Why is my router responding on port 80?
Have you ever had the experience that even you change the HTTP management port,
still find the 80 port is open?
Because, TCP port 80 is not only used for default HTTP port of router's GUI but also for the blockpage of DNS filter of firewall. The blockpage is displayed when users are accessing a forbidden website.
The blockpage can be disabled to make TCP port 80 closed on LAN by command:
csm dnsf blockpage off
then reboot router.
Scan port 80 again, and it's filtered.
However, users will not be redirected to blockpage when they try to access the forbidden websites, browser will consider the page is not working and show the error page instead.