ICMP6(4) MidnightBSD Kernel Interfaces Manual ICMP6(4)

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 listerner 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 (obselete)

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 {

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 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

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 .

MidnightBSD 0.3 December 20, 2004 MidnightBSD 0.3