Network Layer Addressing

Network Layer Addressing

You have already encountered the Data Link layer’s physical device addresses, which uniquely identify each device on a network. On larger networks, it is impractical to deliver network data soley by means of physical addresses. (Imagine if your network adapter had to check every packet sent from anywhere on the Internet to look for a matching physical address.) Larger networks require a means of routing and filtering packets in order to reduce network traffic and minimize transmission time. The Network layer uses logical network addresses to route packets to specific networks on an internetwork.

Logical network addresses are assigned during configuration of the networks. A network installer must make sure that each network address is unique on a given internetwork.

The Network layer also supports service addresses. A service address specifies a channel to a specific process on the destination PC. The operating systems on most computers can run several processes at once. When a packet arrives, you must determine which process on the computer should receive the data in the packet. You do so by assigning service addresses, which identify upper-layer processes and protocols. These service addresses are included with the physical and logical network addresses in the data frame. (Some protocols refer to service addresses as sockets or ports.)

Some service addresses, called well-known addresses, are universally defined for a given type of network. Other service addresses are defined by the vendors of network products.