Linux Network Protocol Stack: From Socket to Driver

The Linux network protocol stack is one of the most critical and optimized subsystems in the kernel. Understanding its internals is essential for systems programmers, network engineers, and performance-oriented developers. This article takes a deep dive into the complete packet processing pipeline.

Architecture Overview

The Linux networking stack spans multiple layers, from user-space socket APIs down to hardware device drivers. Key layers include:

• Socket Layer (BSD Socket) - User-space interface via syscalls
• Transport Layer - TCP, UDP, SCTP protocols
• Network Layer - IP, routing, netfilter/iptables
• Link Layer - ARP, bridge, VLAN
• Driver Layer - NIC drivers, NAPI polling

Socket Layer: The Entry Point

When an application calls socket(), the kernel creates a struct socket along with its associated struct sock (inet_sock for TCP/UDP). The socket-file bridge connects VFS to the networking subsystem:

// Socket creation skelleton
struct socket *sock = sock_alloc();
sock->type = SOCK_STREAM;
sock->ops =