Why Agents are getting disconnected

Hi

Symantec Endpoint agents are installed in every sytem. I will get to know the status of each agent in the machine through enforce console.

But some of the agents will be in  down status, even though the machines are connected to internet. I need to re-install  agents for these machines every time.

Please let us know the root cause why these machines are getting disconnected. Please let us know is there any other method to resolve this type of issues.

Thanks

Manjunath