ddp(7) — Linux manual page


ddp(7)              Miscellaneous Information Manual              ddp(7)

NAME         top

       ddp - Linux AppleTalk protocol implementation

SYNOPSIS         top

       #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         top

       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 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/.

              The time interval (in seconds) before an AARP cache entry

              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.

ERRORS         top

       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.

              Tried to bind to an address already in use.

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

       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 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.

              The socket was unconfigured, or an unknown socket type was

VERSIONS         top

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

NOTES         top

       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

BUGS         top

       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         top

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

COLOPHON         top

       This page is part of the man-pages (Linux kernel and C library
       user-space interface documentation) project.  Information about
       the project can be found at 
       ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report
       for this manual page, see
       This page was obtained from the tarball man-pages-6.9.1.tar.gz
       fetched from
       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
       2024-06-26.  If you discover any rendering problems in this HTML
       version of the page, or you believe there is a better or more up-
       to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to

Linux man-pages 6.9.1          2024-05-02                         ddp(7)

Pages that refer to this page: bind(2)socket(2)address_families(7)socket(7)