What is the network layer in the OSI model?

The network layer is the third layer of the OSI model and is, above all, responsible for assigning addresses to participants within a network. Routing, which can be described as the best way to move through a network, is also managed by the network layer.

The network layer is the third layer in the OSI model. It is responsible for addressing, which is important for creating connections with a network. By completing this task, it allows two systems to connect securely with each other, even if they need to connect over different networks.

For two different systems to be able to communicate and exchange data with one another in a network, correct addressing is required. To accomplish this, the network layer has different services and functions that it makes available to the transport layer, the fourth layer in the OSI model.

In addition to relaying addresses, one of the main tasks of the network layer is to create and abort connections. In doing so, secured system connections are created, even when they need to be run over multiple networks. To do this, the network layer offers routing options, providing the higher levels a transparent connection between the source and target system.

Features of the network layer include flow control, troubleshooting and monitoring of the physical connection. Flow control allows the transferred data to be limited in circumstances where the flow of data is interrupted from the receiver’s side. To do this, the OSI network layer adapts the size of the data packet to the availability of the corresponding network, ensuring the most seamless transfer possible.

With packet-oriented services, the network layer is also important for congestion avoidance. The network layer can support both connectionless and connection-oriented networks, however, it can only handle one network type at a time.

The network layer offers a wide range of services. If it is not possible to connect the sender and the receiver directly, the network layer ensures that the packets are first forwarded to nodes, without sending them to higher layers.

Alongside network connections, the network layer also makes the correct network address available. These addresses are unique and structured hierarchically. Other services offered by the network layer include the actual transfer of data units as well as the identification of relevant connection points between the sender and the receiver. In contrast to the data link layer (layer 2), the information in the network layer can move beyond the boundaries of the local network.

There are many network layer protocols. These include among others:

• CLNS (connectionless-mode network service): A network protocol used in administrative telecommunication networks
• DDP (datagram delivery protocol): A data transfer protocol from AppleTalk
• EGP (exterior gateway protocol): A protocol that checks the availability of networks from two different autonomous systems
• EIGRP (enhanced interior gateway routing protocol): A protocol that saves the router and routes between two networks
• ICMP (internet control message protocol): A protocol used to exchange information and error messages in networks, belongs to IPv4
• IGMP (internet group management protocol): A network protocol used to organize group communications
• IPsec (internet protocol security): A protocol stack to allow a secure connection in potentially unsecure networks
• IPv4: The fourth version of the standard internet protocol (IP)
• IPv6: A new internet standard, which expands addresses from 32 to 128 bits.
• IPX (internetwork packet exchange): A network protocol primarily used for the NetWare operating system
• OSPF (open shortest path first): A routing protocol from IETF used in the networks of large companies
• NetBEUI (NetBIOS extended user interface): A network protocol which has since been replaced by TCP/IP
• PIM (protocol independent multicast): A process for dynamic routing in group communications
• RIP (routing information protocol): A routing protocol used within an automatic system
• X.25: A protocol family for wide area networks that also use the network layer