Some users may experience a loss of network access in their Hyper-V guest environments when Symantec Endpoint Protection (SEP) 12.1 with NTP is installed on Hyper-V Host
Due to changes made in the NTP components as of SEP 12.1 RU4 MP1, Hyper-V Guest network activity is handled differently than it was in previous versions.
The issue was addressed in SEP 12.1 RU6. Upgrading to SEP 12.1 RU6 or later will resolve the issue.
In lieu of upgrading to SEP 12.1 RU6, users can workaround this issue by implementing one of the following solutions: