[mdnsext] Hierarchical (host) domain names in mDNS?

["Albrecht, Harald" <[e-mail]>]

Hello,

something I couldn't find a proper answer to I would like to ask the mDNS experts on this list: is it possible to apply mDNS also to situations where the decentralized, configuration-free operation of mDNS is required but where the individual hosts within the same network need to make use of hierarchical domain names? Such as "controller.machine2.local"?

I'll illustrate this situation now in more detail: for instance, consider something like machines for producing bread rolls ... bakeries can buy such equipment from specialized machine manufacturers. Such (OEM) machines may very well be modular and with an inner structure that results on such a single machine equipped with several networked nodes, such as a user panel, a controller, and several devices for sensors and actuators. The OEM machine builder builds the machine and programs the networked nodes. Part of this process is, of course, to assign host names to the nodes. For instance, "hmi", "controller", "stamper", "former", "cooler", and so on. mDNS can be used in this situation to allow the individual nodes to communicate with each other independently of any concrete IP addresses set.

After the machine has been built, it is essentially sealed in terms of its setup. In particular, when the machine gets delivered to a customer and commissioned on site, it is not possible to change the host names as such anymore.

This is no problem if a customer just orders a single machine. However, if you need such machines, you surely need more than one. So we end up with multiple instances of the same blueprint. Of course, you could try to separate these machines into different subnets and thus different mDNS "domains". However, a bakery surely does not want to spend money on several routers just to make the name resolution work. Also, routers may very well increase administrative efforts ; something that these customers surely don't need and don't want.

So what is needed in this situation is to view the individual machines as domains, such as "machine1", "machine2", et cetera. The individual networked nodes inside these machines then would live in the sub name spaces, such as "controller.machine1" and "controller.machine2". We even see (in other applications) three levels of hierarchy, such as cells, machines, nodes inside these machines. However, these installations don't want to go the extra mile for a proper DNS infrastructure, but instead want to rely on a peer-based name resolution system, such as mDNS is one example of.

My (limited) understanding of mDNS is that this is not possible, as "controller.machine1.local" isn't allowed. Or am I mistaken here? Can mDNS handle such situations? Would IETF87 Berlin be the right place to discuss my situation and how to properly apply mDNS?

With best regards,
Harald Albrecht

Siemens AG
Industry Sector
Industry Automation Division
Industrial Automation Systems
I IA AS CTO DH 1
Gleiwitzer Str. 555
90475 Nürnberg, Deutschland
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