DNS problems for satellite offices

Here is the setup...

One main office that has two physical DNS servers. 192.200.200.10 and 192.200.200.11

6 satellite offices (in same city) that are very small and connect to the main site by MPLS or VPN.

Each satellite has a Sonicwall TZ100 firewall with DNS configured as the following

DNS SErver 1: 192.200.200.10
DNS Server 2: 192.200.200.11
DNS Server 3: null

The problem..

When they lose connectivity to the main site they cannot surf the internet. We attempted to add a public DNS (ex:4.2.2.1) for the third DNS server. When we do this it causes problems. The computers will randomly not be able to ping main site hostnames and/or connect to the terminal server farm. We have to manually log into the machine and flushdns registerdns to get them back up.

The questions...

Having a DNS server at each satellite is out of the question. What is the best way to configure this? Also how can I prevent the problem i am having? Any assistance is appreciated.
Jryals8900Asked:
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Darius GhassemCommented:
Well here is the issue you really can't get around the issue. Here is the problem you clients must connect to internal DNS servers only so, when you have all DNS servers at HQ site and the remote sites lose connection then they will lose DNS resolution. You can NOT have external DNS servers at all in the TCP\IP properties of any system connected to a domain. Even if the external DNS server listed listed third the external DNS server will stilled be used like you have seen and cause issues.

If the internet goes you are kind of stuck unless you had DNS onsite locally.

Normally the clients have to connect to the HQ to get DNS resolution. Does the remote sites connect to the internet directly or through you HQ site?

Not much you can do. You can change DHCP so, when they lose HQ connection they can get a new IP lease with the local DNS servers removed and external added but this can be a pain.
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ColinMDCommented:
How many computers do you have at each site? It may be worth editing the hosts files on the computers instead. This is a sure way of getting DNS resolution working perfectly. I assume you have a VPN tunnel between sites? In this case, having one central DNS server and obviously having all the clients configured to point to this DNS server should work fine. Maybe have an external DNS server, i.e. 8.8.8.8 as a second server to help with internet surfing.
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