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



NAME
       ddp - Linux AppleTalk protocol implementation

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

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

DESCRIPTION
       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
       AF_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 spec-
       ify ATPROTO_DDP.

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

   Address format
       An AppleTalk socket address is defined as a combination	of  a  network
       number, a node number, and a port number.

	   struct at_addr {
	       unsigned short s_net;
	       unsigned char  s_node;
	   };

	   struct sockaddr_atalk {
	       sa_family_t    sat_family;    /* address family */
	       unsigned 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  mem-
       ber  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 address.

   Socket options
       No protocol-specific socket options are supported.

   /proc interfaces
       IP  supports  a	set  of	 /proc	interfaces  to	configure  some global
       AppleTalk parameters.  The parameters can be  accessed  by  reading  or
       writing files in the directory /proc/sys/net/atalk/.

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

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

       aarp-retransmit-limit
	      The  number  of retransmissions of an AARP query before the node
	      is declared dead.

       aarp-tick-time
	      The timer rate (in seconds) for the timer driving AARP.

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

   Ioctls
       All ioctls described in socket(7) apply to DDP.

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

       EADDRINUSE
	      Tried to bind to an address already in use.

       EADDRNOTAVAIL
	      A	 nonexistent  interface	 was requested or the requested source
	      address was not local.

       EAGAIN Operation on a nonblocking socket would block.

       EALREADY
	      A connection operation on a nonblocking  socket  is  already  in
	      progress.

       ECONNABORTED
	      A connection was closed during an accept(2).

       EHOSTUNREACH
	      No routing table entry matches the destination address.

       EINVAL Invalid argument passed.

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

       EMSGSIZE
	      Datagram is bigger than the DDP MTU.

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

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

       ENOMEM and ENOBUFS
	      Not enough memory available.

       ENOPKG A kernel subsystem was not configured.

       ENOPROTOOPT and EOPNOTSUPP
	      Invalid socket option passed.

       ENOTCONN
	      The  operation  is  defined  only on a connected socket, but the
	      socket wasn't connected.

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

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

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

VERSIONS
       AppleTalk is supported by Linux 2.0 or higher.	The  /proc  interfaces
       exist since Linux 2.2.

NOTES
       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.

   Compatibility
       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 alter-
       native CAP package and AppleTalk monitoring tools more easily.

BUGS
       There are too many inconsistent error values.

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

SEE ALSO
       recvmsg(2), sendmsg(2), capabilities(7), socket(7)

COLOPHON
       This  page  is  part of release 4.10 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest	  version     of     this    page,    can    be	   found    at
       https://www.kernel.org/doc/man-pages/.



Linux				  2016-12-12				DDP(7)