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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-compati-
       ble 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 only opened 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 address.

   Socket Options
       No protocol-specific socket options are supported.

   /proc interfaces
       IP  supports  a  set of /proc interfaces to configure some global AppleTalk parame-
       ters.  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 without having the broadcast
              flag set, and trying to bind to a reserved port without effective user ID  0
              or CAP_NET_BIND_SERVICE.

       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 non-blocking socket would block.

       EALREADY
              A connection operation on a non-blocking 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 only defined on a connected socket, but the  socket  wasn't
              connected.

       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.

       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  alternative  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 3.22 of the Linux man-pages project.  A description of
       the  project, and information about reporting bugs, can be found at http://www.ker-
       nel.org/doc/man-pages/.



Linux                             2008-11-20                            DDP(7)

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