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       ddp - Linux AppleTalk protocol implementation


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

       ddp_socket = socket(AF_APPLETALK, SOCK_DGRAM, 0);
       raw_socket = socket(AF_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 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 specify 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  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

   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

              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.


       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

              Tried to bind to an address already in use.

              A nonexistent interface was requested or  the  requested  source  address  was  not

       EAGAIN Operation on a nonblocking socket would block.

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

              A connection was closed during an accept(2).

              No routing table entry matches the destination address.

       EINVAL Invalid argument passed.

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

              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.

              Not enough memory available.

       ENOPKG A kernel subsystem was not configured.

              Invalid socket option passed.

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

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

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

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


       Appletalk  is  supported  by  Linux 2.0 or higher.  The /proc interfaces exist since Linux


       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.

       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.


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


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