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VLSM is the process of dividing up an IP space into subnets of different sizes.

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The octets create classes of IP addresses that can be assigned to a particular business, government or other entity based on size and need.

Class A - This is for very large networks, such as those a major international company might have. They occupy IPs where the first octet ranges from 1 to 126. The other three octets identify a host on the network.

Class B - This is for medium-sized networks, such as a large college campus. They occupy IPs where the first octet ranges from 128 to 191. The second octet is also part of the Net identifier and the other two identify each Host.

Class C - This is for small/medium-sized businesses. They occupy IPs where the first octet ranges from 192 to 223. The second and third octets are also parts of the Net identifier. The last octet identifies each Host.

The IP address of 0.0.0.0 is used for the default network.

The IP address 127.0.0.1 is used as the loopback address. This means that it is used by the host computer to send a message back to itself.

The IP address 255.255.255.255 is used for broadcasts across a network.

Class D - This is used for multicasts. This is where information is sent to a group of computers simultaneously. They occupy the IPs where the first octet ranges from 224 to 239. The other 3 octets are used to identify the group of computers the multicast is indtended for.

Class E - This is used for experimental purposes only. They occupy the IPs where the first octet ranges from 240 to 255.

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Every machine on the Internet has a unique identifying number, an IP Address.
To make it easier for humans to remember and use them, IPs are shown in decimal format. For example 216.27.61.137
However computers communicate in binary, so the same IP in binary is 11011000.00011011.00111101.10001001

The four numbers of an IP are called octets as they have 8 parts in binary. The total number of combinations per octet is 256.

Octets are split into Net and Host. Net identifies the network that a computer belongs to, whereas Host  identifies the actual computer on the network.

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[HOME]

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If a workstation (computer) has an internet connection then there is (most likely) a router somewhere that that computer sends data to. This is the first router the computer will connect to in order to get to the internet. It is also known as a default gateway.

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A subnet mask defines the IP range of a private network. For example, if a private network has a base IP address of 192.168.0.0 and has a subnet mask of 255.255.255.0, then any data going to an IP address outside of 192.168.0.X will be sent to that network's gateway.

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A Gateway is a network node that interfaces with another network that uses different protocols.

A gateway is an essential feature of most routers, although other devices (such as any PC or server) can function as a gateway.

Both the computers of Internet users and the computers that serve pages to users are host nodes, while the nodes that connect the networks in between are gateways. For example, the computers that control traffic between company networks or the computers used by Internet Service Providers to connect users to the internet are gateway nodes.

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A router is a kind of computer that is specialized to move data between computer networks.

Anytime you make a connection your computer looks up the IP address using the look-up service DNS (Domain Name Service). Once the destination address has been found your computer connects to your gateway router. The gateway then sends data to a router at your Internet Service Provider, that router connects to other routers until the data reaches the destination