DNS Server

[EliWaldner]

We have been running a program that includes a few HTTPCMD blocks and lately are are getting the following error....... "DNS server was unable to find address". When we use the "IP Address Lookup" tool, we find the IP address of the domain. The PLC is using the same DNS server as the machine running Do-More Designer so I would assume if the DNS address can be found with Do-More Designer, then the PLC should find it also? So why would we keep getting the error?
BTW we are running 2.9.7 OS in the PLC.


Any help would be greatly appreciated!

[franji1]

Designer is using your PC to use the DNS lookup, not the PLC's.

So, use NetEdit and please provide the following for your PLC having issues:

PLC's IP Address
PLC's Subnet Mask
PLC's Gateway Address
PLC's DNS Server

Make sure it's the main Ethernet port that NetEdit is looking at, and not an ECOMLT POM (are you using an ECOMEX by chance?).

Compare those to what your PC is using.  Are they on the same subnet?  Are they using the same Gateway?  Are they using the same DNS Server?  This is not a requirement (your PLC could be on a completely different network w/different server/gateway; this is actually OK, it would just explain why one may work ane the other does not).

[EliWaldner]

All the settings you mentioned are the same. I have even tried using different dns servers (ie 1.1.1.1). I tried running the same project on the Do-More Simulator and am not getting the DNS server errors. The biggest difference I see is the scan time for the simulator is from 90-120 and on the PLC it is around 2200-2400. Could that be the issue? If so, what can be done about it?

[franji1]

All the settings you mentioned are the same.

Please provide a screen shot from NetEdit.  Make sure the IP Address of the PLC is not the same as anything else on your network.

I have even tried using different dns servers (ie 1.1.1.1).

It may be an issue with the IP Address, Subnet Mask, Gateway Address, and DNS (can't get to an external DNS).

Please provide all those.

I tried running the same project on the Do-More Simulator and am not getting the DNS server errors. The biggest difference I see is the scan time for the simulator is from 90-120 and on the PLC it is around 2200-2400. Could that be the issue? If so, what can be done about it?

No.  The Simulator is running on a multi GHz PC vs. the PLC on 75 MHz.  Your PLC scan time is not bad (2.4ms).

You might try just a DNSLOOKUP instruction with the same text as your HTTPCMD - make sure the URL is same/correct (0 vs O, 1 vs l vs I, etc.).

Are you using the onboard Ethernet port (no POM)?

[EliWaldner]

Attached is the NetEdit screen shot. The IP address is not the same as anything else on the network.

We are using the onboard Ethernet port.

I tried DNSLOOKUP with the same results. "DNS address not found....." See the attached screen shot.

[BobO]

And 192.168.1.26 is the value returned by the "Get PC's DNS Server Address" button?

[EliWaldner]

Yes. That is the IP for the site gateway.

[BobO]

Yes. That is the IP for the site gateway.

I am unaware of any issue accessing DNS servers, so the only thing I can think of is that the gateway's DNS function is behaving differently in a way the PLC isn't happy with. If we were able to dupe it we might be able to fix it, but presumably we'd need to duplicate the gateway setup.

[EliWaldner]

It seems we found an issue with the gateway. I'll post what we found after I get a better explanation of what was changed to resolve the issue.

Thanks for your help and I'm sorry for the confusion.

[EliWaldner]

Yes, there was a problem with the DNS server on site. The issue has been solved.

Thanks again!