This document describes a mechanism for IPv4 NAT traversal for LISP tunnel routers (xTR) and LISP Mobile Nodes (LISP-MN) behind a NAT device. A LISP device both detects the NAT and initializes its state. Forwarding to the LISP device through a NAT is enabled by the LISP Re-encapsulating Tunnel Router (RTR) network element, which acts as an anchor point in the data plane, forwarding traffic from unmodified LISP devices through the NAT.