The 9.0 update for Dynamics 365 (online) will begin requiring connections to customer engagement applications to utilize TLS 1.2 (or better) security. This aligns with updated Microsoft and industry security policies and best practices, and you will be required to take following actions to maintain connectivity to Dynamics 365 Customer Engagement applications. Read more about the same here (https://blogs.msdn.microsoft.com/crm/2017/09/28/updates-coming-to-dynamics-365-customer-engagement-connection-security/)
In order to connect to the CRM online instances running the version 9.0, the in-market versions of Unified Service Desk client desktops must have the following registry entries set:
For more details on suggested actions for .Net Framework and TLS 1.2 security advisory, please visit https://technet.microsoft.com/en-us/library/security/2960358.aspx#ID0ETHAE
You can get the latest Unified Service Desk client from (https://docs.microsoft.com/en-us/dynamics365/customer-engagement/unified-service-desk/download-unified-service-desk)
This information does not apply on Dynamics 365(online) versions 8.2 and below and Dynamics CRM on-premise versions as of now. The future versions of Unified Service Desk clients will automatically handle the TLS 1.2 mandate.