Odd port closed problem: tcpdump shows packets are arriving to the right port but being ignored by transmission-daemon

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Dundu
Posts: 1
Joined: Fri Apr 23, 2021 5:05 am

Odd port closed problem: tcpdump shows packets are arriving to the right port but being ignored by transmission-daemon

Post by Dundu »

Hi

I have an odd case of the port closed problem, that I have no idea how to solve.

I run transmission-daemon in a Ubuntu 20.04 based container in my home server, from the transmissionbt repos, not the Ubuntu repos, current version is 3.00. It was working fine, until I had to reboot the server. No updates performed. Since then the test in transmission-remote says the port is closed, an external test says the port is closed and two torrents I downloaded since then with over 30 peers had not even one incoming connection (at first I though it was a problem of the test, but it seems the port is closed).

To try to find which part of my network was the problem, I started by running tcpdump in the container to see if connections were reaching. Everytime I press the test port button in transmission-remote, tcpdump shows a bunch of connections comming from vm4.transmissionbt.com reach the container and in the right port. So it seems the network is not the problem, the port forwarding is working fine. What makes it puzzling is that, after checking that the daemon had the right port configured, I run netstat in the container, and it shows that transmission-daemon is listening in the right port.

So tcpdump is showing the packets reach the container in the right port, and transmission-daemon is listening in that same port, but for some reason the packets are still ignored. And this was working fine before the reboot (and there has been no updates).

Any idea what could be happening? Do not heasitate to ask me to run any test.
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