Port forwarding impossible

[MatzDerTrainer]

Hello, I have another question.
I tried opening ports for Teredo, but no matter how I tried, be it v2/ray or via VPN, the ports remained closed during the subsequent test.
After some difficulties, the port forwarding for my NAS finally worked. I set up port forwarding for Teredo the same way I did for the NAS, but as I said, it didn't work.
The following ports are involved: 3544, 3074, 53, 80, 500, and 4500. Only port 80 could be opened.

[Ysurac]

Follow https://github.com/Ysurac/openmptcprouter/wiki/Port-forwarding#debug

[MatzDerTrainer]

Yes, that's right. I switched to Glorytun UDP because port 3544 should be opened via UDP, and I was hoping that would open it, but unfortunately it isn't. I'll switch back to Glortun TCP and run another tcpdump on the VPS.

When I run tcpdump on the router I get the following message:

root@OpenMPTCProuter:~# tcpdump -i any -p port 3544
Error relocating /usr/bin/tcpdump: pcap_open: symbol not found
Error relocating /usr/bin/tcpdump: pcap_findalldevs_ex: symbol not found

Now all that's left to do is run the following command on the VPS using the tcpdump command:
root@v1730XXXXXX:~# tcpdump -i any -p port 3544
tcpdump: data link type LINUX_SLL2
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on any, link-type LINUX_SLL2 (Linux cooked v2), snapshot length 262144 bytes

How the hell does the full log appear?

Sorry for my ignorance.

[Ysurac]

tcpdump was working before in your tests, you changed something ?

[MatzDerTrainer]

Yes, I switched to Glorytun TCP. After the tcpdump was so meaningless, I switched back to Glorytun UDP, but it looked the same.
Is there a folder where the full log is saved?

[Ysurac]

Nothing that you can see in log.
tcpdump should be running the same on both VPS and router side and give output on both side.
On VPS side, every lines with eth0 mean something enter or exit from VPS and with gt-* mean same from VPN. So in previous log you have VPN traffic on both side.
On router side you should see same traffic that enter or exit from tun0.

If there is in fact really traffic on both side, you may need to set SNAT.

[MatzDerTrainer]

I think I'm slowly starting to understand how tcpdump works. It's basically a live view of the port being monitored. So, something should only show up when the port is accessed, right?

What exactly is SNAT's function, and what do I need to configure? Port disclosure shouldn't be done via V2ray, but rather via VPN, right?