This post discuss an issue trying to join certain workstations to the domain. We would see that every workstation in one site would join successfully and all the workstations in another site would fail with an error indicating that we could not locate a domain controller for that domain. My first hunch was either the domain controllers in the one site were broken, or there were networking issues in that problem site. The first step in troubleshooting is “Check the Event Logs!” We did not see any alarming events on any of the domain controllers in the problem site. So my next step was to take a network trace of the issue. With the help of a networking engineer here at Microsoft, Tim Quinn, we analyzed the traffic of a successful domain join and a failure. We took a simultaneous trace from the workstation and authenticating domain controller to ensure that we could see both sides of the conversation and uncover any failures across the wire.