Zero-configuration networking (zeroconf) is a set of technologies that automatically creates a usable

computer network A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are m ...

based on the

Internet Protocol Suite The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...

(TCP/IP) when computers or network peripherals are interconnected. It does not require manual operator intervention or special configuration servers. Without zeroconf, a network administrator must set up

network service In computer networking, a network service is an application running at the network application layer and above, that provides data storage, manipulation, presentation, communication or other capability which is often implemented using a client� ...

s, such as

Dynamic Host Configuration Protocol The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on Internet Protocol (IP) networks for automatically assigning IP addresses and other communication parameters to devices connected to the network using a cli ...

(DHCP) and

Domain Name System The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned to ...

(DNS), or configure each computer's network settings manually. Zeroconf is built on three core technologies: automatic assignment of numeric

network address A network address is an identifier for a node or host on a telecommunications network. Network addresses are designed to be unique identifiers across the network, although some networks allow for local, private addresses, or locally administere ...

es for networked devices, automatic distribution and resolution of computer

hostname In computer networking, a hostname (archaically nodename) is a label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication, such as the World Wide Web. H ...

s, and automatic location of network services, such as printing devices.

Background

Computer networks use numeric

es to identify communications endpoints in a network of participating devices. This is similar to the

telephone network A telephone network is a telecommunications network that connects telephones, which allows telephone calls between two or more parties, as well as newer features such as fax and internet. The idea was revolutionized in the 1920s, as more and more ...

which assigns a string of digits to identify each telephone. In modern

networking protocol A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics and synchroni ...

s, information to be transmitted is divided into a series of

network packet In telecommunications and computer networking, a network packet is a formatted unit of data carried by a packet-switched network. A packet consists of control information and user data; the latter is also known as the ''payload''. Control info ...

s. Every packet contains the source and destination addresses for the transmission.

Network router A router is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions between networks and on the global Internet. Data sent through a network, such as a web page or email, ...

s examine these addresses to determine the best network path in forwarding the data packet at each step toward its destination. Similarly to telephones being labeled with their telephone number, it was a common practice in early networks to attach an address label to networked devices. The dynamic nature of modern networks, especially residential networks in which devices are powered up only when needed, desire dynamic address assignment mechanisms that do not require user involvement for initialization and management. These systems automatically give themselves common names chosen either by the equipment manufacturer, such as a brand and model number or chosen by users for identifying their equipment. The names and addresses are then automatically entered into a

directory service In computing, a directory service or name service maps the names of network resources to their respective network addresses. It is a shared information infrastructure for locating, managing, administering and organizing everyday items and network ...

. Early computer networking was built upon technologies of the telecommunications networks and thus protocols tended to fall into two groups: those intended to connect local devices into a

local area network A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a larger ...

(LAN), and those intended primarily for long-distance communications. The latter

wide area network A wide area network (WAN) is a telecommunications network that extends over a large geographic area. Wide area networks are often established with leased telecommunication circuits. Businesses, as well as schools and government entities, us ...

(WAN) systems tended to have centralized setup, where a

network administrator A network administrator is a person designated in an organization whose responsibility includes maintaining computer infrastructures with emphasis on local area networks (LANs) up to wide area networks (WANs). Responsibilities may vary between or ...

would manually assign addresses and names. LAN systems tended to provide more automation of these tasks so that new equipment could be added to a LAN with a minimum of operator and administrator intervention. An early example of a zero-configuration LAN system is

AppleTalk AppleTalk is a discontinued proprietary suite of networking protocols developed by Apple Computer for their Macintosh computers. AppleTalk includes a number of features that allow local area networks to be connected with no prior setup or the ...

, a protocol introduced by

Apple Inc. Apple Inc. is an American multinational technology company headquartered in Cupertino, California, United States. Apple is the largest technology company by revenue (totaling in 2021) and, as of June 2022, is the world's biggest company b ...

for the early

Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and software en ...

computers in the 1980s. Macs, as well as other devices supporting the protocol, could be added to the network by simply plugging them in; all further configuration was automated. Network addresses were automatically selected by each device using a protocol known as AppleTalk Address Resolution Protocol (AARP), while each machine built its own local directory service using a protocol known as Name Binding Protocol (NBP). NBP included not only a name but the type of device and any additional user-provided information such as its physical location or availability. Users could look up any device on the network with the application Chooser, which filtered names based on the device type. On

Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. ...

