HI,

What sep feature do you have installed in DC ?

I have managed clients installed with:

Antivirus and antispyware protection 

Proactive threat protection (standard disabled on servers)

Network threat protection 

Hi,

Try to Disable NTP feature ?

Hello,

I guess this should fix it but this doesnt look like a good solution for me.

Disabling the firewall is not a good idea. Any recommended firewall setting on DCs?

LEVD

HI,

New fixes and features in Symantec Endpoint Protection 12.1 Release Update 1

http://www.symantec.com/business/support/index?page=content&id=TECH174565

Ping time increases every 5-10 pings when SEP 12.1 is installed
Fix ID: 2497875
Symptom: When SEP 12.1 client is installed, the ping time increases every 5-10 pings.
Solution: The SEP client was modified to increase performance of ping times

im running a managed version of 11.0.7 mp2, 12.1 was just a test.

Im reading here: that it is recommened not to enable NTP / FW on servers? Strange... but i guess i have to disable it on servers having issues.

https://www-secure.symantec.com/connect/forums/symantec-endpoint-protection-domain-controller

You can have NTP running on servers however much more care and attention to detail is needed. If you have the time than you can monitor and add the necessary rules but if you don't than it's best to remove NTP.