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DDP(7)				    Linux Programmer's Manual				   DDP(7)

       ddp - Linux AppleTalk protocol implementation

       #include <sys/socket.h>
       #include <netatalk/at.h>

       ddp_socket = socket(PF_APPLETALK, SOCK_DGRAM, 0);
       raw_socket = socket(PF_APPLETALK, SOCK_RAW, protocol);

       Linux  implements  the  Appletalk  protocols  described in Inside Appletalk.  Only the DDP
       layer and AARP are present in the kernel. They are designed to be used  via  the  netatalk
       protocol  libraries.  This  page documents the interface for those who wish or need to use
       the DDP layer directly.

       The communication between Appletalk and the user  program  works  using	a  BSD-compatible
       socket interface. For more information on sockets, see socket(7).

       An  AppleTalk  socket  is  created  by  calling the socket(2) function with a PF_APPLETALK
       socket family argument. Valid socket types are SOCK_DGRAM to open a ddp socket or SOCK_RAW
       to  open  a  raw  socket.   protocol is the Appletalk protocol to be received or sent. For
       SOCK_RAW you must specify ATPROTO_DDP.

       Raw sockets may be only opened by a process with effective user id 0 or when  the  process
       has the CAP_NET_RAW capability.

       An  Appletalk  socket address is defined as a combination of a network number, a node num-
       ber, and a port number.

	      struct at_addr {
		  u_short	  s_net;
		  u_char	  s_node;

	      struct sockaddr_atalk {
		  sa_family_t	  sat_family; /* address family */
		  u_char	  sat_port;   /* port */
		  struct at_addr  sat_addr;   /* net/node */

       sat_family is always set to AF_APPLETALK.  sat_port contains the port.  The  port  numbers
       below 129 are known as reserved ports.  Only processes with the effective user id 0 or the
       CAP_NET_BIND_SERVICE capability may bind(2)  to	these  sockets.   sat_addr  is	the  host
       address.   The  net  member  of	struct	at_addr contains the host network in network byte
       order.  The value of AT_ANYNET is a wildcard and also implies "this  network."	The  node
       member  of  struct  at_addr  contains  the host node number.  The value of AT_ANYNODE is a
       wildcard and also implies "this node." The value of ATADDR_BCAST is a link local broadcast

       No protocol-specific socket options are supported.

       IP supports a sysctl interface to configure some global AppleTalk parameters.  The sysctls
       can be accessed by  reading  or	writing  the  /proc/sys/net/atalk/*  files  or	with  the
       sysctl(2) interface.

	      The time interval (in seconds) before an AARP cache entry expires.

	      The time interval (in seconds) before an AARP cache entry is resolved.

	      The number of retransmissions of an AARP query before the node is declared dead.

	      The timer rate (in seconds) for the timer driving AARP.

       The default values match the specification and should never need to be changed.

       All ioctls described in socket(7) apply to ddp.

       Be  very  careful with the SO_BROADCAST option - it is not privileged in Linux. It is easy
       to overload the network with careless sending to broadcast addresses.

       Appletalk is supported by Linux 2.0 or higher. The sysctl interface is new in Linux 2.2.

	      The operation is only defined on a connected socket, but	the  socket  wasn't  con-

       EINVAL Invalid argument passed.

	      Datagram is bigger than the DDP MTU.

       EACCES The  user  tried	to  execute an operation without the necessary permissions. These
	      include sending to a broadcast address without having the broadcast flag	set,  and
	      trying  to bind to a reserved port without effective user id 0 or CAP_NET_BIND_SER-

	      Tried to bind to an address already in use.

	      Not enough memory available.

	      Invalid socket option passed.

       EPERM  User doesn't have permission to set high priority, make a configuration change,  or
	      send signals to the requested process or group,

	      A  non-existent  interface  was  requested  or the requested source address was not

       EAGAIN Operation on a nonblocking socket would block.

	      The socket was unconfigured, or an unknown socket type was requested.

	      connect(2) was called on an already connected socket.

	      A connection operation on a non-blocking socket is already in progress.

	      A connection was closed during an accept(2).

       EPIPE  The connection was unexpectedly closed or shut down by the other end.

       ENOENT SIOCGSTAMP was called on a socket where no packet arrived.

	      No routing table entry matches the destination address.

       ENODEV Network device not available or not capable of sending IP.

       ENOPKG A kernel subsystem was not configured.

       The basic AppleTalk socket interface is compatible with netatalk on  BSD-derived  systems.
       Many  BSD  systems fail to check SO_BROADCAST when sending broadcast frames; this can lead
       to compatibility problems.

       The raw socket mode is unique to Linux and exists to support the alternative  CAP  package
       and AppleTalk monitoring tools more easily.

       There are too many inconsistent error values.

       The  ioctls  used  to configure routing tables, devices, AARP tables and other devices are
       not yet described.

       sendmsg(2), recvmsg(2), socket(7)

Linux Man Page				    1999-05-01					   DDP(7)
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