5 ms·

Industrial-IOT: Introduction to MODBUS protocol

22 points by shiv4nsh 10y ago

fest 10y ago
MODBUS over TCP is nice and good, but I'm worried that many people will soon start using it to communicate data with web-based monitoring platforms and will do it in plaintext. The current generation of PLCs are severely limited in the security aspect (example: Siemens S7-1200 series, designed in 2009 has no libraries for secure communications. Answer from Siemens: oh, you need security? buy our security gateway then!)
- lithos 10y ago
  I hope not. Most of the security for modbus are in the form of MasterLocks (those locks everyone learning to pick lock buy a dozen of). If you have physical access to the system it's assumed you're supposed to be there. At least in the limited number of systems I've seen, modbus is used for communicating status rather than control.
  - fest 10y ago
    Yes, MODBUS is usually used between locally connected devices (but not always for status, often also to control motors and valves). However, it's the thing everyone in industry knows how to use so it will likely be misused to send everything in plaintext over the Internet.
    - altstar 10y ago
      If you are using MODBUS over the internet you should be fired immediately. Any SCADA/DCS/PLC communication should not be allowed on the internet at all.
kristoffer 10y ago
Hmm the article plagiarises one of it references pretty verbatim (https://www.lammertbies.nl/comm/info/modbus.html https://www.lammertbies.nl/comm/info/modbus.html). Tacky!
- shiv4nsh 10y ago
  The points that were taken frim there are required for a full overview, because they have described it perfectly. Hence provided it as a reference.
  - kristoffer 10y ago
    You can't copy & paste paragraphs of text from your references, especially without quotation marks ...
  - revta 10y ago
    The points that were taken are incomplete. In both places they fail to mention the 30000-39999 range of addresses, which are known as input registers, Function code 04.
kevinherron 10y ago
Oooph. Modbus is grossly inappropriate for use in IIoT architectures. It's 20 years old and has not even the slightest hint of security. One thing we're seeing in practice is lower-powered industrial PCs running at remote sites exporting data from Modbus and other field protocols via something like MQTT on SSL. That being said, there are thousands of Modbus-speaking (and other protocols, too) devices sitting out there on the public internet behind a cellular modem waiting to be polled or actively being polled by SCADA systems built before anybody bothered to think about security.
- CptMauli 10y ago
  If you are not using a VPN tunnel to access your modbus devices, then you are criminally negligent. But I also discovered that an entire line of heat controllers is accessible via Modbus on the open internet. So if I want to shut down the heating for a few hundred appartment blocks, I could do that easily. And these are not actually old devices. There is even an app which you can download and control these.
jpfr 10y ago
Why use modbus, a protocol that is nothing more than remote access to a bitfield, when you can have OPC UA, a semantic object-database with an (encrypted) meta-object protocol for remote access and real-time notifications. If you look at the offerings of GE, Siemens, and the like, all signs point towards OPC UA as the TCP based protocol for industry that everybody agrees to use.
- kevinherron 10y ago
  Funny seeing you here :) I think we've worked out some interop issues between our OPC UA stacks in the past.
  - jpfr 10y ago
    Hey Kevin, It's a small world, apparently. :)
- CptMauli 10y ago
  In principle I agree. But OPC UA from an implementation standpoint of view is much more complicated and involved compared to modbus. I also would express your second paragraph slightly different. Each industry has its own preferred protocols and they are enhancing them and creating new ones. Additionally most companies offer OPC (UA) interfaces, thus making OPC the only protocol which is used over all industries. So if you want to interface with industrial systems, there is a good chance that the only thing you need is indeed OPC UA.

22 points by shiv4nsh 10y ago

fest 10y ago

MODBUS over TCP is nice and good, but I'm worried that many people will soon start using it to communicate data with web-based monitoring platforms and will do it in plaintext. The current generation of PLCs are severely limited in the security aspect (example: Siemens S7-1200 series, designed in 2009 has no libraries for secure communications. Answer from Siemens: oh, you need security? buy our security gateway then!)

lithos 10y ago
I hope not. Most of the security for modbus are in the form of MasterLocks (those locks everyone learning to pick lock buy a dozen of). If you have physical access to the system it's assumed you're supposed to be there. At least in the limited number of systems I've seen, modbus is used for communicating status rather than control.
- fest 10y ago
  Yes, MODBUS is usually used between locally connected devices (but not always for status, often also to control motors and valves). However, it's the thing everyone in industry knows how to use so it will likely be misused to send everything in plaintext over the Internet.
  - altstar 10y ago
    If you are using MODBUS over the internet you should be fired immediately. Any SCADA/DCS/PLC communication should not be allowed on the internet at all.

kristoffer 10y ago

Hmm the article plagiarises one of it references pretty verbatim (https://www.lammertbies.nl/comm/info/modbus.html https://www.lammertbies.nl/comm/info/modbus.html). Tacky!

shiv4nsh 10y ago
The points that were taken frim there are required for a full overview, because they have described it perfectly. Hence provided it as a reference.
- kristoffer 10y ago
  You can't copy & paste paragraphs of text from your references, especially without quotation marks ...
- revta 10y ago
  The points that were taken are incomplete. In both places they fail to mention the 30000-39999 range of addresses, which are known as input registers, Function code 04.

kevinherron 10y ago

Oooph. Modbus is grossly inappropriate for use in IIoT architectures. It's 20 years old and has not even the slightest hint of security. One thing we're seeing in practice is lower-powered industrial PCs running at remote sites exporting data from Modbus and other field protocols via something like MQTT on SSL. That being said, there are thousands of Modbus-speaking (and other protocols, too) devices sitting out there on the public internet behind a cellular modem waiting to be polled or actively being polled by SCADA systems built before anybody bothered to think about security.

CptMauli 10y ago
If you are not using a VPN tunnel to access your modbus devices, then you are criminally negligent. But I also discovered that an entire line of heat controllers is accessible via Modbus on the open internet. So if I want to shut down the heating for a few hundred appartment blocks, I could do that easily. And these are not actually old devices. There is even an app which you can download and control these.

jpfr 10y ago

Why use modbus, a protocol that is nothing more than remote access to a bitfield, when you can have OPC UA, a semantic object-database with an (encrypted) meta-object protocol for remote access and real-time notifications. If you look at the offerings of GE, Siemens, and the like, all signs point towards OPC UA as the TCP based protocol for industry that everybody agrees to use.

kevinherron 10y ago
Funny seeing you here :) I think we've worked out some interop issues between our OPC UA stacks in the past.
- jpfr 10y ago
  Hey Kevin, It's a small world, apparently. :)
CptMauli 10y ago
In principle I agree. But OPC UA from an implementation standpoint of view is much more complicated and involved compared to modbus. I also would express your second paragraph slightly different. Each industry has its own preferred protocols and they are enhancing them and creating new ones. Additionally most companies offer OPC (UA) interfaces, thus making OPC the only protocol which is used over all industries. So if you want to interface with industrial systems, there is a good chance that the only thing you need is indeed OPC UA.