ICMP6(4) Kernel Interfaces Manual ICMP6(4)
NAME
icmp6Internet 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
redir
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 { 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.
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 ICMPV6_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)
W. Stevens, M. Thomas, Advanced Sockets API for IPv6, RFC 2292, February 1998.
A. Conta, S. Deering, Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification, RFC 2463, December 1998.