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(PF_APPLETALK, SOCK_DGRAM, 0);
       raw_socket = socket(PF_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 doc-
       uments 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
       PF_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  spec-
       ify 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 {
                  u_short         s_net;
                  u_char          s_node;
              };

              struct sockaddr_atalk {
                  sa_family_t     sat_family; /* address family */
                  u_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  mem-
       ber  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.

SYSCTLS
       IP  supports  a  sysctl  interface  to  configure some global AppleTalk
       parameters.  The sysctls can be accessed  by  reading  or  writing  the
       /proc/sys/net/atalk/* files or with the sysctl(2) interface.

       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.

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.

VERSIONS
       Appletalk  is supported by Linux 2.0 or higher. The sysctl interface is
       new in Linux 2.2.

ERRORS
       ENOTCONN
              The operation is only defined on a  connected  socket,  but  the
              socket wasn't connected.

       EINVAL Invalid argument passed.

       EMSGSIZE
              Datagram is bigger than the DDP MTU.

       EACCES The  user  tried  to  execute an operation without the necessary
              permissions.  These include sending to a broadcast address with-
              out  having  the  broadcast  flag  set,  and trying to bind to a
              reserved port without effective user ID 0  or  CAP_NET_BIND_SER-
              VICE.

       EADDRINUSE
              Tried to bind to an address already in use.

       ENOMEM and ENOBUFS
              Not enough memory available.

       ENOPROTOOPT and EOPNOTSUPP
              Invalid socket option passed.

       EPERM  User  doesn't  have permission to set high priority, make a con-
              figuration change, or send signals to the requested  process  or
              group,

       EADDRNOTAVAIL
              A  non-existent  interface was requested or the requested source
              address was not local.

       EAGAIN Operation on a nonblocking socket would block.

       ESOCKTNOSUPPORT
              The socket was unconfigured,  or  an  unknown  socket  type  was
              requested.

       EISCONN
              connect(2) was called on an already connected socket.

       EALREADY
              A  connection  operation  on a non-blocking socket is already in
              progress.

       ECONNABORTED
              A connection was closed during an accept(2).

       EPIPE  The connection was unexpectedly closed or shut down by the other
              end.

       ENOENT SIOCGSTAMP was called on a socket where no packet arrived.

       EHOSTUNREACH
              No routing table entry matches the destination address.

       ENODEV Network device not available or not capable of sending IP.

       ENOPKG A kernel subsystem was not configured.

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 alter-
       native 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 Page                    1999-05-01                            DDP(7)