netatalk: AppleTalk Protocol Family

netatalk 4.5.0
Free and Open Source Apple Filing Protocol (AFP) Server
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AppleTalk Protocol Family

AppleTalk is a network protocol family for Macintosh and Apple II computers, created by Apple in 1985 at a time when TCP/IP was not yet widely adopted. It contains different protocols for different uses: address resolution, address/name mapping, service location, establishing connections, and the like.

The AppleTalk protocols are layered above the Datagram Delivery Protocol (DDP), and using AppleTalk address format. The AppleTalk family may provide SOCK_STREAM (ADSP), SOCK_DGRAM (DDP), SOCK_RDM (ATP), and SOCK_SEQPACKET (ASP).

Netatalk implements the AppleTalk protocols to serve files over AFP and provide other services to very old Mac and Apple II clients.

It supports EtherTalk Phase I and II, RTMP, NBP, ZIP, AEP, ATP, PAP, and ASP, while expecting the host OS kernel to supply DDP.

- DDP is a socket to socket protocol that all other AppleTalk protocols are built on top of.
- ATP, ASP, and NBP are implemented as statically linked libraries in Netatalk's libatalk shared library.
- The atalkd daemon implements RTMP, ZIP, and AEP.
- The papd daemon implements PAP, allowing Mac clients to spool to a Unix print spooler or CUPS on the netatalk host computer.

# Addressing

AppleTalk addresses are three byte quantities, stored in network byte order. The include file <netatalk/at.h> defines the AppleTalk address format.

Sockets in the AppleTalk protocol family use the following address structure:

    struct sockaddr_at {
        short sat_family;
        unsigned char sat_port;
        struct at_addr sat_addr;
        char sat_zero[8];
    };

The port of a socket may be set with bind. The node for bind must always be ATADDR_ANYNODE: "this node." The net may be ATADDR_ANYNET or ATADDR_LATENET. ATADDR_ANYNET corresponds to the machine's "primary" address (the first configured). ATADDR_LATENET causes the address in outgoing packets to be determined when a packet is sent, i.e. determined late. ATADDR_LATENET is equivalent to opening one socket for each network interface. The port of a socket and either the primary address or ATADDR_LATENET are returned with getsockname.

# AppleTalk address parsing

The atalk_aton() routine converts an ASCII representation of an AppleTalk address to a format appropriate for system calls. Acceptable ASCII representations include both hex and base 10, in triples or doubles. For instance, the address `0x1f6b.77' has a network part of `8043' and a node part of `119'. This same address could be written `8043.119', `31.107.119', or `0x1f.6b.77'. If the address is in hex and the first digit is one of `A-F', a leading `0x' is redundant.

# NBP name parsing

nbp_name() parses user supplied names into their component object, type, and zone. obj, type, and zone should be passed by reference, and should point to the caller's default values. nbp_name() will change the pointers to the parsed-out values. name is of the form object:type@zone, where each of object, :type, and @zone replace obj, type, and zone, respectively. type must be proceeded by `:', and zone must be preceded by `@'.

# DDP Implementations

## Linux

The Linux kernel has had DDP support since version 1.3.0, released in June 1995. See the Linux 1.3.0 Changes file.

The source code for the appletalk driver lives under net/appletalk in the Linux kernel source tree.

## NetBSD

Kernel support for DDP appeared in NetBSD 1.3 in April 1997. See the NetBSD 1.3 release notes

The NetBSD kernel module is confusingly named netatalk and is located under sys/netatalk in the NetBSD source tree.

## Solaris

Historical versions of Netatalk (until v2.3) distributed code for a Solaris STREAMS module that implements DDP.

The source code is located under sys/solaris in the netatalk source tree. It is written for the SPARC architecture.

## Generic

If you would like DDP support on another operating system, you will need either need a kernel module for your operating system, or a userland AppleTalk stack.

Look at the above Solaris STREAMS module if your operating system supports that framework. Otherwise, look at the DDP code in NetBSD if your operating system is BSDish in nature.

If your operating system looks different than these two cases, you'll have to roll your own implementation.