Backup Domain Controller can't join Domain - ERROR: Invalid IP address


Hello everyone,

I just tried to join a backup domain controller to my domain. All the join scripts work except for 96univention-samba4.inst and 98univention-samba4-dns.inst. The samba4 of these scripts throw an error like this:

Join against S4 Connector server: ucs
ERROR: Invalid IP address ''!
Samba currently not available on S4 Connector server ucs.
Make sure the server is online or if this server is no longer in use,
please completely remove the server object from the domain.
ERROR: Invalid IP address ''!
ERROR: Invalid IP address ''!
Failed to join the domain.

This error is thrown even though I have confirmed that both s4-connector and samba4 are running on the domain controller.

Can anyone shed some light as to why this is happening, and how I can fix it? Both servers are running UCS version 4.3.3 errata419, and both servers have the other server’s IP address set as one of their Domain name servers.



I spent a couple hours troubleshooting this, and it turned out it was a firewall at the network level blocking outgoing ports that are necessary according to this.