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Internet Engineering Task Force                                    H. Xu
Internet-Draft                                                    Q. Sun
Intended status: Informational                             China Telecom
Expires: March 1, 2018                                             Y. Fu
                                                                   CNNIC
                                                         August 28, 2017


               A Redundancy Mechanism for Dual-Stack Lite
                  draft-xu-v6ops-dslite-redundancy-01

Abstract

   Dual-Stack Lite is a solution to offer both IPv4 and IPv6
   connectivity to customers that are addressed only with an IPv6
   prefix.  This document provide a redundancy mechanism for Dual-Stack
   Lite.

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
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   This Internet-Draft will expire on March 1, 2018.

Copyright Notice

   Copyright (c) 2017 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
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of




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   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.  Reliability Considerations of AFTR  . . . . . . . . . . . . .   3
   4.  The Redundancy Machanism Overview . . . . . . . . . . . . . .   4
   5.  The difference between the software process of the BRAS . . .   5
   6.  New requirements for the AFTR device  . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Dual-Stack Lite [RFC6333] is a solution to offer both IPv4 and IPv6
   connectivity to customers crossing an IPv6 only infrastructure.  The
   internet service provider no longer to provide publice IPv4 address
   but an IPv6 prefix to the customers as the issue of the IPv4 public
   address shortage.  One of its key components is an IPv4-over-IPv6
   tunnel, which is used to provide IPv4 connectivity across a service
   provider's IPv6 network.  Another key component is a carrier-grade
   IPv4-IPv4 Network Address Translation (NAT) to share service provider
   IPv4 addresses among customers.  As the exhaustion of the public IPv4
   address, service providers have deployed DS-Lite in their network
   widely in nowadays, where a large number of customers are located.
   These customers within a network which is served by a single CGN
   function embedded in AFTR element may experience service degradation
   due to the presence of the single point of failure or loss of state
   information.  Therefore, redundancy capabilities of the AFTR devices
   are strongly desired in order to deliver highly available services to
   customers.  Failure detection and repair time should be therefore
   shortened.

   This document describes a redundancy mechanism for DS-Lite.  Some
   deployment consideration and recommendations for network elements are
   also provided.








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2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119] when they appear in ALL CAPS.  When these words are not in
   ALL CAPS (such as "should" or "Should"), they have their usual
   English meanings, and are not to be interpreted as [RFC2119] key
   words.

3.  Reliability Considerations of AFTR

   As described in [RFC6908], for the robustness, reliability, and load
   distribution purposes, operators may deploy multiple AFTRs in their
   network.  There are many deployment mechanism for the AFTR in ISP
   network, the most common type are distribution mode and
   centralization mode.

   For the distribution mode, the CGN card is integrated into the free
   slot of the BRAS in a metro network.  As the BRAS integrates the AFTR
   function of DS-lite, it provides DS-Lite connection service for a
   small area customers in this metro network.  The service providers
   always integrated two CGN cards in the BRAS for reduncdancy
   consideration as the primary AFTR and backup AFTR.The capital cost of
   this mode is expensive because it always need two CGN cards for every
   BRAS.  But 50 percent of these cards are idle most of time so that it
   is a big waste of money.  There are various types and versions of
   BRAS have been deployed in the service provider's network . Some of
   them have been used for over ten years and may not support the card
   insertion.  Some of them may also don't have free slot for the CGN
   card.  It is not operational to replace all of them in a short period
   which result that it could deploy DS-Lite in some area and others can
   not in the same metro network.

   For the centralization mode, a stand-alone AFTR device is deployed
   nearby the core router device at the exit of a metro network.  It
   provides the DS-Lite connection service for the whole customers in
   this metro network.  Service providers always deploy two stand-alone
   AFTR devices nearby the two core router device for the load
   distribution and redundancy purpose.  The capital cost of this mode
   is more less than the distribution mode.  It does not consume the
   slot resource of the BRAS.  But it takes a big chanllenge for AFTR
   device for this mode in the large scale metro network because it
   takes performance requirements for the speed of the session creation
   and the maximum number of session maintenance.  On the other side, it
   will create exta traffic when the users belong to the same BRAS are
   conmmunicating with eath other because it will connect to the AFTR
   device in the centralization mode first.  It is a waste of bandwidth.



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   As described above, whether to use distribution mode or
   centralization mode depends on the trade-off between the investment
   and operational efficiency requirement of the service providers.

