What is Split Brain D.N.S ? How do you set Up this ?

Its a way to provide security to your internal network, by providing seperated DNS service from public network.

Split-Brain DNS is nothing more than setting up two independant set of DNS infrastructures hosting the same domain.  These two sets of infrastructures do not participate in any type of zone transfers.   Generally, the external DNS servers host external records, and the internal DNS servers host both the internal and external records.

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What is Split-Brain, Split-Horizon, or Split DNS? http://www.anitkb.com/2010/09/what-is-split-brain-split-horizon-or.html

Configuration:

http://msmvps.com/blogs/acefekay/archive/2009/09/04/split-zone-or-no-split-zone-can-t-access-internal-website-with-external-name.aspx

Reference: http://social.technet.microsoft.com/Forums/windowsserver/en-US/c38035f8-b975-4c58-99b2-952f3de9db74/configuring-splitbrain-dns?forum=winserverNIS

Split-brain DNS is a Domain Name System (DNS) configuration method that enables proper name resolution of local resources from both inside and outside of your local network. Use split-brain DNS when your edge router or firewall is configured to drop packets when it sees one of its connected networks trying to send information to itself. You configure a new primary DNS zone with the New Zone Wizard to set up split-brain DNS.