standard. The first thing we must guarantee is that the switch or switches in our network have their access ports and VLAN assignment correctly configured. For that reason, we are going to demonstrate its operation through the configuration via CLI (Command Line Interface) of the Cisco router itself. How to configure the sub-interfacesĪt the beginning, we commented that the sub-interfaces are applied to a great extent in the devices of the manufacturer Cisco. That is why the concept of Router-on-a-Stick allows the creation of sub-interfaces in the router, that is, in the same physical interface of the router, we can create virtual interfaces or sub-interfaces, and each of them It will be associated with one of the VLANs that our network has.Īs for the switch, if we apply Router-on-a-Stick, we will only need a trunk port. Very easily both the router and switch ports will be occupied, which causes the management of both devices to present with various difficulties. If we scale the case to four, five, six or more VLANs, this would be practically unfeasible. Therefore and for this case, the switch would have to have two trunk ports. If we speak strictly at the physical level, if you have two VLANs, you can choose to occupy one port of the router for each port so that it connects to the switch. On the other side of the switch there is a connection between it and a router. That is, the switch has two ports occupied by both computers. These computers are connected to a switch through their corresponding interfaces. Two computers are presented, each of them is connected to a VLAN. What does Router-on-a-Stick mean? Let’s look at this example network: In case you have a “normal” L2 switch, you will need the services of a router to intercommunicate the VLANs, decapsulating and encapsulating the VLANs to communicate them correctly. If your network has more than one VLAN, it is not possible for the switch to fulfill the function of allowing a computer in VLAN 1 to communicate with VLAN 2, except if it is an L2 + or 元 switch that incorporates the Inter functionality. The router has all the necessary features to be able to make decisions about which is the best way to go, so that no data packet is discarded or is blocked at some point in its journey through the network. Each router has a routing table in which are the possible destinations where the path followed by each data packet should be redirected. The routing itself is made possible by the routing tables. In turn, it can connect with other routers in order to exchange routing information. On the other hand, what exactly is the role of the router? This device has the ability to connect to one or more networks.
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