What happens if all the DC in a site fails?

Question

We are in a process to migrating DC from legacy to 2019. I wanted to know where does the load goes if all the DCs in a Site fails or demoted?

Answer 1

Hello,

Thank you so much for posting here.

By default, clients who cannot authenticate with DC's in their site, will try to authenticate with DC's in other sites. By default clients will use any available domain controller, unless the Group Policy setting is enabled: Try Next Closest Site

Then the client leverages the Windows DC Locator Process to identify domain controllers using a combination of AD site cost data and DNS LDAP weights/priorities.

References:

https://learn.microsoft.com/en-us/windows-server/identity/ad-ds/plan/enabling-clients-to-locate-the-next-closest-domain-controller

https://learn.microsoft.com/en-us/archive/blogs/askds/sites-sites-everywhere

For any question, please feel free to contact us.

Best regards,
Hannah Xiong

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Answer 2

Assuming the clients have the address of a domain controller for another site they could authenticate there, so check the DHCP server config.

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Answer 3

Hi,

If all domain controllers in same are offilne , it generate a authentication issue if there is no network flow opened woth other DC in snother active directory site.

You can encounter a DNS issue if all clients use local domain controllers for DNS resolution.

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