networklayer

Networklayer refers to the network layer in computer networking, commonly identified as layer 3 in the OSI model, and corresponds to the Internet layer in the TCP/IP model. It is responsible for moving data packets across multiple networks from a source to a destination, enabling internetwork communication. The network layer provides logical addressing, routing, and packet forwarding, while working with the data link layer below and the transport layer above.

Key functions include logical addressing, where addresses identify endpoints irrespective of the underlying physical network; routing, where routers determine a feasible path and forward packets toward their destination; and packet forwarding, which involves examining the destination address and delivering packets to the next hop. The network layer may also perform fragmentation and reassembly when a packet traverses links with smaller Maximum Transmission Units, though fragmentation is often handled at the link layer as well. Error reporting and diagnostics can occur through control messages such as ICMP.

Core protocols and concepts center on IP (IPv4 and IPv6), which define the addressing and routing mechanics, plus auxiliary protocols like ICMP for error reporting and IGMP for multicast group management. Dynamic routing protocols including OSPF, IS-IS, BGP, and RIP enable routers to build and update routing tables in response to topology changes. Security considerations include filtering, access control, and, where appropriate, encryption at higher layers or IPsec at the network layer.

In practice, the network layer is implemented within routing devices and software stacks, interfacing with the data link layer to transmit frames and with the transport layer to support end-to-end communication. In the TCP/IP model, its responsibilities align with the Internet layer.