DNS Design (9/11)
Install a DNS server on at least two DCs in each AD domain and one DC in each site
Delegate a DNS zone for each AD domain to the DNS servers running on a DC in that AD domain
If different domains of the forest are connected over slow links, delegate the zone _msdcs. and make at least one DNS server in every site secondary for this zone
Each client should be configured to query at least two DNS servers one of which is in the same site