ICMP(7P)
NAME
icmp, ICMP - Internet Control Message Protocol
SYNOPSIS
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip_icmp.h>
s = socket(AF_INET, SOCK_RAW, proto);
t = t_open("/dev/icmp", O_RDWR);
DESCRIPTION
ICMP is the error and control message protocol used by the
Internet protocol family. It is used by the kernel to handle
and report errors in protocol processing. It may also be
accessed by programs using the socket interface or the Tran-
sport Level Interface (TLI) for network monitoring and diag-
nostic functions. When used with the socket interface, a
"raw socket" type is used. The protocol number for ICMP,
used in the proto parameter to the socket call, can be
obtained from getprotobyname(3SOCKET). ICMP file descriptors
and sockets are connectionless, and are normally used with
the t_sndudata / t_rcvudata and the sendto() / recvfrom()
calls.
Outgoing packets automatically have an Internet Protocol
(IP) header prepended to them. Incoming packets are provided
to the user with the IP header and options intact.
ICMP is an datagram protocol layered above IP. It is used
internally by the protcol code for various purposes includ-
ing routing, fault isolation, and congestion control.
Receipt of an ICMP "redirect" message will add a new entry
in the routing table, or modify an existing one. ICMP mes-
sages are routinely sent by the protocol code. Received
ICMP messages may be reflected back to users of higher-level
protocols such as TCP or UDP as error returns from system
calls. A copy of all ICMP message received by the system is
provided to every holder of an open ICMP socket or TLI
descriptor.
SEE ALSO
getprotobyname(3SOCKET), recv(3SOCKET), send(3SOCKET),
t_rcvudata(3NSL), t_sndudata(3NSL), inet(7P), ip(7P),
routing(7P)
Postel, Jon, Internet Control Message Protocol - DARPA
Internet Program Protocol Specification, RFC 792, Network
Information Center, SRI International, Menlo Park, Calif.,
September 1981.
DIAGNOSTICS
A socket operation may fail with one of the following errors
returned:
EISCONN
An attempt was made 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
An attempt was made to send a datagram, but no desti-
nation address is specified, and the socket has not
been connected.
ENOBUFS
The system ran out of memory for an internal data
structure.
EADDRNOTAVAIL
An attempt was made to create a socket with a network
address for which no network interface exists.
NOTES
Replies to ICMP "echo" messages which are source routed are
not sent back using inverted source routes, but rather go
back through the normal routing mechanisms.
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