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.\"     @(#)idp.4	1.4 (Berkeley) 3/28/91
.\"
.Dd March 28, 1991
.Dt IDP 4
.Os BSD 4.3
.Sh NAME
.Nm idp
.Nd Xerox Internet Datagram Protocol
.Sh SYNOPSIS
.Fd #include <sys/socket.h>
.Fd #include <netns/ns.h>
.Fd #include <netns/idp.h>
.Ft int
.Fn socket AF_NS SOCK_DGRAM 0
.Sh DESCRIPTION
.Tn IDP
is a simple, unreliable datagram protocol which is used
to support the
.Dv SOCK_DGRAM
abstraction for the Internet
protocol family.
.Tn IDP
sockets are connectionless, and are
normally used with the
.Xr sendto
and
.Xr recvfrom
calls, though the
.Xr connect 2
call may also be used to fix the destination for future
packets (in which case the 
.Xr recv 2
or
.Xr read 2
and 
.Xr send 2
or
.Xr write 2
system calls may be used).
.Pp
Xerox protocols are built vertically on top of
.Tn IDP .
Thus,
.Tn IDP
address formats are identical to those used by
.Tn SPP .
Note that the
.Tn IDP
port
space is the same as the
.Tn SPP
port space (i.e. a
.Tn IDP
port
may be
.Dq connected
to a
.Tn SPP
port, with certain
options enabled below).
In addition broadcast packets may be sent
(assuming the underlying network supports
this) by using a reserved
.Dq broadcast address ;
this address
is network interface dependent.
.Sh DIAGNOSTICS
A socket operation may fail with one of the following errors returned:
.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 EADDRINUSE
when an attempt
is made to create a socket with a port which has already been
allocated;
.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 SOCKET OPTIONS
.Bl -tag -width [SO_HEADERS_ON_OUTPUT]
.It Bq Dv SO_ALL_PACKETS
When set, this option defeats automatic processing of Error packets,
and Sequence Protocol packets.
.It Bq Dv SO_DEFAULT_HEADERS
The user provides the kernel an
.Tn IDP
header, from which
it gleans the Packet Type.
When requested, the kernel will provide an
.Tn IDP
header, showing
the default packet type, and local and foreign addresses, if
connected.
.It Bq Dv SO_HEADERS_ON_INPUT
When set, the first 30 bytes of any data returned from a read
or recv from will be the initial 30 bytes of the
.Tn IDP
packet,
as described by
.Bd -literal -offset indent
struct idp {
	u_short		idp_sum;
	u_short		idp_len;
	u_char		idp_tc;
	u_char		idp_pt;
	struct ns_addr	idp_dna;
	struct ns_addr	idp_sna;
};
.Ed
.Pp
This allows the user to determine the packet type, and whether
the packet was a multi-cast packet or directed specifically at
the local host.
When requested, gives the current state of the option,
.Pf ( Dv NSP_RAWIN
or 0).
.It Bq Dv SO_HEADERS_ON_OUTPUT
When set, the first 30 bytes of any data sent
will be the initial 30 bytes of the
.Tn IDP
packet.
This allows the user to determine the packet type, and whether
the packet should be multi-cast packet or directed specifically at
the local host.
You can also misrepresent the sender of the packet.
When requested, gives the current state of the option.
.Pf ( Dv NSP_RAWOUT
or 0).
.It Bq Dv SO_SEQNO
When requested, this returns a sequence number which is not likely
to be repeated until the machine crashes or a very long time has passed.
It is useful in constructing Packet Exchange Protocol packets.
.El
.Sh SEE ALSO
.Xr send 2 ,
.Xr recv 2 ,
.Xr intro 4 ,
.Xr ns 4
.Sh HISTORY
The
.Nm
protocol appeared in
.Bx 4.3 .