B1300 How to block all UDP traffic

Hi guys. Is there any proper way to block or drop UDP traffic going in and out of this router? I tried to apply iptables rules, firewall rules as well but no luck. Any device that tries to send UDP package (such as wireguard) still able to pass and receive the packages.

The reason behind this is because I want to force some applications (android) to use their TCP insted of UDP. I realize that for some application that only use UDP will not work but it doesn’t matter for now.

Can you try this?

Thanks, that’s good tutorial but after several trials I need to change several things. So for B1300 with current firmware I did this in terminal:

iptables -A INPUT -p udp -j REJECT --reject-with icmp-proto-unreachable
iptables -A OUTPUT -p udp -j REJECT --reject-with icmp-proto-unreachable
iptables -I FORWARD -p udp -j DROP
iptables -I FORWARD -p udp -m udp --dport 3478 -j ACCEPT

The last port is for whatsapp calling because it still tries to contact server with UDP, so I have to add them. For the forward rules I changed to Insert because append option is ignored or maybe overridden by other line or script that I don’t know where.