net-mdns

A simple Multicast Domain Name Service based on RFC 6762. Can be used as both a client (sending queries) or a server (responding to queries).

A higher level DNS Service Discovery based on RFC 6763 that automatically responds to any query for the service or service instance.

Features

• Targets Framework 4.6.1, .NET Standard 1.4 and 2.0
• Supports IPv6 and IPv4 platforms
• CI on Circle (Debian GNU/Linux), Travis (Ubuntu Xenial and OSX) and AppVeyor (Windows Server 2016)
• Detects new and/or removed network interfaces
• Supports multicasting on multiple network interfaces
• Supports reverse address mapping
• Supports service subtypes (features)
• Handles legacy unicast queries, see #61

Getting started

Published releases are available on NuGet. To install, run the following command in the Package Manager Console

PM> Install-Package Makaretu.Dns.Multicast

or using .NET CLI run the following command in the project folder

> dotnet add package Makaretu.Dns.Multicast

Usage Service Discovery

Advertising

Always broadcast the service ("foo") running on local host with port 1024.

using Makaretu.Dns;

var service = new ServiceProfile("x", "_foo._tcp", 1024);
var sd = new ServiceDiscovery();
sd.Advertise(service);

See the example advertiser for a working program.

Discovery

Find all services running on the local link.

using Makaretu.Dns;

var sd = new ServiceDiscovery();
sd.ServiceDiscovered += (s, serviceName) => { // Do something };

Find all service instances running on the local link.

using Makaretu.Dns;

var sd = new ServiceDiscovery();
sd.ServiceInstanceDiscovered += (s, e) => { // Do something };

See the example browser for a working program.

Usage Multicast

Event Based Queries

Get all the Apple TVs. The query is sent when a network interface is discovered. The AnsweredReceived callback contains any answer that is seen, not just the answer to the specific query.

using Makaretu.Dns;

var mdns = new MulticastService();
mdns.NetworkInterfaceDiscovered += (s, e) => mdns.SendQuery("appletv.local");
mdns.AnswerReceived += (s, e) => { // do something with e.Message };
mdns.Start();

Async Queries

Get the first answer to Apple TVs. Wait 2 seconds for an answer.

using Makaretu.Dns;

var service = "appletv.local";
var query = new Message();
query.Questions.Add(new Question { Name = service, Type = DnsType.ANY });
var cancellation = new CancellationTokenSource(2000);

using (var mdns = new MulticastService())
{
    mdns.Start();
    var response = await mdns.ResolveAsync(query, cancellation.Token);
    // Do something
}

Broadcasting

Respond to a query for the service. Note that ServiceDiscovery.Advertise is much easier.

using Makaretu.Dns;

var service = "...";
var mdns = new MulticastService();
mdns.QueryReceived += (s, e) =>
{
    var msg = e.Message;
    if (msg.Questions.Any(q => q.Name == service))
    {
        var res = msg.CreateResponse();
        var addresses = MulticastService.GetIPAddresses()
            .Where(ip => ip.AddressFamily == AddressFamily.InterNetwork);
        foreach (var address in addresses)
        {
            res.Answers.Add(new ARecord
            {
                Name = service,
                Address = address
            });
        }
        mdns.SendAnswer(res);
    }
};
mdns.Start();

Related projects

• net-dns - DNS data model and Name Server with serializer for the wire and master file format
• net-udns - client for unicast DNS, DNS over HTTPS (DOH) and DNS over TLS (DOT)

License

Copyright © 2018-2019 Richard Schneider (makaretu@gmail.com)

The package is licensed under the MIT license. Refer to the LICENSE file for more information.