(IP) networks, the

database for a network was initially maintained manually by a network administrator. Efforts to automate maintenance of this database, led to the introduction of a number of new protocols providing automated services, such as the

(DHCP).

Address selection

Hosts on a network must be assigned

IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface iden ...

es that uniquely identify them to other devices on the same network. On some networks, there is a central authority that assigns these addresses as new devices are added. Mechanisms were introduced to handle this task automatically, and both IPv4 and IPv6 now include systems for

address autoconfiguration In computer networking, a link-local address is a unicast network address that is valid only for communications within the subnetwork that the host is connected to. Link-local addresses are most often assigned automatically with a process known ...

, which allows a device to determine a safe address to use through simple mechanisms. For

link-local address In computer networking, a link-local address is a unicast network address that is valid only for communications within the subnetwork that the host is connected to. Link-local addresses are most often assigned automatically with a process known ...

ing, IPv4 uses the special block , while IPv6 hosts use the prefix . More commonly addresses are assigned by a

DHCP server The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on Internet Protocol (IP) networks for automatically assigning IP addresses and other communication parameters to devices connected to the network using a cli ...

, often built into common networking hardware like computer hosts or routers. Most IPv4 hosts use link-local addressing only as a last resort when a DHCP server is unavailable. An IPv4 host otherwise uses its DHCP-assigned address for all communications, global or link-local. One reason is that IPv4 hosts are not required to support multiple addresses per interface, although many do. Another is that not every IPv4 host implements distributed name resolution (e.g.,

multicast DNS In computer networking, the multicast DNS (mDNS) protocol resolves hostnames to IP addresses within small networks that do not include a local name server. It is a zero-configuration service, using essentially the same programming interfaces, pac ...

), so discovering the autoconfigured link-local address of another host on the network can be difficult. Discovering the DHCP-assigned address of another host requires either distributed name resolution or a unicast DNS server with this information; Some networks feature DNS servers that are automatically updated with DHCP-assigned host and address information. IPv6 hosts are required to support multiple addresses per interface; moreover, every IPv6 host is required to configure a link-local address even when global addresses are available. IPv6 hosts may additionally self-configure additional addresses on receipt of router advertisement messages, thus eliminating the need for a DHCP server. Both IPv4 and IPv6 hosts may randomly generate the host-specific part of an autoconfigured address. IPv6 hosts generally combine a prefix of up to 64 bits with a 64-bit EUI-64 derived from the factory-assigned 48-bit

IEEE The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operatio ...

MAC address A media access control address (MAC address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. This use is common in most IEEE 802 networking techn ...

. The MAC address has the advantage of being globally unique, a basic property of the EUI-64. The IPv6 protocol stack also includes duplicate address detection to avoid conflicts with other hosts. In IPv4, the method is called ''link-local address autoconfiguration''. However,

Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washi ...

refers to this as ''

Automatic Private IP Addressing In computer networking, a link-local address is a unicast network address that is valid only for communications within the subnetwork that the host is connected to. Link-local addresses are most often assigned automatically with a process known ...

'' (APIPA) or ''Internet Protocol Automatic Configuration'' (IPAC). The feature is supported in Windows since at least

Windows 98 Windows 98 is a consumer-oriented operating system developed by Microsoft as part of its Windows 9x family of Microsoft Windows operating systems. The second operating system in the 9x line, it is the successor to Windows 95, and was releas ...

