I can not figure what a subnet Mask is? Can You Please Help Me Figure Out What A Subnet Mask Is?

In networking the subnet mask is used with IP address to get the Network ID. The Network ID is used to identify that the particular IP address belongs to which network. To get the network ID the Subnet Mask is AND ed with the IP address in binary format.

Example:-

IPv4 address contains 4 fields and each field is 8bit

IP Address - 192.168.10.2

Subnet Mask (Default)- 255.255.255.0

Binary

192 -> 11000000

168 -> 10101000

10 -> 00001010

2 -> 00000010

255 -> 11111111

Logical AND (formula)

* 0 AND 0 = 0
* 0 AND 1 = 0
* 1 AND 0 = 0
* 1 AND 1 = 1

192.168.10.2 ------> 11000000.10101000.00001010.00000010

255.255.255.0 ------> 11111111.11111111.11111111.11111111
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11000000.10101000.00001010.00000000 (AND ing)
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Hence after AND ing we get the network ID that is 192.168.10.0, so the IP address 192.168.10.2 belongs to this network.

Enjoy networking.

A subnet mask is a 32-bit binary number, very similar to an IP address. And like an IP address, the subnet mask is usually expressed as a set of four octets written in decimal form, with each octet separated by a period.

The subnet mask is used by routers and switches to determine which part of a computer or other device's IP address is the network identifier, and which part is the host identifier. There are three default subnet masks, one for each of the IP classes A, B, or C. The default subnet masks are:

Class A = 255.0.0.0
Class B = 255.255.0.0
Class C = 255.255.255.0

To determine the default subnet mask for your network, all you need to do is see which class your network falls into. A network's class is assigned based on the first octet (the set of digits before the first period) of the IP address. For example, to find out which class the network 123.22.8.0 belongs to, you would see where "123" fits into the following table:

First Octet: Class:
1-126 = Class A
128-191 = Class B
192-223 = Class C

So for the example above, 123.22.8.0 is a Class A network, which means it would have a default subnet mask of 255.0.0.0.

Most home and office networks will be Class C networks, so your default subnet mask will typically be (you guessed it) 255.255.255.0. Not all networks use the default subnets, but for those that do, figuring it out is easy once you know which class your network fits into.