man > ddp(7)

ddp(7)                            Miscellaneous Information 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 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 be‐
       low 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  im‐
       plies “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 pa‐
       rameters 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 in‐
              clude 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 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.

       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)

Linux man-pages 6.7                          2023-10-31                                       ddp(7)