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 255.0.0.0

Class B = 16 bits default address is 255.255.0.0

Class C = 8 bits default address is 255.255.255.0

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 255.0.0.0 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