From the course: Career Essentials in System Administration by Microsoft and LinkedIn

VLANs and subnets

From the course: Career Essentials in System Administration by Microsoft and LinkedIn

VLANs and subnets

“

- [Instructor] Subnet masks separate networks from hosts by adding or subtracting numbers from left to right. The networks appear on the left side of a subnet mask and hosts appear on the right. This is a sliding scale that can be adjusted as more or less hosts are needed. Subnet masks keep our network portion of the IP address separate from our hosts. Masks are represented by contiguous 1s and 0s. They're also represented by the CIDR, C-I-D-R, standard. Here's an example of a 24-bit subnet mask. Each section has a value of bits. There are four of them and eight times four of course is 32. And 32 bits is 2 to the 32nd power, which adds up to around 4 billion IP addresses. Here's an example of how the CIDR standard represented by the forward slash can change the amount of usable IPs and networks. With a /24, we see 254 usable IP addresses for things like computers and phones that we refer to as hosts. If we change to a /28, then it increases the amount of networks but decreases the amount of available IP addresses. In this example, we can see a traditional setup using routers to route traffic between subnets. VLANs are virtual local area networks that live inside a network switch. Prior to VLANs, we just called them subnets and connected them with routers. With the invention of the layer three switch, we're now able to mimic this inside a high-end switch and route between the subnets without any separate routers. Now we see subnets known as VLANs are being routed using a layer three switch. Each port in a layer three switch can be a router all by itself if we configure it that way. First, we create a VLAN in the switch that tells us what subnet we want to use. And then we assign it to a port on the layer switch to route it. We can then create access control list to keep users from communicating with certain equipment that may need to stay secure, or for other reasons known to the company. Subnets and VLANs make it easier to segment and route to subnets. Having additional subnets allows sys admins to separate traffic between users and devices to increase security and cut down on broadcast traffic.

Contents