OSI Layer 3 Design Goals

OSI Layer 3 Design Goals

One of the more popular reasons to put a group of devices into the same VLAN relates to OSI Layer 3 concepts, and in particular, the Internet Protocol (IP). Unfortunately, you've not read enough about IP to appreciate the details yet. You will learn a lot more about IP in Chapters 10, "Delivering the Goods to the Right Street (IP) Address," and 11, "Knowing Where to Turn at Each Intersection (Router)." While you continue reading, keep in mind that IP uses concepts called networks and subnetworks, or subnets. As it turns out, the devices in the same LAN or VLAN are also in the same TCP/IP network or subnet.

You might have motivations for putting some devices in one IP network or subnet, and some in another. To be in two different IP networks or subnets, those devices must be in two different LANs, so using VLANs could be a convenient way to meet your Layer 3 design goals.