‫So a network masks helps you know which portion of the address identifies a network and which portion
‫of the address identifies the node.
‫An IPv4 subnet mask consists of 32 bits, a sequence of one followed by a block of zero.
‫The trailing block of zeros designates that part as being the host identifier.
‫Class A, B and C networks have default masks, also known as natural masks, and these masks are.
‫Two five five zero zero zero for class.
‫Two five five two five five zero zero for Class B and 255.255.255.0 for Class C networks.
‫So an IP address on a class-A network that has not been subnet would have an address mask pair similar
‫to one three one one zero 7.1.2 being the address and two five 5.0.2 0.0 would be this subnet mask,
‫right?
‫Now, in order to see how the mask helps you identify the network and node parts of the address, convert
‫the address and mask into binary numbers as seen in the slide.
‫So once you have the address in a mask represented in binary.
‫Then identification of the network and the host ID is a lot easier.
‫Any address bits which have corresponding mask bits set to one represent the network ID.
‫And he addressed bits that have corresponding mask bits set to zero represent the host ID.
‫So in this example, the first part, one three one one zero seven is the network part of the IP address,
‫where the rest one that two represents the host.
‫All devices on this segment share the same network ID and the same subnet mask.
‫Now you can customize the subnet mask to divide a network into many smaller portions.
‫So here's a little brain Tingler for you.
‫The Network ID may be expressed in classless inter domain routing or sidr notation written as the first
‫address of a network followed by a slash character and ending with a bit length of the prefix.
‫So in our example, one three one one zero seven eight zero zero one six is the prefix of the IPV four
‫network, starting at the given address, having 16 bits allocated for the network prefix and the remaining
‫16 bits reserved for host addressing.