Name service discovery

Internet protocols use IP addresses for communications, but these are not easy for humans to use; IPv6 in particular uses very long strings of digits that are not easily entered manually. To address this issue, the internet has long used DNS, which allows human-readable names to be associated with IP addresses, and includes code for looking up these names from a hierarchical database system. Users type in domain names, such as ''example.org'', which the computer's DNS software looks up in the DNS databases to retrieve an IP address, and then hands off that address to the

protocol stack The protocol stack or network stack is an implementation of a computer networking protocol suite or protocol family. Some of these terms are used interchangeably but strictly speaking, the ''suite'' is the definition of the communication protoc ...

for further communications.Marshall Brain and Stephanie Crawford
"How Domain Name Servers Work"
howstuffworks Looking up an address using DNS requires the IP address of the DNS server to be known. This has normally been accomplished by typing in the address of a known server into a field in one of the devices on the network. In early systems, this was normally required on every device, but this has been pushed up one layer in the hierarchy to the DHCP servers or

broadband In telecommunications, broadband is wide bandwidth data transmission which transports multiple signals at a wide range of frequencies and Internet traffic types, that enables messages to be sent simultaneously, used in fast internet connections ...

devices like

cable modem A cable modem is a type of network bridge that provides bi-directional data communication via radio frequency channels on a hybrid fibre-coaxial (HFC), radio frequency over glass (RFoG) and coaxial cable infrastructure. Cable modems are prima ...

s that receive this information from their

internet service provider An Internet service provider (ISP) is an organization that provides services for accessing, using, or participating in the Internet. ISPs can be organized in various forms, such as commercial, community-owned, non-profit, or otherwise privat ...

. This has reduced the user-side administration requirements and provides a key element of zero-configuration access. DNS was intended to provide uniform names to groups of devices within the same administration realm, such as ''example.org'', provided by a name service. Assigning an address to a local device, e.g., ''thirdfloorprinter.example.org'', normally requires administrator access to the DNS server and is often accomplished manually. Additionally, traditional DNS servers are not expected to automatically correct for changes in configuration. For instance, if a printer is moved from one floor to another it might be assigned a new IP address by the local DHCP server. To address the need for automatic configuration, Microsoft implemented NetBIOS Name Service, part of which is the Computer Browser Service already in Microsoft Windows for Workgroups 3.11 as early as 1992. NetBIOS Name Service is zero-configuration on networks with a single subnet and may be used in conjunction with a WINS server or a Microsoft DNS server that supports secure automatic registration of addresses. This system has small, but not zero, management overhead even on very large enterprise networks. The protocols NetBIOS can use are part of the

Server Message Block Server Message Block (SMB) is a communication protocol originally developed in 1983 by Barry A. Feigenbaum at IBM and intended to provide shared access to files and printers across nodes on a network of systems running IBM's OS/2. It also provid ...

(SMB) suite of open protocols which are also available on Linux and iOS, although Windows typically supports a wider range of so-called dialects which can be negotiated between Windows clients that support it. For example, Computer Browser Services running on server operating systems or later versions of Windows are elected as so-called ''master browser'' over those that are not running a server operating system or running older versions of Windows. In 2000, Bill Manning and Bill Woodcock described the ''Multicast Domain Name Service'' which spawned the implementations by Apple and Microsoft. Both implementations are very similar. Apple's

Multicast DNS In computer networking, the multicast DNS (mDNS) protocol resolves hostnames to IP addresses within small networks that do not include a local name server. It is a zero-configuration service, using essentially the same programming interfaces, pac ...

(mDNS) is published as a standards track proposal , while Microsoft's Link-local Multicast Name Resolution (LLMNR) is published as informational . LLMNR is included in every Windows version from Windows Vista onwards and acts as a side-by-side alternative for Microsoft's NetBIOS Name Service over IPv4 and as a replacement over IPv6, since NetBIOS is not available over IPv6. Apple's implementation is available as the Bonjour service since 2002 in Mac OS X v10.2. The Bonjour implementation (mDNSResponder) is available under the Apache 2 Open Source License and is included in

Android Jelly Bean Android Jelly Bean, or Android 4.1 is the codename given to the tenth version of the Android mobile operating system developed by Google, spanning three major point releases (versions 4.1 through 4.3.1). Among the devices that run Android 4.1 t ...

and later under the same license. Use of either NetBIOS or LLMNR services on Windows is essentially automatic, since using standard DNS client APIs will result in the use of either NetBIOS or LLMNR depending on what name is being resolved (whether the name is a local name or not), the network configuration in effect (e.g. DNS suffixes in effect) and (in corporate networks) the policies in effect (whether LLMNR or NetBIOS are disabled), although developers may opt into bypassing these services for individual address lookups. The mDNS and LLMNR protocols have minor differences in their approach to name resolution. mDNS allows a network device to choose a domain name in the

local Local may refer to: Geography and transportation * Local (train), a train serving local traffic demand * Local, Missouri, a community in the United States * Local government, a form of public administration, usually the lowest tier of administ ...

