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Versions: (draft-gupta-ospf-ospfv3-auth) 00 01 02 03 04 05 06 07 08 RFC 4552

   Network Working Group                                       M. Gupta
   Internet Draft                                                 Nokia
   Document: draft-ietf-ospf-ospfv3-auth-00.txt                N. Melam
   Expires: May 2003                                              Nokia
                                                          November 2002


                 Authentication/Confidentiality for OSPFv3


Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
        http://www.ietf.org/ietf/1id-abstracts.txt
   The list of Internet-Draft Shadow Directories can be accessed at
        http://www.ietf.org/shadow.html.

Abstract

   This document describes means/mechanisms to provide
   authentication/confidentiality to OSPFv3 using IPv6 AH/ESP Extension
   Header.

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [5].

Table of Contents

   1. Introduction...................................................2
   2. OSPFv2 to OSPFv3...............................................2
   3. Authentication.................................................2
   4. Confidentiality................................................3
   5. Authentication and Encryption Algorithms.......................3
   6. Key Management.................................................3


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   7. SA Granularity and Selectors...................................4
   8. Virtual Links..................................................5
   9. IPsec rules....................................................5
   10. Replay Protection.............................................6
   Security Considerations...........................................6
   References........................................................6
   Acknowledgments...................................................6
   Authors' Addresses................................................7


1. Introduction

   In OSPFv3 for IPv6, authentication fields have been removed from OSPF
   headers. When running over IPv6, OSPF relies on the IPv6
   Authentication Header (AH) and IPv6 Encapsulating Security Payload
   (ESP) to ensure integrity, authentication and/or confidentiality of
   routing exchanges.

   This document describes how IPv6 AH/ESP extension headers can be used
   to provide authentication/confidentiality to OSPFv3.

   It is assumed that the reader is familiar with OSPFv3 [1], AH [4],
   ESP [3], the concept of security associations, tunnel and transport
   mode of IPsec and the key management options available for AH and ESP
   (manual keying and IKE) [2].

2. OSPFv2 to OSPFv3

   Security concerns MUST be taken away from OSPFv3 protocol and IPv6
   stack MUST provide inherent security to OSPFv3 by using AH/ESP
   extension headers. It means OSPFv3 protocol MUST not receive any
   unauthenticated packets. As OSPFv2 has its own security mechanisms,
   no inherent security needs to be provided by the IPv4 stack. As
   OSPFv2 is only for IPv4 and OSPFv3 is only for IPv6, the distinction
   between the packets can be easily made by IP version.

   Authentication and confidentiality, if provided, MUST be provided to
   the entire OSPFv3 header and data. Authentication to the selected
   portions of IPv6 header, selected portions of extension headers and
   selected options may also be provided optionally.

3. Authentication

   Transport mode SA is the security association between two hosts or
   security gateways that are acting as hosts. SA must be tunnel mode if
   either end of the security association is a security gateway. OSPFv3
   packets are exchanged between the routers but as the packets are
   destined to the routers, the routers act like host in this case. So



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   transport mode SA MUST be used in order to provide required security
   to OSPFv3.

   In order to support OSPFv3 authentication, "ESP with NULL encryption"
   MUST be supported in transport mode. "AH" in transport mode SHOULD
   also be provided. AH in transport mode provides authentication to
   higher layer protocols, selected portions of IPv6 header, selected
   portions of extension headers and selected options. ESP with NULL
   encryption in transport mode will provide authentication to only
   higher layer protocol data and not to the IPv6 header, extension
   headers and options.

   OSPF packets received in clear text and OSPF received with incorrect
   AH ICV MUST be dropped when authentication is enabled.

4. Confidentiality

   Providing confidentiality to OSPFv3 in addition to authentication is
   optional. Confidentiality must be implemented using ESP extension
   header of IPv6 if it is being provided. ESP with non-null encryption
   in transport mode MUST be used for the providing confidentiality to
   OSPFv3.

5. Authentication and Encryption Algorithms

   hmac-md5-96 must be implemented as the authentication algorithm and
   DES-CBC must be implemented as the encryption algorithm.

6. Key Management

   OSPFv3 exchanges both multicast and unicast packets. While running
   OSPFv3 over a broadcast interface, the authentication/confidentiality
   required is "one to many". Since IKE is based on the Diffie-Hellman
   key agreement protocol and works only for two communicating parties,
   it is not possible to use IKE for providing the required "one to
   many" authentication/confidentiality. Manual keying MUST be used for
   this purpose. In manual keying SAs are statically installed on the
   routers and these static SAs are used to encrypt/authenticate the
   data.

   Since security associations (SAs) are directional, generally
   different security associations are used for inbound and outbound
   processing for providing higher security. The following figure
   explains that it is not possible to use different security
   associations for inbound and outbound processing in order to provide
   the required "one to many" security.