4.  The Redundancy Machanism Overview

   The fundamental principle of redundacncy machanism is to make the
   centralization mode to backup for the distribution mode.  The
   architecture of the redundancy mechanism is illustrated as Figure 1.
   It deploys one AFTR card into every BRAS which surport card insertion
   in metro network, as to provide bassic distributed DS-Lite connection
   service.  Moreover, it deploy two stand-alone AFTR device near the
   core router at the exit of the metro network.  So it could provide
   the DS-lite connection service for the users of the BRAS which don't
   surpport card insertion and don't have free slot for the AFTR card.
   One advantage of this mechanism is that the stand-alone AFTR device
   is not only a redundancy device but also can provide DS-Lite
   conection service for the BRAS without AFTR card slot.  Then the IGP
   routing would be configured on the BRAS which has the AFTR card
   insertion.































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                         +-------+ +-------+
                         | IPv4  | | IPv6  |
                         | APP   | | APP   |
                         +---+---+ +----+--+
                             |    X     |
                             |   / \    |
                         +---+--+   +---+---+
                         |      |   |       |
                         | CR   +---+  CR   |
                         |(AFTR)|   | (AFTR)|
                         +---+--+   +----+--+
                             |   \ /     |
                             |    X      |
                         +---+---+  +----+--+
                         |       |  |       |
                         | BRAS  |  | BRAS  |
                         | (AFTR)|  |       |
                         |       |  |       |
                         +---+---+  +----+--+
                             |           |
                         +---+---+  +----+--+
                         |       |  |       |
                         |  B4   |  |  B4   |
                         |       |  |       |
                         +-------+  +-------+


           Figure 1: The architecture of the redunancy mechanism

   It is made that the routing prior selected to the AFTR card on the
   BRAS and then selected the AFTR stand-alone device near the core
   router through the Metric value configuration.As the metric values of
   the two stand-alone AFTR device in centralization mode are the same,
   it ensure that the traffic of the same session would be forwarded to
   the same centralized AFTR device by the random selection of the hash
   algorithm.This mechanism is based on the IPv6 anycast function: when
   the AFTR card in distribution mode is breakdown,the AFTR address in
   router advertise message will disappear in the IGP routing table.The
   IP address of AFTR device in centralization mode is becoming the
   optimal routing.  All the traffic for DS-Lite will be directed to the
   AFTR decive in the centralization mode as to keep the application
   alive.

5.  The difference between the software process of the BRAS

   The software process of the BRAS for distribution mode is described
   as Figure 2




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                  ----------
                ///          \\\
              //                \\
             |   The traffic for  |
            |  IPv6 is flow into   |
             |  the inbound card  |
              \\                //
                \\\          ///
                   -----+----
                        |
            +-----------+-----------+
            |  Decapsulation for    |
            |  PPP                  |
            +------------+----------+
                         |
            +------------+----------+
            |   Look for IPv6 FIB   |
            +-----------|-----------+
                     ---|-----
                  ///         \\\
               /                   \      +-----------------+
              |  Whether the AFTR   |  Y  |                 |
             |   Card Breakdown?     -----| PPP Session     |
               \                   /      | Interruption    |
                  \\\         ///         |                 |
                     ---|-----            +------|----------+
                      N |                        |
               +--------------------+     +-----------------+
               |   The local AFTR   |     |                 |
               |   decapsulated     |     | The DS-Lite     |
               |   the packets from |     | Service are     |
               |   the IPv6 tunnel  |     | Terminated      |
               +--------|-----------+     +-----------------+
                        |
               +--------|-----------+
               |      NAT44         |
               +--------|-----------+
                        |
               +--------|-----------+
               | Look for IPv4 FIB  |
               +---------|----------+
                      ---|-----
                   ///         \\\
                  /               \
                |   The traffic for |
               |    IPv4 flow out to |
               |    the outbound     |
                |   card            |



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                  \               /
                   \\\         ///
                      ---------

     Figure 2: The software process of the BRAS for distribution mode

   And the software process of the BRAS for the new machanism is
   described as Figure 3:

                  ----------
                ///          \\\
              //                \\
             |   The traffic for  |
            |  IPv6 is flow into   |
             |  the inbound card  |
              \\                //
                \\\          ///
                   -----+----
                        |
            +-----------+-----------+
            |  Decapsulation for    |
            |  PPP                  |
            +------------+----------+
                         |
            +------------+----------+
            |   Look for IPv6 FIB   |
            +-----------|-----------+
                        |
                     ---|-----
                  ///         \\\
               /                   \      +-----------------+
              |  Whether the AFTR   |  Y  | The traffic for |
             |   Card Breakdown?     -----| IPv6 flow are   |
               \                   /      | out to the      |
                  \\\         ///         | outbound card   |
                     ---|-----            +------|----------+
                      N |                        |
               +--------------------+     +------------------+
               |   The local AFTR   |     |                  |
               |   decapsulated     |     | The centralized  |
               |   the packets from |     | AFTR decapsulated|
               |   the IPv6 tunnel  |     | the packets from |
               +--------|-----------+     | the IPv6 tunnel  |
                        |                 |                  |
               +--------|-----------+     +------|-----------+
               |      NAT44         |            |
               +--------|-----------+     +------|-----------+
                        |                 |                  |



