[TUTORIAL] How to join a Proxmox cluster to an Active Directory Domain

Hello and sorry for bringing this old post up.
I have an issue when I'm trying to test the connectivity or join the domain:

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root@hlpve01:~# realm -v discover domain-name.com
* Resolving: _ldap._tcp.domain-name.com
* Performing LDAP DSE lookup on: 172.16.20.10
* Performing LDAP DSE lookup on: 172.16.20.11
! Can't contact LDAP server
! Can't contact LDAP server
domain-name.com
type: kerberos
realm-name: DOMAIN-NAME.COM
domain-name: domain-name.com
configured: no

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It seems that the cluster node/s could not contact the DC's/DNS servers via LDAP, even though I can ping both of my DC's/DNS servers from both of my cluster nodes and I have a rule defined via port forward for my cluster nodes to access the DC's from my LAN subnet 192.168.5.0/24 towards 172.16.0.0/16 network where my DC's are located on all protocols. There's a Firewall in between but that should not be the problem as I've mentioned that both cluster nodes have the rules defined to access both DC's on all protocols.
Do I need to configure/install something on the DC's ? like LDAP server roles ?

Does anybody have an idea what the issue could be ?
I would appreciate your help !

Kind regards.
 
Found myself the solution and I'll share it here just in case:

I had to make another DNS registrations for my DC's/DNS servers using the NAT virtual IP adress configured in my firewall and used by 192.168.5.0/24 subnet where my proxmox nodes are hosted.
 

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