Different with VMware ESX/i 4.1 and older, In the VMware vSphere ESXi 5.0 and newer ( 5.1, 5.5, and ESXi 6) you can't access the ESXi shell or remote using SSH because by default the settings are disable.
To make enable accessing ESXi Shell by direct or remote using SSH :
1. Go directly to the host
2. Press F2 Key (Customize System/View Logs)
3. Login using Administrator/root account.
4. Choose Troubleshooting Options, (use arrow key at the keyboard to highlight, then press Enter)
5. You can see the status of ESXi Shell and SSH at the right window, to toggle between disable and enable press Enter key
6. Press Escape key to back to main menu.
7. To start accessing ESXi shell directly, Press Alt + F1
8. To go back to main menu, press Alt + F2