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       A                  |
     SAa     ------------>|
     SAb     <------------|
                          |
       B                  |
     SAb     ------------>|
     SAa     <------------|
                          |
       C                  |
     SAa/SAb ------------>|
     SAa/SAb <------------|
                      Broadcast
                       Network

   If we consider communication between A and B in the above diagram,
   everything seems to be fine. A uses security association SAa for
   outgoing packets and B uses the same for incoming packets and vice
   versa. Now if we include C in the group and C sends a packet out
   using SAa then only A will be able to understand it or if C sends the
   packets out using SAb then only B will be able to understand it.
   Since the packets are multicast packets and they are going to be
   processed by both A and B, there is no SA for C to use so that A and
   B both can understand it.

   The problem can be solved with the following figure where all of them
   use the same SA for incoming and outgoing direction.

      A                   |
     SAs     ------------>|
     SAs     <------------|
                          |
      B                   |
     SAs     ------------>|
     SAs     <------------|
                          |
      C                   |
     SAs     ------------>|
     SAs     <------------|
                      Broadcast
                       Network

   So, all the adjacent routers on a broadcast medium MUST use the same
   SA and the same SA MUST be used for inbound and outbound processing.

7. SA Granularity and Selectors

   The user SHOULD be given a choice to share the same SA among multiple
   interfaces or using unique SA per interface.



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8. Virtual Links

   Different SA than the SA of underlying interface MUST be provided for
   virtual links. Packets sent out on virtual links use unicast site
   local or global IPv6 addresses as the IPv6 source address and all the
   other packets use multicast and unicast link local addresses. This
   difference in the IPv6 source address should be used in order to
   differentiate the packets sent on interfaces and virtual links.

   As the end point IP addresses of the virtual links are not known at
   the time of configuration, the secure channel for these packets need
   to be setup dynamically. The end point IP addresses of virtual links
   are learnt during the routing table build up process. The packet
   exchange over the virtual links starts only after the discovery of
   end point IP addresses. In order to provide security to these
   exchanges, the routing module should setup a secure IPsec channel
   dynamically once it acquires the required information.

9. IPsec rules

   The following set of rules can be installed in a typical IPsec
   implementation to provide the authentication/confidentiality to
   OSPFv3 packets.

   Outbound Rules for interface running OSPFv3 security:

   No. interface      source       destination      protocol      action
   1     iface      fe80::/16        any             OSPF         apply
   2      any        src/128       dst/128           OSPF         apply

   Inbound Rules for interface running OSPFv3 security:

   No. interface      source       destination      protocol      action
   3     iface      fe80::/16        any           ESP or AH      apply
   4     iface      fe80::/16        any             OSPF         drop
   5      any        src/128       dst/128         ESP or AH      apply
   6      any        src/128       dst/128           OSPF         drop

   For outbound rules, action "apply" means encrypting/calculating ICV
   and adding ESP or AH header. For inbound rules, action "apply" means
   decrypting/authenticating the packets and stripping ESP or AH header.

   Rules 4 and 6 are to drop the in-secure OSPFv3 packets without ESP/AH
   headers.

   Rules 2, 5 and 6 are meant to secure the packets being exchanged over
   virtual links. These rules are dynamically installed after learning
   the end point IP addresses of a virtual link. These rules are
   installed on all the interfaces.


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   Rules 1, 3 and 4 are meant to secure the unicast and multicast
   packets that are not being exchanged over the virtual links. These
   rules are interface specific.

10. Replay Protection

   As it is not possible as per the current standards to provide
   complete replay protection while using manual keying, the proposed
   solution will not provide protection against replay attacks.

   Fields LS age, LS Sequence Number and LS checksum in LSA header are
   kept intact in OSPFv3. Though these fields do not provide the
   complete protection, they certainly help against replay attacks.

Security Considerations

   This memo discusses the use of IPsec AH and ESP headers in order to
   provide security to OSPFv3 for IPv6.

   The use of manual keying does not provide very high level of security
   as compared to IKE but the security provided should be adequate for a
   routing protocol.

References


  1. Coltun, R., Ferguson, D. and Moy, J., "OSPF for IPv6", RFC 2740,
     December 1999

  2. Kent, S. and Atkinson, R., "Security Architecture for the Internet
     Protocol", RFC 2401, November 1998

  3. Kent, S. and Atkinson, R., "IP Encapsulating Security Payload
     (ESP)", RFC 2406, November 1998

  4. Kent, S. and Atkinson, R., "IP Authentication Header (AH)", RFC
     2402, November 1998

  5. Bradner, S., "Key words for use in RFCs to Indicate Requirement
     Level", BCP 14, RFC 2119, March 1997.

Acknowledgments

   Authors would like to extend sincere thanks to Marc Solsona, Janne
   Peltonen, John Cruz and Dhaval Shah for providing useful information
   and critiques in order to write this memo.




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   We would also like to thank IPsec and OSPF WG people to provide
   valuable review comments.

Authors' Addresses

   Mukesh Gupta
   Nokia
   313 Fairchild Drive
   Mountain View, CA 94043
   Phone: 650-625-2264
   Email: Mukesh.Gupta@nokia.com

   Nagavenkata Suresh Melam
   Nokia
   313 Fairchild Drive
   Mountain View, CA 94043
   Phone: 650-625-2949
   Email: Nagavenkata.Melam@nokia.com

































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