News:

  • February 05, 2023, 06:25:17 PM

Login with username, password and session length

Author Topic: Modbus TCP via Port Forward on StrideLinx VPN Router  (Read 327 times)

Bolt

  • Hero Member
  • *****
  • Posts: 493
Modbus TCP via Port Forward on StrideLinx VPN Router
« on: November 28, 2022, 02:43:04 AM »
I'm trying to Modbus TCP to a BRX that is behind a StrideLinx VPN router, via a network local to the WAN port, not through the VPN. I can't get it to work.

I have port 502 forwarded in the router setup
I have 4 sessions, port 502, 60 second time out, enabled for Modbus/TCP Server Settings
I am testing it via modpoll, and instantly get response Network connection was closed by remote peer!
I tried same modpoll test on test BRX and a PC on the local LAN, and succeed.
I can "login" via telnet routeripaddress 502
I get no activity in ModbusTCPServer.ActiveSessions, .Errors, .Transactions

Any other things I can check or test?

franji1

  • Bit Weenie
  • Host Moderator
  • Hero Member
  • *****
  • Posts: 3468
    • Host Engineering
Re: Modbus TCP via Port Forward on StrideLinx VPN Router
« Reply #1 on: November 28, 2022, 10:17:43 AM »
I'd also post this on ADC's community website to get some StrideLinx eyes looking at this too.
https://community.automationdirect.com

Bolt

  • Hero Member
  • *****
  • Posts: 493
Re: Modbus TCP via Port Forward on StrideLinx VPN Router
« Reply #2 on: November 28, 2022, 10:21:30 AM »
Thought about it, will do. But kinda leaning towards a BRX issue nuance, because as far as I can tell it is forwarding through the router.

Controls Guy

  • Internal Dev
  • Hero Member
  • ****
  • Posts: 3478
  • Darth Ladder
Re: Modbus TCP via Port Forward on StrideLinx VPN Router
« Reply #3 on: November 29, 2022, 01:05:48 AM »
Put a PC in the PLC LAN and try to Modbus to it from the same place from which you're trying to reach the BRX.  Run Wireshark on that new PC.
I retract my earlier statement that half of all politicians are crooks.  Half of all politicians are NOT crooks.  There.

franji1

  • Bit Weenie
  • Host Moderator
  • Hero Member
  • *****
  • Posts: 3468
    • Host Engineering
Re: Modbus TCP via Port Forward on StrideLinx VPN Router
« Reply #4 on: November 29, 2022, 09:11:12 AM »
Put a PC in the PLC LAN and try to Modbus to it from the same place from which you're trying to reach the BRX.  Run Wireshark on that new PC.
Great idea!  I was thinking mirroring router, but this is much simpler and gets you 99% of the "same" setup.

Just make sure PC subnet and mask match the BRX subnet and mask exactly, e.g. 192.168.x.x and 255.255.0.0

Bolt

  • Hero Member
  • *****
  • Posts: 493
Re: Modbus TCP via Port Forward on StrideLinx VPN Router
« Reply #5 on: November 29, 2022, 10:47:08 AM »
Put a PC in the PLC LAN and try to Modbus to it from the same place from which you're trying to reach the BRX.  Run Wireshark on that new PC.

So I don't need a modbus server on the PC, just the captured port traffic will be enough?

Controls Guy

  • Internal Dev
  • Hero Member
  • ****
  • Posts: 3478
  • Darth Ladder
Re: Modbus TCP via Port Forward on StrideLinx VPN Router
« Reply #6 on: November 29, 2022, 11:17:07 AM »
Correct.   Wireshark will even recognize it as a Modbus/TCP request and tell you the request code, register(s), etc.
I retract my earlier statement that half of all politicians are crooks.  Half of all politicians are NOT crooks.  There.

BobO

  • Host Moderator
  • Hero Member
  • *****
  • Posts: 5793
  • Yes Pinky, Do-more will control the world!
Re: Modbus TCP via Port Forward on StrideLinx VPN Router
« Reply #7 on: November 29, 2022, 12:40:35 PM »
Correct.   Wireshark will even recognize it as a Modbus/TCP request and tell you the request code, register(s), etc.

Unless something is accepting connections on 502, I don't think you'll ever get to the Modbus request. Has to be a server running somewhere.
"It has recently come to our attention that users spend 95% of their time using 5% of the available features. That might be relevant." -BobO

Controls Guy

  • Internal Dev
  • Hero Member
  • ****
  • Posts: 3478
  • Darth Ladder
Re: Modbus TCP via Port Forward on StrideLinx VPN Router
« Reply #8 on: November 29, 2022, 01:13:42 PM »
Hmmm, see your point.   Maybe run the BRX Sim.
« Last Edit: November 29, 2022, 01:25:11 PM by Controls Guy »
I retract my earlier statement that half of all politicians are crooks.  Half of all politicians are NOT crooks.  There.

franji1

  • Bit Weenie
  • Host Moderator
  • Hero Member
  • *****
  • Posts: 3468
    • Host Engineering
Re: Modbus TCP via Port Forward on StrideLinx VPN Router
« Reply #9 on: November 29, 2022, 02:06:31 PM »
Hmmm, see your point.   Maybe run the BRX Sim.

Good idea.  The BRX Sim should be listening on port 502.

Bolt

  • Hero Member
  • *****
  • Posts: 493
Re: Modbus TCP via Port Forward on StrideLinx VPN Router
« Reply #10 on: December 01, 2022, 12:05:48 PM »
So I get the same "Network connection was closed by remote peer!" response when connected to the local side of the router with laptop and sending a test modbus command to the BRX in question. I can modbus to another BRX behind the same router with no problem.
I also get the same "Network connection was closed by remote peer!" when trying it on a different local network, no router, just switch, to the BRX via an ECOMX POM.
If I change the parameters to be "wrong", I get a "Can't reach server/slave! Check TCP/IP and firewall settings." response, so it is connecting to the BRX in the first scenarios.
« Last Edit: December 01, 2022, 12:08:30 PM by Bolt »

Bolt

  • Hero Member
  • *****
  • Posts: 493
Re: Modbus TCP via Port Forward on StrideLinx VPN Router
« Reply #11 on: December 01, 2022, 12:46:32 PM »
I have tried disabling Modbus TCP Server, writing to PLC, re-enabling Server and write, etc. Changed port numbers, etc. No change. I have been able to write to and from my laptop to other BRX's, other PC's, inside and outside the VPN router, so the port forwards are working just fine.

Bolt

  • Hero Member
  • *****
  • Posts: 493
Re: Modbus TCP via Port Forward on StrideLinx VPN Router
« Reply #12 on: December 01, 2022, 01:05:59 PM »
Well, that was easy. There were some old, forgotten whitelist settings in the PLC. Now it works just fine. Thanks for reading!