Port exposed on client

[Leen15]

Hi, I'm trying haven on a test environment, but I would like to know what is the scope of the port 8761 that should be exposed from the agent.
If the agent connect to the server with port 2379, why the server must connected to a port on the agent?
This is a really big limitation for all agents that stay behind a firewall, nat or a simple router.
It there a way to make it works without exposing a port on the agent?

Thanks