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.\"     @(#)clnp.4	6.3 (Berkeley) 7/31/91
.\"
.Dd July 31, 1991
.Dt CLNP 4
.Os
.Sh NAME
.Nm clnp
.Nd Connectionless-Mode Network Protocol
.Sh SYNOPSIS
.Fd #include <sys/socket.h>
.Fd #include <netiso/iso.h>
.Fd #include <netiso/clnp.h>
.Ft int
.Fn socket AF_ISO SOCK_RAW 0
.Sh DESCRIPTION
.Tn CLNP
is the connectionless-mode network protocol used by the 
connectionless-mode network service. This protocol is specified in
.Tn ISO
8473.
It may be accessed
through a
.Dq raw socket
for debugging purposes only.
.Tn CLNP
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 read 2
or
.Xr recv 2
and 
.Xr write 2
or
.Xr send 2
system calls may be used).
.Pp
Outgoing packets automatically have a
.Tn CLNP
header prepended to
them. Incoming packets received by the user contain the full
.Tn CLNP
header.
The following
.Xr setsockopt
options apply to
.Tn CLNP :
.Bl -tag -width CLNPOPT_FLAGS
.It Dv CLNPOPT_FLAGS
Sets the flags which are passed to clnp when sending a datagram.
Valid flags are:
.Pp
.Bl -tag -width "CLNP_NO_CKSUM" -offset indent -compact
.It Dv CLNP_NO_SEG
Do not allow segmentation
.It Dv CLNP_NO_ER
Suppress ER pdus
.It Dv CLNP_NO_CKSUM
Do not generate the
.Tn CLNP
checksum
.El
.Pp
.It Dv CLNPOPT_OPTS
Sets
.Tn CLNP
options. The options must be formatted exactly as specified by
.Tn ISO
8473, section 7.5
.Dq Options Part.
Once an option has been set, it will
be sent on all packets until a different option is set.
.El
.Sh CONGESTION EXPERIENCE BIT
Whenever a packet is transmitted, the globally unique quality of
service option is added to the packet. The sequencing preferred bit and
the low transit delay bit are set in this option.
.Pp
If a packet is forwarded containing the globally unique quality of
service option, and the interface through which the packet will be 
transmitted has a queue length greater than
.Em congest_threshold ,
then the congestion experienced bit is set in the quality of service option.
.Pp
The threshold value stored in
.Em congest_threshold
may be tuned.
.Pp
When a packet is received with the 
globally unique quality of service option present, and the
congestion experienced bit is set, then the transport congestion
control function is called.
.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 EADDRNOTAVAIL
When an attempt is made to create a 
socket with a network address for which no network interface
exists;
.It Bq Er EHOSTUNREACH
When trying to send a datagram, but no route to the destination
address exists.
.It Bq Er EINVAL
When specifying unsupported options.
.El
.Sh SEE ALSO
.Xr send 2 ,
.Xr recv 2 ,
.Xr intro 4 ,
.Xr iso 4
.Sh HISTORY
The
.Nm
protocol implementation
.Ud
.Sh BUGS
Packets are sent with the type code of 0x1d (technically an invalid
packet type) for lack of a better way to identify raw
.Tn CLNP
packets.
.Pp
No more than
.Dv MLEN
bytes of options can be specified.