DNS

namespace In computing, a namespace is a set of signs (''names'') that are used to identify and refer to objects of various kinds. A namespace ensures that all of a given set of objects have unique names so that they can be easily identified. Namespaces ...

and announce it using a special multicast IP address. This introduces special semantics for the domain ''local'', which is considered a problem by some members of the IETF. The current LLMNR draft allows a network device to choose any domain name, which is considered a security risk by some members of the IETF. mDNS is compatible with DNS-SD as described in the next section, while LLMNR is not.

Service discovery

Name services such as mDNS, LLMNR and others do not provide information about the type of device or its status. A user looking for a nearby printer, for instance, might be hindered if the printer was given the name "Bob".

Service discovery Service discovery is the process of automatically detecting devices and services on a computer network. This reduces the need for manual configuration by users and administrators. A service discovery protocol (SDP) is a network protocol that he ...

provides additional information about devices. Service discovery is sometimes combined with a

name service In computing, a directory service or name service maps the names of network resources to their respective network addresses. It is a shared information infrastructure for locating, managing, administering and organizing everyday items and network ...

, as in Apple's Name Binding Protocol and Microsoft's

NetBIOS NetBIOS () is an acronym for Network Basic Input/Output System. It provides services related to the session layer of the OSI model allowing applications on separate computers to communicate over a local area network. As strictly an API, Ne ...

NetBIOS Service Discovery

NetBIOS on Windows supports individual hosts on the network to advertise services, such as file shares and printers. It also supports, for example, a network printer to advertise itself as a host sharing a printer device and any related services it supports. Depending on how a device is attached (to the network directly, or to the host which shares it) and which protocols are supported. However, Windows clients connecting to it may prefer to use SSDP or WSD using NetBIOS. NetBIOS is one of the providers on Windows implementing the more general discovery process dubbed ''function discovery'' which includes built-in providers for PnP, Registry, NetBIOS, SSDP and WSD of which the former two are local-only and the latter three support discovery of networked devices. None of these need any configuration for use on the local subnet. NetBIOS has traditionally been supported only in expensive printers for corporate use though some entry-level printers with Wi-Fi or Ethernet support it natively, allowing the printer to be used without configuration even on very old operating systems.

WS-Discovery

Web Services Dynamic Discovery (

WS-Discovery Web Services Dynamic Discovery (WS-Discovery) is a technical specification that defines a multicast discovery protocol to locate services on a local network. It operates over TCP and UDP port 3702 and uses IP multicast address or . As the name s ...

) is a technical specification that defines a multicast discovery protocol to locate services on a local network. It operates over TCP and UDP port 3702 and uses IP multicast address . As the name suggests, the actual communication between nodes is done using web services standards, notably

SOAP-over-UDP SOAP-over-UDP is an OASIS In ecology, an oasis (; ) is a fertile area of a desert or semi-desert environment'ksar''with its surrounding feeding source, the palm grove, within a relational and circulatory nomadic system.” The location of o ...

. Windows supports it in the form of Web Services for Devices and Devices Profile for Web Services. Many devices, such as HP and Brother printers, support it.

DNS-based service discovery

allows clients to discover a named list of service instances and to resolve those services to hostnames using standard DNS queries. The specification is compatible with existing unicast DNS server and client software, but works equally well with mDNS in a zero-configuration environment. Each service instance is described using a DNS SRV and DNS TXT record. A client discovers the list of available instances for a given service type by querying the DNS PTR record of that service type's name; the server returns zero or more names of the form <Service>.<Domain>, each corresponding to a SRV/TXT record pair. The

SRV record A Service record (SRV record) is a specification of data in the Domain Name System defining the location, i.e., the hostname and port number, of servers for specified services. It is defined iRFC 2782 and its type code is 33. Some Internet protoc ...

resolves to the domain name providing the instance, while the TXT can contain service-specific configuration parameters. A client can then resolve the A/AAAA record for the domain name and connect to the service. Service types are given on a first-come-first-serve basis. A service type registry was originally maintained by DNS-SD.org, but has since been merged into IANA's registry for DNS SRV records.

