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Looks like I'm currently under a DOS attack or something like that, I've been monitoring the traffic on the server using jnettop, this is a of what I see during normal conditions:

and this is an example of when the issue is happeing:

SO my question is: what does that "IP" in protocol and also "0" in port means????

I replaced the ip of my server with: to make it more readable. Of course this is just an entry of the output, in nomral operation the list has many more entries, and when I'm under the attack, also I see several entries with the same HUGE RX and 0 TX, so the solution is not just block that IP in the example.

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Could be that the attackers are using some exotic protocol on top of IP, that jnettop doesn't recognize.

You could try to use a network capture tool, with a filter such as not tcp and not udp, and see what remains.

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