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SAVI                                                               J. Bi
Internet-Draft                                                    G. Yao
Intended status: Standards Track                          Tsinghua Univ.
Expires: November 14, 2015                                    J. Halpern
                                                               Newbridge
                                                   E. Levy-Abegnoli, Ed.
                                                                   Cisco
                                                            May 13, 2015


           SAVI for Mixed Address Assignment Methods Scenario
                         draft-ietf-savi-mix-08

Abstract

   In case that multiple IP address assignment methods are allowed in a
   network, the corresponding SAVI methods should be enabled to prevent
   spoofing in the network.  This document reviews how multiple SAVI
   methods can coexist in a single SAVI device and collisions are
   resolved when the same binding entry is discovered by two or more
   methods.

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 November 14, 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem Scope . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Architecture  . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Recommendations for preventing collisions . . . . . . . . . .   5
   6.  Resolving binding collisions  . . . . . . . . . . . . . . . .   5
     6.1.  Same Address on Different Binding Anchors . . . . . . . .   5
       6.1.1.  Basic preference  . . . . . . . . . . . . . . . . . .   6
       6.1.2.  Overwritten preference  . . . . . . . . . . . . . . .   6
       6.1.3.  Multiple SAVI Device Scenario . . . . . . . . . . . .   7
     6.2.  Same Address on the Same Binding Anchor . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Acknowledgment  . . . . . . . . . . . . . . . . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   There are currently several SAVI documents ([RFC6620], [savi-dhcp]
   and [RFC7219]) that describe the different methods by which a switch
   can discover and record bindings between a node's IP address and a
   binding anchor and use that binding to perform source address
   validation.  Each of these documents specifies how to learn on-link
   addresses, based on the method used for their assignment,
   respectively: StateLess Autoconfiguration (SLAAC), Dynamic Host
   Control Protocol (DHCP) and Secure Neighbor Discovery (SeND).  Each
   of these documents describes separately how one particular method
   deals with address collisions (same address, different binding
   anchor).

   While multiple IP assignment methods can be used in the same layer-2
   domain, a SAVI device might have to deal with a mix of SAVI methods.
   The purpose of this document is to provide recommendations to avoid
   collisions and to review collisions handling when two or more such
   methods come up with competing bindings.





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2.  Requirements Language

   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 [RFC2119].

3.  Problem Scope

   There are three IP address assignment methods identified and reviewed
   in one of the SAVI document:

   1.  StateLess Address AutoConfiguration (SLAAC) - reviewed in SAVI-
       FCFS[RFC6620]

   2.  Dynamic Host Control Protocol address assignment (DHCP) -
       reviewed in SAVI-DHCP[savi-dhcp]

   3.  Secure Neighbor Discovery (SeND) address assignment, reviewed in
       SAVI-SEND[RFC7219]

   In addition, there is a fourth method for installing a bindings on
   the switch, referred to as "manual".  It is based on manual (address
   or prefix) binding configuration and is reviewed in [RFC6620] and
   [RFC7039].

   All combinations of address assignment methods can coexist within a
   layer-2 domain.  A SAVI device will have to implement the
   corresponding binding setup methods (referred to as a "SAVI method")
   to enable Source Address Validation.  If more than one SAVI method is
   enabled on a SAVI device, the method is referred to as "mix address
   assignment method" in this document.

   SAVI methods are independent from each other, each one handling its
   own entries.  In the absence of reconciliation, each method will
   reject packets sourced with an address it did not discovered.  To
   prevent addresses discovered by one method to be filtered out by
   another, the binding table should be shared by all the solutions.
   However this could create some conflict when the same entry is
   discovered by two different methods: the purpose of this document is
   of two folds: provide recommendations and method to avoid conflicts,
   and resolve conflicts if and when they happen.  Collisions happening
   within a given method are outside the scope of this document.

4.  Architecture

   A SAVI device may enable multiple SAVI methods.  This mechanism,
   called SAVI-MIX, is proposed as a arbiter of the binding generation
   algorithms, generating the final working binding entries Figure 1.



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   Once a SAVI method generates a candidate binding, it will request
   SAVI-MIX to set up a corresponding entry in the binding table.  Then
   SAVI-MIX will check if there is any conflict in the binding table.  A
   new binding will be generated if there is no conflict.  If there is a
   conflict, SAVI-MIX will determine whether to replace the existing
   binding or reject the candidate binding based on the policies
   specified in Section 6.

