Which firewall chain is appropriate for filtering client HTTP traffic through the router?

Filtering client HTTP traffic through the router typically requires that the traffic be monitored as it passes through the router to its intended destination. The forward chain is specifically designed to handle packets that are routed through the device and destined for another host. This makes it ideal for filtering traffic that is not originated from the router itself but is instead passing through it, such as client HTTP requests heading to web servers on the internet.

In the context of Mikrotik's firewall configuration, the forward chain ensures that all traffic coming into the router's interfaces (from clients) and going out to other interfaces (toward the destination) can be filtered based on specific criteria, such as HTTP protocols, source or destination addresses, or port numbers.

Using other chains like prerouting, output, or input would not be appropriate for this scenario. The prerouting chain is utilized for packets that are destined for the router itself before they are routed elsewhere, the output chain is for traffic originating from the router, and the input chain deals with packets directed to the router itself. None of these chains would effectively manage or filter client HTTP traffic that is simply passing through the router to reach an external host.