The correct term is subnet mask instead of subnet mass. A subnet mask separates an IP address into the host address and the network address. It is a 32-bit number that can mask an IP address.
Use the 'ifconfig' command on your adaptor, or just 'ifconfig -a'
It does not require a subnet mask.
If this is a default subnet mask, then it would be a class C subnet mask. If you are subnetting a network and this is not the default subnet mask, then it could be either a class A or class B.
The default subnet mask has a standard size. The custom subnet mask allows you to make subnets that are smaller or larger than the default.
2 given subnets
255.255.255.0
255.255.255.0
Subnet mask for the above is 255.0.0.0
The default subnet mask would be 255.255.0.0 for a class B address.
if the ip address is 192.168.2.1 then the subnet mask should be 255.255.255.0
This is a Class B address. So if classful addressing scheme we can say that the default mask of any Class B address is 255.255.0.0. But it may not be always this. There is a concept called VLSM (variable length subnet mask) with which we have the option to give different subnet masks.