Network Working Group H. Levkowetz Request for Comments: 3519 ipUnplugged Category: Standards Track S. Vaarala Netseal April 2003 Mobile IP Traversal of Network Address Translation (NAT) Devices Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract Mobile IP's datagram tunnelling is incompatible with Network Address Translation (NAT). This document presents extensions to the Mobile IP protocol and a tunnelling method which permits mobile nodes using Mobile IP to operate in private address networks which are separated from the public internet by NAT devices. The NAT traversal is based on using the Mobile IP Home Agent UDP port for encapsulated data traffic. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Problem description . . . . . . . . . . . . . . . . . . 3 1.3 Assumptions . . . . . . . . . . . . . . . . . . . . . . 4 2. NAT Traversal Overview. . . . . . . . . . . . . . . . . . . . 5 2.1 Basic Message Sequence. . . . . . . . . . . . . . . . . 5 3. New Message Formats . . . . . . . . . . . . . . . . . . . . . 6 3.1 UDP Tunnel Request Extension. . . . . . . . . . . . . . 6 3.1.1 F (Force) Flag. . . . . . . . . . . . . . . . . . 7 3.1.2 R (Registration through FA Required) flag . . . . 8 3.1.3 Reserved Fields . . . . . . . . . . . . . . . . . 8 3.1.4 Encapsulation . . . . . . . . . . . . . . . . . . 8 3.1.5 Mobile IP Registration Bits . . . . . . . . . . . 9 3.2 UDP Tunnel Reply Extension. . . . . . . . . . . . . . . 9 3.2.1 Reply Code. . . . . . . . . . . . . . . . . . . . 10 Levkowetz & Vaarala Standards Track