DDP(7)                    (2017-09-15)                     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 pro-
          tocol 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 capabil-
          ity.

        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

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          CAP_NET_BIND_SERVICE capability may bind(2) to these sock-
          ets.  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 lqthis network.rq The node member of struct at_addr
          contains the host node number.  The value of AT_ANYNODE is a
          wildcard and also implies lqthis node.rq 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 glo-
          bal 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 nec-
               essary permissions.  These include sending to a broad-
               cast 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

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               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 configuration change, or send signals to the
               requested process or group.

          EPIPE
               The connection was unexpectedly closed or shut down by

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               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 5.10 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/.

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