icmp(4)

NAME

icmp - Internet Control Message Protocol

SYNOPSIS

#include <sys/types.h>
#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 Internet protocol family. It may be accessed through a ``raw

socket'' for
network monitoring and diagnostic functions. The proto pa

rameter to the
socket call to create an ICMP socket is obtained from get

protobyname(3).
ICMP 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 the

read(2) or recv(2)
and write(2) or send(2) 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.

MIB Variables

The ICMP protocol implements a number of variables in the

net.inet.icmp
branch of the sysctl(3) MIB.

maskrepl (boolean) Enable/disable replies to ICMP

Address Mask

Request packets. Defaults to false.

maskfake (unsigned integer) When maskrepl is set

and this

value is non-zero, it will be used in

stead of the
real address mask when the system

replies to an ICMP
Address Mask Request packet. Defaults

to 0.

icmplim (integer) Bandwidth limit for ICMP

replies in pack

ets/second. Used when icmplim_output is

non-zero.
Defaults to 200.

icmplim_output (boolean) Enable/disable bandwidth lim

iting of ICMP

replies. Defaults to true.

drop_redirect (boolean) Enable/disable dropping of

ICMP Redirect

packets. Defaults to false.

log_redirect (boolean) Enable/disable logging of ICMP

Redirect

packets. Defaults to false.

bmcastecho (boolean) Enable/disable ICMP replies

received via

broadcast or multicast. Defaults to

false.

reply_src (str) An interface name used for the

ICMP reply

source in response to packets which are

not directly
addressed to us. By default continue

with normal
source selection.

ERRORS

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 speci

fied and the
socket is already connected;

[ENOTCONN] when trying to send a datagram, but no

destination

address is specified, and the socket has

not been connected;

[ENOBUFS] when the system runs out of memory for an

internal

data structure;

[EADDRNOTAVAIL] when an attempt is made to create a sock

et with a net

work address for which no network inter

face exists.

SEE ALSO

recv(2), send(2), inet(4), intro(4), ip(4)

HISTORY

The icmp protocol appeared in 4.3BSD.

BSD March 21, 2003

BSD