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ipsecme                                                        A. Antony
Internet-Draft                                          Phenome Networks
Intended status: Informational                                J. Gilmore
Expires: September 10, 2015
                                                              P. Wouters
                                                                 Red Hat
                                                          March 09, 2015


             NAT-Traversal support for Opportunistic IPsec
                    draft-antony-ipsecme-oppo-nat-00

Abstract

   This document specifies how to support NATed IPsec peers for use with
   Opportunistic IPsec.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on September 10, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   2
   2.  The pre-NAT IP address conflict . . . . . . . . . . . . . . .   2
   3.  Creating the NAT workaround on the initiator  . . . . . . . .   3
     3.1.  The Initial Exchange  . . . . . . . . . . . . . . . . . .   3
     3.2.  Handling the NAT problem on the initiator . . . . . . . .   4
     3.3.  Handling the NAT problem on the responder . . . . . . . .   4
     3.4.  Implementation details  . . . . . . . . . . . . . . . . .   4
   4.  Creating the NAT workaround on the responder  . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The Internet Key Exchange Protocol version 2 (IKEv2), specified in
   [RFC7296], provides a way to negotiate tunnel mode IPsec SA's for
   peers behind NAT.  It does not provide guidance on how to resolve the
   problem of multiple peers using the same pre-NAT IP address.

   Responder assigned IP addresses for NATed peers also do not fully
   resolve the address conflict when the NATed peers are deploying
   opportunistic IPsec to many remote endpoints.  Additional complexity
   of configuring many source IP addresses on the NATed peers is
   undesirable.

   This problem is expected to be a significant issue for large scale
   Opportunistic IPsec deployments.

   The goal of this draft is to put the burden of the additional effort
   required for NAT onto the host that is NAT'ed.  In a hypothetical
   future with no NAT, no residual protocol changes would remain.

1.1.  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 [RFC2119].

2.  The pre-NAT IP address conflict





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   A peer that is behind NAT is only aware of its own native IP address.
   While the IKEv2 NATD payloads allow the peer to find out it is behind
   NAT, it either has to use its own native IP address or a remote peer
   assigned IP address to build IPsec SA's.

   Two initiators behind different NAT routers can have the same pre-NAT
   IP address.  When these initiators attempt to setup an IPsec SA to
   the same responder, there will be a conflict on the responder.  When
   the first initiator connects, the responder will install an IPsec SA
   for for the specific pre-NAT IP.  For the second initiator, the
   responder cannot install an IPsec SA with the same source and
   destination selectors without creating a conflict.  Even if it could
   install two identical IPsec SAs, it still needs a mechanism to decide
   between these two IPsec SA's. While connection tracking might be used
   to distinguish reply packets, there is no method for initiating a
   connection from the responder to one of the initiators without
   somehow specifying for which of the initiators the packet is meant.

   When initiators behind NAT let the remote peer assign their IP to use
   for building the IPsec SA, the problem reverses.  Initiators behind
   NAT can setup many IPsec SA's to different remote peers, and those
   remote peers might use the conflicting IP addresses.  Additionally,
   using many IP addresses requires that the host or applications need
   to be aware of which source IP to use for which remote peer.

3.  Creating the NAT workaround on the initiator

   In the below workflow, the following example IP addresses are used:

      The initiator ("road") has a private IP address of 192.1.3.209

      The NAT router has an internal (private) IP address of 192.1.3.254

      The NAT router has an external (public) IP address of 192.1.2.254

      The responder ("east") has a public IP address of 192.1.2.42

      The responder ("east") has a private IP address pool of 10.1.2.0/
      24

   Tunnel mode is used for all IPsec SA's.

3.1.  The Initial Exchange

   In IKEv2, the IKE_INIT exchange allows the initiator and responder to
   detect the presense of a NAT.  In this case both "road" and "east"
   become aware of the NAT in front of "road".




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   In IKEv2, the initiator can signal via the TSi payload that it is
   willing to receive a responder-assigned IP address for use in the
   IPsec SA.  The responder needs to be configured with an addresspool
   from which it assigns unique IP addresses to the connecting
   initiators.

   "road" sends a TSi(0.0.0.0/0) and TSr(192.1.2.42/32) request to
   "east" in the IKE_AUTH Exchange.

   "east" assigns the first free IP address from its pool - 10.1.2.1 -
   to this prospective client and sends a TSI(10.1.2.1/32) and
   TSr(192.1.2.42/32) back to "road".

   The IKE_AUTH Exchange completes as normal.  This could be an
   authenticated exchange or an exchange without authentication using
   AUTH_NULL as specified in [IKE-AUTH-NULL].

3.2.  Handling the NAT problem on the initiator

   "road", upon receiving east's TSi/TSr - and a successfull completion
   of the IKE_AUTH Exchange - two tasks:

   1.  It installs the negotiated inbound and outbound IPsec SAs
       (10.1.2.1/32 <=> 192.1.2.42/32)

   2.  It installs a destination based NAT rule for 192.1.3.209 ->
       192.1.2.42/32 ==> 10.1.2.1/32 -> 192.1.2.42/32

   It ensures that the destination based NAT rule is processed before
   IPsec processing begins.

3.3.  Handling the NAT problem on the responder

   The responder has no specific handling it needs to perform apart from
   a willingness to assign IP addresses if an initiator requests one via
   the special TSi(0.0.0.0/0).  If the initiator sends a TSi() that
   matches the IP address of the IKE message, the responder should agree
   to use that address instead of assigning one from its addresspool.

3.4.  Implementation details

   The NAT rule can be implemented in the Networking subsystem of the
   host kernel, but this specific IPsec-NAT rule could also be
   implemented as part of the IPsec subsystem.







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   The initiator host and any application running on the initiator
   should not need to be aware of this construct.  The responder
   assigned IP address does not need to be configured on the host.  It
   only needs to exist in the NAT rule and the IPsec SA.

4.  Creating the NAT workaround on the responder

   [placeholder]

5.  Security Considerations

   This NAT mapping method MUST only be used for host-to-host IPsec
   tunnels.  It MUST NOT be used for net-to-net IPsec tunnels.

   An address from the addresspool should not be re-used quickly to
   avoid sending traffic meant for one initiator to another initiator.

6.  Acknowledgments

   None so far

7.  IANA Considerations

   This Internet Draft includes no request to IANA.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, October 2014.

   [IKE-AUTH-NULL]
              Smyslov, Valery. and Paul. Wouters, "The NULL
              Authentication Method in IKEv2 Protocol", draft-ietf-
              ipsecme-ikev2-null-auth (work in progress), February 2015.

8.2.  Informative References

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, May 2014.



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   [RFC7435]  Dukhovni, V., "Opportunistic Security: Some Protection
              Most of the Time", RFC 7435, December 2014.

Authors' Addresses

   Antony Antony
   Phenome Networks

   Email: antony@phenome.org


   John Gilmore

   Email: gnu@toad.com


   Paul Wouters
   Red Hat

   Email: pwouters@redhat.com































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