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App on iOS and DNS - any issues or quirks?


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  • MVP 2014


I am working with an issue on the Remote Operator App for iOS.

The issue seems related to DNS.  The following works fine:

* iPhone connected to WiFi - the app connects to any active remote PLC I have tested with
* iPhone connected to Cellular data, PC tethered to iPhone - PC Remote Operator connects to any active remote PLC I have tested with
* iPhone connected to cellular data, app connecting to a remote PLC via it's direct IP address (not hostname) - OK

Where I see the issue is with the iPhone connected to cellular data, and connecting a remote site using a dyn-dns hostname.

* if I manually do an nslookup on the hostname, and enter that direct IP address into the app, it works
* if I enter the hostname directly into the app and allow the app to do the NS lookup, the communication fails.

I have peformed a packet trace from my phone for both types of connection.  With the hostname connection, it appears that the app successfully obtains the IP address and attempts communication with the PLC, but is not successful.  Hence I have confirmed the same underlying IP address is used with both the direct IP address entry and the hostname entry.  However the commuincation works for the direct IP address, and doesn't work for the hostname.

I have submitted this question to Unitronics support and they are working on it.  I'm interested to know if anyone else has seen anything like this.  Does anyone happen to have a test site set up using a hostname for access, rather than a direct IP address?


Thanks, Simon





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