When using a KVM remote control session over LAN, the transition from in-Band to Out-Of-Band is seamless. However, KVM over wireless is a different story: when the OS shuts down the KVM session drops during transition from OS control of the interface to Intel ME control of the interface! The operator needs to close and re-start a new session or use some workaround (ex. SOL). Same issue when the system goes from OOB back to OS, session drops and important screen messages are lost.
Undoubtedly, not a smooth user experience! Fortunately, there is a solution.
Changing Link Preference:
In Intel AMT 6.0 a new feature was introduced: ability to manually switch who is in control of the wireless network interface: the OS or the Intel ME. The selection of who is in control of the interface is called Link Preference.
With this feature, the solution to the KVM issue is simple: manually switch to ME control of the interface BEFORE shutting down the OS. By switching to ME in advance, when the OS shuts down, the ME is already in control of the interface and KVM will not experience the transition that causes the session to drop.
The only impact when switching Link Preference (either from OS to ME or ME to OS) there is a temporary disconnection (a brief screen refresh) and in some implementations a popup message:
The two Link Preference options are:
- Host Link Preference. In this mode the OS is in control of the interface. The ME will only take control when the OS is down. However, transition will cause KVM session to drop.
- ME Link Preference. In this mode, AMT is always in control of the network and it never relinquishes control to the OS. KVM session will be un-disrupted regardless of reboot or any other state of the system.
Which begs the Question: Why not use the ME Link Preference all the time? After all, you get continuous un-disrupted connectivity between in-band and Out-of-Band!
Here is the catch: LAN & WLAN are two different animals. Unlike LAN, in WLAN when the ME is in control of the network, the OS does not have access to the network, any OS connectivity to the network is lost. So if you are in KVM session with ME Link Preference, even if the OS is up, the only network activity possible is AMT related!
Typical session flow to a client in In-Band state:
- Start your KVM session, Link preference by default is Host OS, do all your In-Band work with Host Link.
- When you are ready to bring down the OS, before executing the shutdown command, switch to ME Link.
- When you are done with Out-Of-Band work, restart the OS.
- When the OS is fully up, switch back to Host Link Preference.
With this flow you are in the same un-disrupted KVM session throughout your support activity.
Typical session flow to a client in Out-Of-Band state:
- First, change Link Preference on the viewer to ME Link Preference and start VNC session.
- Perform OOB maintenance functions
- When you are done with OOB work, restart the OS
- When the OS is fully up, switch to Host Link Preference.
Why Connecting to OOB client with ME Link preference?
As mentioned earlier, both transition from OS-to-ME and from ME-to-OS control will cause the KVM session to drop. When initiating a session to OOB client, the ME is in control. If your KVM viewer is configured to use OS Link, upon reboot the viewer expects to transition to Host Link that would cause the session to drop.
How to change Link Preference
The location of the Link Preference option will vary between the viewer applications.
SDK sample application “KVM Console”: the option appears at the top menu under “Wireless”
When you click on “Wireless”, the following menu appears:
In VNC-Plus, feature is located under Options -> Advanced -> AMT Server tab
Note: Link Preference selection is available only in VNC Viewer PLUS.