This document describes the framework, messages, and procedures for the Diameter NAT Control Application (DNCA), allowing for per- endpoint control of large scale NAT devices, which are put in place to cope with IPv4-address space completion. The Diameter NAT Control Application allows external devices to configure and manage a Large Scale NAT (LSN) device - expanding the existing Diameter-based AAA and policy control capabilities with a NAT control component. These external devices can be network elements in the data plane such as a Network Access Server (NAS), or can be more centralized control plane devices such as AAA-servers. DNCA establishes a context to commonly identify and manage endpoints on a gateway or server, and a large scale NAT device. This includes, for example, the control of the total number of NAT-bindings allowed or the allocation of a specific NAT-binding for a particular endpoint. In addition, it allows large scale NAT devices to provide information relevant to accounting purposes.