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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
       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
       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
       specify 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
       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.

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
              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.

       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
              configuration 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
       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)