libNetwork join method needs access to docker host

In LibNetwork, to create an interface within a container, 2 calls are made from the LibNetwork-Driver interaction viewpoint. One is CreateEndpoint and other is Join. In the Join call (see, we need information about the Docker Host on which the container to be joined exists. It seems like closest thing that Join call has is the sandboxKey. Is there any way to get host information?

We are configuring some things on the host (using our own mechanism) as part of joining the container to endpoint.

Thanks Rags