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alvin0_0's avatar
alvin0_0
Copper Contributor
Sep 22, 2025

Clients failed to obtain internet right after DC 01 failover to DC02.

Hi, Recently, our team conducted a Disaster Recovery (DR) exercise where we successfully failed over from DC01 to DC02. The objective was to verify that DC02 could take over Windows services such as...
Active Directory
clustering
Windows Server
VGSandz's avatar
VGSandz
Copper Contributor
Sep 26, 2025

Hello ,
Active Directory should work in the DR scenario,

provided the clients lookup of domain has both the IPs.

provided the Client NICs have both DC1,DC2 as DNS, if AD is DNS integrated.

1.Clients began losing internet connectivity.

the clients may still hold on to stale IPs and may have lost GW.

2.DHCP failed to lease addresses to clients.


Is the DHCP configured to handle the DR scenario?
https://learn.microsoft.com/en-us/windows-server/networking/technologies/dhcp/dhcp-failover

Is your DHCP on DC01 or stanalone?, is DC02 authorized to lease ?  
Source : https://learn.microsoft.com/en-us/windows-server/networking/technologies/dhcp/quickstart-install-configure-dhcp-server?tabs=powershell#authorize-the-dhcp-server-in-active-directory

3.Connectivity on client machines was only restored after running the ipconfig /flushdns command, which forced them to communicate with DC02.


is your AD server also DNS? the DCDIAG /test:DNS /v has all the checks passed on both DCs - if successful it means DHCP and lease could be the issues.

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