Zero configuration networking

Zero agreement networking (zeroconf), is a set of techniques that automatically creates a accessible Internet Protocol (IP) arrangement after chiral abettor action or appropriate agreement servers.

Zero agreement networking allows accessories such as computers and printers to affix to a arrangement automatically. After zeroconf, a arrangement ambassador have to set up services, such as Dynamic Host Agreement Protocol (DHCP) and Domain Name System (DNS), or configure anniversary computer's arrangement settings manually, which may be difficult and time-consuming.

Zeroconf is congenital on three amount technologies:

Assignment of numeric arrangement addresses for networked devices

Automatic resolution and administration of computer hostnames

Automatic area of arrangement services, such as press devices

Address selection

Both IPv4 and IPv6 accept accepted methods for abode autoconfiguration. For link-local acclamation IPv4 uses the appropriate block 169.254.0.0/16 as declared in RFC 3927 while IPv6 hosts use the prefix fe80::/10.

Most IPv4 hosts use link-local acclamation (IPv4LL) alone as a endure resort if a DHCP server is unavailable. An IPv4 host contrarily uses its DHCP-assigned abode for all communications, all-around or link-local. One acumen is that IPv4 hosts are not appropriate to abutment assorted addresses per interface, although abounding do. Addition is that not every IPv4 host accouterments advertisement name resolution (e.g., multicast DNS), so advertent the autoconfigured link-local abode of addition host on the arrangement can be difficult. However, advertent the DHCP-assigned abode of addition host aswell requires either advertisement name resolution or a unicast DNS server with this information, and some networks affection DNS servers that are automatically adapted with DHCP-assigned host and abode information.

IPv6 hosts are appropriate to abutment assorted addresses per interface; moreover, every IPv6 host is appropriate to configure a link-local abode even if all-around addresses are available. IPv6 hosts may additionally self-configure one or added all-around addresses on cancellation of one or added router advertisement messages, appropriately eliminating the charge for a DHCP6 server; see RFC 4862.

Both IPv4 and IPv6 hosts may about accomplish the host-specific allotment of an autoconfigured address. IPv6 hosts about amalgamate a prefix of up to 64 $.25 with a 64-bit EUI-64 acquired from the factory-assigned 48-bit IEEE MAC address. The MAC abode accept the advantage of getting globally unique, a acreage affiliated by the EUI-64. The host is commonly appropriate to ensure, through advertisement queries, that the addresses it generates are not in use by any added host on the bounded network.

The abode is alleged Link-Local abode appointment in RFC 3927. However, Microsoft refers to this as Automatic Private IP Acclamation (APIPA) or Internet Protocol Automatic Configuration (IPAC) (supported back at atomic Windows 98 1).

Name resolution

In 2000, Bill Manning and Bill Woodcock declared the Multicast Area Name Service2 which spawned the implementations by Apple and Microsoft. Both implementations are actual similar. Apple's Multicast DNS (mDNS) is an accessible specification, while Microsoft's Link-local Multicast Name Resolution (LLMNR) is little acclimated and the blueprint is not an IETF standards clue publication. The closing was appear as advisory RFC 4795.

The two protocols accept accessory differences in their access to name resolution. mDNS allows a arrangement accessory to accept a area name in the bounded namespace and advertise it application a appropriate multicast IP address. This introduces appropriate semantics for the bounded domain,3 which is advised a botheration by some associates of the IETF.4 The accepted LLMNR abstract allows a arrangement accessory to accept any area name, which is advised a aegis accident by some associates of the IETF.5 mDNS is accordant with DNS-SD as declared in the next section, while LLMNR is not.6

Service discovery

Apple's protocol: Multicast DNS/DNS-SD

Multicast DNS (mDNS) is a agreement that uses APIs agnate to unicast Area Name System but implemented over a multicast protocol. Each computer on the LAN food its own account of DNS ability annal (e.g., A, MX, SRV) and joins the mDNS multicast group. When an mDNS applicant wants to apperceive the IP abode of a PC accustomed its name, mDNS applicant sends a appeal to a acclaimed multicast address; the PC with the agnate A almanac replies with its IP address. The mDNS multicast abode is 224.0.0.251 for IPv4 and ff02::fb for IPv6 link-local addressing.

DNS based Account Analysis (DNS-SD) is the added bisected of Apple's solution, congenital on top of the Area Name System. It is acclimated in Apple products, abounding arrangement printers and a amount of third affair articles and applications on assorted operating systems. The Apple band-aid uses DNS messages, in adverse to Microsoft's aggressive technology, SSDP, which uses HTTP messages. It uses DNS SRV, TXT, and PTR annal to acquaint Account Instance Names. The hosts alms casework broadcast data of accessible services: instance, account type, area name and alternative agreement parameters. Account types are accustomed artlessly on a first-come basis. A account blazon anthology is maintained and appear by DNS-SD.org.

