VMware ESXi lockdown mode is used to prevent local host access and, instead, require all host management to go through vCenter. That means that with lockdown mode enabled, you cannot login to the sever using SSH, configure it via PowerCLI, or even locally using Tech Support Mode (watch my video on tthe new 4.1 TSM here). You can even take this a setup further and enable “total lockdown”. With total lockdown, you won’t even be able to use the direct console user interface (DCUI) so there will be no local host management. Watch my video below on how each of these lockdown modes work, how to configure them, and how to test them to ensure that they are really enabled.
If you have more quetions on lockdown mode, please checkout Charu Chaubal’s post at VMware Blogs about the new 4.1 lockdown modes (which also contains my video).