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Versions: 00 01 02 03 04 05 06                                          
Internet Engineering Task Force                             T. Tsou, Ed.
Internet-Draft                                 Huawei Technologies (USA)
Intended status: Informational                             March 5, 2012
Expires: September 7, 2012


                          BFD Support DS-Lite
                   draft-tsou-softwire-bfd-ds-lite-00

Abstract

   In DS-Lite, there is no state information of the tunnel, which make
   it difficult to mange and diagnose.  BFD can be used in this case to
   detect the state of the IPv4-in-IPv6 tunnel by creating BFD session
   between CPE and AFTR.

Status of this Memo

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

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   This Internet-Draft will expire on September 7, 2012.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  BFD for DS-Lite . . . . . . . . . . . . . . . . . . . . . . . . 3
     3.1.  DS-Lite Scenario  . . . . . . . . . . . . . . . . . . . . . 4
     3.2.  Parameters for BFD  . . . . . . . . . . . . . . . . . . . . 4
     3.3.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . 5
     3.4.  Failover  . . . . . . . . . . . . . . . . . . . . . . . . . 6
     3.5.  Implementation Considerations . . . . . . . . . . . . . . . 7
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 8


































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1.  Introduction

   In DS-Lite [RFC6333], there is no status information about the IPv4-
   in-IPv6 tunnel, no keep-alive mechanism available, it is difficult to
   know whether the tunnle is up or down, which causes trouble to
   operation and maintenance.  Although administor can use ping to test
   the connectivity, but that is not a commonly used keep-alive
   mechanism.

   BFD [RFC5880] is a mechanism intended to detect faults in the
   bidirectional path.  It is uaually used in conjunction with
   applications like OSPF, IS-IS, etc, for fast fault recover -- fast
   re-route.

   BFD [RFC5880] can be used in DS-Lite, creating BFD session between
   CPE and AFTR, to provide tunnel status information.  If a fault is
   detected CPE can try to create DS-Lite tunnel with another AFTR, and
   terminate the existing one, so as to continue network service.

   [I-D.vinokour-bfd-dhcp] proposes using DHCP option to distribute BFD
   parameters to CPE.  But in case of DS-Lite, some of the key BFD
   parameters are already available, e.g. peer ip address is already
   available, and other parameters can be negotiated by BFD signaling,
   or statically configured, no extra DHCP option(s) need to be defined.

1.1.  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].


2.  Terminology

   BFD:      Bidirectional Forwarding Detection.

   AFTR:     Address Family Transition Router.

   CPE:      Customer Premise Equipment.

   FQDN      Fully Qualified Domain Name


3.  BFD for DS-Lite







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3.1.  DS-Lite Scenario

   In DS-Lite [RFC6333], BFD packet SHOULD be sent through IPv6 tunnel,
   as shown Figure 1.  The IPv4 address of CPE and AFTR SHOULD be the
   endpoint of a BFD session.

                    +--------------+                  +--------------+
        +-----+     |              |     +------+     |              |
        |     |-----+--------------+-----|      |     |              |
        | CPE |       IPv6 Tunnel        | AFTR |-----| IPv4 Network |
        |     |-----+--------------+-----|      |     |              |
        +-----+     | IPv6 Network |     +------+     |              |
       192.0.0.2    +--------------+    192.0.0.1     +--------------+

                        Figure 1: DS-Lite Scenario

3.2.  Parameters for BFD

   In order to setup a BFD session, the following parameters are needed,
   as shown in session 4.1 of [RFC5880]:

   o  Peer IP address

   o  My Discriminator

   o  Your Discriminator

   o  Desired Min TX Interval

   o  Required Min RX Interval

   o  Required Min Echo RX Interval

   In DS-Lite [RFC6334], CPE WAN port IPv4 address is a well known
   address 192.0.0.2, and AFTR's IPv4 address is 192.0.0.1, as defined
   in section 5.7 of [RFC6333].  Because all the CPEs and AFTRs are
   using well known IP address, IPv4 address is not suffient for setting
   up a BFD session.  From the CPE's point of view, CPE needs to create
   an IPv6 tunnel to an AFTR so as to get network connectivity to the
   AFTR, and send IPv4 BFD packets through the tunnel.  From the AFTR's
   point of view, a lot of CPEs with the same IPv4 address will setup
   BFD session with itself, in order to distinguish the CPEs, AFTR needs
   to combine both the IPv4 address and the IPv6 address of a CPE with a
   BFD session.

   When a CPE gets online, set up a tunnel with a AFTR, then it should
   iniitate a BFD session with the AFTR, generating a local
   discriminator, and send the first BFD packet to AFTR with peer



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   discriminator set to zero; when receiving the first BFD packet from
   CPE, AFTR should get a local discriminator and put it in the response
   BFD packet to the CPE.

