ICMP(4) BSD Programmer's Manual ICMP(4)NAMEicmp - 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).
ICMP sockets are connectionless, and are normally used with the sendto
and recvfrom 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) unless IP_HDRINCL option has been specified.
Incoming packets are received with the IP header and options intact.
SYSCTL VARIABLES
Some ICMP options can be read or written via the sysctl(3) facility.
Variables specific to ICMP are:
CTL_NET, PF_INET, IPPROTO_ICMP
These variables are used to get or set various global ICMP options.
Fourth level name Type Changeable
ICMPCTL_MASKREPL integer yes
ICMPCTL_PRINTFS integer yes
ICMPCTL_REDIRACCEPT integer yes
ICMPCTL_REDIRTIMEOUT integer yes
ICMPCTL_STATS struct no
ICMPCTL_MASKREPL
Returns 1 if ICMP network mask requests are to be answered.
ICMPCTL_PRINTFS
Returns 1 if certain ICMP debugging statements are enabled if the
kernel is compiled with this facility enabled.
ICMPCTL_REDIRACCEPT
Returns 1 when ICMP redirects are allowed to update the routing
table. ICMP redirects are normally enabled on hosts and disabled
on routers that use a dynamic routing protocol.
ICMPCTL_REDIRTIMEOUT
Returns the length of time in seconds before routing table en-
tries created by ICMP redirects are removed.
ICMPCTL_STATS
Returns the struct icmpstat structure containing statistics on
the processing of ICMP packets.
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 al-
ready connected;
[ENOTCONN] when trying to send a datagram, but no destination ad-
dress is specified, and the socket hasn't been connect-
ed;
[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.
SEE ALSOsend(2), recv(2), sysctl(3), intro(4), inet(4), ip(4)HISTORY
The icmp protocol appeared in 4.3BSD.
4.3 Berkeley Distribution June 5, 1993 2