History

In 1997 Stuart Cheshire proposed adapting Apple's mature Name Binding Protocol to IP networks to address the lack of service discovery capability. Cheshire subsequently joined Apple and authored

IETF The Internet Engineering Task Force (IETF) is a standards organization for the Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster or requirements and ...

draft proposals for mDNS and DNS-based Service Discovery, supporting the transition from AppleTalk to IP networking. In 2002, Apple announced an implementation of both protocols under the name Rendezvous (later renamed Bonjour). It was first included in Mac OS X 10.2, replacing the

Service Location Protocol The Service Location Protocol (SLP, srvloc) is a service discovery protocol that allows computers and other devices to find services in a local area network without prior configuration. SLP has been designed to scale from small, unmanaged networks ...

(SLP) used in 10.1. In 2013, the proposals were ratified as and .

DNS-SD with multicast

mDNS uses packets similar to unicast DNS to resolve hostnames except they are sent over a multicast link. Each host listens on the mDNS port, 5353, transmitted to a well-known multicast address and resolves requests for the

DNS record The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned ...

of its ''.local'' hostname (e.g. the A, AAAA,

CNAME A Canonical Name record (abbreviated as CNAME record) is a type of resource record in the Domain Name System (DNS) that maps one domain name (an alias) to another (the canonical name). This can prove convenient when running multiple services (li ...

) to its IP address. When an mDNS client needs to resolve a local hostname to an IP address, it sends a DNS request for that name to the well-known multicast address; the computer with the corresponding A/AAAA record replies with its IP address. The mDNS multicast address is for IPv4 and for IPv6 link-local addressing. DNS Service Discovery (DNS-SD) requests can also be sent using mDNS to yield zero-configuration DNS-SD. This uses DNS PTR, SRV, TXT records to advertise instances of service types, domain names for those instances, and optional configuration parameters for connecting to those instances. But SRV records can now resolve to ''.local'' domain names, which mDNS can resolve to local IP addresses.

Support

DNS-SD is used by Apple products, most network printers, many Linux distributions including

Debian Debian (), also known as Debian GNU/Linux, is a Linux distribution composed of free and open-source software, developed by the community-supported Debian Project, which was established by Ian Murdock on August 16, 1993. The first version of De ...

and

Ubuntu Ubuntu ( ) is a Linux distribution based on Debian and composed mostly of free and open-source software. Ubuntu is officially released in three editions: ''Desktop'', '' Server'', and ''Core'' for Internet of things devices and robots. All th ...

, and a number of third-party products for various operating systems. For example, many

OS X macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac (computer), Mac computers. Within the market of ...

network applications written by Apple, including

Safari A safari (; ) is an overland journey to observe wild animals, especially in eastern or southern Africa. The so-called "Big Five" game animals of Africa – lion, leopard, rhinoceros, elephant, and Cape buffalo – particularly form an importa ...

iChat iChat (previously iChat AV) is a discontinued instant messaging software application developed by Apple Inc. for use on its Mac OS X operating system. It supported instant text messaging over XMPP/Jingle or OSCAR ( AIM) protocol, audio and vi ...

, and Messages, can use DNS-SD to locate nearby servers and peer-to-peer clients. Windows 10 includes support for DNS-SD for applications written using JavaScript. Individual applications may include their own support in older versions of the operating system, such that most instant messaging and

VoIP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet ...

clients on Windows support DNS-SD. Some

Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...

BSD The Berkeley Software Distribution or Berkeley Standard Distribution (BSD) is a discontinued operating system based on Research Unix, developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, B ...

, and Linux distributions also include DNS-SD. For example, Ubuntu ships Avahi, an mDNS/DNS-SD implementation, in its base distribution.

UPnP

UPnP Universal Plug and Play (UPnP) is a set of networking protocols that permits networked devices, such as personal computers, printers, Internet gateways, Wi-Fi access points and mobile devices to seamlessly discover each other's presence on the ...

has some protocol components with the purpose of service discovery.

