What is conntrack and what is it for?

Question

linux

Hello! task, install an ftp server and set up conntrack to run the ftp service. Installed vsftpd , everything works fine. But I still don't understand what conntrack is for. The value is written on the Internet, but I never got it. Can you please explain in plain language.

Answer 1

CONFIG_NF_CONNTRACK:

Connection tracking keeps a record of what packets have passed
through your machine, in order to figure out how they are related
into connections.

This is required to do Masquerading or other kinds of Network
Address Translation.  It can also be used to enhance packet
filtering (see `Connection state match support' below).

Answer 2

Set up an FTP server behind NAT with only 21 ports forwarded - you will immediately understand what conntrack is :)

Answer 3

This is a connection tracking module. It is mainly used when tracking connections when forwarding from one network to another.

Answer 4

In short, this is a Firewall
More details - https://ru.wikipedia.org/wiki/Netfilter