#!/bin/bash

RULESET='add table ip filter
add chain ip filter filter { type filter hook prerouting priority mangle; policy accept; }
add ct helper ip filter ftp { type "ftp" protocol tcp; };
add rule ip filter filter tcp dport 33 ct helper set "ftp"'

set -e
$NFT -f - <<< "$RULESET"

RULESET='flush chain ip filter filter
delete chain filter filter
delete ct helper ip filter ftp'

$NFT -f - <<< "$RULESET"