Does not ping the domain controller by IP?

Question

Domain Name System

Good day! I ask to help to deal with a network based on Windows Server 2008 R2. A strange glitch constantly occurs: client machines entered into the domain (Windows 7 Pro) lose access to the Internet. At the same time, it is noticed that the domain controller stops pinging, this situation occurs periodically on any arbitrary computer.
Server configuration:
WAN - receives settings via DHCP from provider
DNS1 127.0.0.1
LAN 192.168.2.1
Mask 255.255.255.0
Gateway -
DNS1 192.168.2.1 not specified
RRAS (NAT) and DHCP services are up on the domain controller. DNS has 2 forwarders configured for Yandex DNS (77.88.8.8 and 77.88.8.1).
The client receives all settings via DHCP:
Connection DNS suffix name: domain.local
IP address 192.168.2.22
Mask 255.255.255.0
Gateway 192.168.2.1
DNS1 192.168.2.1
In this case, the computer can ping other clients by IP addresses, but cannot ping a domain controller even by IP address. When you try to log into a computer via the network, an authorization window appears and the message "The system detected an attempt to violate security. Please check that you have access to the server through which you logged in."
At the same time, if you try to ping this computer from a domain controller, pings also do not go. I just can't understand what the reason is, because the rest of the network computers successfully access the Internet and get access to local resources.

Answer 1

On the domain controller, RRAS services (NAT

Don't do it! For the role of the gateway, put a separate piece of iron.

Answer 2

Antivirus? more like a blocking from the client side, the server as "attacking"
What is "treated"?