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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 spec‐
ify 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 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.
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.
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 with‐
out having the broadcast flag set, and trying to bind to a
reserved port without effective user ID 0 or CAP_NET_BIND_SER
VICE.
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 con‐
figuration 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.
VERSIONS
Appletalk is supported by Linux 2.0 or higher. The sysctl interface is
new in 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.
recvmsg(2), sendmsg(2), capabilities(7), socket(7)