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DDP(7)                     Linux Programmer's ManualDDP(7)NAME       ddp - Linux AppleTalk protocol implementationSYNOPSIS       #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  de-       signed to be used via the netatalk protocol libraries.  This page docu-       ments the interface for those who wish or need to use the DDP layer di-       rectly.       The  communication between AppleTalk and the user program works using a       BSD-compatible socket interface.  For more information on sockets,  seesocket(7).       An AppleTalk socket is created by calling thesocket(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 spec-       ify 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 maybind(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.   /proc interfaces       IP  supports  a  set  of  /proc interfaces to configure some global Ap-       pleTalk parameters.  The parameters can be accessed by reading or writ-       ing files in the directory /proc/sys/net/atalk/.       aarp-expiry-time              The  time  interval  (in seconds) before an AARP cache entry ex-              pires.       aarp-resolve-time              The time interval (in seconds) before an AARP cache entry is re-              solved.       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 insocket(7) apply to DDP.ERRORS       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 re-              served 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 anaccept(2).       EHOSTUNREACH              No routing table entry matches the destination address.       EINVAL Invalid argument passed.       EISCONNconnect(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 con-              figuration 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  re-              quested.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 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 ALSOrecvmsg(2),sendmsg(2),capabilities(7),socket(7)COLOPHON       This page is part of release 5.05 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       https://www.kernel.org/doc/man-pages/.Linux                             2017-09-15DDP(7)