Recommendation for Prefix Binding in the Softwire DS-Lite Context

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Authors Suresh Vinapamula  , Mohamed Boucadair 
Last updated 2013-07-29
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Network Working Group                                      S. Vinapamula
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                            M. Boucadair
Expires: January 30, 2014                                 France Telecom
                                                           July 29, 2013

   Recommendation for Prefix Binding in the Softwire DS-Lite Context


   This document describes possible issues induced by the change of the
   B4 IPv6 address and sketches a set of recommendations.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  The Problem . . . . . . . . . . . . . . . . . . . . . . . . .   2
   4.  Recommendations . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     8.1.  Normative references  . . . . . . . . . . . . . . . . . .   4
     8.2.  Informative references  . . . . . . . . . . . . . . . . .   5

1.  Introduction

   IPv6 deployment models assumes IPv6 prefixes are delegated by Service
   Providers to the connected CPEs (Customer Premise Equipments) or
   hosts, which in their turn derive IPv6 addresses out of that prefix.
   In the case of DS-Lite [RFC6333], the B4 element derives an address
   for the softwire setup purposes.

   A B4 element might obtain a new external IPv6 address, for a variety
   of reasons including a reboot of the CPE, power outage, DHCP lease
   expiry, or other action undertaken by the Service Provider.  If this
   occurs, traffic forwarded to a B4's previous address might be
   delivered to another B4 that now acquired that address.  This affects
   all mapping types, whether implicit (e.g., by sending a TCP SYN) or
   explicit (e.g., using PCP [RFC6887]).

   The main goal of this document is to propose a recommendation to
   soften the impact of such renumbering issues.

   Note that in some deployments, CPE renumbering may be require to
   accommodate some privacy-related requirements to avoid the same
   prefix be assigned to the same customers.  It is out of scope of this
   document to discuss such contexts.

   This document complements [RFC6908].

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  The Problem

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   Since the network behind B4 can be overlapping across multiple CPEs,
   B4 address plays a key role in identifying associated resources
   assigned for each of the connections.  These resources maintain state
   of EIM, EIF, APP, and PCP mappings and flows.

   However, there can be change in B4 address for any reason, may be
   because of change in CPE device or may be because of security
   extensions enabled in generating the IPv6 address.  When the address
   change, the associated mappings created in the AFTR are no more
   valid.  This may result in creation of new set of mappings.

   ISPs may want to limit the usage of these resources on per subscriber
   basis for fair usage of resources.  To do so, a subscriber is
   identified by an IPv6 prefix mask (i.e., the length of the prefixes
   assigned to customers, for example /56 or /48).  These policies are
   used for dimensioning purposes and also to ensure that AFTR resources
   are not exhausted.  However, this policy doesn't resolve stale
   mappings hanging around in the system, consuming not only system
   resources, but also reducing the available quota of resources per

   When services are hosted behind B4 element, these services has to
   advertise about their change, when ever there is a change of the B4
   address.  Means to discover the change of B4 address are therefore

   Clearing those mappings can be envisaged, but that will causes a lot
   of churn in the AFTR, and it doesn't address the latency issue where
   a service has to advertise its new assigned external IP address and
   port and the clients have to consume and re-initiate connections.

   PCP-specific failure scenarios are discussed in

4.  Recommendations

   In order to mitigate the issues discussed in Section 3, the following
   recommendations are made:

   1.  A policy SHOULD enforced at the AFTR level to limit the amount of
       active softwires per subscriber.  The default value MUST be 1.

   2.  Resource contexts created at the AFTR level SHOULD be based on
       the prefix mask (or the prefix if it is explicitly configured),
       and not based on the derived B4 address.  Administrators SHOULD
       configure per prefix limits of resource usage, instead of per
       tunnel limits.  These resources include, number of flows,
       mappings including PCP, NAT pool resources, etc.

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   3.  In the event a new IPv6 address is assigned to B4, the AFTR
       SHOULD migrate existing state to be bound to the new B4's IP
       address.  This ensures the traffic destined to the previous IPv6
       address will redirected to the new IPv6 address.  The destination
       address for tunneling return traffic SHOULD be the last seen
       address from the CPE.  The source address of the tunnel would
       remain same as AFTR.

   4.  In the event of change of the CPE WAN IPv6 prefix, unsolicited
       PCP ANNOUNCE messages SHOULD be sent by the B4 element to
       internal hosts to update their mappings.

   5.  When a new prefix is assigned to the CPE, stale mappings may
       exist in the AFTR.  This will consume both implicit and explicit
       resources.  In order to avoid such issues, stable IPv6 prefix are

   6.  In case for any reason a prefix has to be reassigned, it is
       RECOMMENDED to reassign a prefix only when all the resources in
       use associated with that prefix are cleared from the AFTR.

5.  Security Considerations

   Security considerations related to DS-Lite are discussed in

6.  IANA Considerations

   This document does not require any action from IANA.

7.  Acknowledgements

   G. Krishna reviewed document and provided useful comments

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.

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

   [RFC6887]  Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)", RFC 6887, April

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8.2.  Informative references

              Boucadair, M. and R. Penno, "Analysis of Port Control
              Protocol (PCP) Failure Scenarios", draft-boucadair-pcp-
              failure-06 (work in progress), May 2013.

   [RFC6908]  Lee, Y., Maglione, R., Williams, C., Jacquenet, C., and M.
              Boucadair, "Deployment Considerations for Dual-Stack
              Lite", RFC 6908, March 2013.

Authors' Addresses

   Suresh Vinapamula
   Juniper Networks
   1194 North Mathilda Avenue
   Sunnyvale, CA  94089

   Phone: +1 408 936 5441

   Mohamed Boucadair
   France Telecom
   Rennes  35000


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