RCM6760 responds with RST, ACK over VLAN but responds with proper SYN, ACK when using direct cable connection

We have several models of the Rabbit RCM modules in the field. At one facility we have an RCM2200 on the same VLAN and switches as an RCM6760.

Using Wireshark, when monitoring the RCM2200, we can see the proper SYN, SYN,ACK, ACK.

When monitoring the RCM6760, we see the SYN from the software, but get a RST,ACK response from the RCM6760.

We can disconnect the 6760 from the network, connect a laptop directly to the 6760, and the software connects every time. Therefore we know the host application is running and the port is being listened to.

Our customer is desperate for a resolution to this issue. Please advise.

I found this forum post which describes a very similar scenario. I could not see if their recommendation was successful or was advisable.

Hello, Please provide more information about your issue.
I would like to know, below details.

What type of application are you running on the modules(RCM2200, RCM6760)?

When the modules connected in the network, what is your expected out put?

I could not understand what resolution you are expecting?

Please explain the problem clearly.

Thank you.

Thank you for asking. I will gladly produce more information at your request. This is a huge issue we need to get addressed.

We are running a simple “weld monitoring” application on the RCM 6760. It is basically running the embedded system and providing ethernet communications.

The RCM 2200 is simply being used for ethernet communications…so the program is simpler.

We have a software application we have developed which initiates a socket connection with the RCM modules. This has worked without much excitement for many, many years.

We have since added our system using the RCM6760 to a more complex network. The RCM2200 had no issues on this same network…so we expected the RCM6760 to work the same.

The system running the RCM6760 will simply not successfully establish an ethernet connection to the PC application in the VLAN scenario where default gateway is required to resolve the ip address. We can connect the PC software directly to the RCM6760, and the PC software and the 6760 communicates brilliantly. When you try to connect over the VLAN, it will not connect.

So we opened up Wireshark, and found that the 6760 is responding to the SYN request from the PC software with a RST, ACK. Searching this, we have found no real answers. The answers they offer online are not valid because we can prove the system is functioning properly with a direct connection, and we know the firewalls are not blocking because the RCM2200 system is working as expected in the exact same network topology.

The desired output is for the 6760 to respond properly to the SYC request in a VLAN scenario.

Thank you again for looking into this.

Hello, You mean the RCM6760 is not getting the IP address? Did you add proper network configurations in the application?
Did you try to run any default network sample application that comes with the Dynamic C 10.72? You can find the network samples at the below path

Try to run sample applications on the module with the proper network settings. If it runs,then check your custom application.

I would like to know how this matter ended up, because we are facing problems with vlans too.

Fortunately for us, the customer changed something on their network and the issue was resolved. Unfortunately I did not pursue what they did to rectify the issue.

Same here, kind of.