Supporting Windows

The following domain controllers were identified by the query:
siteb.tek-experts.com
sitea.tek-experts.com

However no domain controllers could be contacted.
Common causes of this error include:
- Host (A) or (AAAA) records that map the names of the domain controllers to their IP addresses are missing or contain incorrect addresses.
- Domain controllers registered in DNS are not connected to the network or are not running.

DNS address has been set properly in the tcp/ip settings. The weird thing is i can join PCs to the domain from sitea and siteb, but from sitec none of the PCs are able join to the domain with the same error. Its still in early stages, so i didnt make any changes in DNS server or anything else. Not sure why I cant join machines from siteC to the domain. 

Host (A) records in the DNS are properly set to the correct IP address. 

Win firewall was disabled. No AV installed at the moment to any of the DCs. The server from siteC can ping the other DCs via IP, FQDN and NETBIOS name and the DCs from siteA and siteB can ping the server in siteC. But still server in siteC cant join to the domain and promote it as DC for AD. Nslookup resolve the server names, because i made the reverse lookup zone. 

I am thinking about network issues. 

Any ideas from you? Every opinion will be good, what to check ..etc.

Best Regards,