ddp - Linux AppleTalk protocol implementation

#include <sys/socket.h>
#include <netatalk/at.h>
ddp_socket = socket(AF_APPLETALK, SOCK_DGRAM, 0);
raw_socket = socket(AF_APPLETALK, SOCK_RAW, protocol);

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 “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 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.

recvmsg(2), sendmsg(2), capabilities(7), socket(7)