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 DNS, DHCP, and Active Directory (AD) to ensure business continuity.

However, after shutting down DC01, we observed the following issues:

1. Clients began losing internet connectivity.
2. DHCP failed to lease addresses to clients.
3. Connectivity on client machines was only restored after running the ipconfig /flushdns command, which forced them to communicate with DC02.
4. Everything when back to normal when we resumed AD01.

For additional context, our environment is also using ClearPass as the RADIUS server and has no issue authenticating clients.

I would like to seek advice from anyone with expertise in this area: did we overlook any critical steps during or after the failover process?