public Optional<Output<String>> ipv6() {
        return Optional.ofNullable(this.ipv6);
    }
@return IPv6 defines an IPv6 IP block in CIDR notation(e.g. &#34;2001:db8::/64&#34;). At least one of IPv4 and IPv6 must be specified. This field is immutable.
sdk/java/src/main/java/com/pulumi/kubernetes/networking/v1alpha1/inputs/ClusterCIDRSpecPatchArgs.java