How do nisyscfg.lvlib:Find.vi (And MAX) actually find systems?

[MarkBowles]

Hi, all,

We have a LabVIEW 20 SP1 app consisting of a Windows-based HMI and a cRIO-based processor.  When the HMI starts up, it calls nisyscfg.lvlib:Find.vi to get a list of systems available to connect to.

This has worked great for years, but we are expanding and are facing the prospect of breaking our network into subnets. Up until now, the HMI machines and the cRIOs have all been part of the same network: 10.1.1/255.255.255.0, and both our HMI and MAX have been able to find the cRIOs.  A quick experiment has shown that an HMI on 192.168.1.30 can't find the cRIO at 10.1.1.29, even though a "ping" command from the HMI to the cRIO is successful. MAX (running on the 192.198 machine) doesn't see this cRIO, either.

It would be helpful to know how the two parties find each other.  How does the library "know" where the systems are?  Does it periodically sequence through network addresses and attempt to query them?  Is there IP broadcast or multicast involved? Do the systems "register" with the library somehow, and if so, how do they "know" where it is?

I'm hoping we can configure our routers to enable this rendezvous protocol to reach out into and across subnets. 

Thanks,

-- Mark

[ZYOng · Accepted solution]

Excerpt from How does NI MAX discover RT targets on a different subnet?

MAX is not capable of spontaneously discovering controllers on other subnets, because as others have pointed out, discovery is fundamentally a link-local process — it doesn't cross network gateways. It can only connect to remote targets if you give its IP, or its hostname if it's registered in DNS.

FWIW, this has a couple of esoteric implications for target formatting and reimaging. If you reformat a controller on the local network, and its IP address changes, MAX is able to identify the new IP address based on its link-local broadcast announcements. But if a remote target's address changes — i.e., it's addressed by IP and its IP changes, or it's addressed by hostname and its hostname is  changed or is removed from DNS — then you're out of luck.