Unintended Consequences of NAT Deployments

This document identifies two deployment scenarios that have arisen from the unconventional network topologies formed using Network Address Translator (NAT) devices. First, the simplicity of administering networks through the combination of NAT and DHCP has increasingly lead to the deployment of multi-level inter-connected private networks involving overlapping private IP address spaces. Second, the proliferation of private networks in enterprises, hotels and conferences, and the wide-spread use of Virtual Private Networks (VPNs) to access an enterprise intranet from remote locations has increasingly lead to overlapping private IP address space between remote and corporate networks. This document does not dismiss these unconventional scenarios as invalid, but recognizes them as real and offers recommendations to help ensure these deployments can function without a meltdown.