Ping the engineering station from Laptop via the Router through the IOT2040

Hello,

i got a similar problem. My setup is the following: My Laptop is connected to a router. So is the IOT2040 (eth1). The engineering station is connected to eth0 of the IOT2040. I wanted to ping the engineering station from my Laptop via the Router through the IOT2040. Later i want to establish a TeamViewer Connection between the Laptop and the engineering station through the IOT2040. But i am not even able to ping the engineering station. I used Wireshark and i could see, that the packets arrived at my engineering station but somehow the response didn't go back through the IOT2040. I activated ip forwarding. Philipp said something about "enable routing the other way around". But i don't know how and where i can do that.

Can someone help me with this?

Best regards!

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Split from IOT as Router / OpenVPN .

Yes sure!

I attached a .png which describes my setup, also with the current IP Addresses. Eth1 of the IOT2040 gets its IP Address from the Router. Eth0 is static and has 192.168.200.1 like in the picture. The NIC of the engineering station has 192.168.200.10.

On my IOT2040 i activated ip forwarding by uncommenting net.ipv4.net_forward=1 in /etc/sysctl.conf. Furthermore, i used the following rules:

iptables -A FORWARD -i eth1 -j ACCEPT

iptables -t nat -A PREROUTING -i eth1 -j DNAT --to-destination 192.168.200.10

I can see Ping Requests coming when i open Wireshark on my engineering station. Also, when using TeamViewer, i can see a TCP Request but there is never an answer. With TCP there are always retransmissions, since the SYN+ACK is not sent back from the Engineering station, with ICMP i always get "no response found". So it seems the packets don't find their way back through the IOT2040. 

I hope this explains my problem better.

Best Regards!

I also tried it with a different Router, because i thought that maybe my first Router somehow blocks specific packets. But the result stays the same.

Does anyone else have an idea or any news? It seems that the IOT is the problem but I really can't see what i am missing..

I solved the problem. TeamViewer as well as Ping works now.

I forgot to use another rule. So the rules for tunneling through the IOT2040 with TeamViewer or Ping are:

iptables -t nat -A PREROUTING -i eth1 -j DNAT --to-destination 192.168.200.xxx

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

And of course, like already mentioned in the Post above, enabling ip forwarding.

Best regards!