If you want to prohibit access to your host for specified AS, you can use solution below. I made it some time ago, when I found out, that mail.ru hunting for hosts which help to bypass telegram censorship. It’s not perfect because I didn’t make much effort to it. Whois can return sub-networks and networks to which they belong in same response, so ipset set can contain duplicated ranges. Change ‘AS47764’ to AS which you want to block, ‘input_drop’ is an ipset set name.

ipset create input_drop hash:net comment
for i in $(whois -h whois.radb.net -- '-i origin AS47764' | grep 'route:'|cut -d : -f 2)
do
ipset add input_drop $i comment mail.ru
done
iptables -A INPUT -m set --match-set input_drop src -m comment --comment "DROP INPUT packets for AS47764" -j DROP

Also, i would recommend that solution, to make ipset rules persistent: https://github.com/BroHui/systemd-ipset-service