Network Layer

The next layer in the OSI reference model is the Network Layer (layer 3). This layer is responsible for providing the means to establish, maintain, and tear down network connections between network devices and computing systems in an interconnected system. It provides a means to transparently transfer data between transport layer protocols in different machines. This transportation of data is facilitated by network addresses, which uniquely identify each end system in an OSI interconnected system. The OSI model stipulates that network connections at this layer must be point-to-point (from a single system to only one other system), although it supports complex physical networking configurations.

Additionally, the Network Layer provides services for routing and relaying (moving data around networks and subnetworks), and error detection and recovery. Devices that operate at this layer include routers and layer 3 switches. Examples of protocols at this layer include the Intermediate System to Intermediate System (IS-IS) intra-domain routing protocol and the End System to Intermediate System (ES-IS) routing exchange protocol.