icmp.4p

<B>Digital的Unix操作系统VAX 4.2源码</B>

.TH icmp 4p
.SH Name
icmp \- Internet Control Message Protocol
.SH Syntax
.B #include <sys/socket.h>
.br
.B #include <netinet/in.h>
.PP
.B s = socket(AF_INET, SOCK_RAW, \fIproto\fP);
.SH Description
The ICMP is the error and control message protocol used
.NXR "ICMP error and control message protocol"
.NXS "network protocol" "ICMP error and control message protocol"
.NXA "IP protocol family" ICMP error and Control message protocol"
by
the Internet Protocol (IP) transport layer
and the Internet protocol family.  It can be accessed
through a ``raw socket'' for network monitoring
and diagnostic functions.
The
.I proto
argument to the socket call to create an ICMP socket
is obtained from the
.MS getprotobyname 3n
routine.
ICMP sockets are connectionless,
and are normally used with the
.MS sendto 2
and
.MS recvfrom 2
system calls.  The
.MS connect 2
call can also be used to fix the destination for future
packets (in which case the 
.MS read 2
or
.MS recv 2
and 
.MS write 2
or
.MS send 2
system calls can then be used).
.PP
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.
.SH Diagnostics
On failure, a socket operation returns any of the following errors:
.TP 15
[EISCONN]
Tried to establish a connection on a socket that
already has one, or tried to send a datagram with the destination
address specified and the socket was already connected.
.TP 15
[ENOTCONN]
Tried to send a datagram, but
no destination address was specified, and the socket has not
connected.
.TP 15
[ENOBUFS]
The system ran out of memory for
an internal data structure.
.TP 15
[EADDRNOTAVAIL]
An attempt was made to create a 
socket with a network address for which no network interface
exists.
.SH See Also
inet(4f), intro(4n), ip(4p)