April 2, 1994 CLNP 4

### NAME

clnp - Connectionless-Mode Network Protocol

### SYNOPSIS

```int` socket(```AF_ISO``, SOCK_RAW``, 0`)

### DESCRIPTION

CLNP is the connectionless-mode network protocol used by the connectionless-mode network service. This protocol is specified in ISO 8473. It may be accessed through a ``raw socket'' for debugging purposes only. CLNP sockets are connectionless, and are normally used with the sendto(2) and recvfrom(2) system calls, though the connect(2) call may also be used to fix the destination for future packets (in which case the read(2) or recv(2) and write(2) or send(2) system calls may be used).

Outgoing packets automatically have a CLNP header prepended to them. Incoming packets received by the user contain the full CLNP header. The following setsockopt(2) options apply to CLNP:

```CLNPOPT_FLAGS`
  Sets the flags which are passed to clnp when sending a datagram. Valid flags are:

  ```CLNP_NO_SEG`
    Do not allow segmentation
  ```CLNP_NO_ER`
    Suppress ER pdus
  ```CLNP_NO_CKSUM`
    Do not generate the CLNP checksum

```CLNPOPT_OPTS`
  Sets CLNP options. The options must be formatted exactly as specified by ISO 8473, section 7.5 ``Options Part''. Once an option has been set, it will be sent on all packets until a different option is set.

### 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.

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 congest_threshold, then the congestion experienced bit is set in the quality of service option.

The threshold value stored in congest_threshold may be tuned.

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.

### DIAGNOSTICS

A socket operation may fail with one of the following errors returned:

[```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;

[```ENOTCONN`]
  When trying to send a datagram, but no destination address is specified, and the socket hasn't been connected;

[```ENOBUFS`]
  When the system runs out of memory for an internal data structure;

[```EADDRNOTAVAIL`]
  When an attempt is made to create a socket with a network address for which no network interface exists;

[```EHOSTUNREACH`]
  When trying to send a datagram, but no route to the destination address exists.

[```EINVAL`]
  When specifying unsupported options.

### SEE ALSO

recv(2), send(2), intro(4), iso(4)

### BUGS

Packets are sent with the type code of 0x1d (technically an invalid packet type) for lack of a better way to identify raw CLNP packets.

No more than ```MLEN` bytes of options can be specified.