Static IP RCM 4300 cannot be reached from sub network


I am using a RCM 4300 with dcrtcp.lib and http.lib. It is configured as a static IP on a subnet, called “A”.
From a computer on another subnet, called “B”, physically linked to “A” with the following IP configured I want to access my RCM using a web browser to display a web page. The thing is that the RCM 4300 can be pinged from the computer but the web page is not displaying on a web browser.

It seems that the RCM 4300 is resetting the connection.

3: 15:18:56.697290 802.1Q vlan#205 P0 INLINE-TAG 32 > R 0:0(0) ack 1189365308 win 0
4: 15:18:56.697931 802.1Q vlan#205 P0 INLINE-TAG 32 > R 0:0(0) ack 171557416 win 0

For more details, RCM 4300 is working on a http (not https), port 80, the web page is launching correctly if the computer is on the subnet “A”.

What should I look into in order to understand why it is not working correctly ? Feel free to ask me more details.

Thank you in advance for your time !

What are the subnet mask and default gateway settings for both the RCM4300 and your PC?

Are the subnets the same physical network? In the Rabbit’s TCP/IP stack, when sending data to a device not on the current subnet, the Rabbit will direct it to the default gateway for delivery to the target device.

To determine whether a device is on the same subnet, devices check whether “(src_ip & netmask) == (dst_ip & netmask)” (that’s a bitwise and). My guess is that the PC has the correct net mask ( so it can directly address the Rabbit, but the Rabbit thinks it’s on a smaller network (say and it should use the default gateway to reach the target.


Both equipements are on the same “physical” network, they’re just on a different “ips range”.
The PC is set as below:
IP : range
Gateway :
Subnet mask :

The RCM4300 is set as below:
IP :
Gateway :
Subnet mask :

For your information, from the PC the customer can “ping” the RCM 4300 via command prompt with this configuration.

However, I forgot to mention that on field, on the same subnetwork as RCM 4300, there are RCM 6700 which are communicating with RCM 4300, the configuration is similar to RCM 4300 (static IP):
IP :
Gateway :
Subnet mask :

Should I adapt these informations as well ?

Thank you

Is it possible this is a firewall issue? Can you run Wireshark or tcpdump on a computer on each network to capture traffic to help identify what might be happening? Maybe another device on the RCM4300 network is using the same IP address? That could explain the different ACK packets in close succession in the capture you included in your original question.
Are you using Dynamic C 10.72 or later (preferably 10.72E)?
If you think this is some sort of bug with the RCM4300 TCP/IP stack, you can open a ticket with Digi’s tech support department.

From the customer perspective, it is a RCM4300 fault. However, I have managed to ask them Wireshark traces.

As I don’t know how to share this data here, I have opened a ticket with technical support.