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 infor-
       mation 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 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  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 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 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 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2008-11-20                                                     DDP(7)