Block unwanted IPs

[hobyte]

I'm running a single node k3s cluster on ubuntu. To block unwanted an badly behaving IPs, I use this rule: ipables -I INPUT -s <IP> -j DROP. when k3s is not installed, this rule works and the IPs are blocked. But when k3s is installes, the block rule has no effect and those IPs can still reach services running in my cluster. So how can I block IPs from reaching services in k3s?