ICMP6 is a critical component of IPv6 because it allows the Neighbor Discovery Protocol (NDP). The default global firewall policies include an ICMP6 rule by default. If a custom policy is created with a cluster that has IPv6 subnets and pools, the ICMP6 rule must be added to the policy. The best practice is to clone the global policy and customize rules, accordingly, allowing for a baseline of necessary rules. For more information about IPv6, see the IPv6 section.