Networking — The Linux Kernel documentation
The development of the Internet has led to an exponential increase in network applications and, as a consequence, to increasing the speed and productivity requirements of an operating system's networking subsystem. The networking subsystem is not an essential component of an operating system kernel (the Linux kernel can be compiled without networking support). It is, however, quite unlikely for a computing system (or even an embedded device) to have a non-networked operating system due to the need for connectivity. Modern operating systems use the TCP/IP stack. Their kernel implements protocols up to the transport layer, while application layer protocols are typically implemented in user space (HTTP, FTP, SSH, etc.). In user space the abstraction of network communication is the socket. The socket abstracts a communication channel and is the kernel-based TCP/IP stack interaction interface. An IP socket is associated with an IP address, the transport layer protocol used (TCP, UDP etc) an