The virtual filesystem that we call /proc contains loads and loads of different datastructures and information gathered from the kernel at runtime, and updated whenever you try to list or view the information. The information is all gathered and shown as a normal filesystem, and hence you can read files, traverse catalog structures, etcetera. Everything that you can do in a normal filesystem in other words. However, most of the files available through the /proc filesystem are only available read only, which means they can't be changed. This is because they only supply us with informational data.
One section is read-writable on the other hand, and that section is placed within the /proc/sys. All of the variables located in this directory and subdirectories are writable as well as readable.
This document will focus on the Internet Protocol version 4 (IPv4) section of the /proc located in /proc/sys/net/ipv4 which contains all the configurable settings for the IPv4 stack, including TCP, UDP, ICMP and ARP tunable settings