nixos/hosts/genesis/nftables.nft

#!/usr/bin/env nft -f

table ip filter {
	chain output {
		type filter hook output priority 100; policy accept;
	}

	chain input {
		type filter hook input priority 0; policy drop;

		iifname lo accept

		# Open the specific ports that we allow
		{% for port in tcpPorts %}
		iifname { {{ lanInterfaces | join(", ") }}, "tailscale0" } tcp dport {{ port }} accept
		{% endfor %}
		{% for port in udpPorts %}
		iifname { {{ lanInterfaces | join(", ") }}, "tailscale0" } udp dport {{ port }} accept
		{% endfor %}

		iifname { {{ lanInterfaces | join(", ") }} } accept comment "Allows LAN traffic and outgoing"
		iifname { {{ wanInterface }} } ct state { established, related } accept comment "Allows existing connections"
		iifname { {{ wanInterface }} } icmp type { echo-request, destination-unreachable, time-exceeded } counter accept comment "Allow some ICMP traffic"
		iifname { {{ wanInterface }} } counter drop comment "Drop other incoming traffic, and count how much"
	}
	chain forward {
		type filter hook forward priority 0; policy drop;
		iifname { {{ (lanInterfaces + limitedLan) | join(", ") }} } oifname { {{ wanInterface }} } accept comment "Forward LAN to WAN"
		iifname { {{ wanInterface }} } oifname { {{ (lanInterfaces + limitedLan) | join(", ") }} } ct state established, related accept comment "Allow incoming established traffic"
	}
}

table ip nat {
	chain postrouting {
		type nat hook postrouting priority 100; policy accept;
		oifname { {{ wanInterface }} } masquerade
	}
}

table ip6 filter {
	chain input {
		type filter hook input priority 0; policy drop;
	}
	chain forward {
		type filter hook forward priority 0; policy drop;
	}
}