ddp(7) — Linux manual page


DDP(7)                    Linux Programmer's 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 ad‐
       dress.  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 broad‐
       cast address.

   Socket options
       No protocol-specific socket options are supported.

   /proc interfaces
       IP supports a set of /proc interfaces to configure some global Ap‐
       pleTalk 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 ex‐

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

              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

              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

              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

       The raw socket mode is unique to Linux and exists to support the
       alternative CAP package and AppleTalk monitoring tools more easily.

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 release 5.09 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

Linux                            2017-09-15                           DDP(7)

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