Zero Configuration Networking (Zeroconf)
http://www.zeroconf.org/
The IETF Zeroconf Working Group was chartered September 1999 and held its first
official meeting at the 46th IETF in Washington, D.C., in November 1999. By the
time the Working Group completed its work on Dynamic Configuration of IPv4 LinkLocal Addresses and wrapped up in July 2003, IPv4LL was implemented and
shipping in Mac OS (9 & X), Microsoft Windows (98, ME, 2000, XP, 2003), in every
network printer from every major printer vendor, and in many assorted network
devices from a variety of vendors. IPv4LL is available for Linux and for embedded
operating systems. If you're making a networked device today, there's no excuse not to
include IPv4 Link-Local Addressing.
The specification for IPv4 Link-Local Addressing is complete, but the work to
improve network ease-of-use (Zero Configuration Networking) continues. That means
making it possible to take two laptop computers, and connect them with a crossover
Ethernet cable, and have them communicate usefully using IP, without needing a man
in a white lab coat to set it all up for you. Zeroconf is not limited to networks with just
two hosts, but as we scale up our technologies to larger networks, we always have to
be sure we haven't forgotten the two-devices (and no DHCP server) case.
Historically, AppleTalk handled this very well. Back in the 1980s if you took a group
of Macs and connected them together with LocalTalk cabling, you had a working
AppleTalk network, without any expert intervention, without needing to set up special
servers like a DHCP server or a DNS server. In the 1990s the same was true using
Ethernet — if you took a group of Macs and plugged them into an Ethernet hub, you
had a working AppleTalk network, using AppleTalk-over-Ethernet. Now that it's
common for computers to have IEEE 802.11 ("AirPort")networking built-in, you don't
even need cables or a hub.
On Windows PCs, Microsoft NETBIOS and Novell IPX provided similar ease-of-use
on small networks.
One major problem with using IP for wide-area communication and AppleTalk,
NETBIOS, or something else for local communication, was that it required
application developers to support multiple different protocols with different
semantics, conventions, and operational models. For example, a game developer
writing a multi-player game would usually support IP to allow game-play across the
Internet. However, a developer selling a game for $50 doesn't have the technical
support budget to provide telephone support for people trying to configure their own
"Net 10" IP network at home, so for the sake of ease-of-use, that developer also had to
support AppleTalk (in the Macintosh version) and NETBIOS or IPX (in the Windows
version) for people to play network games at home. Unfortunately, even after doing
all that work the developers still hadn't really solved their problem, because if
someone with a Mac laptop wanted to play a network game with a friend with a
Windows laptop, they were still in the position of having to set up their own IP
network, because IP is the only cross-platform protocol their two machines had in
common. It was clear that what the world needed was the ease-of-use of AppleTalk,
applied to IP, the ubiquitous platform-agnostic communications protocol.
To achieve AppleTalk ease-of-use in IP, there are four main requirements:

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Allocate addresses without a DHCP server (IPv4 Link-Local Addressing)
Translate between names and IP addresses without a DNS server (Multicast
DNS)
Find services, like printers, without a directory server (DNS Service Discovery)
Allocate IP Multicast addresses without a MADCAP server (future work)
A final requirement is that the solutions in the four areas must coexist gracefully with
larger configured networks. Zeroconf protocols MUST NOT cause harm to the
network when a machine is plugged into a large network.
It is important to understand that the purpose of Zero Configuration Networking is
not solely to make current personal computer networking easier to use, though this is
certainly a useful benefit. The long-term goal of Zero Configuration Networking is to
enable the creation of entirely new kinds of networked products, products that today
would simply not be commercially viable because of the inconvenience and support
costs involved in setting up, configuring, and maintaining a network to allow them to
operate.
Documents

Zeroconf Requirements (draft-ietf-zeroconf-reqts-12.txt) defines the protocol
requirements for zero configuration networking. This document was never
published by the IETF, but the draft is made available here for historical
interest.

Zeroconf Host Profile (draft-ietf-zeroconf-host-prof-01.txt) outlines which
protocols are available that could meet the requirements specified in the
requirements document. In effect this draft is the embyonic form of a possible
future RFC which could become an update to RFC 1122 (Host Requirements).
This document was never published by the IETF, but the draft is made
available here for historical interest.

Autoconfiguration for IP Networking: Enabling Local Communication is a
Zeroconf tutorial article by Erik Guttman, which appeared in the June 2001
issue of IEEE Internet Computing.

IPv4 Address Conflict Detection (RFC 5227) describes how a host can detect
when some other host on the same link is trying to use the same IP address (a
Bad Thing). This is the same mechanism used for Link-Local Addresses, but it
is equally useful and applicable no matter how an address was configured,
whether via manual entry by a human user, via information received from a
DHCP server, or via any other source of configuration information.

Dynamic Configuration of IPv4 Link-Local Addresses (RFC 3927) specifies
how IP hosts can assign addresses in the absence of outside configuration
information. That means assigning addresses without depending on information
entered by a human user, and without depending on information obtained over
the network from a special server, such as a DHCP server.

