A checklist for Active Directory connection troubleshooting:
- Verify Domain Name System (DNS) settings – Make sure the DNS settings are manually configured or configured to use Dynamic Host Configuration Protocol (DHCP) to get DNS settings from the server.
- Ensure that necessary firewall ports are open – Confirm that ports 88, 135, 137, 138, and 445 are open in the host or domain firewall so that communication between client machines and domain controllers is allowed.
- Check the network cables and other hardware – Verify that everything is properly plugged in, including network cables and monitor cables. Ensure all cables are securely connected, and there are no loose connections.
- Restart the domain controller – Reboot the domain controller to ensure all services are running. This should allow the computers in the domain to communicate with the router.
