Definitions

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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