Definitions
| Host Device | Device on Network (PC, Phone, ..) |
| Network Device | Connects Devices (Routers) |
| Subnets | Host devices that can be present. |
| Subnet Mask | Ratio of ==Network : Host== Devices. |
CIDR Notation for Subnetting
Defines the Subnet via this format: [ip/mask]
Examples:
192.168.172.10/24 => 24 bits for Network : 8 remaining for Host
192.168.172.10/16 => 16 bits for Network : 16 remaining for Host
192.168.172.10/12 => 12 bits for Network : 20 remaining for Host
In Binary & Decimal Formats, these CIDR masks are:
/24 => 255.255.255.0 => 11111111.11111111.11111111.00000000 (24 bits)
/16 => 255.255.0.0 => 11111111.11111111.11111111.00000000 (16 bits)
/12 => 255.240.0.0 => 11111111.11110000.00000000.00000000 (12 bits)
IP allocation in Subnets
Overview: The first & last IP of a subnet is allocated.
| Network Device IP | First Subnet of IP allocated |
| First Usable IP | IP after first |
| Last Usable IP | IP before last |
| Broadcast IP | Last Subnet of IP allocated |
Example: IP =>
172.16.12.36/24
Here: Subnet Mask: /24 => 255.255.0.0 => 24 for Network : 8 for Host
Then IPs in this subnet will look like these:
172.16.12.0 => Network IP
172.16.12.1 => First Host IP
172.16.12.2
.
.
.
172.16.12.254 => Last Host IP
172.16.12.255 => Broadcast IP