I'm using a router cascade out of two Fritzbox 7390 to implement a light version of a DMZ. Every Fritzbox has its own subnet. Fritzbox 1 (192.168.178.0/24) is connected to the Internet Service Provider. The Fritzbox 2 (192.168.188.0/24) uses the WAN Port to connect to Fritzbox 1. I have a samba and SSH server running in the 192.168.178.0 net. Accessing Samba in this network is working perfectly. In my 192.168.188.0 net I'm able to access the internet. I can also establish a SSH connection to the server in the other network. But samba on the same server is not reachable(Timeout). On my Fritbox 1 theres a static port sharing rule for SSH but not for Samba because the server should only be accessible by SSH over the internet. I tried to create a port forwarding rule on my Fritzbox 2 for Samba (139 UDP and 445 TCP) but the user interface on the FB2 denies creating the rules. Do I really need the port forwarding rules on FB2 because SSH on the same machine is also reachable without a rule?
Following this troubleshooting manual helped me a lot: https://www.samba.org/samba/docs/using_samba/ch12.html. SSH, Telnet and FTP was working charmingly except from samba. So browsing the web I discovered that the Fritzbox blocks netbios packets by default for security reasons what makes totally sense. In my scenario I had to disable this filter using the Fritzbox web interface. In previous versions altering the settings export file should worked as well (Not tested)