SSDP

Simple Service Discovery Protocol The Simple Service Discovery Protocol (SSDP) is a network protocol based on the Internet protocol suite for advertisement and discovery of network services and presence information. It accomplishes this without assistance of server-based configurat ...

(SSDP) is a UPnP protocol, used in

Windows XP Windows XP is a major release of Microsoft's Windows NT operating system. It was release to manufacturing, released to manufacturing on August 24, 2001, and later to retail on October 25, 2001. It is a direct upgrade to its predecessors, Wind ...

and later. SSDP uses HTTP notification announcements that give a service-type

URI Uri may refer to: Places * Canton of Uri, a canton in Switzerland * Úri, a village and commune in Hungary * Uri, Iran, a village in East Azerbaijan Province * Uri, Jammu and Kashmir, a town in India * Uri (island), an island off Malakula Isla ...

and a Unique Service Name (USN). Service types are regulated by the Universal Plug and Play Steering Committee. SSDP is supported by many printer, NAS and appliance manufacturers such as Brother. It is supported by certain brands of network equipment, and in many

SOHO Soho is an area of the City of Westminster, part of the West End of London. Originally a fashionable district for the aristocracy, it has been one of the main entertainment districts in the capital since the 19th century. The area was devel ...

firewall appliances, where host computers behind it may pierce holes for applications. It is also used in home theater PC systems to facilitate media exchange between host computers and the media center.

DLNA

Digital Living Network Alliance (DLNA) is another suite of standards that uses UPnP for the discovery of networked devices. DLNA has a long list of prominent manufacturers producing devices such as TVs, NAS devices and so forth that support it. DLNA is supported by all major operating systems. DLNA service discovery is layered on top of SSDP.

Efforts toward an IETF standard protocol

SLP is supported by

Hewlett-Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...

's network printers,

Novell Novell, Inc. was an American software and services company headquartered in Provo, Utah, that existed from 1980 until 2014. Its most significant product was the multi- platform network operating system known as Novell NetWare. Under the lea ...

, and

Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java programming language, the Solaris operating system, ZFS, t ...

. SLP is described in and and implementations are available for both Solaris and

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whic ...

AllJoyn

AllJoyn is an open-source software stack for a myriad of devices, ranging from IoT devices to full-size computers, for discovery and control of devices on networks (Wifi, Ethernet) and other links (Bluetooth, ZigBee, etc.). It uses mDNS and HTTP over UDP and other protocols.

Standardization

, the SLP standard for figuring out where to get services, was published in June 1999 by the SVRLOC IETF working group. , a standard for choosing addresses for networked items, was published in March 2005 by the IETF Zeroconf working group. The group included individuals from Apple, Sun, and Microsoft. LLMNR was submitted for official adoption in the IETF DNSEXT working group, however, failed to gain consensus and thus was published as informational in January 2007. Following the failure of LLMNR to become an Internet standard and given that mDNS/DNS-SD is used much more widely than LLMNR, Apple was asked by the IETF to submit the mDNS/DNS-SD specs for publication as Informational RFC as well. In February 2013 mDNS and DNS-SD were published as Standards Track Proposals and .

Security issues

Because mDNS operates under a different trust model than unicast DNS—trusting the entire network rather than a designated DNS server, it is vulnerable to

spoofing attack In the context of information security, and especially network security, a spoofing attack is a situation in which a person or program successfully identifies as another by falsifying data, to gain an illegitimate advantage. Internet Spoofing an ...

s by any system within the same

broadcast domain A broadcast domain is a logical division of a computer network, in which all nodes can reach each other by broadcast at the data link layer. A broadcast domain can be within the same LAN segment or it can be bridged to other LAN segments. In t ...

. Like

SNMP Simple Network Management Protocol (SNMP) is an Internet Standard protocol for collecting and organizing information about managed devices on IP networks and for modifying that information to change device behaviour. Devices that typically ...

and many other network management protocols, it can also be used by attackers to quickly gain detailed knowledge of the network and its machines. Because of this, applications should still authenticate and encrypt traffic to remote hosts (e.g. via RSA,

SSH The Secure Shell Protocol (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network. Its most notable applications are remote login and command-line execution. SSH applications are based on a ...