Zeroconf Multicast Address Allocation Protocol (ZMAAP) (draft-ietfzeroconf-zmaap-02.txt) defines how IP hosts can allocate multicast addresses in
the absence of outside configuration information. This document was never
published by the IETF, but the draft is made available here for historical
interest.

An API for the Zeroconf Multicast Address Allocation Protocol
(ZMAAP) (draft-ietf-zeroconf-zmaap-api-00.txt) is an informational draft
extending RFC 2771 ("An Abstract API for Multicast Address Allocation") to
the Zeroconf environment. This document was never published by the IETF,
but the draft is made available here for historical interest.
Further Information

Multicast DNS provides name-to-address translation and other DNS-like
operations in the absence of a conventional DNS server.
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DNS Service Discovery uses DNS SRV records to provide simple service
discovery (network browsing), and works with both conventional unicast DNS
and with multicast DNS.
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Simple IPv4LL implementation from Arthur van Hoff. For platforms that don't
already have IPv4LL support built-in, there are various third-party
implementations, but they tend to rely on existing libraries which may not be
present on all platforms. This version is just 380 lines, and is self-contained and
doesn't depend on things like libpcap or similar packet capture libraries.
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WiSe-Zeroconf, an embedded Zeroconf stack.
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Why should we adopt Zeroconf instead of UPnP? See How does Zeroconf
compare with Viiv/DLNA/DHWG/UPnP?
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How hard is to implement IPv4LL? See Quick-and-Dirty IPv4 Link-Local
Addressing
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May 2002: Apple announced their Zero Configuration Networking solution
under the product name Rendezvous. Apple is keen to leave AppleTalk behind
and move to all-IP networking, and Rendezvous makes that possible.
Rendezvous is now used by iChat, iTunes, iPhoto, Safari, file sharing, printing,
and just about every other piece of software that does networking on a Mac,
including trusty old favorites like telnet, ssh, and ftp.
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July 2004: The IETF Zeroconf Working Group concludes its work and wraps
up.
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August 2004: Apple's Rendezvous for Windows Technology Preview now
available.
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April 2005: Apple announces Bonjour, its new name for "Rendezvous 2",
including wide-area service registration and browsing, extending Rendezvous
beyond the local link, inbound NAT traversal (with compatible NAT
gateways), new programming APIs for Java programmers, and all of the above
for Windows too. The iFelix technical suport pages include a good "HowTo"
page including four step-by-step screen shots on Printing from Windows XP
using Bonjour. (Actually, the first screen shot is the "Welcome" screen, and the
last is the "Congratulations printer set up is complete" screen, so actually there
are only two real steps — pick the printer, and verify that the Wizard picked the
right driver.)
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May 2005: The Asterisk Voice-Over-IP software PBX gets support for zeroconfiguration client setup using Zeroconf.
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August 2005: Avahi released, a complete DNS-SD/mDNS implementation,
licensed under LGPL.
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November 2005: Stuart Cheshire gives a Zeroconf talk to the Google engineers,
which was also recorded and made available on Google Video.
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December 2005: Zero Configuration Networking: The Definitive Guide by
Daniel Steinberg and Stuart Cheshire, published by O'Reilly Media. There's a
wealth of information on the Web about Zeroconf, perhaps so much that it can
be overwhelming. This book gathers the essential material into a single
convenient source, describing how the protocols work, and giving
programming examples in C, Java, Python, and Ruby. Whether you're
programming for Mac OS X, Windows, Linux, Solaris, FreeBSD (or any of the
other supported Unix variants), or building a hardware device running an
embedded OS like VxWorks, the cross-platform programming examples in this
book will show you what you need to know to create a great Zeroconf product.
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January 2006: Computer Language Company releases new edition of its
Computer Desktop Encyclopedia, available both on CD and via the web, with
entries for Zeroconf, Bonjour and Link-Local Address.
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June 2006: With the help of Apple's Bonjour, setting up Windows XP to
generate PDF from any Windows application that supports printing takes less
than a minute and a half from startup. See the video on YouTube.
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July 2006: More praise for the Bonjour for Windows Printer Setup Wizard, this
time in an Ars Technica article about Parallels Desktop for Mac OS X.
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31st March 2009: Time to introduce the broader embedded systems community
to the technologies of Zero Configuration Networking: Stuart Cheshire speaks
at the Embedded Systems Conference.
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June 2009: The Bonjour Sleep Proxy wakes your Mac automatically when you
access it over the network.
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October 2013: Presto from Collobos Software is an AirPrint-compatible IPP
print server that also implements enough of a DNS server to
answer unicast DNS-SD queries for the print services it is offering, making it
a Wide-Area AirPrint Server. This means that the printers it offers are visible to
iOS AirPrint clients anywhere on a university or enterprise campus (and even
remote clients connected via VPN), in contrast to conventional multicastonly AirPrint services, which are visible only to clients on the same local link.