   The packet filtering will not be performed by each SAVI method
   separately.  Instead, SAVI-MIX will perform filtering based on the
   entries in the binding table.


   +--------------------------------------------------------+
   |                                                        |
   |                                        SAVI Device     |
   |                                                        |
   |                                                        |
   |     +------+    +------+    +------+                   |
   |     | SAVI |    | SAVI |    | SAVI |                   |
   |     |      |    |      |    |      |                   |
   |     | FCFS |    | DHCP |    | SEND |                   |
   |     +------+    +------+    +------+                   |
   |        |            |           |   Binding            |
   |        |            |           |   setup              |
   |        v            v           v   requests           |
   |     +------------------------------+                   |
   |     |                              |                   |
   |     |            SAVI-MIX          |                   |
   |     |                              |                   |
   |     +------------------------------+                   |
   |                     |                                  |
   |                     v               Final Binding      |
   |             +--------------+                           |
   |             |   Binding    |                           |
   |             |              |                           |
   |             |   Table      |                           |
   |             +--------------+                           |
   |                                                        |
   +--------------------------------------------------------+


                      Figure 1: SAVI-Mix Architecture

   Each entry in the binding table will contain the following fields:

   1.  IP source address




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   2.  Binding anchor

   3.  Lifetime

   4.  Creation time

   5.  Binding methods: the methods which request the binding setup.

5.  Recommendations for preventing collisions

   If each solution has a dedicated address space, collisions won't
   happen.  Using non overlapping address space across SAVI solutions is
   therefore recommended.  To that end, one should:

   1.  DHCP/SLAAC: use non-overlapping prefix for DHCP and SLAAC.  Set
       the A bit in Prefix information option of Router Advertisement
       for SLAAC prefix, and set the M bit in Router Advertisement for
       DHCP prefix.  For detail explanations on these bits, refer to
       [RFC4861][RFC4862].

   2.  SeND/non-SeND: avoid mixed environment (where SeND and non-SeND
       nodes are deployed) or separate the prefixes announced to SeND
       and non-SenD nodes.  One way to separate the prefixes is to have
       the router(s) announcing different (non-overlapping) prefixes to
       SeND and to non-SeND nodes, using unicast Router Advertisements,
       in response to SeND/non-SeND Router Solicit.

6.  Resolving binding collisions

   In situations where collisions could not be avoided, two cases should
   be considered:

   1.  The same address is bound on two different binding anchors by
       different SAVI methods.

   2.  The same address is bound on the same binding anchor by different
       SAVI methods.

6.1.  Same Address on Different Binding Anchors

   This would typically occur in case assignment address spaces could
   not be separated.  For instance, an address is assigned by SLAAC on
   node X, installed in the binding table using SAVI-FCFS, anchored to
   "anchor-X".  Later, the same address is assigned by DHCP to node Y,
   and SAVI-DHCP will generate a candidate binding entry, anchored to
   "anchor-Y".





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6.1.1.  Basic preference

   The SAVI device must decide whom the address should be bound with
   (anchor-X or anchor-Y in this example).  Current standard documents
   of address assignment methods have implied the prioritization
   relationship (first-come).  In the absence of any configuration or
   protocol hint (see Section 6.1.2) the SAVI device should choose the
   first-come binding anchor, whether it was learnt from SLACC, SeND or
   DHCP.

6.1.2.  Overwritten preference

   There are two identified exceptions to the general prioritization
   model, one of them being CGA addresses, another one controlled by the
   configuration of the switch.

6.1.2.1.  CGA preference

   When CGA addresses are used, and a collision is detected, preference
   should be given to the anchor that carries the CGA credentials once
   they are verified, in particular the CGA parameters and the RSA
   options.  Note that if an attacker was trying to replay CGA
   credentials, he would then compete on the base of fcfs (first-come,
   first-serve).

