Editing Zero-configuration networking (section)

===DNS-based service discovery===
'''{{vanchor|DNS-SD}}''' (DNS Service Discovery<ref name="dotorg">{{Citation | url = http://www.dns-sd.org/ | title = DNS-SD}}</ref>) 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<ref>{{IETF RFC|2782}}</ref> and DNS TXT<ref name="IETF RFC|1035">{{IETF RFC|1035}}</ref> record. A client discovers the list of available instances for a given service type by querying the DNS PTR<ref name="IETF RFC|1035"/> record of that service type's name; the server returns zero or more names of the form &lt;Service&gt;.&lt;Domain&gt;, each corresponding to a SRV/TXT record pair. The [[SRV record]] 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,<ref name="dotorg" /> but has since been merged into IANA's registry for DNS SRV records.<ref>{{Citation | url = http://www.dns-sd.org/ServiceTypes.html | publisher = DNS-SD | title = Service types}}</ref>

====History====
In 1997 [[Stuart Cheshire]] proposed adapting Apple's mature [[Name Binding Protocol]] to IP networks to address the lack of service discovery capability.<ref>{{Citation | url = http://www.stuartcheshire.org/rants/NBPIP.html | title = Name Binding Protocol over IP | type = rant | first = Stuart | last = Cheshire | author-link = Stuart Cheshire}}{{self-published-inline|date=May 2013}}</ref> Cheshire subsequently joined Apple and authored [[IETF]] 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<ref>{{Citation | title = Zero conf | url = http://www.zeroconf.org/}}{{self-published-inline|date=March 2020}}</ref> (later renamed Bonjour). It was first included in [[Mac OS X 10.2]], replacing the [[Service Location Protocol]] (SLP) used in [[Mac OS X 10.1|10.1]].{{Citation needed|date=May 2013}} In 2013, the proposals were ratified as {{IETF RFC|6762}}<ref>{{cite IETF |author1=S. Cheshire |author2=M. Krochmal |publisher=[[IETF]] |title=Multicast DNS |rfc=6762 |date=February 2013}}</ref> and {{IETF RFC|6763}}.<ref>{{cite IETF |author1=S. Cheshire |author2=M. Krochmal |publisher=[[IETF]] |title=DNS-Based Service Discovery |rfc=6763 |date=February 2013}}</ref>

====DNS-SD with multicast====
mDNS uses packets similar to [[Domain Name System#DNS message format|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]] of its ''.local'' hostname (e.g. the [[List of DNS record types#A|A]], [[List of DNS record types#AAAA|AAAA]], [[CNAME]]) 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 {{IPaddr|224.0.0.251}} for IPv4 and {{IPaddr|ff02::fb}} for IPv6 link-local addressing.

DNS Service Discovery aka [[DNS-SD]] requests can also be sent using mDNS to yield zero-configuration DNS-SD.{{Ref RFC|6763}} This uses DNS [[PTR record|PTR]], SRV, [[TXT record|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]] and [[Ubuntu]],<ref>{{cite web|title=Ubuntu 15.10 desktop manifest|url=http://releases.ubuntu.com/wily/ubuntu-15.10-desktop-amd64.manifest|publisher=Ubuntu|access-date=23 October 2015}}</ref> and a number of third-party products for various operating systems. For example, many [[OS X]] network applications written by Apple, including [[Safari (web browser)|Safari]], [[iChat]], and [[Messages (Apple)|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.<ref name="WindowsDnssdNamespace">{{cite web|title=Windows.Networking.ServiceDiscovery.Dnssd namespace|url=https://msdn.microsoft.com/en-us/library/windows/desktop/bb870632(v=vs.85).aspx|website=Windows Dev Center|publisher=Microsoft|access-date=1 November 2015}}</ref> Individual applications may include their own support in older versions of the operating system, such that most instant messaging and [[VoIP]] clients on Windows support DNS-SD. Some [[Unix]], [[BSD]], and Linux distributions also include DNS-SD. For example, Ubuntu ships [[Avahi (software)|Avahi]], an mDNS/DNS-SD implementation, in its base distribution.