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