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.Dd December 20, 2004
.Dt ICMP6 4
.Os
.Sh NAME
.Nm icmp6
.Nd Internet Control Message Protocol for IPv6
.Sh SYNOPSIS
.In sys/socket.h
.In netinet/in.h
.In netinet/icmp6.h
.Ft int
.Fn socket AF_INET6 SOCK_RAW IPPROTO_ICMPV6
.Sh DESCRIPTION
ICMPv6 is the error and control message protocol used by IPv6 and the
IPv6 protocol family (see
.Xr ip6 4
and
.Xr inet6 4 ) .
It may be accessed through a
.Dq raw socket
for network monitoring and diagnostic functions.
.Pp
The
.Fa proto
parameter to the
.Xr socket 2
call to create an ICMPv6 socket may be obtained from
.Xr getprotobyname 3 .
ICMPv6 sockets are connectionless, and are normally used with the
.Xr sendto 2
and
.Xr recvfrom 2
calls, though the
.Xr connect 2
call may also be used to fix the destination for future packets
(in which case
.Xr read 2
or
.Xr recv 2
and
.Xr write 2
or
.Xr send 2
system calls may be used).
.Pp
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.
.Ss 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
.Xr pf.conf 5 .
The following types are defined:
.Bl -column x xxxxxxxxxxxx -offset indent
.It Sy Num Ta Sy Abbrev. Ta Sy Description
.It 1 Ta unreach Ta "Destination unreachable"
.It 2 Ta toobig Ta "Packet too big"
.It 3 Ta timex Ta "Time exceeded"
.It 4 Ta paramprob Ta "Invalid IPv6 header"
.It 128 Ta echoreq Ta "Echo service request"
.It 129 Ta echorep Ta "Echo service reply"
.It 130 Ta groupqry Ta "Group membership query"
.It 130 Ta listqry Ta "Multicast listener query"
.It 131 Ta grouprep Ta "Group membership report"
.It 131 Ta listenrep Ta "Multicast listener report"
.It 132 Ta groupterm Ta "Group membership termination"
.It 132 Ta listendone Ta "Multicast listerner done"
.It 133 Ta routersol Ta "Router solicitation"
.It 134 Ta routeradv Ta "Router advertisement"
.It 135 Ta neighbrsol Ta "Neighbor solicitation"
.It 136 Ta neighbradv Ta "Neighbor advertisement"
.It 137 Ta redir Ta "Shorter route exists"
.It 138 Ta routrrenum Ta "Route renumbering"
.It 139 Ta fqdnreq Ta "FQDN query"
.It 139 Ta niqry Ta "Node information query"
.It 139 Ta wrureq Ta "Who-are-you request"
.It 140 Ta fqdnrep Ta "FQDN reply"
.It 140 Ta nirep Ta "Node information reply"
.It 140 Ta wrurep Ta "Who-are-you reply"
.It 200 Ta mtraceresp Ta "mtrace response"
.It 201 Ta mtrace Ta "mtrace messages"
.El
.Pp
The following codes are defined:
.Bl -column x xxxxxxxxxxxx xxxxxxxx -offset indent
.It Sy Num Ta Sy Abbrev. Ta Sy Type Ta
.Sy Description
.It 0 Ta noroute-unr Ta unreach Ta "No route to destination"
.It 1 Ta admin-unr Ta unreach Ta "Administratively prohibited"
.It 2 Ta beyond-unr Ta unreach Ta "Beyond scope of source address"
.It 2 Ta notnbr-unr Ta unreach Ta "Not a neighbor (obselete)"
.It 3 Ta addr-unr Ta unreach Ta "Address unreachable"
.It 4 Ta port-unr Ta unreach Ta "Port unreachable"
.It 0 Ta transit Ta timex Ta "Time exceeded in transit"
.It 1 Ta reassemb Ta timex Ta "Time exceeded in reassembly"
.It 0 Ta badhead Ta paramprob Ta "Erroneous header field"
.It 1 Ta nxthdr Ta paramprob Ta "Unrecognized next header"
.It 2 Ta "" Ta redir Ta "Unrecognized option"
.It 0 Ta redironlink Ta redir Ta "Redirection to on-link node"
.It 1 Ta redirrouter Ta redir Ta "Redirection to better router"
.El
.Ss Headers
All ICMPv6 messages are prefixed with an ICMPv6 header.
This header corresponds to the
.Vt icmp6_hdr
structure and has the following definition:
.Bd -literal -offset indent
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*/
.Ed
.Pp
.Va icmp6_type
describes the type of the message.
Suitable values are defined in
.Aq Pa netinet/icmp6.h .
.Va icmp6_code
describes the sub-type of the message and depends on
.Va icmp6_type .
.Va 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.
.Ss 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
.Xr recv 2
family of calls to an application.
.Pp
The
.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:
.Bl -tag -width Ds
.It Fn "void ICMP6_FILTER_SETPASSALL" "struct icmp6_filter *filterp"
Allow all incoming messages.
.Va filterp
is modified to allow all message types.
.It Fn "void ICMP6_FILTER_SETBLOCKALL" "struct icmp6_filter *filterp"
Ignore all incoming messages.
.Va filterp
is modified to ignore all message types.
.It Fn "void ICMP6_FILTER_SETPASS" "int type" \
    "struct icmp6_filter *filterp"
Allow ICMPv6 messages with the given
.Fa type .
.Va filterp
is modified to allow such messages.
.It Fn "void ICMP6_FILTER_SETBLOCK" "int type" \
    "struct icmp6_filter *filterp"
Ignore ICMPv6 messages with the given
.Fa type .
.Va filterp
is modified to ignore such messages.
.It Fn "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.
.It Fn "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.
.El
.Pp
The
.Xr getsockopt 2
and
.Xr setsockopt 2
calls may be used to obtain and install the filter on ICMPv6 sockets at
option level
.Dv IPPROTO_ICMPV6
and name
.Dv ICMPV6_FILTER
with a pointer to the
.Vt icmp6_filter
structure as the option value.
.Ss "Non-privileged ICMPv6"
.Pp
.Tn ICMPv6
sockets can be opened with the 
.Dv SOCK_DGRAM
socket type without requiring root privileges. The synopsis is the following:
.Pp
.Fn socket AF_INET6 SOCK_DGRAM IPPROTO_ICMPV6
.Pp
This can only be used to send 
.Tn ICMPv6
echo requests to gauge the quality of the connectivity to a host, to receive 
destination unreachable message for path MTU discovery, or to receveive 
time exceeded message for traceroute. 
.Pp
A socket opened with superuser privileges can send any kind of 
.Tn ICMPv6 
message and can also use the 
.Xr ip6 4
options that require superuser privileges.
.Sh SEE ALSO
.Xr getsockopt 2 ,
.Xr recv 2 ,
.Xr send 2 ,
.Xr setsockopt 2 ,
.Xr socket 2 ,
.Xr getprotobyname 3 ,
.Xr inet6 4 ,
.Xr ip6 4 ,
.Xr netintro 4
.Rs
.%A W. Stevens
.%A M. Thomas
.%T Advanced Sockets API for IPv6
.%N RFC 2292
.%D February 1998
.Re
.Rs
.%A A. Conta
.%A S. Deering
.%T "Internet Control Message Protocol (ICMPv6) for the Internet" \
    "Protocol Version 6 (IPv6) Specification"
.%N RFC 2463
.%D December 1998
.Re