NAT Behavioral Requirements for ICMP
RFC 5508

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Network Working Group                                       P. Srisuresh
Request for Comments: 5508                                Kazeon Systems
BCP: 148                                                         B. Ford
Category: Best Current Practice                                  MPI-SWS
                                                            S. Sivakumar
                                                           Cisco Systems
                                                                 S. Guha
                                                              Cornell U.
                                                              April 2009

                 NAT Behavioral Requirements for ICMP

Status of This Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

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Srisuresh, et al.        Best Current Practice                  [Page 1]
RFC 5508          NAT Behavioral Requirements for ICMP        April 2009

Abstract

   This document specifies the behavioral properties required of the
   Network Address Translator (NAT) devices in conjunction with the
   Internet Control Message Protocol (ICMP).  The objective of this memo
   is to make NAT devices more predictable and compatible with diverse
   application protocols that traverse the devices.  Companion documents
   provide behavioral recommendations specific to TCP, UDP, and other
   protocols.

Table of Contents

   1. Introduction and Scope ..........................................3
   2. Terminology .....................................................4
   3. ICMP Query Handling .............................................6
      3.1. ICMP Query Mapping .........................................6
      3.2. ICMP Query Session Timeouts ................................7
   4. ICMP Error Forwarding ...........................................8
      4.1. ICMP Error Payload Validation ..............................8
      4.2. ICMP Error Packet Translation .............................10
           4.2.1. ICMP Error Packet Received from the External Realm .11
           4.2.2. ICMP Error Packet Received from the Private Realm ..13
      4.3. NAT Sessions Pertaining to ICMP Error Payload .............15
   5. Hairpinning Support for ICMP Packets ...........................16
   6. Rejection of Outbound Flows Disallowed by NAT ..................17
   7. Conformance to RFC 1812 ........................................17
      7.1. IP Packet Fragmentation ...................................19
           7.1.1.  Generating "Packet Too Big" ICMP Error Message ....19
           7.1.2.  Forwarding "Packet Too Big" ICMP Error Message ....20
      7.2. Time Exceeded Message .....................................20
      7.3. Source Route Options ......................................20
      7.4. Address Mask Request/Reply Messages .......................20
      7.5. Parameter Problem Message .................................21
      7.6. Router Advertisement and Solicitations ....................21
      7.7. DS Field Usage ............................................21
   8. Non-QueryError ICMP Messages ...................................22
   9. Summary of Requirements ........................................22
   10. Security Considerations .......................................25
   11. Acknowledgements ..............................................26
   12. References ....................................................27
      12.1. Normative References .....................................27
      12.2. Informative References ...................................27

Srisuresh, et al.        Best Current Practice                  [Page 2]