Many Mac OS X networking clients, such as the Safari browser and the iChat burning messaging software, use DNS-SD to locate adjacent servers. On Windows, some burning messaging and VoIP audience abutment DNS-SD. Some unix, BSD, and GNU/Linux distributions aswell cover DNS-SD functionality.

mDNS/DNS-SD was developed by Apple Computer agent Stuart Cheshire in the company's move from AppleTalk to IP.

edit Microsoft's protocol: UPnP SSDP

Simple Account Analysis Agreement (SSDP) is a UPnP protocol, acclimated in Windows XP and several brands of arrangement equipment. SSDP uses HTTP notification announcements that accord a service-type URI and a Unique Account Name (USN). Account types are adapted by the Universal Plug and Play Steering Committee.

SSDP is accurate in abounding SOHO firewall appliances, area host computers abaft it may bore holes for applications. It is aswell acclimated in media centermost systems, area media barter amid host computers and the media centermost is facilitated application SSDP.

edit Efforts against an IETF accepted protocol

Service Location Agreement (SLP), the alone agreement for account analysis to accept accomplished the IETF Proposed Accepted status, is accurate by Hewlett-Packard's arrangement printers, Novell, and Sun Microsystems, but abandoned by some added ample vendors. SLP is declared in RFC 2608 and RFC 3224 and implementations are accessible for both Solaris and Linux.

Standardization

RFC 3927, a accepted for allotment addresses for networked items, was appear in March 2005 by the Zeroconf IETF alive group, which included individuals from Apple, Sun, and Microsoft.7

LLMNR was submitted for official acceptance in the DNSEXT IETF alive group, about bootless to accretion accord and appropriately has been appear as advisory RFC only: RFC 4795.8 Following the abortion of LLMNR to become an Internet accepted Apple was asked by the IETF to abide the mDNS/DNS-SD specs for publishing as advisory RFC as well, accustomed that mDNS/DNS-SD is acclimated abundant added broadly than LLMNR. They are currently appear as an Internet Draft.9

RFC 2608, the SLP accepted for addition out area to get services, was appear by the SVRLOC IETF alive group.10

Security issues

Because mDNS operates beneath a altered assurance archetypal than unicast DNS—trusting the absolute arrangement rather than a appointed DNS server—it is accessible to bluffing attacks by any arrangement aural the multicast IP range. Like SNMP and abounding added arrangement administration protocols, it can aswell be acclimated by attackers to bound accretion abundant ability of the arrangement and its machines.11

Major implementations

Apple Bonjour

Bonjour (formerly accepted as Rendezvous) from Apple Inc., uses multicast DNS and DNS Service Discovery. Apple afflicted its adopted zeroconf technology from SLP to mDNS and DNS-SD amid Mac OS X 10.1 and 10.2, admitting SLP continues to be accurate by Mac OS X.

Apple's mDNSResponder has interfaces for C and Java12 and is accessible on BSD, Mac OS X, Linux, added POSIX based operating systems and Windows. The Windows downloads are accessible from Apple's website.13

edit Avahi

Avahi is a Zeroconf accomplishing for Linux and BSDs. It accouterments IPv4LL, mDNS and DNS-SD. It is allotment of a lot of Linux distributions, and is installed by absence on some. If run in affiliation with nss-mdns it aswell offers host name resolution.14

Avahi aswell accouterments bifold affinity libraries that challenge Bonjour and the actual mDNS accomplishing Howl, so software fabricated to use those implementations can aswell advance Avahi through the appetite interfaces.

edit Windows CE 5.0

Windows CE 5.0 includes Microsoft's own accomplishing of LLMNR.

edit Link-local IPv4 addresses

There are some implementations available:

Windows and Mac OS accept both accurate link-local addresses back 1998. Apple appear its open-source accomplishing in the Darwin bootp package.

Avahi contains an accomplishing of IPv4LL in the avahi-autoipd tool.

zcip (Zero-Conf IP)

BusyBox can bury a simple IPv4LL implementation

Stablebox, a angle from Busybox, offers a hardly adapted IPv4LL accomplishing called llad.

zeroconf, a amalgamation based on Simple IPv4LL, a beneath accomplishing by Arthur van Hoff.15

The aloft implementations are all stand-alone daemons or plugins for DHCP audience that alone accord with link-local IP addresses. Another access is to cover abutment in new or absolute DHCP clients:

Elvis Pfützenreuter has accounting a application for the uDHCP client/server.16

dhcpcd is an opensource DHCP applicant for Linux and BSD that includes IPv4LL support. It is included as accepted in NetBSD.

Neither of these implementations addresses atom issues like the broadcasting of ARP replies17 or closing of absolute arrangement connections.