Address Masks in Networks

• How can an IP address be divided at an arbitrary boundary?

•It requires an additional piece of information to be stored with each address. This information specifies the exact boundary between the network prefix and the host suffix.

•To use classless or subnet addressing the routers must store 2 pieces of information:

–the 32 bit address and

–another 32 bit value that specifies the boundary between the prefix and suffix.

•This second value is called the called the subnet mask and 1 bits mark the network prefix and zero bits mark the host portion. This makes computation efficient.