6.1.2.2.  configuration preference

   For configuration driven exceptions, the SAVI device may allow the
   configuration of a triplet ("prefix", "anchor", "method") or
   ("address", "anchor", "method"), where at least one of ("anchor",
   "method") should be specified.  Later, if a DAD message is received
   with the following conditions verified:

   1.  The target in the DAD message does not exist in the binding table

   2.  The target is within configured "prefix" (or equal to "address")

   3.  The anchor bound to target is different from the configured
       anchor, when specified

   4.  The configured method, if any, is different from SAVI-FCFS

   the switch should defend the address by responding to the DAD
   message.  It should not at this point install the entry into the
   binding table.  It will simply prevent the node to assign the
   address, and will de-facto prioritize the configured anchor.  This is
   especially useful to protect well known bindings such as a static
   address of a server over anybody, even when the server is down.  It



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   is also a way to give priority to a binding learnt from SAVI-DHCP
   over a binding for the same address, learnt from SAVI-FCFS.

6.1.3.  Multiple SAVI Device Scenario

   A single SAVI device doesn't have the information of all bound
   addresses on the perimeter.  Therefore it is not enough to lookup
   local bindings to identify a collision.  However, assuming DAD is
   performed throughout the security perimeter for all addresses
   regardless of the assignment method, then DAD response will inform
   all SAVI devices about any collision.  In that case, FCFS will apply
   the same way as in a single switch scenario.  If the admin configured
   on one the switches a prefix (or a single static binding) to defend,
   the DAD response generated by this switch will also prevent the
   binding to be installed on other switches of the perimeter.

6.2.  Same Address on the Same Binding Anchor

   A binding may be set up on the same binding anchor by multiple
   methods, typically SAVI-FCFS and SAVI-DHCP.  If the binding lifetimes
   obtained from the two methods are different, priority should be given
   to 1) Manual configuration 2) SAVI-DHCP 3) SAVI-FCFS as the least
   authoritative.  The binding will be removed when the prioritized
   lifetime expires, even if a less authoritative method had a longer
   lifetime.

7.  Security Considerations

   SAVI MIX does not eliminate the security problems of each SAVI
   method.  Thus, the potential attacks, e.g., the DoS attack against
   the SAVI device resource, can still happen.  In deployment, the
   security threats from each enabled SAVI methods should be prevented
   by the corresponding proposed solutions in each document.

   SAVI MIX is only a binding setup/removal arbitration mechanism.  It
   does not introduce additional security threats only if the principle
   of decision is reasonable.  However, there is a slight problem.  SAVI
   MIX is more tolerant about binding establish than each SAVI method
   alone.  As long as one of the enabled SAVI method generates a
   binding, the binding will be applied.  As a result, the allowed
   binding number limitation or allowed binding setup rate limitation
   will be the sum of all the enabled SAVI methods.  In deployment,
   whether a SAVI device is capable to support that resource requirement
   should be evaluated.







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8.  IANA Considerations

   This memo asks the IANA for no new parameters.

9.  Acknowledgment

   Thanks to Christian Vogt, Eric Nordmark, Marcelo Bagnulo Braun and
   Jari Arkko for their valuable contributions.

10.  References

10.1.  Normative References

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

   [RFC7039]  Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt,
              "Source Address Validation Improvement (SAVI) Framework",
              RFC 7039, October 2013.

   [RFC6620]  Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS
              SAVI: First-Come, First-Served Source Address Validation
              Improvement for Locally Assigned IPv6 Addresses", RFC
              6620, May 2012.

   [RFC7219]  Bagnulo, M. and A. Garcia-Martinez, "SEcure Neighbor
              Discovery (SEND) Source Address Validation Improvement
              (SAVI)", RFC 7219, May 2014.

   [savi-dhcp]
              Bi, J., Wu, J., Yao, G., and F. Baker, "SAVI Solution for
              DHCP", draft-ietf-savi-dhcp-34 (work in progress), Feb
              2015.

10.2.  Informative References

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

Authors' Addresses







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   Jun Bi
   Tsinghua University
   Network Research Center, Tsinghua University
   Beijing  100084
   China

   EMail: junbi@tsinghua.edu.cn


   Guang Yao
   Tsinghua University
   Network Research Center, Tsinghua University
   Beijing  100084
   China

   EMail: yaoguang.china@gmail.com


   Joel M. Halpern
   Newbridge Networks Inc

   EMail: jmh@joelhalpern.com


   Eric Levy-Abegnoli (editor)
   Cisco Systems
   Village d'Entreprises Green Side - 400, Avenue Roumanille
   Biot-Sophia Antipolis  06410
   France

   EMail: elevyabe@cisco.com




















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