All Linux distros won't connect to the net, internal or external.
From internal it could be based on many points here, vlans, firewall rules and and and....
From external it must be over VPN or if you talk about your servers inside of the DMZ it is another point we should now first.
It might be sounding strange, but you should be providing us perhaps with some more informations, that we not have to "digging all out of your nose". VLANs, DMZ, LAN or 2 DMZs, who is doing the DCHP job, if more the than one, were all the others set up as a DHCP-Relay or not?
What is all installed and activated?