man page icmp section 4 (original) (raw)

icmp(4) BSD Kernel Interfaces Manual icmp(4)

NAME

 **icmp** -- Internet Control Message Protocol

SYNOPSIS

 **#include** **<sys/socket.h>**
 **#include** **<netinet/in.h>**

 _int_
 **socket**(_AF_**_**_INET_, _SOCK_**_**_RAW_, _proto_);

DESCRIPTION

 ICMP is the error and control message protocol used by IP and the Inter-
 net protocol family.  It may be accessed through a ``raw socket'' for
 network monitoring and diagnostic functions.  The _proto_ parameter to the
 socket call to create an ICMP socket is obtained from **[getprotobyname(3)](/man/3/getprotobyname/)**.
 ICMP sockets are connectionless, and are normally used with the sendto
 and recvfrom calls, though the **[connect(2)](/man/2/connect/)** call may also be used to fix
 the destination for future packets (in which case the **[read(2)](/man/2/read/)** or **[recv(2)](/man/2/recv/)**
 and **[write(2)](/man/2/write/)** or **[send(2)](/man/2/send/)** system calls may be used).

 Outgoing packets automatically have an IP header prepended to them (based
 on the destination address).  Incoming packets are received with the IP
 header and options intact.  Note that the ip_off and ip_len fields are in
 host byte order.  For more information about the IP header structure, see
 **[ip(4)](/man/4/ip/)**.

Non-privileged ICMP ICMP sockets can be opened with the SOCK_DGRAM socket type without requiring root privileges. The synopsis is the following:

 **socket**(_AF_**_**_INET_, _SOCK_**_**_DGRAM_, _IPPROTO_**_**_ICMP_)

 Datagram oriented ICMP sockets offer a subset of the functionality avail-
 able to raw ICMP sockets. Only IMCP request messages of the following
 types can be sent: ICMP_ECHO, ICMP_TSTAMP or ICMP_MASKREQ.  The code
 field must be the value zero (0).  The minimal length of an ICMP message
 request is eight (8) octets.

 The advantage of using datagram oriented ICMP sockets is that even a non-
 privileged process can use ICMP echo requests to gauge the quality of the
 connectivity to a host, or to receive ICMP destination unreachable mes-
 sage for path MTU discovery, or to receive time exceeded messages for
 traceroute.

 The following IP level option can be used with datagram oriented ICMP
 sockets:

     IP_OPTIONS
     IP_HDRINCL
     IP_TOS
     IP_TTL
     IP_RECVOPTS
     IP_RECVRETOPTS
     IP_RECVDSTADDR
     IP_RETOPTS
     IP_MULTICAST_IF
     IP_MULTICAST_TTL
     IP_MULTICAST_LOOP
     IP_ADD_MEMBERSHIP
     IP_DROP_MEMBERSHIP
     IP_MULTICAST_VIF
     IP_PORTRANGE
     IP_RECVIF
     IP_IPSEC_POLICY
     IP_STRIPHDR

 When the IP option IP_HDRINCL is used, the provided IP header must obey
 the following rules:

     ip_v       Must be IPVERSION (4);
     ip_hl      Between 5 and 10 (inclusive);
     ip_tos     Any value;
     ip_len     Must be the total length of IP datagram (IP header + ICMP
                message);
     ip_id      Must be zero, will be automatically set;
     ip_off     Must be zero, will be automatically set;
     ip_ttl     Any value;
     ip_p       Must be IPPROTO_IP;
     ip_sum     Value ignored, will be automatically set;
     ip_src     Must be an IP address currently assigned to one of the
                local interface or INADDR_ANY;
     ip_dst     Any address;
     ip_opts    Any option.

 The maximum length of a IMCP message that can be sent is controlled by
 the sysctl variable net.inet.raw.maxdgram.

DIAGNOSTICS

 A socket operation may fail with one of the following errors returned:

 [EISCONN]        when trying to establish a connection on a socket which
                  already has one, or when trying to send a datagram with
                  the destination address specified and the socket is
                  already connected;

 [ENOTCONN]       when trying to send a datagram, but no destination
                  address is specified, and the socket hasn't been con-
                  nected;

 [ENOBUFS]        when the system runs out of memory for an internal data
                  structure;

 [EADDRNOTAVAIL]  when an attempt is made to create a socket with a net-
                  work address for which no network interface exists;

 [EINVAL]         when an invalid value is used with IMCP datagram socket
                  for a field of the IP or ICMP header.

HISTORY

 The **icmp** protocol appeared in 4.3BSD.

4.3 Berkeley Distribution June 19, 2002 4.3 Berkeley Distribution