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     icmp6 — Internet Control Message Protocol for IPv6


     #include <sys/socket.h>
     #include <netinet/in.h>
     #include <netinet/icmp6.h>



     ICMPv6 is the error and control message protocol used by IPv6 and the IPv6 protocol family
     (see ip6(4) and inet6(4)).  It may be accessed through a “raw socket” for network monitoring
     and diagnostic functions.

     The proto parameter to the socket(2) call to create an ICMPv6 socket may be obtained from
     getprotobyname(3).  ICMPv6 sockets are connectionless, and are normally used with the
     sendto(2) and recvfrom(2) calls, though the connect(2) call may also be used to fix the
     destination for future packets (in which case read(2) or recv(2) and write(2) or send(2)
     system calls may be used).

     Outgoing packets automatically have an IPv6 header prepended to them (based on the
     destination address).  Incoming packets on the socket are received with the IPv6 header and
     any extension headers removed.

     ICMPv6 messages are classified according to the type and code fields present in the ICMPv6
     header.  The abbreviations for the types and codes may be used in rules in pf.conf(5).  The
     following types are defined:

           Num  Abbrev.         Description
           1    unreach         Destination unreachable
           2    toobig          Packet too big
           3    timex           Time exceeded
           4    paramprob       Invalid IPv6 header
           128  echoreq         Echo service request
           129  echorep         Echo service reply
           130  groupqry        Group membership query
           130  listqry         Multicast listener query
           131  grouprep        Group membership report
           131  listenrep       Multicast listener report
           132  groupterm       Group membership termination
           132  listendone      Multicast listener done
           133  routersol       Router solicitation
           134  routeradv       Router advertisement
           135  neighbrsol      Neighbor solicitation
           136  neighbradv      Neighbor advertisement
           137  redir           Shorter route exists
           138  routrrenum      Route renumbering
           139  fqdnreq         FQDN query
           139  niqry           Node information query
           139  wrureq          Who-are-you request
           140  fqdnrep         FQDN reply
           140  nirep           Node information reply
           140  wrurep          Who-are-you reply
           200  mtraceresp      mtrace response
           201  mtrace          mtrace messages

     The following codes are defined:

           Num  Abbrev.         Type        Description
           0    noroute-unr     unreach     No route to destination
           1    admin-unr       unreach     Administratively prohibited
           2    beyond-unr      unreach     Beyond scope of source address
           2    notnbr-unr      unreach     Not a neighbor (obsolete)
           3    addr-unr        unreach     Address unreachable
           4    port-unr        unreach     Port unreachable
           0    transit         timex       Time exceeded in transit
           1    reassemb        timex       Time exceeded in reassembly
           0    badhead         paramprob   Erroneous header field
           1    nxthdr          paramprob   Unrecognized next header
           2                    redir       Unrecognized option
           0    redironlink     redir       Redirection to on-link node
           1    redirrouter     redir       Redirection to better router

     All ICMPv6 messages are prefixed with an ICMPv6 header.  This header corresponds to the
     icmp6_hdr structure and has the following definition:

           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 */
                           uint16_t icmp6_un_data16[2]; /* type-specific */
                           uint8_t  icmp6_un_data8[4];  /* type-specific */
                   } icmp6_dataun;
           } __packed;

           #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*/

     icmp6_type describes the type of the message.  Suitable values are defined in
     ⟨netinet/icmp6.h⟩.  icmp6_code describes the sub-type of the message and depends on
     icmp6_type.  icmp6_cksum contains the checksum for the message and is filled in by the
     kernel on outgoing messages.  The other fields are used for type-specific purposes.

     Because of the extra functionality of ICMPv6 in comparison to ICMPv4, a larger number of
     messages may be potentially received on an ICMPv6 socket.  Input filters may therefore be
     used to restrict input to a subset of the incoming ICMPv6 messages so only interesting
     messages are returned by the recv(2) family of calls to an application.

     The icmp6_filter structure may be used to refine the input message set according to the
     ICMPv6 type.  By default, all messages types are allowed on newly created raw ICMPv6
     sockets.  The following macros may be used to refine the input set:

     void ICMP6_FILTER_SETPASSALL(struct icmp6_filter *filterp)
             Allow all incoming messages.  filterp is modified to allow all message types.

     void ICMP6_FILTER_SETBLOCKALL(struct icmp6_filter *filterp)
             Ignore all incoming messages.  filterp is modified to ignore all message types.

     void ICMP6_FILTER_SETPASS(int type, struct icmp6_filter *filterp)
             Allow ICMPv6 messages with the given type.  filterp is modified to allow such

     void ICMP6_FILTER_SETBLOCK"(int type, struct icmp6_filter *filterp)
             Ignore ICMPv6 messages with the given type.  filterp is modified to ignore such

     int ICMP6_FILTER_WILLPASS"(int type, const struct icmp6_filter *filterp)
             Determine if the given filter will allow an ICMPv6 message of the given type.

     int ICMP6_FILTER_WILLBLOCK"(int type, const struct icmp6_filter *filterp)
             Determine if the given filter will ignore an ICMPv6 message of the given type.

     The getsockopt(2) and setsockopt(2) calls may be used to obtain and install the filter on
     ICMPv6 sockets at option level IPPROTO_ICMPV6 and name ICMP6_FILTER with a pointer to the
     icmp6_filter structure as the option value.


     getsockopt(2), recv(2), send(2), setsockopt(2), socket(2), getprotobyname(3), inet6(4),
     ip6(4), netintro(4)

     W. Stevens and M. Thomas, Advanced Sockets API for IPv6, RFC 2292, February 1998.

     A. Conta and S. Deering, Internet Control Message Protocol (ICMPv6) for the Internet
     Protocol Version 6 (IPv6) Specification, RFC 2463, December 1998.