.\"	$NetBSD: imp.4,v 1.3 1994/11/30 16:22:16 jtc Exp $
.\"
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.\"     @(#)imp.4	6.5 (Berkeley) 3/28/91
.\"
.Dd March 28, 1991
.Dt IMP 4
.Os BSD 4.2
.Sh NAME
.Nm imp
.Nd
.Tn IMP
raw socket interface
.Sh SYNOPSIS
.Fd #include <sys/socket.h>
.Fd #include <netinet/in.h>
.Fd #include <netimp/if_imp.h>
.Ft int
.Fn socket AF_IMPLINK SOCK_RAW proto
.Sh DESCRIPTION
The raw imp socket provides direct access to the
.Nm imp
network interface.  Users send packets through
the interface using the 
.Xr send 2
calls, and receive packets with the
.Xr recv 2 ,
calls.  All outgoing packets must have an 1822 96-bit
leader on the front.  Likewise, packets received
by the user will have this leader on the front.  The
1822 leader and the legal values for the various fields
are defined in the include file
.Aq Pa netimp/if_imp.h .
The raw imp interface automatically installs the length
and destination address in the 1822 leader of all
outgoing packets; these need not be filled in by the user.
.Pp
If the protocol selected,
.Fa proto ,
is zero,
the socket will receive
all
.Tn IMP
messages except RFNM and incompletes
which are not input data for a kernel protocol.
If
.Fa proto
is non-zero,
only messages for the specified link type will be received.
.Sh DIAGNOSTICS
An operation on a socket may fail with one of the following
errors:
.Bl -tag -width [EADDRNOTAVAIL]
.It Bq Er 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;
.It Bq Er ENOTCONN
when trying to send a datagram, but
no destination address is specified, and the socket hasn't been
connected;
.It Bq Er ENOBUFS
when the system runs out of memory for
an internal data structure;
.It Bq Er ENOBUFS
eight messages to the destination host are outstanding,
and another eight are already queued for output;
.It Bq Er EADDRNOTAVAIL
when an attempt is made to create a 
socket with a network address for which no network interface
exists.
.El
.Sh SEE ALSO
.Xr netintro 4 ,
.Xr inet 4 ,
.Xr imp 4
.Sh HISTORY
The
.Nm
driver appeared in
.Bx 4.2 .