If you are having trouble with your Linked Mode group, consider the following points.
When you have multiple vCenter Server instances, each instance must have a working relationship with the domain controller and not conflict with another machine that is in the domain. Conflicts can occur, for example, when you clone a vCenter Server instance that is running in a virtual machine and you do not use sysprep or a similar utility to ensure that the cloned vCenter Server instance has a globally unique identifier (GUID).
If the domain controller is unreachable, vCenter Server might be unable to start. You might be unable to change the Linked Mode configuration of the affected vCenter Server system. If this occurs, resolve the problem with the domain controller and restart vCenter Server. If resolving the problem with the domain controller is impossible, you can restart vCenter Server by removing the vCenter Server system from the domain and isolating the system from its current Linked Mode group.
The DNS name of the machine must match with the actual machine name. Symptoms of machine names not matching the DNS name are data replication problems, ticket errors when trying to search, and missing search results from remote instances.
Make sure your Windows and network-based firewalls are configured to allow Linked Mode.