+.\" Copyright (c) 1985 Regents of the University of California.
+.\" All rights reserved. The Berkeley software License Agreement
+.\" specifies the terms and conditions for redistribution.
+.\"
+.\" @(#)idp.4 1.1 (Berkeley) %G%
+.\"
+.TH IDP 4P "July 30, 1985"
+.UC 6
+.SH NAME
+idp \- Xerox Internet Datagram Protocol
+.SH SYNOPSIS
+.B #include <sys/socket.h>
+.br
+.B #include <netns/ns.h>
+.br
+.B #include <netns/idp.h>
+.PP
+.B s = socket(AF_NS, SOCK_DGRAM, 0);
+.SH DESCRIPTION
+IDP is a simple, unreliable datagram protocol which is used
+to support the SOCK_DGRAM abstraction for the Internet
+protocol family. IDP sockets are connectionless, and are
+normally used with the
+.I sendto
+and
+.IR recvfrom
+calls, though the
+.IR connect (2)
+call may also be used to fix the destination for future
+packets (in which case the
+.IR recv (2)
+or
+.IR read (2)
+and
+.IR send (2)
+or
+.IR write(2)
+system calls may be used).
+.PP
+Xerox protocols are built vertically on top of IDP.
+Thus, IDP address formats are identical to those used by
+SPP.
+Note that the IDP port
+space is the same as the SPP port space (i.e. a IDP port
+may be \*(lqconnected\*(rq to a SPP port, with certain
+options enabled below).
+In addition broadcast packets may be sent
+(assuming the underlying network supports
+this) by using a reserved \*(lqbroadcast address\*(rq; this address
+is network interface dependent.
+.SH DIAGNOSTICS
+A socket operation may fail with one of the following errors returned:
+.TP 15
+[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;
+.TP 15
+[ENOTCONN]
+when trying to send a datagram, but
+no destination address is specified, and the socket hasn't been
+connected;
+.TP 15
+[ENOBUFS]
+when the system runs out of memory for
+an internal data structure;
+.TP 15
+[EADDRINUSE]
+when an attempt
+is made to create a socket with a port which has already been
+allocated;
+.TP 15
+[EADDRNOTAVAIL]
+when an attempt is made to create a
+socket with a network address for which no network interface
+exists.
+.SH SOCKET OPTIONS
+.TP 15
+[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 IDP packet,
+as described by
+.nf
+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;
+};
+.fi
+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,
+(NSP_RAWIN or 0).
+.TP 15
+[SO_HEADERS_ON_OUTPUT]
+When set, the first 30 bytes of any data sent
+will be the initial 30 bytes of the 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.
+(NSP_RAWOUT or 0).
+.TP 15
+[SO_DEFAULT_HEADERS]
+The user provides the kernel an IDP header, from which
+it gleans the Packet Type.
+When requested, the kernel will provide an IDP header, showing
+the default packet type, and local and foreign addresses, if
+connected.
+.TP 15
+[SO_ALL_PACKETS]
+When set, this option defeats automatic processing of Error packets,
+and Sequence Protocol packets.
+.TP 15
+[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.
+.SH SEE ALSO
+send(2),
+recv(2),
+intro(4N),
+ns(4F)
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