struct icmp6_hdr {
  uint8_t     icmp6_type;   /* type field */
  uint8_t     icmp6_code;   /* code field */
  uint16_t    icmp6_cksum;  /* checksum field */
  union {
    uint32_t  icmp6_un_data32[1]; /* type-specific field */
    uint16_t  icmp6_un_data16[2]; /* type-specific field */
    uint8_t   icmp6_un_data8[4];  /* type-specific field */
  } icmp6_dataun;
};

#define icmp6_data32    icmp6_dataun.icmp6_un_data32
#define icmp6_data16    icmp6_dataun.icmp6_un_data16
#define icmp6_data8     icmp6_dataun.icmp6_un_data8
#define icmp6_pptr      icmp6_data32[0]  /* parameter prob */
#define icmp6_mtu       icmp6_data32[0]  /* packet too big */
#define icmp6_id        icmp6_data16[0]  /* echo request/reply */
#define icmp6_seq       icmp6_data16[1]  /* echo request/reply */
#define icmp6_maxdelay  icmp6_data16[0]  /* mcast group membership */

#define ICMP6_DST_UNREACH             1
#define ICMP6_PACKET_TOO_BIG          2
#define ICMP6_TIME_EXCEEDED           3
#define ICMP6_PARAM_PROB              4

#define ICMP6_INFOMSG_MASK  0x80    /* all informational messages */

#define ICMP6_ECHO_REQUEST          128
#define ICMP6_ECHO_REPLY            129
#define ICMP6_MEMBERSHIP_QUERY      130
#define ICMP6_MEMBERSHIP_REPORT     131
#define ICMP6_MEMBERSHIP_REDUCTION  132

#define ICMP6_DST_UNREACH_NOROUTE     0 /* no route to destination */
#define ICMP6_DST_UNREACH_ADMIN       1 /* communication with destination */
                                        /* administratively prohibited */
#define ICMP6_DST_UNREACH_NOTNEIGHBOR 2 /* not a neighbor */
#define ICMP6_DST_UNREACH_ADDR        3 /* address unreachable */
#define ICMP6_DST_UNREACH_NOPORT      4 /* bad port */

#define ICMP6_TIME_EXCEED_TRANSIT     0 /* Hop Limit == 0 in transit */
#define ICMP6_TIME_EXCEED_REASSEMBLY  1 /* Reassembly time out */

#define ICMP6_PARAMPROB_HEADER        0 /* erroneous header field */
#define ICMP6_PARAMPROB_NEXTHEADER    1 /* unrecognized Next Header */
#define ICMP6_PARAMPROB_OPTION        2 /* unrecognized IPv6 option */

#define ND_ROUTER_SOLICIT           133
#define ND_ROUTER_ADVERT            134
#define ND_NEIGHBOR_SOLICIT         135
#define ND_NEIGHBOR_ADVERT          136
#define ND_REDIRECT                 137

struct nd_router_solicit {     /* router solicitation */
  struct icmp6_hdr  nd_rs_hdr;
    /* could be followed by options */
};

#define nd_rs_type               nd_rs_hdr.icmp6_type
#define nd_rs_code               nd_rs_hdr.icmp6_code
#define nd_rs_cksum              nd_rs_hdr.icmp6_cksum
#define nd_rs_reserved           nd_rs_hdr.icmp6_data32[0]

struct nd_router_advert {      /* router advertisement */
  struct icmp6_hdr  nd_ra_hdr;
  uint32_t   nd_ra_reachable;   /* reachable time */
  uint32_t   nd_ra_retransmit;  /* retransmit timer */
    /* could be followed by options */
};

#define nd_ra_type               nd_ra_hdr.icmp6_type
#define nd_ra_code               nd_ra_hdr.icmp6_code
#define nd_ra_cksum              nd_ra_hdr.icmp6_cksum
#define nd_ra_curhoplimit        nd_ra_hdr.icmp6_data8[0]
#define nd_ra_flags_reserved     nd_ra_hdr.icmp6_data8[1]
#define ND_RA_FLAG_MANAGED       0x80
#define ND_RA_FLAG_OTHER         0x40
#define nd_ra_router_lifetime    nd_ra_hdr.icmp6_data16[1]

struct nd_neighbor_solicit {   /* neighbor solicitation */
  struct icmp6_hdr  nd_ns_hdr;
  struct in6_addr   nd_ns_target; /* target address */
    /* could be followed by options */
};

#define nd_ns_type               nd_ns_hdr.icmp6_type
#define nd_ns_code               nd_ns_hdr.icmp6_code
#define nd_ns_cksum              nd_ns_hdr.icmp6_cksum
#define nd_ns_reserved           nd_ns_hdr.icmp6_data32[0]

struct nd_neighbor_advert {    /* neighbor advertisement */
  struct icmp6_hdr  nd_na_hdr;
  struct in6_addr   nd_na_target; /* target address */
    /* could be followed by options */
};

#define nd_na_type               nd_na_hdr.icmp6_type
#define nd_na_code               nd_na_hdr.icmp6_code
#define nd_na_cksum              nd_na_hdr.icmp6_cksum
#define nd_na_flags_reserved     nd_na_hdr.icmp6_data32[0]
#define ND_NA_FLAG_ROUTER        0x80000000
#define ND_NA_FLAG_SOLICITED     0x40000000
#define ND_NA_FLAG_OVERRIDE      0x20000000

struct nd_redirect {           /* redirect */
  struct icmp6_hdr  nd_rd_hdr;
  struct in6_addr   nd_rd_target; /* target address */
  struct in6_addr   nd_rd_dst;    /* destination address */
    /* could be followed by options */
};

#define nd_rd_type               nd_rd_hdr.icmp6_type
#define nd_rd_code               nd_rd_hdr.icmp6_code
#define nd_rd_cksum              nd_rd_hdr.icmp6_cksum
#define nd_rd_reserved           nd_rd_hdr.icmp6_data32[0]

struct nd_opt_hdr {            /* Neighbor discovery option header */
  uint8_t  nd_opt_type;
  uint8_t  nd_opt_len;        /* in units of 8 octets */
    /* followed by option specific data */
};

#define  ND_OPT_SOURCE_LINKADDR       1
#define  ND_OPT_TARGET_LINKADDR       2
#define  ND_OPT_PREFIX_INFORMATION    3
#define  ND_OPT_REDIRECTED_HEADER     4
#define  ND_OPT_MTU                   5

struct nd_opt_prefix_info {    /* prefix information */
  uint8_t   nd_opt_pi_type;
  uint8_t   nd_opt_pi_len;
  uint8_t   nd_opt_pi_prefix_len;
  uint8_t   nd_opt_pi_flags_reserved;
  uint32_t  nd_opt_pi_valid_time;
  uint32_t  nd_opt_pi_preferred_time;
  uint32_t  nd_opt_pi_reserved2;
  struct in6_addr  nd_opt_pi_prefix;
};

#define ND_OPT_PI_FLAG_ONLINK        0x80
#define ND_OPT_PI_FLAG_AUTO          0x40

struct nd_opt_rd_hdr {         /* redirected header */
  uint8_t   nd_opt_rh_type;
  uint8_t   nd_opt_rh_len;
  uint16_t  nd_opt_rh_reserved1;
  uint32_t  nd_opt_rh_reserved2;
    /* followed by IP header and data */
};

struct nd_opt_mtu {            /* MTU option */
  uint8_t   nd_opt_mtu_type;
  uint8_t   nd_opt_mtu_len;
  uint16_t  nd_opt_mtu_reserved;
  uint32_t  nd_opt_mtu_mtu;
};