DHCP functionality for M172-18 I/O

[Kunal_ch]

Hi,

We are using M172 controller for our products that are installed in various locations having BACnet IP network.

Currently we have implemented static IP addressing in which we provide the ability to set the IP, Gateway, net-Mask from the PLC itself (during commissioning) with the intent that it shall stay the same throughout its lifetime, unless someone manually changes it again.

I realized that there is an "Enable DHCP_ETH_PI" BIOS parameter that is used to turn ON/OFF the DHCP capability (OFF by default).

If I change this to true for one of the controllers on site (already in the network) and run a power cycle, would it accept the IP address that was manually fed into the PLC (Ip_1_ETH_PI, Ip_2_ETH_PI, IP_2_ETH_PI, IP_4_ETH_PI) or the one assigned by the DHCP server upon bootup?

Also, are there any issues around using DHCP with BACnet? 

Thank you. 

[Bastian_Schmitz · Accepted solution]

The DHCP feature should work proper. You have from Programming site the possibility to read back the actual IP Settings which receive the controller via DHCP through the bios values 

I did not know any problems with DHCP and BACnet together with DHCP. 

[Kunal_ch]

Yeah, I tried it and realized if the PLC is booted up while connected to the network having a DHCP server, it gets assigned an IP through that.

If I reboot the PLC while keeping it disconnected from the network, then it accepts the static IP that was saved in the EEPROM.

I tried connecting to it through YABE using the IP address that was assigned by the DHCP and the connection was successful. I could read and write, from and to the BACnet objects.

That solves my doubts. 

Thank you.  

[Daniel_G]

I might be doing something wrong, but I am seeing a different behavior on my M172. If it is booted while disconnected from the network, the PLC does not ever finish booting (seemingly stuck somewhere). Plugging in the network is not sufficient; a reboot appears to be required. The PLC is running 'Msk668_14'.

The other strange behavior I noticed is that the BIOS values (as shown above by @Bastian_Schmitz ) do not show the assigned IP address (in my case, they're always 0.0.0.0).

[Daniel_G]

I downloaded an empty project and validated that the DHCP behavior was as expected (finishes booting if cable is not present, takes default IP address). I reverted to my original project, and the PLC still behaves as expected. Not sure what caused it to hang during booting previously.

In regards to the current IP address, I was looking at the wrong properties. I had not noticed the second "Ethernet" folder in the Commissioning view of the project which show the actual IP address octets.