When I launch an FTP transfer from a client machine, it fails because it cannot connect to the server. With tcpdump I can see that the client sends a SYN to the server, and I can also see that the server received the SYN but it does not respond.
I made sure that the source/destination MAC address is correct, same for IP address.
There is absolutely no firewall rules whatsoever.
Any ideas how I can debug the issue?