IP Addressing IP addressing is the role of the layer-3 'Network Layer' in OSI Model or Layer-2 'Internet layer' in TCP/IP model. IPv4 Header The IP header is used to support two key operations, routing and fragmentation. Routing is the mechanism that allows traffic from a given network to be forwarded to other networks, since the data link layer represents a single network for which network boundaries exist. Fragmentation refers to the breaking down of data into manageable blocks that can be transmitted over the network.   Classes of IP Addresses The IPv4 addresses are classified into following five categories: Class A for instance consist of 126 potential networks, each of which can support 254. Class B for instance consist of 64534 potential networks, each of which can