.\" This man page is Copyright (C) 1998 Alan Cox.

.\"

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.\" $Id: ddp.7,v 1.3 1999/05/13 11:33:22 freitag Exp $

.\"

.TH DDP  7 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

ddp \- Linux AppleTalk protocol implementation

.SH SYNOPSIS

.B #include <sys/socket.h>

.br

.B #include <netatalk/at.h>

.PP

.IB ddp_socket " = socket(AF_APPLETALK, SOCK_DGRAM, 0);"

.br

.IB raw_socket " = socket(AF_APPLETALK, SOCK_RAW, " protocol ");"

.SH DESCRIPTION

Linux implements the AppleTalk protocols described in

.IR "Inside AppleTalk" .

Only the DDP layer and AARP are present in

the kernel.

They are designed to be used via the

.B netatalk

protocol

libraries.

This page documents the interface for those who wish or need to

use the DDP layer directly.

.PP

The communication between AppleTalk and the user program works using a

BSD-compatible socket interface.

For more information on sockets, see

.BR socket (7).

.PP

An AppleTalk socket is created by calling the

.BR socket (2)

function with a

.B AF_APPLETALK

socket family argument.

Valid socket types are

.B SOCK_DGRAM

to open a

.B ddp

socket or

.B SOCK_RAW

to open a

.B raw

socket.

.I protocol

is the AppleTalk protocol to be received or sent.

For

.B SOCK_RAW

you must specify

.BR ATPROTO_DDP .

.PP

Raw sockets may be opened only by a process with effective user ID 0

or when the process has the

.B CAP_NET_RAW

capability.

.SS Address format

An AppleTalk socket address is defined as a combination of a network number,

a node number, and a port number.

.PP

.in +4n

.EX

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 */

};

.EE

.in

.PP

.I sat_family

is always set to

.BR AF_APPLETALK .

.I sat_port

contains the port.

The port numbers below 129 are known as

.IR "reserved ports" .

Only processes with the effective user ID 0 or the

.B CAP_NET_BIND_SERVICE

capability may

.BR bind (2)

to these sockets.

.I sat_addr

is the host address.

The

.I net

member of

.I struct at_addr

contains the host network in network byte order.

The value of

.B AT_ANYNET

is a

wildcard and also implies \(lqthis network.\(rq

The

.I node

member of

.I struct at_addr

contains the host node number.

The value of

.B AT_ANYNODE

is a

wildcard and also implies \(lqthis node.\(rq The value of

.B ATADDR_BCAST

is a link

local broadcast address.

.\" FIXME . this doesn't make sense [johnl]

.SS Socket options

No protocol-specific socket options are supported.

.SS /proc interfaces

IP supports a set of

.I /proc

interfaces to configure some global AppleTalk parameters.

The parameters can be accessed by reading or writing files in the directory

.IR /proc/sys/net/atalk/ .

.TP

.I aarp-expiry-time

The time interval (in seconds) before an AARP cache entry expires.

.TP

.I aarp-resolve-time

The time interval (in seconds) before an AARP cache entry is resolved.

.TP

.I aarp-retransmit-limit

The number of retransmissions of an AARP query before the node is declared

dead.

.TP

.I aarp-tick-time

The timer rate (in seconds) for the timer driving AARP.

.PP

The default values match the specification and should never need to be

changed.

.SS Ioctls

All ioctls described in

.BR socket (7)

apply to DDP.

.\" FIXME . Add a section about multicasting

.SH ERRORS

.TP

.B 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

.BR CAP_NET_BIND_SERVICE .

.TP

.B EADDRINUSE

Tried to bind to an address already in use.

.TP

.B EADDRNOTAVAIL

A nonexistent interface was requested or the requested source address was

not local.

.TP

.B EAGAIN

Operation on a nonblocking socket would block.

.TP

.B EALREADY

A connection operation on a nonblocking socket is already in progress.

.TP

.B ECONNABORTED

A connection was closed during an

.BR accept (2).

.TP

.B EHOSTUNREACH

No routing table entry matches the destination address.

.TP

.B EINVAL

Invalid argument passed.

.TP

.B EISCONN

.BR connect (2)

was called on an already connected socket.

.TP

.B EMSGSIZE

Datagram is bigger than the DDP MTU.

.TP

.B ENODEV

Network device not available or not capable of sending IP.

.TP

.B ENOENT

.B SIOCGSTAMP

was called on a socket where no packet arrived.

.TP

.BR ENOMEM " and " ENOBUFS

Not enough memory available.

.TP

.B ENOPKG

A kernel subsystem was not configured.

.TP

.BR ENOPROTOOPT " and " EOPNOTSUPP

Invalid socket option passed.

.TP

.B ENOTCONN

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

connected.

.TP

.B EPERM

User doesn't have permission to set high priority,

make a configuration change,

or send signals to the requested process or group.

.TP

.B EPIPE

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

.TP

.B ESOCKTNOSUPPORT

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

.SH VERSIONS

AppleTalk is supported by Linux 2.0 or higher.

The

.I /proc

interfaces exist since Linux 2.2.

.SH NOTES

Be very careful with the

.B SO_BROADCAST

option; it is not privileged in Linux.

It is easy to overload the network

with careless sending to broadcast addresses.

.SS Compatibility

The basic AppleTalk socket interface is compatible with

.B netatalk

on BSD-derived systems.

Many BSD systems fail to check

.B SO_BROADCAST

when sending broadcast frames; this can lead to compatibility problems.

.PP

The

raw

socket mode is unique to Linux and exists to support the alternative CAP

package and AppleTalk monitoring tools more easily.

.SH BUGS

There are too many inconsistent error values.

.PP

The ioctls used to configure routing tables, devices,

AARP tables, and other devices are not yet described.

.SH SEE ALSO

.BR recvmsg (2),

.BR sendmsg (2),

.BR capabilities (7),

.BR socket (7)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I 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/.