What is the different between internal DNS and external DNS?

How can I configure a windows DNS server to prioritize several host entries, related to the same hostname but with different IPs, according to the IP of the resolver?

• The scenario in detail: I have a windows DNS server (2012 r2) that manage the hostname entries of a 192.168.100.0/24 network. In this network there is an openwrt router with the address 192.168.100.190. Another network, 172.22.1.1/24, is connected to the network 192.168.100.0/24 through VPN using the openwrt router mentioned above. The openwrt router is also doing IP mapping, so for the devices in the network 172.22.1.1/24 the network 192.168.100.0/24 appears as the network 172.24.1.1/24. Instead for the devices in the network 192.168.100.0/24 the requests that come from 172.22.1.1/24 are seen as requests from the router 192.168.100.190. The problem is that if a device in the network 172.22.1.1/24 ask for a name resolution to the DNS in the network 192.168.100.0/24 it receives an ip belonging to the network 192.168.100.0/24. I cannot use http://technet.microsoft.com/en-us/library/cc961422.aspx because for the DNS the device that is asking is the router, that belongs to the 192.168.100.0/24 network. So, before using static mapping in the hosts file, i would like to know if is possible to configure the windows DNS server to reply with different ip resolution (in this case, replying with 172.24.1.x instead of 192.168.100.x) if the router, and only it, asks for ip resolutions.

• Answer:

  Have you looked at http://technet.microsoft.com/en-us/library/cc961422.aspx , http://technet.microsoft.com/en-us/library/cc787373%28WS.10%29.aspx and http://windowsitpro.com/networking/how-can-i-enable-or-disable-subnet-prioritization-dns-server? If this doesn't do it for you, I'll share something I have previously done in a (possibly) similar situation. Since the OpenWRT router is the device asking, why not set the WRT router to redirect DNS requests (perhaps via DNSmasq), and point it to a secondary DNS server that would specify the correct/desirable IP mappings for a secondary (perhaps your VPN) network?  I've mapped DD-WRT routers on different networks to their DNS servers through OpenVPN this way, but it's perhaps not identical to your networked infrastructure or a fit for your particular needs. I entirely understand that this does not directly answer your question in the way you've framed it, but this is what I've done to help map DNS resolutions to the correct IPs on differing networks, where the same VoIP server was responsible for several networks and we didn't want to have different URIs for each network's phones configurations, and networks weren't allowed to be routed between each other for security reasons.