Also referred to as a network layer, this layer is responsible for establishing a virtual communication channel. These include locating a path to the target computer, messaging and packets (a "long" message is thus divided into individual packets). In both cases, the data transmission passes over the entire communication network and includes the routing between the network nodes. Since direct communication between the sender and the destination is not always possible, packets from nodes on the way must be forwarded. Forwarded packets do not get into the higher layers, but are provided with a new waypoint and sent to the next node.
If one follows the path of a package from one's own computer to a computer "at the other end of the world", one finds that the route leads through numerous subnets, which sometimes completely different technologies (fiber optics, radio, Ethernet, modem ... ) underlie. For each transition to a new subnet, a protocol change in the "lower" layers becomes necessary. To which computer of such a subnet the packet is next to "route" remains the matter of the network layer.
To the most prominent representatives of this layer, IP, ICMP and ARP, we turn to below. Other protocols include X.25, Exterior Gateway Protcol EGP, Border Gateway Proctocol BGP, Open Shortest Path First OSPF, and Routing Information Protocol RIP.
Hardware on this Layer: Router, Layer 3 Switch (BRouter)