# man > ddp(7) [DDP(7)](https://www.chedong.com/phpMan.php/man/DDP/7/markdown) Linux Programmer's Manual [DDP(7)](https://www.chedong.com/phpMan.php/man/DDP/7/markdown) ## NAME ddp - Linux AppleTalk protocol implementation ## SYNOPSIS ### #include ### #include _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)](https://www.chedong.com/phpMan.php/man/socket/7/markdown). An AppleTalk socket is created by calling the [**socket**(2)](https://www.chedong.com/phpMan.php/man/socket/2/markdown) 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)](https://www.chedong.com/phpMan.php/man/bind/2/markdown) 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)](https://www.chedong.com/phpMan.php/man/socket/7/markdown) 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)](https://www.chedong.com/phpMan.php/man/accept/2/markdown). **EHOSTUNREACH** No routing table entry matches the destination address. **EINVAL** Invalid argument passed. **EISCONN** [**connect**(2)](https://www.chedong.com/phpMan.php/man/connect/2/markdown) 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)](https://www.chedong.com/phpMan.php/man/recvmsg/2/markdown), [**sendmsg**(2)](https://www.chedong.com/phpMan.php/man/sendmsg/2/markdown), [**capabilities**(7)](https://www.chedong.com/phpMan.php/man/capabilities/7/markdown), [**socket**(7)](https://www.chedong.com/phpMan.php/man/socket/7/markdown) ## COLOPHON This page is part of release 5.10 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)](https://www.chedong.com/phpMan.php/man/DDP/7/markdown)