multicast-dns

What is multicast-dns?

The multicast-dns npm package allows for low-level network discovery and communication using multicast DNS, which is often used in zero-configuration networking to resolve hostnames to IP addresses within small networks that do not include a local name server.

What are multicast-dns's main functionalities?

Discover services on the local network

This code sets up a multicast DNS instance to listen for responses to queries on the local network. It then sends out a query for the A (address) record for 'brunhilde.local'.

const mdns = require('multicast-dns')();

mdns.on('response', function(response) {
  console.log('Got a response to an mDNS query:', response)
});

mdns.query({
  questions:[{
    name: 'brunhilde.local',
    type: 'A'
  }]
});

Advertise services on the local network

This code listens for mDNS queries and responds with the IP address '192.168.1.5' when a query for 'brunhilde.local' is received.

const mdns = require('multicast-dns')();

mdns.on('query', function(query) {
  if (query.questions[0] && query.questions[0].name === 'brunhilde.local') {
    mdns.respond({
      answers: [{
        name: 'brunhilde.local',
        type: 'A',
        ttl: 300,
        data: '192.168.1.5'
      }]
    })
  }
});

Other packages similar to multicast-dns

bonjour

Bonjour is a higher-level mDNS package that provides an easy-to-use API for discovering and publishing network services. It builds on top of multicast-dns and abstracts some of the complexities involved in handling the mDNS protocol.

mdns

The mdns package is a more comprehensive solution for mDNS/DNS-SD service discovery. It is built on top of Apple's mDNSResponder, which is the same underlying technology used by Bonjour, Apple's implementation of zero-configuration networking. It provides a rich set of features but is not as lightweight as multicast-dns.

node-dns-sd

node-dns-sd is another package for service discovery using multicast DNS. It is similar to multicast-dns but focuses on the DNS Service Discovery (DNS-SD) protocol, which is built on top of mDNS and provides a standard way to discover services on a local network.

README

multicast-dns

Low level multicast-dns implementation in pure javascript

npm install multicast-dns

Usage

var mdns = require('multicast-dns')()

mdns.on('response', function(response) {
  console.log('got a response packet:', response)
})

mdns.on('query', function(query) {
  console.log('got a query packet:', query)
})

// lets query for an A record for 'brunhilde.local'
mdns.query({
  questions:[{
    name: 'brunhilde.local',
    type: 'A'
  }]
})

Running the above (change brunhilde.local to your-own-hostname.local) will print an echo of the query packet first

got a query packet: { type: 'query',
  qdcount: 1,
  ancount: 0,
  nscount: 0,
  arcount: 0,
  questions: [ { name: 'brunhilde.local', type: 'A', class: 1 } ],
  answers: [],
  authorities: [],
  additionals: [] }

And then a response packet

got a response packet: { type: 'response',
  qdcount: 0,
  ancount: 1,
  nscount: 0,
  arcount: 2,
  questions: [],
  answers:
   [ { name: 'brunhilde.local',
       type: 'A',
       class: 1,
       ttl: 120,
       flush: true,
       data: '192.168.1.5' } ],
  authorities: [],
  additionals:
   [ { name: 'brunhilde.local',
       type: 'A',
       class: 1,
       ttl: 120,
       flush: true,
       data: '192.168.1.5' },
     { name: 'brunhilde.local',
       type: 'AAAA',
       class: 1,
       ttl: 120,
       flush: true,
       data: 'fe80::5ef9:38ff:fe8c:ceaa' } ] }

CLI

npm install -g multicast-dns

multicast-dns brunhilde.local
> 192.168.1.1

API

A packet has the following format

{
  questions: [{
    name:'brunhilde.local',
    type:'A'
  }],
  answers: [{
    name:'brunhilde.local',
    type:'A',
    ttl:seconds,
    data:(record type specific data)
  }],
  additionals: [
    (same format as answers)
  ],
  authorities: [
    (same format as answers)
  ]
}

Currently data from SRV, A, PTR, TXT, AAAA and HINFO records is passed

mdns = multicastdns([options])

Creates a new mdns instance. Options can contain the following

{
  multicast: true // use udp multicasting
  interface: '192.168.0.2' // explicitly specify a network interface. defaults to all
  port: 5353, // set the udp port
  ip: '224.0.0.251', // set the udp ip
  ttl: 255, // set the multicast ttl
  loopback: true, // receive your own packets
  reuseAddr: true // set the reuseAddr option when creating the socket (requires node >=0.11.13)
}

mdns.on('query', (packet, rinfo))

Emitted when a query packet is received.

mdns.on('query', function(query) {
  if (query.questions[0] && query.questions[0].name === 'brunhilde.local') {
    mdns.respond(someResponse) // see below
  }
})

mdns.on('response', (packet, rinfo))

Emitted when a response packet is received.

The response might not be a response to a query you send as this is the result of someone multicasting a response.

mdns.query(packet, [cb])

Send a dns query. The callback will be called when the packet was sent.

The following shorthands are equivalent

mdns.query('brunhilde.local', 'A')
mdns.query([{name:'brunhilde.local', type:'A'}])
mdns.query({
  questions: [{name:'brunhilde.local', type:'A'}]
})

mdns.respond(packet, [cb])

Send a dns response. The callback will be called when the packet was sent.

// reply with a SRV and a A record as an answer
mdns.respond({
  answers: [{
    name: 'my-service',
    type: 'SRV',
    data: {
      port:9999,
      weigth: 0,
      priority: 10,
      target: 'my-service.example.com'
    }
  }, {
    name: 'brunhilde.local',
    type: 'A',
    ttl: 300,
    data: '192.168.1.5'
  }]
})

The following shorthands are equivalent

mdns.respond([{name:'brunhilde.local', type:'A', data:'192.158.1.5'}])
mdns.respond({
  answers: [{name:'brunhilde.local', type:'A', data:'192.158.1.5'}]
})

mdns.destroy()

Destroy the mdns instance. Closes the udp socket.

Development

To start hacking on this module you can use this example to get started

git clone git://github.com/mafintosh/multicast-dns.git
npm install
node example.js
node cli.js $(hostname).local

License

MIT