If you read the original SRV RFC, it says that all protocol labels are followed by either _tcp or _udp, and that is why they are used for DNSSD as well. The reason for this is that the TCP port namespace and the UDP port namespace are separate namespaces, so without specifying the port namespace in the label, the SRV record is actually ambiguous, since it itself does not specify a transport type.
This whole model is probably not ideal, but it's what we have. So in this context, the fact that the protocol label precedes a transport label does not mean that it therefore does not need to be registered: just the opposite. With respect to SRV records, there _aren't_ any labels other than _tcp and _udp that immediately precede the domain containing the service name. The service type is always followed by one or the other. > On 2 Oct 2026, at 23:55, Paul Wouters <[email protected]> wrote: > > On Fri, 2 Oct 2026, Stuart Cheshire wrote: > >>> Or if phrased differently, you wouldn't put DNS-SD entries in your >>> public forward DNS zone that is hosted on the internet. >> >> Absolutely you would, and people do. >> >> This is described in the O’Reilly book “Zero Configuration Networking: The >> Definitive Guide” >> >> <https://www.oreilly.com/library/view/zero-configuration-networking/0596101007/> >> >> For an example closer to home, consider the IETF itself. For many years, >> IETF meetings provided a printer in the “terminal room”. The NOC staff added >> DNS records to describe that printer. This made the printer discoverable >> from any wired or wireless network in any of the IETF meeting rooms, not >> just from the local Ethernet in the terminal room. A step-by-step >> explanation of precisely how this worked is available here: >> >> <https://datatracker.ietf.org/doc/html/draft-cheshire-dnssd-roadmap-03#appendix-A> > > Ahh, thank you for that clarification. But I still see in such an example: > > term-printer._pdl-datastream._tcp.meeting.ietf.org. srv > > It is still below _tcp, so I would argue that falls outside the scope of > the Underscored and Globally Scoped DNS Node Names, which only talks > about the most parental underscore domain registrations. > > It seems pdl-datastreama (without underscore) is registered in the regular > ports and services registry, eg > > https://www.iana.org/assignments/service-names-port-numbers?search=9100 > > So this still leads me to believe that these entries below the protocol > identigier in dns-sd, do not belong in the Underscored and Globally > Scoped DNS Node Names Registry. > > If I am still getting this wrong, please do let me know. > > Paul > _______________________________________________ > DNSOP mailing list -- [email protected] > To unsubscribe send an email to [email protected] _______________________________________________ DNSOP mailing list -- [email protected] To unsubscribe send an email to [email protected]
