DDP
Section: Linux Programmer's Manual (7)
Updated: 2017-09-15
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NAME
ddp - Linux AppleTalk protocol implementation
SYNOPSIS
#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 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
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 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 lqthis network.rq
The
node
member of
struct at_addr
contains the host node number.
The value of
AT_ANYNODE
is a
wildcard and also implies lqthis node.rq 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 parameters 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)
apply to DDP.
ERRORS
- 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.
- 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).
- EHOSTUNREACH
-
No routing table entry matches the destination address.
- EINVAL
-
Invalid argument passed.
- EISCONN
-
connect(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 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),
sendmsg(2),
capabilities(7),
socket(7)
COLOPHON
This page is part of release 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- Address format
-
- Socket options
-
- /proc interfaces
-
- Ioctls
-
- ERRORS
-
- VERSIONS
-
- NOTES
-
- Compatibility
-
- BUGS
-
- SEE ALSO
-
- COLOPHON
-
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