Default Subnet masks


How many bits in a default subnet mask?

Well let's look at the main 3 which are,

Class A = 24 bits default address is

Class B = 16 bits default address is

Class C = 8 bits default address is

The table below show the default subnet mask and it's number in binary

Remember "1" are for the network and "0" is for the host

So a class A network has a default subnet mask of the binary number for that is 11111111000000000000000000000000

What I like to do is break that binary number up in to octets which stops it looking so intimidating.



Look at my table below which shows the default for class a, b, c network




 IP Range Reminder

1-126 Class A Network
128-191 Class B Network
192-223 Class C Network



You will notice we have left the number 127out this is because it is reserved for the loopback test. This allows you to send & receive data from the same port so you can see it works