Technical data

icmp(7P) Protocols SunOS 5.5

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 Transport Level Interface (TLI) for

network monitoring and diagnostic 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(3N). 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 including routing, fault isolation, and congestion control. Receipt of

an ICMP “redirect” message will add a new entry in the routing table, or modify an exist-

ing one. ICMP messages are routinely sent by the protocol code. Received ICMP mes-

sages 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 pro-

vided to every holder of an openICMP socket or TLI descriptor.

SEE ALSO getprotobyname(3N), recv(3N), send(3N), t_rcvudata(3N), t_sndudata(3N), routing(4),

inet(7P), ip(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 desti-

nation address speciﬁed and the socket is already connected.

ENOTCONN An attempt was made to send a datagram, but no destination

address is speciﬁed, and the socket has not been connected.

7P-128 modiﬁed 3 Jul 1990