Install libnetfilter-cttimeout-dev by entering the following commands in the terminal:
sudo apt update sudo apt install libnetfilter-cttimeout-dev
fine-grain connection tracking timeout infrastructure for netfilter
libnetfilter_cttimeout is the userspace library that provides the programming interface to the fine-grain connection tracking timeout infrastructure. With this library, you can create, update and delete timeout policies that can be attached to traffic flows. This library is used by conntrack-tools. . This package provides development files and static libraries.