franck
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README was missing the continuous-caching and RFC 2308 negative response behavior added in recent commits. CLAUDE.md is new, providing architecture guidance for future Claude Code sessions.
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This is a Discovery Proxy for Multicast DNS-Based Service Discovery, written in pure Python. It makes use of zeroconf to obtain mDNS advertisements on the local network and Twisted to re-publish them as a unicast DNS service.
Both IPv4 and IPv6 are supported on the mDNS side. For IPv6, only Unique Local Addresses (ULA, fc00::/7) are published in AAAA records: link-local addresses aren't usable by unicast DNS clients (DNS has no way to express the required zone index), and globally routable addresses are filtered out so that only internal ULA addresses are advertised.
Rather than issuing a one-shot mDNS query and blocking for a timeout on every lookup, the proxy keeps a live mDNS cache warm in the background: browsing and previously-seen names/services are re-queried periodically, so most unicast DNS queries are answered straight from cache with a TTL that reflects the underlying record's real remaining lifetime. Negative responses (e.g. a name or service that doesn't exist) are returned per RFC 2308, with a synthesized SOA record in the authority section so resolvers can negative-cache them too.
This kind of proxy is specified by RFC 8766. I did not actually follow the standard in implementing it, which means that it doesn't abide by many of the finer details. Nevertheless, it works fine with clients like macOS 10.15 and iOS 13. Any violations of the standard are to be considered bugs and should be fixed over time.
Other implementations of discovery proxies are ohybridproxy and included with mDNSResponder. Since the former only runs on OpenWRT and mDNSResponder is not readily available on Linux, I decided to put together my own implementation in Python. Its dependencies are pure Python, so it should be possible to run it pretty much anywhere.
To use the discovery proxy, run it while specifying a domain to use and a port number to listen on:
python3 proxy.py home.arpa 35353
Then, delegate that domain to the machine the proxy is running on (192.0.2.2 in the example below) and advertise it by adding the necessary records to your network's DNS search domain (example.com in the example below). If you are using dnsmasq, this can be done using
server=/home.arpa/192.0.2.2#35353
ptr-record=b._dns-sd._udp.example.com,home.arpa
ptr-record=lb._dns-sd._udp.example.com,home.arpa
ptr-record=db._dns-sd._udp.example.com,home.arpa
To check whether it is working, you can try some of the following queries (assuming your computer is named yourcomputer and advertises an SSH service):
dig yourcomputer.home.arpa
dig yourcomputer.home.arpa aaaa
dig _ssh._tcp.home.arpa ptr
dig yourcomputer._ssh._tcp.home.arpa srv