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DHCPv6 Failover Requirements
RFC 7031

Internet Engineering Task Force (IETF)                      T. Mrugalski
Request for Comments: 7031                                           ISC
Category: Informational                                       K. Kinnear
ISSN: 2070-1721                                                    Cisco
                                                          September 2013

                      DHCPv6 Failover Requirements

Abstract

   The DHCPv6 protocol, defined in RFC 3315, allows for multiple servers
   to operate on a single network; however, it does not define any way
   the servers could share information about currently active clients
   and their leases.  Some sites are interested in running multiple
   servers in such a way as to provide increased availability in case of
   server failure.  In order for this to work reliably, the cooperating
   primary and secondary servers must maintain a consistent database of
   the lease information.  RFC 3315 allows for, but does not define, any
   redundancy or failover mechanisms.  This document outlines
   requirements for DHCPv6 failover, enumerates related problems, and
   discusses the proposed scope of work to be conducted.  This document
   does not define a DHCPv6 failover protocol.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7031.

Mrugalski & Kinnear           Informational                     [Page 1]
RFC 7031              DHCPv6 Failover Requirements        September 2013

Copyright Notice

   Copyright (c) 2013 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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   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 ....................................................3
   2. Definitions .....................................................3
   3. Scope of Work ...................................................5
      3.1. Alternatives to Failover ...................................5
           3.1.1. Short-Lived Addresses ...............................5
           3.1.2. Redundant Servers ...................................6
           3.1.3. Distributed Databases ...............................6
           3.1.4. Load Balancing ......................................7
   4. Failover Scenarios ..............................................7
      4.1. Hot Standby Model ..........................................7
      4.2. Geographically Distributed Failover ........................7
      4.3. Load Balancing .............................................8
      4.4. 1-to-1, m-to-1, and m-to-n Models ..........................8
      4.5. Split Prefixes .............................................8
      4.6. Long-Lived Connections .....................................8
      4.7. Partial Server Communication Loss ..........................9
   5. Principles of DHCPv6 Failover ...................................9
      5.1. Failure Modes ..............................................9
           5.1.1. Server Failure .....................................10
           5.1.2. Network Partition ..................................10
      5.2. Synchronization Mechanisms ................................11
           5.2.1. Lockstep ...........................................11
           5.2.2. Lazy Updates .......................................12
   6. DHCPv4 and DHCPv6 Failover Comparison ..........................12
   7. DHCPv6 Failover Requirements ...................................13
      7.1. Features out of Scope .....................................14
   8. Security Considerations ........................................15
   9. Acknowledgements ...............................................15

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