Ok, parece que adicionar as duas regras a seguir ajudou.
-A INPUT -p udp -m udp --dport 546 -m state --state NEW,ESTABLISHED -j ACCEPT
-A INPUT -p ipv6-icmp -j ACCEPT
Aqui, o% completorules.v6
# Generated by ip6tables-save v1.4.21 on Wed May 17 10:14:19 2017
*filter
:INPUT DROP [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [110:14552]
-A INPUT -i lo -j ACCEPT
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT
-A INPUT -p udp -m udp --dport 546 -m state --state NEW,ESTABLISHED -j ACCEPT
-A INPUT -p ipv6-icmp -j ACCEPT
COMMIT
# Completed on Wed May 17 10:14:19 2017