, etc.) after discovering and resolving them through DNS-SD/mDNS. LLMNR suffers from similar vulnerabilities.

Major implementations

Apple Bonjour

Bonjour from Apple, uses mDNS and DNS Service Discovery. Apple changed its preferred zeroconf technology from SLP to mDNS and DNS-SD between

Mac OS X 10.1 Mac OS X 10.1 (code named Puma) is the second major release of macOS, Apple's desktop and server operating system. It superseded Mac OS X 10.0 and preceded Mac OS X Jaguar. Mac OS X 10.1 was released on September 25, 2001, as a free updat ...

and 10.2, though SLP continues to be supported by Mac OS X. Apple's mDNSResponder has interfaces for C and

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...

and is available on BSD, Apple Mac OS X, Linux, other

POSIX The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines both the system- and user-level application programming interf ...

based operating systems and MS Windows. The Windows downloads are available from Apple's website.

Avahi

Avahi is a Zeroconf implementation for

and

s. It implements IPv4LL, mDNS and DNS-SD. It is part of most Linux distributions, and is installed by default on some. If run in conjunction with nss-mdns, it also offers host name resolution. Avahi also implements binary compatibility libraries that emulate Bonjour and the historical mDNS implementation Howl, so software made to use those implementations can also utilize Avahi through the emulation interfaces.

MS Windows CE 5.0

Microsoft

Windows CE Windows Embedded Compact, formerly Windows Embedded CE, Windows Powered and Windows CE, is an operating system subfamily developed by Microsoft as part of its Windows Embedded family of products. Unlike Windows Embedded Standard, which is ba ...

5.0 includes Microsoft's own implementation of LLMNR.

Systemd

Systemd systemd is a software suite that provides an array of system components for Linux operating systems. Its main aim is to unify service configuration and behavior across Linux distributions; Its primary component is a "system and service manage ...

implements both mDNS and LLMNR in systemd-resolved.

Link-local IPv4 addresses

Where no DHCP server is available to assign a host an IP address, the host can select its own

. Using a link-local address, hosts can communicate over this link but only locally; Access to other networks and the Internet is not possible. There are some link-local IPv4 address implementations available: * Apple Mac OS and MS Windows have supported link-local addresses since 1998. Apple released its open-source implementation in the Darwin bootp package. * Avahi contains an implementation of IPv4LL in the avahi-autoipd tool. * Zero-Conf IP (zcip) *

BusyBox BusyBox is a software suite that provides several Unix utilities in a single executable file. It runs in a variety of POSIX environments such as Linux, Android, and FreeBSD, although many of the tools it provides are designed to work with inte ...

can embed a simple IPv4LL implementation. * Stablebox, a fork from Busybox, offers a slightly modified IPv4LL implementation named llad. * Zeroconf is a package based on Simple IPv4LL, a shorter implementation by Arthur van Hoff. The above implementations are all stand-alone daemons or plugins for

DHCP The Dynamic Host Configuration Protocol (DHCP) is a network protocol, network management protocol used on Internet Protocol (IP) networks for automatically assigning IP addresses and other communication parameters to devices connected to the net ...

clients that only deal with link-local IP addresses. Another approach is to include support in new or existing DHCP clients: * Elvis Pfützenreuter has written a patch for the uDHCP client/server. * dhcpcd is an

open source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product. The open-source model is a decentralized sof ...

client for

and

that includes IPv4LL support. It is included as standard in

NetBSD NetBSD is a free and open-source Unix operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was forked. It continues to be actively developed and is ava ...

. Neither of these implementations addresses kernel issues like broadcasting ARP replies or closing existing network connections.

References

Notes Sources *

External links

* , a pure Java implementation of mDNS/DNS-SD. * , a pure Python implementation of mDNS/DNS-SD. * , a cross platform (Linux, MS Windows, Apple Mac), unified Mono/.NET library for Zeroconf, supporting both Bonjour and Avahi. * , a cross-platform wxWidgets-based service discovery module without external dependencies. * . * . * . * , including Internet drafts. * , DNS based Service Discovery * * * . {{DEFAULTSORT:Zero Configuration Networking Apple Inc. software Computer configuration Domain Name System Network protocols Windows communication and services