What is the Network Layer? – Definition from Techopedia

Logical connection setup, data forwarding, routing and delivery error reporting are the network layer’s primary responsibilities. Layer 3 can be either able to support connection-oriented or connectionless networks (but not both of them at the same time).

The network layer is the third level (Layer 3) of the Open Systems Interconnection Model (OSI Model) and the layer that provides data routing paths for network communication. Data is transferred to the receiving device in the form of packets via logical network paths in an ordered format controlled by the network layer.

The network layer is a portion of online communications that allows for the connection and transfer of data packets between different devices or networks.

Techopedia Explains Network Layer

The network layer is considered the backbone of the OSI Model. It selects and manages the best logical path (virtual circuit) for data transfer between nodes by assigning destination and source IP addresses to each data segment.

In the OSI model, the network layer responds to requests from the layer above it (transport layer) and issues requests to the layer below it (data link layer). Information about the source and destination hosts is already contained in the data link layer (Layer 2), but it’s the network layer that interconnects different networks allowing data to move between them. Quality of Service (QoS) allows for the prioritization of certain types of traffic.

Data is checked for errors by the Internet Control Message Protocol (ICMP), which ensures that packets are sent correctly by Layer 3.

Layer 3 contains hardware devices such as routers, bridges, firewalls and switches, but it actually creates a logical image of the most efficient communication route and implements it with a physical medium.

Network layer protocols exist in every host or router. The router examines the header fields of all the IP packets that pass through it. Networking software is used to attach the header to each data packet sent as well as to read it to determine how the packet is handled at the receiving end.

All the connection, encryption, checking, and routing processes occur at the network layer and are made by several different protocols, including:

• IP
• IPsec
• IPX/SPX
• ICMP
• IGMP
• GRE

Internet Protocol (IP) and Netware IPX/SPX are the most common protocols associated with the network layer.

The network layer infrastructure is inherently vulnerable to malicious attacks since it is exposed on the Internet. Distributed denial-of-service (DDoS) attacks can be launched to overwhelm all the physical network interfaces such as routers and stop data transmission.

Although this comparison can be misleading, the OSI network layer is often referenced as the equivalent of the Internet layer of the TCP/IP model. However, there are several differences between the two, and the TCP/IP Internet layer only has a limited amount of the functions covered by the OSI network layer.