LAN Clients have no DNS resolution

[lexycode]

Hello Folks,
I hope anyone here can help me with with my problem.
I have a root server in a datacenter - running a Proxmox instance with 2 public IP's (one for the proxmox management and one for a pfsense VM WAN interface). The pfsense VM hast 2 NIC's WAN/LAN.

The pfsense get there static WAN IP from the datacenter DHCP (MAC based). That all works fine - pfsense can ping / nslookup works / VPN works.

Now I have some other VM's connected on the LAN interface (10.0.0.0/8 by pfsense DHCP) - all VM's can ping LAN IP's and all public IP's but there is no DNS resolution

resolf.conf on the LAN VM's show DNS server provided by datacenter / and they get IP's in the configured range-> DHCP works.

Firewall rules are factory default.

Can anyone give me a hint to solve this problem?

THX