Overview

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

int
socket(AF_INET6, SOCK_RAW, IPPROTO_ICMPV6);

ICMPv6 (Internet Control Message Protocol for IPv6) is the error and control message protocol used by IPv6 and the IPv6 protocol family (see IP6 and INET6). It may be accessed through a 'raw socket' for network monitoring and diagnostic functions.

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

Types

ICMPv6 messages are classified according to the type and code fields present in the ICMPv6 header. The following types are defined:

The following codes are defined:

Headers

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 {
       u_int8_t    icmp6_type;     /* type field */
       u_int8_t    icmp6_code;     /* code field */
       u_int16_t           icmp6_cksum;    /* checksum field */
       union {
               u_int32_t icmp6_un_data32[1]; /* type-specific */
               u_int16_t icmp6_un_data16[2]; /* type-specific */
               u_int8_t  icmp6_un_data8[4];  /* type-specific */
       } 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*/

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.

Filters

Note: Not implemented in INtime.

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 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 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 and setsockopt calls may be used to obtain and install the filter on ICMPv6 sockets at option level IPPROTO_ICMPV6 and name ICMPV6_FILTER with a pointer to the icmp6_filter structure as the option value.

Requirements

See Also

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.