RFC 3519 NAT Traversal for Mobile IP April 2003 3.3 MIP Tunnel Data Message . . . . . . . . . . . . . . . . 10 3.4 UDP Tunnelling Flag in Agent Advertisements . . . . . . 11 3.5 New Registration Reply Codes. . . . . . . . . . . . . . 12 4. Protocol Behaviour. . . . . . . . . . . . . . . . . . . . . . 12 4.1 Relation to standard MIP tunnelling . . . . . . . . . . 12 4.2 Encapsulating IP Headers in UDP . . . . . . . . . . . . 13 4.3 Decapsulation . . . . . . . . . . . . . . . . . . . . . 15 4.4 Mobile Node Considerations. . . . . . . . . . . . . . . 15 4.5 Foreign Agent Considerations. . . . . . . . . . . . . . 16 4.6 Home Agent Considerations . . . . . . . . . . . . . . . 18 4.6.1 Error Handling. . . . . . . . . . . . . . . . . . 19 4.7 MIP signalling versus tunnelling. . . . . . . . . . . . 20 4.8 Packet fragmentation. . . . . . . . . . . . . . . . . . 21 4.9 Tunnel Keepalive. . . . . . . . . . . . . . . . . . . . 21 4.10 Detecting and compensating for loss of NAT mapping. . . 22 4.11 Co-located registration through FA. . . . . . . . . . . 24 5. Implementation Issues . . . . . . . . . . . . . . . . . . . . 24 5.1 Movement Detection and Private Address Aliasing . . . . 24 5.2 Mobility Binding Lifetime . . . . . . . . . . . . . . . 25 6. Security Considerations . . . . . . . . . . . . . . . . . . . 26 6.1 Traffic Redirection Vulnerabilities . . . . . . . . . . 27 6.1.1 Manipulation of the Registration Request Message . . . . . . . . . . . . . . . . . 27 6.1.2 Sending a Bogus Keepalive Message . . . . . . . . 27 6.2 Use of IPsec. . . . . . . . . . . . . . . . . . . . . . 28 6.3 Firewall Considerations . . . . . . . . . . . . . . . . 28 7. UNSAF Considerations. . . . . . . . . . . . . . . . . . . . . 28 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 9. Intellectual Property Rights. . . . . . . . . . . . . . . . . 30 10. Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . 31 11. Normative References. . . . . . . . . . . . . . . . . . . . . 31 12. Informative References. . . . . . . . . . . . . . . . . . . . 32 13. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . 33 14. Full Copyright Statement. . . . . . . . . . . . . . . . . . . 34 1. Introduction 1.1 Terminology The Mobile IP related terminology described in RFC 3344 [10] is used in this document. In addition, the following terms are used: Forward Tunnel A tunnel that forwards packets towards the mobile node. It starts at the home agent, and ends at the mobile node's care-of address. Levkowetz & Vaarala Standards Track