Setting up IP addresses, DNS servers, and gateways on the Edge Server adapters can be a point of confusion in a deployment because of the requirement for dual network adapters. To begin with, an Edge Server must have two separate network adapters: one that is internal-facing and one that is external- or public-facing.
It was possible to use three separate adapters for each external-facing Edge service in Office Communications Server, but Microsoft recommends using a single external-facing adapter with Lync Server 2013. The extra adapters were really unnecessary and complicated the deployment.
The internal adapter should have a single IP address, and the external adapter should have three separate IP addresses ...