No user login to Yealink telephone possible

In some scenarios, it could be possible that a user cannot log in to a Yealink telephone. This occurs frequently when Yealink is newly provisioned and connected to SwyxWare / SwyxON. It can occur with a direct Yealink SwyxWare / SwyxON connection as well as with a Yealink RemoteConnector connection to SwyxON.

The Yealink telephone display shows the login prompt.

When the login details are entered here and ‘Login’ is pressed, the display shows ‘Login - Please wait’. However, the login is not carried out; instead, the display jumps to this screen:


If further login attempts are made, they will continue to fail and the display will remain in this state.  We were able to observe this when a TFTP option (DHCP Option 66) is active via the DHCP server and information is being distributed. The Yealink evaluates this DHCP option by default, which leads to the behaviour described here.  

It is possible to disable the evaluation of DHCP Option 66 in the Yealink telephone.  This can be done via the web configuration.  

There is the possibility to disable the evaluation of DHCP option 66 in the Yealink telephone. 
This can be done via the web configuration. 
Go to ‘Settings - Auto Provision’ and switch the ‘DHCP Active’ toggle switch from “ON” to ‘OFF’.

This change must then be confirmed by pressing the ‘Confirm’ button.
The telephone must then be rebooted (Settings - Upgrade - Reboot).
 

After rebooting, the Yealink telephone display will either show the initial login screen for user login.


Alternatively, the Yealink telephone can also display the logged out screen.

If this is the case, press ‘Login’ and the login screen for user login will be displayed.

Now log in the user – the login will then be carried out immediately.

TIP:
To avoid having to manually switch off the ‘DHCP Active’ toggle switch on each Yealink telephone, you can do this  by using the customer-specific provisioning file possibility for several Yealink telephones.
Here, the parameter static.auto_provision.dhcp_option.enable must be set to 0.