Control: reassing -1 ufw This is probably a bug in ufw. I can do this here: $ sudo ip6tables-nft -A FORWARD -i eth0 -p icmpv6 -m icmpv6 --icmpv6-type no-route $ sudo ip6tables-legacy -A FORWARD -i eth0 -p icmpv6 -m icmpv6 --icmpv6-type no-route and both work.