Apple Open Source DNS Service Discovery Collection

The ServiceRegistration subdirectory contains implementations for several DNSSD (DNS Service Discovery) extensions. These extensions share a common codebase that is architecturally distinct and largely separate from the main mDNSResponder daemon.

Available extensions include:

• Service Registration
• Advertising Proxy
• Discovery Proxy
• Discovery Relay

The mdnsresponder project provides a variety of client implementations that demonstrate how to use the /usr/include/dns_sd.h APIs. These APIs allow developers to perform DNS Service Discovery (DNS-SD) tasks, such as browsing for services or registering services on a network.

Clients provided in this repository include:

• dns-sd: A command-line tool that can be built for multiple platforms (OS X via XCode or Make, and POSIX via Make).
• DNS Service Browser: A graphical client for OS X (requires Objective C and Cocoa).
• DNS Service Registration: A graphical client for OS X (requires Objective C and Cocoa).

Developers can use these clients as reference implementations to understand how to integrate DNS-SD capabilities into their own applications using the dns_sd.h header.

The DNSSD client library enables applications to interact with the mDNSResponder daemon to perform DNS-SD (DNS Service Discovery) operations. You can use this library to:

• Publish services: Advertise your application's services to the local network using DNS-SD.
• Browse services: Discover and list services being advertised by other devices on the local network.
• Resolve services: Once a service has been discovered/selected, use the library to resolve its specific details (such as IP addresses and ports).

The mdnsNSP is a NameSpace Provider (NSP) for Windows. It hooks into the standard Windows name resolution infrastructure, allowing any software that uses standard Windows APIs to resolve names via DNS-SD (DNS Service Discovery).

Once installed, services advertised via DNS-SD on the local network (e.g., http://computer.local./) will resolve correctly using standard Windows tools like Internet Explorer or other applications relying on Winsock name resolution.

The mDNSResponder daemon serves three primary roles:

1. DNS Stub Resolver: Performs DNS resolution for non-local queries.
2. mDNS Resolver: Resolves queries in the special .local domain using multicast DNS.
3. mDNS Publisher: Monitors multicast traffic on port 5353 to track advertised services and publishes its own mDNS information.

It is used as the system resolver on macOS and can be deployed on Linux and BSD platforms.

The DNSSD Discovery Proxy implements IETF DNSSD Discovery Proxy ([RFC8766]) and DNS Push ([RFC 8765]).

It provides authoritative DNS service for DNS Service Discovery by using mDNS instead of a stateful DNS database. This enables network infrastructure to provide service discovery automatically over DNS, solving the issue where services are only discoverable when a host is connected to a specific link in multi-link networks.

The DNSSD Service Registration Protocol Update Proxy acts as an SRP server that translates SRP registrations into DNS Updates ([RFC2136]).

Workflow:

1. The proxy accepts service registrations from SRP clients.
2. It generates a series of DNS Updates.
3. These updates can be authenticated using TSIG.
4. The proxy responds to the client only after all DNS Updates have completed (or reports if a part of the update fails).

Running this proxy makes the target DNS server behave as if it were natively an SRP server.

To create and test your own Thread Network, you must have the following components:

• A Border Router (BR)
• At least one Thread device (to connect to the border router and form the mesh)
• A computer (to test service discovery and the connection to the Thread accessory via the Border Router)