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Man Pages

Manual Reference Pages  -  ICMP6 (4)


icmp6 - Internet Control Message Protocol for IPv6


See Also


.In sys/socket.h
.In netinet/in.h
.In netinet/icmp6.h int socket AF_INET6 SOCK_RAW IPPROTO_ICMPV6


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
.Vt 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.

.Vt 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 messages.
void ICMP6_FILTER_SETBLOCK int type struct icmp6_filter *filterp
  Ignore ICMPv6 messages with the given type. filterp is modified to ignore such messages.
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
.Vt 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)
.Rs Advanced Sockets API for IPv6
.Rs Internet Control Message Protocol (ICMPv6) for the Internet
"Protocol Version 6 (IPv6) Specification"
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