#!/usr/sbin/nft -f

define out_if = "enp4s0"
define out_ip = 11.22.33.44/32
define vm_if = "br0"
define vm_net = 192.168.122.0/24

flush ruleset


table ip filter {
    chain INPUT {
        type filter hook input priority filter; policy drop;

        iifname $out_if tcp dport 22 counter jump f2b-sshd

        ct state related,established counter accept

        iifname "lo" counter accept
        meta l4proto icmp accept
        tcp dport 22 counter accept
        iifname $out_if udp sport 67-68 udp dport 67-68 counter accept
        iifname $vm_if udp dport 53 counter accept
        iifname $vm_if udp sport 67-68 udp dport 67-68 counter accept

        counter reject with icmp type admin-prohibited
    }

    chain FORWARD {
        type filter hook forward priority filter; policy drop;
        ct state related,established counter accept

        # portforwards are implicitly accepted
        ct status dnat counter accept

        iifname $vm_if ip saddr $vm_net counter accept

        counter reject with icmp type admin-prohibited
    }

    chain OUTPUT {
        type filter hook output priority filter; policy drop;

        counter accept
    }

    chain f2b-sshd {
        counter return
    }
}


table ip nat {
    map portforwards {
        type inet_service : ipv4_addr . inet_service
        elements = {
            16085 : 192.168.122.2 . 22
        }
    }

    chain PREROUTING {
        type nat hook prerouting priority dstnat; policy accept;

        # portforward (+ hairpinning)
        iif {$out_if, $vm_if} ip protocol tcp ip daddr $out_ip   dnat ip addr . port to tcp dport map @portforwards;
    }

    chain INPUT {
        type nat hook input priority 100; policy accept;
    }

    chain OUTPUT {
        type nat hook output priority -100; policy accept;

        # portforwards for local connections
        ip protocol tcp ip daddr $out_ip   dnat ip addr . port to tcp dport map @portforwards;
    }

    chain POSTROUTING {
        type nat hook postrouting priority srcnat; policy accept;

        # masquerade outgoing connections
        iifname $vm_if oifname $out_if counter masquerade
        # masquerade hairpinned connections
        iifname $vm_if oifname $vm_if ct status dnat counter masquerade
    }

}