def create_packet(self, primary_ip_address, vlan_id=None):
        """Prepare a VRRP packet.

        Returns a newly created ryu.lib.packet.packet.Packet object
        with appropriate protocol header objects added by add_protocol().
        It's caller's responsibility to serialize().
        The serialized packet would looks like the ones described in
        the following sections.

        * RFC 3768 5.1. VRRP Packet Format
        * RFC 5798 5.1. VRRP Packet Format

        ================== ====================
        Argument           Description
        ================== ====================
        primary_ip_address Source IP address
        vlan_id            VLAN ID.  None for no VLAN.
        ================== ====================
        """
        if self.is_ipv6:
            traffic_class = 0xc0        # set tos to internetwork control
            flow_label = 0
            payload_length = ipv6.ipv6._MIN_LEN + len(self)     # XXX _MIN_LEN
            e = ethernet.ethernet(VRRP_IPV6_DST_MAC_ADDRESS,
                                  vrrp_ipv6_src_mac_address(self.vrid),
                                  ether.ETH_TYPE_IPV6)
            ip = ipv6.ipv6(6, traffic_class, flow_label, payload_length,
                           inet.IPPROTO_VRRP, VRRP_IPV6_HOP_LIMIT,
                           primary_ip_address, VRRP_IPV6_DST_ADDRESS)
        else:
            header_length = ipv4.ipv4._MIN_LEN // 4      # XXX _MIN_LEN
            total_length = 0
            tos = 0xc0  # set tos to internetwork control
            identification = self.get_identification()
            e = ethernet.ethernet(VRRP_IPV4_DST_MAC_ADDRESS,
                                  vrrp_ipv4_src_mac_address(self.vrid),
                                  ether.ETH_TYPE_IP)
            ip = ipv4.ipv4(4, header_length, tos, total_length, identification,
                           0, 0, VRRP_IPV4_TTL, inet.IPPROTO_VRRP, 0,
                           primary_ip_address, VRRP_IPV4_DST_ADDRESS)

        p = packet.Packet()
        p.add_protocol(e)
        if vlan_id is not None:
            vlan_ = vlan.vlan(0, 0, vlan_id, e.ethertype)
            e.ethertype = ether.ETH_TYPE_8021Q
            p.add_protocol(vlan_)
        p.add_protocol(ip)
        p.add_protocol(self)
        return p