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               +--------|-----------+     |       NAT44      |
               | Look for IPv4 FIB  |     +------|-----------+
               +---------|----------+            |
                         |                +------|-----------+
                      ---|-----           |                  |
                   ///         \\\        | Look for IPv4 FIB|
                  /               \       +------|-----------+
                |   The traffic for |            |
               |    IPv4 flow out to |           |
               |    the outbound     |           |
                |   card            |            |
                  \               /            /-|-------\
                   \\\         ///         ////           \\\\
                      ---------           |   The traffic for |
                                         |   IPv4 flow out to  |
                                          |    the outbound   |
                                           \\\\   card    ////
                                               \---------/

       Figure 3: The software process of the BRAS for new mechanism

   As compared between Figure 2 and Figure 3, the main difference for
   the new mechanism is that if the local AFTR card breakdown, the DS-
   Lite service can be maintained as the backup AFTR will take over the
   function to keep the application alive.

6.  New requirements for the AFTR device

   For this DS-Lite redundancy mechanism, there are some new
   requirements for the AFTR device as below:

   1.  If the ditribution AFTR card breakdown, the AFTR device SHOULD
       ensure that the traffic will not direct to the other distribution
       AFTR card.

   2.  It should use FQDN to decribe the AFTR in the DHCPv6 option as
       described in [RFC6334].

   3.  How many ditribution AFTR device could be covered by one
       centralization AFTR device will be different depends on the
       deployment by different ISPs.

   4.  The speed of the session creation for the centralized AFTR device
       could be calculated by a formula.







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7.  Security Considerations

   The AFTR device of centralization mode will accept the tunnel request
   from the all DS-Lite users in the metro network.  It needs aditional
   requirements to prevent from the spoofing attack.

   1.  Only the user passed the authentication could be assigned IPv6
       prefix from the BRAS.

   2.  After assigned the IPv6 prefix to the authorized user, the BRAS
       will report this address to the AAA sever for recording.

   3.  Create a local database in the AFTR device of he centralized mode
       to record the IPv6 prefix of the authorized user.

   4.  Create an interface of the AAA sever for the AFTR device to
       synchrionize the IPv6 prefix of the authorized user between the
       AAA sever to the local database of the AFTR.

   5.  When the BRAS receive a new request for a new tunnel, it will
       compare with the source IPv6 prefix with the local database of
       the AFTR.  If it is match, it will accept the request for tunnel.
       If not, it will ignore the request regarding it is from a illegal
       user and report the illegal address to the network management
       system.

   6.  If the authorized user offline, BRAS will ask the AAA server to
       delete this user from the database.

8.  IANA Considerations

   This draft does not request any IANA action.

9.  Acknowledgements

   The authors would like to thanks the valuable comments made by XXX
   and other members of v6ops WG.

   This document was produced using the xml2rfc tool [RFC2629].

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
              editor.org/info/rfc2119>.



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   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011,
              <https://www.rfc-editor.org/info/rfc6333>.

   [RFC6334]  Hankins, D. and T. Mrugalski, "Dynamic Host Configuration
              Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite",
              RFC 6334, DOI 10.17487/RFC6334, August 2011,
              <https://www.rfc-editor.org/info/rfc6334>.

10.2.  Informative References

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              DOI 10.17487/RFC2629, June 1999, <https://www.rfc-
              editor.org/info/rfc2629>.

   [RFC6908]  Lee, Y., Maglione, R., Williams, C., Jacquenet, C., and M.
              Boucadair, "Deployment Considerations for Dual-Stack
              Lite", RFC 6908, DOI 10.17487/RFC6908, March 2013,
              <https://www.rfc-editor.org/info/rfc6908>.

Authors' Addresses

   Honglei Xu
   China Telecom
   No.118 Xizhimennei street, Xicheng District
   Beijing, 100035
   P.R. China

   Email: xuhl.bri@chinatelecom.cn


   Qiong Sun
   China Telecom
   No.118 Xizhimennei street, Xicheng District
   Beijing  100035
   P.R. China

   Email: sunqiong.bri@chinatelecom.cn


   Yu Fu
   CNNIC
   No.4 South 4th Street, Zhongguancun
   Hai-Dian District, Beijing, 100190
   P.R. China

   Email: fuyu@cnnic.cn



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