Just trying to understand more on this, assume that we have two AD site, site A and site B. Each site has two domain controllers with DNS. For client machine in each site the DNS server entries are configured for the site domain controllers. For example:
Site A is having domain controller 1 and 2. Site B is having domain controller 3 and 4. User machine is site A is configured with DNS server entries of domain controller 1 and 2. Then for site B machine the DNS is configured for domain controller 3 and 4.
In this case, if site A both domain controllers were down and the user machine in site A can still ping to site B domain controller. How the user machine look for domain controllers in site B automatically since both the DNS server entries were down? Will the machine cache the list of domain controllers in the first place during the DNS record lookup?