M251/M241 UDP Port Broadcasts (1740-1743)

[ryanAstiefes]

I need to shut-off these UDP broadcasts (Ports 1740-1743) that are sent out every 1 minute. I have a system that has 9 M251 which communicates over radio and is bogged down by these broadcasts. I've tried turning every Security Paramater off except Modbus Server since that’s the protocol used to communicate with the SCADA system, eventhough the SCADA system does not work very well due to these broadcasts. 

I have a call into Tier 3 but thought I might as well post here for other suggestions. 

[dnordenberg1]

Did you try turning off services also?

I think I would have solved this with some cheep router with firewall rules that filters out everything else than the wanted traffic.

[Ricard]

Hello My friends,

Ports 1740 to 1743 are CODESYS services, primarily used for communication via UDP and also be TCP. These ports allow for automatic device discovery and data transmission between the development environment and programmable controllers (PLCs) that use CODESYS.

Looking at the attached screenshot, it's true that there are a large number of frames, but they are small—only 60 bytes, which is the minimum frame size—and shouldn't slow down your network performance. The broadcast it generates is localized to the local network 192.168.2.0 and won't propagate to other networks.

However, if you've truly confirmed that it's affecting your SCADA's performance, I would suggest the following.

1. Manage VLANs with a TRUNK for communications with the SCADA
2. Create some ACL rules on the switches for ports 1740 to 1743
3. Manage inbound firewall rules for ports 1740 to 1743

I hope my comments have been helpful.

BR

Ricard