Network Working Group                                       M. Gupta
   Internet Draft                                                 Nokia
   Document: draft-ietf-ospf-ospfv3-auth-02.txt                N. Melam
   Expires: January 2003                                          Nokia
                                                              July 2003

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

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 [N5].

Table of Contents

   1. Introduction...................................................2
   2. OSPFv2 to OSPFv3...............................................2
   3. Authentication.................................................2
   4. Confidentiality................................................3
   5. IPsec Requirements.............................................3
   6. Key Management.................................................4

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

1. Introduction

   In Open Shortest Path First - Version 3 (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 [N1], AH [N4],
   ESP [N3], the concept of security associations, tunnel and transport
   mode of IPsec and the key management options available for AH and ESP
   (manual keying [N2] and Internet Key Exchange (IKE)[I1]).

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 Security Association (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

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   hosts in this case.  So 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 or with incorrect AH Integrity
   Check Value (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 providing the confidentiality to
   OSPFv3.  The user MUST be able to configure the encryption key and
   the authentication key separately.

5. IPsec Requirements

   In order to implement this specification, the following IPsec
   capabilities are required.

   Transport Mode
      IPsec in transport mode MUST be supported.

   Traffic Selectors
      The implementation MUST be able to use interface index, source
      address, destination address, protocol and direction for choosing
      the right security action.

   Manual key support
      Manually configured keys MUST be able to secure the specified

   Encryption and Authentication Algorithms
      The implementations MUST be conformant to the RFCs that describe
      mandatory-to-implement algorithms for use with ESP and AH.

   Dynamic IPsec rule configuration
      Routing module SHOULD be able to configure, modify and delete
      IPsec rules on the fly.  This is needed mainly for securing
      virtual links.

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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

   As 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.

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

   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.

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

   So, all the neighbor routers on a network/subnet 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.

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 is 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 needs
   to be set up 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.

   According to the OSPFv3 RFC [N1], the virtual neighbor's IP address
   is set to the first prefix with the "LA-bit" set from the list of
   prefixes in intra-area-prefix-LSAs originated by the virtual
   neighbor.  But when it comes to choosing the source address for the
   packets that are sent over the virtual link, the RFC simply suggests
   using one of the router's own site-local or global IPv6 addresses.
   In order to install the required security rules for virtual links,
   the source address also needs to be predictable.  So the routers that
   implement this specification MUST change the way the source and

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   destination addresses are chosen for the packets exchanged over
   virtual links when the security is enabled on that virtual link.

   The smallest IP address with the "LA-bit" set from the list of its
   own prefixes being advertised in intra-area-prefix-LSA MUST be used
   as the source address.

   The smallest IP address with the "LA-bit" set from the list of intra-
   area-prefix-LSAs originated by the virtual neighbor MUST be used as
   the destination address.

   This makes both the source and destination addresses of the packets
   exchanged over the virtual link, predictable on both the routers for
   security purposes.

   The old behavior specified in OSPFv3 RFC for choosing the source and
   destination IP addresses MUST be used when the security is not
   enabled on the virtual link. This will insure the interoperability
   with the routers that do not implement this specification.

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::/10        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::/10        any           ESP or AH      apply
   4     iface      fe80::/10        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 insecure OSPFv3 packets without ESP/AH

   Rules 2, 5 and 6 are meant to secure the packets being exchanged over
   virtual links.  These rules are dynamically installed after learning

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   the end point IP addresses of a virtual link.  These rules MUST be
   installed on at least the interfaces that are connected to the
   transit area for the virtual link.  These rules MAY alternatively be
   installed on all the interfaces.  If these rules are not installed on
   all the interfaces, clear text or malicious OSPFv3 packets with same
   source and destination addresses as virtual link end point addresses
   will be delivered to OSPFv3.  Though OSPFv3 drops these packets
   because they were not received on the right interface, OSPFv3
   receives some clear text or malicious packets even when the security
   is on.  Installing these rules on all the interfaces insures that
   OSPFv3 does not receive these clear text or malicious packets when
   security is turned on.  On the other hand installing these rules on
   all the interfaces increases the processing overhead on the
   interfaces where there is no IPsec processing otherwise.  The
   decision of installing these rules on all the interfaces or on just
   the interfaces that are connected to the transit area is a private
   decision and doesn't affect the interoperability in any way.  So this
   decision is left to the implementers.

   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.

Normative References

  N1. Coltun, R., Ferguson, D. and J. Moy, "OSPF for IPv6", RFC 2740,
     December 1999

  N2. Kent, S. and R. Atkinson, "Security Architecture for the Internet
     Protocol", RFC 2401, November 1998.

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  N3. Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
     (ESP)", RFC 2406, November 1998.

  N4. Kent, S. and R. Atkinson, "IP Authentication Header (AH)", RFC
     2402, November 1998.

  N5. Bradner, S., "Key words for use in RFCs to Indicate Requirement
     Level", BCP 14, RFC 2119, March 1997.

Informative References

  I1. Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", RFC
     2409, November 1998.


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

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

Authors' Addresses

   Mukesh Gupta
   313 Fairchild Drive
   Mountain View, CA 94043
   Phone: 650-625-2264

   Nagavenkata Suresh Melam
   313 Fairchild Drive
   Mountain View, CA 94043
   Phone: 650-625-2949

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