NAME
icmp6
—
Internet Control Message Protocol for
IPv6
SYNOPSIS
#include
<sys/socket.h>
#include <netinet/in.h>
#include <netinet/icmp6.h>
int
socket
(AF_INET6,
SOCK_RAW,
IPPROTO_ICMPV6);
DESCRIPTION
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.
Types
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 | paramprob | Unrecognized option | |
0 | redironlink | redir | Redirection to on-link node |
1 | redirrouter | redir | Redirection to better router |
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; } __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.
Filters
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 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
icmp6_filter structure as the option value.
SEE ALSO
getsockopt(2), recv(2), send(2), setsockopt(2), socket(2), getprotobyname(3), inet6(4), ip6(4), netintro(4)
STANDARDS
W. Stevens, M. Thomas, E. Nordmark, and T. Jinmei, Advanced Sockets Application Program Interface (API) for IPv6, RFC 3542, May 2003.
A. Conta, S. Deering, and M. Gupta, Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification, RFC 4443, March 2006.