ICMP(4) MidnightBSD Kernel Interfaces Manual 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 parameter to the socket call to create an ICMP socket is obtained from getprotobyname(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 instead 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 packets/second. Used when icmplim_output is non-zero. Defaults to 200.

icmplim_output

(boolean) Enable/disable bandwidth limiting 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 specified 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 socket with a network address for which no network interface exists.

SEE ALSO

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

HISTORY

The icmp protocol appeared in 4.3BSD.

MidnightBSD 0.3 March 21, 2003 MidnightBSD 0.3