VIrtual Local Area Network (VLAN)

A free video tutorial from Matt Carey
Network and Security Instructor - IPversity
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Cisco Networking Fundamentals - CCNA Prep

Advance your Cisco networking knowledge and prepare for the CCNA exam

05:56:12 of on-demand video • Updated January 2019

Cisco Networking
Configure Cisco Routers and Switches
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In this section, we're going to learn how to configure VLANs on switches and the different switchport modes that will be used for Vlan assignments. Okay, so let's start out with the basics. Let's say we wanted to assign host A and host B here to Vlan two. First we'd have to go to these switch configurations and actually globally define Vlan two. So the first step when configuring VLANs on switches is to define the Vlan. If the Vlan is not defined on the switch, then the switch will not pass traffic for that Vlan. Once our VLANs are defined, then we have to configure our switch ports for that Vlan. So for user A and user B's traffic to be assigned to Vlan two, we have to tell the switch port to do so for this type of setup since we just have end hosts that do not understand VLANs and we're simply just trying to put their traffic on Vlan two. We would use what's called an access mode, port access mode ports. Simply just assign any traffic coming from the connected device to the Vlan that you define in the configuration and any traffic Egressing a access mode port is considered to be untagged, meaning that it does not have any Vlan tag assignments because computers, any type of device that you would connect to an access mode port. We don't assume that it supports VLANs or understands Vlan tags, so when the traffic is sent back to the devices that are connected to access mode ports, it has no Vlan information. So now we've configured the ports that the end hosts are connected to. But what about between the switches? For this example, since we're only using one Vlan, we could actually configure the switch to switch connections the same way with access mode, Vlan two configurations and then we would have Vlan two defined throughout the switched path. So that configuration is fine for this example, but what if we had other VLANs connected to these switches? If any Vlan three traffic were to be sent out of these inter-switch connections, the traffic would be dropped because we're only passing traffic for Vlan two in this access mode inter-switch configuration. So for this scenario, since we need to pass multiple VLANs across these ports, then we would use what's called a trunk mode port. So with a trunk mode port, the switches would actually use Vlan tags to assign to the traffic coming from the connected devices. So that switches across the LAN would know what Vlan to send the traffic out to. So let's take a look at how this configuration would flow if user A and user C were to send ethernet frames to switch one. So here comes user sees frame and user as frame. And since they both entered their access mode Vlan ports, the switch would assign the corresponding Vlan to that traffic. When their frames were going to be sent out of the switch, one port connected to switch to switch one would add Vlan tags to those frames. Since the were vlan tags assigned to these frames. Now switch to knows which vlans to send the traffic to. And that's how we can have multiple VLANs traverse a switch port. Let's look at a quick comparison of access mode and trunk mode Ports. Access mode Ports would have devices like computers, printers or cameras connected to them. Trunk mode ports would have devices like switches, VM hosts, and autonomous or flex connect access points connected to them. And just always remember that traffic leaving an access mode port is going to be untagged and traffic leaving a trunk mode port is going to be tagged.