Subnetting

Subnetting involves breaking a large network into smaller, more manageable networks known as “subnets.” These subnets allow groups of devices to communicate within their own dedicated space, simplifying network operations. This approach enhances security and streamlines network management, as each subnet can be individually monitored and controlled.

A public subnet enables devices to connect directly to the internet, whereas a private subnet remains isolated from the internet and is generally reserved for internal communication within an organisation.

The table below has helped me easily understand subnetting and become efficient in creating subnets.

hosts	subnet size	network address	first host	last host	broadcast address	mask	prefix

We will be using the binary cheat sheet too to help us with the mask and prefix.

128	64	32	16	8	4	2	1

Voice Hosts	53
Office Hosts	46
Management Hosts	20
Multimedia Hosts	14

Lets design a logical IP addressing scheme for a given network using Variable Length Subnet Masking (VLSM) for the IPv4 192.168.150.0/24 network.

Variable Length Subnet Mask (VLSM) is a technique used in IP network design to create subnets with varying subnet masks. This approach enables network administrators to allocate IP addresses more efficiently and effectively by assigning smaller subnet masks to subnets with fewer hosts and larger subnet masks to those with more hosts.

1) Add 2 host devices to each network segment (2 addresses are reserved for the network address and          broadcast address).

    53+2=55, 46+2=48, 20+2=22, 14+2=16.

2)Add each number to the hosts column starting from largest to smallest.

   55, 48, 22, 16

hosts	subnet size	network address	first host	last host	broadcast address	mask	prefix
55
48
22
16

3) Enter the subnet size. Using the binary table, work out the closest number that the hosts will fit into.        55 = 64 subnet size, 48 = 64, 22 = 32, 16 = 16

4) Add the network addresses. The first will always be .0. The network address will be all the subnet            sizes above it added together. For example, to work out the network address for the 22 hosts you              would add all subnet sizes above being 64+64 = 128. We will add another network address                      temporarily by adding all subnet sizes to make a future step easier.

hosts	subnet size	network address	first host	last host	broadcast address	mask	prefix
55	64	192.168.150.0
48	64	192.168.150.64
22	32	192.168.150.128
16	16	192.168.150.160

                                      64+64+32+16=                             .176

5) Add the first hosts. This is simply done by adding 1 to the network addresses.

6) Add the broadcast addresses. Look at the network address below the one you're working out then            take 1 away. This is why we created the extra network address to make this step easy as 176 becomes      175 for the 16 host row.
                                                         

hosts	subnet size	network address	first host	last host	broadcast address	mask	prefix
55	64	192.168.150.0	1		63
48	64	192.168.150.64	65		127
22	32	192.168.150.128	129		159
16	16	192.168.150.160	161		175

                                      64+64+32+16=                             .176  

7) For the last host column all that's needed to be done is remove 1 number from the broadcast addresses so 63 becomes 62. hosts subnet size network address first host last host broadcast address mask prefix 55 64 192.168.150.0 1 62 63 192 26 48 64 192.168.150.64 65 126 127 192 26 22 32 192.168.150.128 129 158 159  224  27  16 16  192.168.150.160 161  174   175  240 28  8) To work out the mask number you need to find the subnet size in the 8-bit binary table and add all the bit numbers up to it. For example, 64 would be 128+64 = 192. The maximum being 255. 9) Lastly to enter the prefix number all you have to do is add however many numbers you used to get the mask to /24. So to get the 192 mask you added 2 numbers so you would add 2 to 24 = 26. If you added the first 3 numbers in the binary table to get the mask of 224 then you would add 3 to 24 = 27.