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the subnet mask can tell you if your network is class A, B, or C , it tells you which part of the IP adress is the unique identifier , so if your subnet mask is255.255.255.0 this means the first3 blocks of the ip address is the unique identifier.
It helps to identify network id and number of hosts
The subnet mask is the network address plus the bits reserved for identifying the subnetwork. It's called a mask because it can be used to identify the subnet to which an IP address belongs by performing a bitwise AND operation on the mask and the IP address. More simply, it is required to tell the computer how the network administrator has created the network. The subnet mask is actually a32-bit number, same as an IP address. It is composed of four octets. Each of the eight bits in the octet can be either1 or0. Unlike an IP address, a subnet mask consists of a number of ones followed by a number of zeros. e.g.... is a valid subnet mask... is NOT valid. Since all those1 and0 are hard to read and type, subnet masks are translated into one of two formats. One option is to just give the number of consecutive1s The other is to convert each octet from a binary number to a decimal number. Thus,... is a valid mask It can also be written as /26 or as255.255.255.192 As you can see, the mask is not restricted to255.255.255.0 Each of the following subnet masks are used at some point within our network: /8 :255.0.0.0 - used for route summarisations /16:255.255.0.0 - used for route summarisations /20 :255.255.240.0 - block size assigned to large buildings /24 :255.255.255.0 - block size assigned to small buildings /26 :255.255.255.192 - block size assigned to small buildings /28 :255.255.255.240 - largest subnet permitted in small building /30 :255.255.255.252 - used for point-to-point links (e.g. T1) /32 :255.255.255.255 - used for router management address The /24 mask (255.255.255.0) is the mask for a Class C network. This mask is most often used with192.168 addresses for home networks because the192.168 Class C address block is assigned by IANA for use by private networks