   Other parameters can be negotiated by BFD signaling; and initial
   values can be set on CPE and AFTR.

3.3.  Procedures

   In DS-Lite [RFC6333], When a CPE gets online, it will be assigned an
   IPv6 prefix/address, and also the FQDN of the AFTR, as defined in
   [RFC6334].  The CPE will create an IPv6 tunnel to the AFTR, With
   which, and also the well know CPE IPv4 address 192.168.0.0.2 and AFTR
   IPv4 address 192.0.0.1, the CPE can initiate a BFD session to the
   AFTR.  BFD packets will be sent through DS-Lite tunnel.

   When sending out the first BFD packet, the CPE can generate a unique
   local discriminator, and set the remote discriminator to zero.  When
   the AFTR receive the first BFD packet from a CPE, the AFTR will also
   generate a corresponding local discriminator, and put it in the
   response packet to the CPE.  This will finish the discriminator
   negotiation, without any manual configuration.

   When the AFTR receive the first packet from a CPE, AFTR will get the
   IPv6 address and discriminator of the CPE, then AFTR can BFD session
   of the other direction.

   The procedures of setting up a BFD session is shown below:























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      CPE                                                        AFTR
       |                   (CPE get online)                       |
       |                       BFD DOWN                           |
       | -------------------------------------------------------> |
       |               local discriminator  = 1234                |
       |               remote discriminator = 0                   |
       |                                                          |
       |                       BFD INIT                           |
       | <------------------------------------------------------- |
       |               local discriminator  = 5678                |
       |               remote discirminator = 1234                |
       |                                                          |
       |                       BFD UP                             |
       | -------------------------------------------------------> |
       |               local discriminator  = 1234                |
       |               remote discriminator = 5678                |
       |                                                          |
       |        (BFD session in one direction is finished)        |
       |        (Start BFD session in the other direction)        |
       |                                                          |
       |                       BFD DOWN                           |
       | <------------------------------------------------------- |
       |               local discriminator  = 5678                |
       |               remote discriminator = 1234                |
       |                                                          |
       |                       BFD INIT                           |
       | -------------------------------------------------------> |
       |               local discriminator  = 1234                |
       |               remote discriminator = 5678                |
       |                                                          |
       |                       BFD UP                             |
       | <------------------------------------------------------- |
       |               local discriminator  = 5678                |
       |               remote discriminator = 1234                |
       |                                                          |
       |           (Bidirectional session created!)               |
       |                                                          |

                  Figure 2: BFD session setup procedures

3.4.  Failover

   The FQDN of AFTR is sent to CPE via DHCP option, as defined in
   [RFC6334].  Multiple IP addresses can be configured for a FQDN on the
   DNS server.  If BFD detect a fault on the link to an AFTR, CPE can
   choose another AFTR address, use a different AFTR to provide network
   sevice.




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   If anycast is used for loadbalance and failover, there might be a
   ICMP error message problem, that is, when a packet is sent from AFTR
   to CPE, one of the routers between them may generate a error ICMP
   message, e.g. packet too big, and the error message is not sent back
   to the source AFTR, but sent to another AFTR.

3.5.  Implementation Considerations

   BFD is usually used for quick fault detection, at a very small time
   scale, e.g. milliseconds.  But in DS-Lite, it may not be necessary to
   detect fault in such a short time.  On the other hand, an AFTR may
   need to tens of thousand CPEs, which means the AFTR will need to
   support the same number of BFD sessions.  In order to performance
   requirement to the AFTR, it may be necessary to reduce the time
   period between BFD packets transmission to a longer time, e.g. 10s or
   30s.


4.  IANA Considerations

   This memo includes no request to IANA.


5.  Security Considerations

   In DS-Lite [RFC6333], CPE may not be directly connected to AFTR,
   there may be other routers between them.  Then there are potential
   spoofing problem, as described in [RFC5883], cryptographic
   authentication should be used.


6.  References

6.1.  Normative References

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

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, June 2010.

   [RFC5883]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for Multihop Paths", RFC 5883, June 2010.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.




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   [RFC6334]  Hankins, D. and T. Mrugalski, "Dynamic Host Configuration
              Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite",
              RFC 6334, August 2011.

6.2.  Informative References

   [I-D.vinokour-bfd-dhcp]
              Vinokour, V., "Configuring BFD with DHCP and Other
              Musings", May 2008.


Author's Address

   Tina Tsou (editor)
   Huawei Technologies (USA)
   2330 Central Expressway
   Santa Clara  CA  95050
   USA

   Phone: +1 408 330 4424
   Email: tina.tsou.zouting@huawei.com






























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