Network Working Group                                            S. Kent
Request for Comments: 2401                                      BBN Corp
Obsoletes: 1825                                              R. Atkinson
Category: Standards Track                                  @Home Network
                                                           November 1998


            Security Architecture for the Internet Protocol

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 (1998).  All Rights Reserved.

Table of Contents

1. Introduction........................................................3
  1.1 Summary of Contents of Document..................................3
  1.2 Audience.........................................................3
  1.3 Related Documents................................................4
2. Design Objectives...................................................4
  2.1 Goals/Objectives/Requirements/Problem Description................4
  2.2 Caveats and Assumptions..........................................5
3. System Overview.....................................................5
  3.1 What IPsec Does..................................................6
  3.2 How IPsec Works..................................................6
  3.3 Where IPsec May Be Implemented...................................7
4. Security Associations...............................................8
  4.1 Definition and Scope.............................................8
  4.2 Security Association Functionality..............................10
  4.3 Combining Security Associations.................................11
  4.4 Security Association Databases..................................13
     4.4.1 The Security Policy Database (SPD).........................14
     4.4.2 Selectors..................................................17
     4.4.3 Security Association Database (SAD)........................21
  4.5 Basic Combinations of Security Associations.....................24
  4.6 SA and Key Management...........................................26
     4.6.1 Manual Techniques..........................................27
     4.6.2 Automated SA and Key Management............................27
     4.6.3 Locating a Security Gateway................................28
  4.7 Security Associations and Multicast.............................29




 
RFC 2401              Security Architecture for IP         November 1998


5. IP Traffic Processing..............................................30
  5.1 Outbound IP Traffic Processing..................................30
     5.1.1 Selecting and Using an SA or SA Bundle.....................30
     5.1.2 Header Construction for Tunnel Mode........................31
        5.1.2.1 IPv4 -- Header Construction for Tunnel Mode...........31
        5.1.2.2 IPv6 -- Header Construction for Tunnel Mode...........32
  5.2 Processing Inbound IP Traffic...................................33
     5.2.1 Selecting and Using an SA or SA Bundle.....................33
     5.2.2 Handling of AH and ESP tunnels.............................34
6. ICMP Processing (relevant to IPsec)................................35
  6.1 PMTU/DF Processing..............................................36
     6.1.1 DF Bit.....................................................36
     6.1.2 Path MTU Discovery (PMTU)..................................36
        6.1.2.1 Propagation of PMTU...................................36
        6.1.2.2 Calculation of PMTU...................................37
        6.1.2.3 Granularity of PMTU Processing........................37
        6.1.2.4 PMTU Aging............................................38
7. Auditing...........................................................39
8. Use in Systems Supporting Information Flow Security................39
  8.1 Relationship Between Security Associations and Data Sensitivity.40
  8.2 Sensitivity Consistency Checking................................40
  8.3 Additional MLS Attributes for Security Association Databases....41
  8.4 Additional Inbound Processing Steps for MLS Networking..........41
  8.5 Additional Outbound Processing Steps for MLS Networking.........41
  8.6 Additional MLS Processing for Security Gateways.................42
9. Performance Issues.................................................42
10. Conformance Requirements..........................................43
11. Security Considerations...........................................43
12. Differences from RFC 1825.........................................43
Acknowledgements......................................................44
Appendix A -- Glossary................................................45
Appendix B -- Analysis/Discussion of PMTU/DF/Fragmentation Issues.....48
  B.1 DF bit..........................................................48
  B.2 Fragmentation...................................................48
  B.3 Path MTU Discovery..............................................52
     B.3.1 Identifying the Originating Host(s)........................53
     B.3.2 Calculation of PMTU........................................55
     B.3.3 Granularity of Maintaining PMTU Data.......................56