ICMP6(4) - Device Drivers Manual #

ICMP6(4) - Device Drivers Manual

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  
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.

STANDARDS #

W. Stevens, M. Thomas, and 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.

OpenBSD 7.5 - August 3, 2017