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Versions: (draft-kostur-dhc-loadbv6) 00 01 02

DHC                                                            A. Kostur
Internet-Draft                                                 Incognito
Intended status: Standards Track                           July 04, 2014
Expires: January 03, 2015

                       Load Balancing for DHCPv6


   This document proposes a method of algorithmic load balancing for
   IPv6 Dynamic Host Configuration Protocol (DHCPv6) traffic.  It
   enables multiple, cooperating servers to decide which one should
   service a client, without necessarily exchanging any information
   between the servers.  The server selection is based on the servers
   hashing client DHCP Unique Identifiers (DUIDs) when multiple DHCPv6
   servers are available to service DHCPv6 clients.  The proposed
   technique provides for efficient server selection when multiple
   DHCPv6 servers offer services on a network without requiring any
   changes to existing DHCPv6 clients.  This algorithm is an extension
   of an already defined and proven algorithm used for DHCPv4, as
   described in RFC 3074.

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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 January 03, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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 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
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  3
   2.  Background and External Requirements . . . . . . . . . . . . .  3
   3.  Operation  . . . . . . . . . . . . . . . . . . . . . . . . . .  3
     3.1.  Messages with a Server Identifier  . . . . . . . . . . . .  3
     3.2.  RENEWs with the DHCPv6 servers sharing lease information .  3
     3.3.  RENEWs with the DHCPv6 servers not sharing lease informatio 4
     3.4.  Selecting the STID . . . . . . . . . . . . . . . . . . . .  4
     3.5.  Replacing the secs field . . . . . . . . . . . . . . . . .  4
   4.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  5
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  5
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     7.1.  Normative References . . . . . . . . . . . . . . . . . . .  5
     7.2.  Informative References . . . . . . . . . . . . . . . . . .  6
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .  6

1.  Introduction

   This document is intended to extend the algorithm described in DHC
   Load Balancing Algorithm [RFC3074] to apply to DHCPv6 [RFC3315]
   traffic.  Most of the terminology and procedures are identical to the
   ones specified in RFC 3074.  As a short summary: servers which are
   participating in load balancing calculate hash values for the Service
   Transaction ID (STID) based on client-specific values (the client
   DUID for DHCPv6, the Client ID or CHADDR field for DHCPv4) for each
   incoming UDP packet.  This hash is then used to select a hash bucket.
   Servers are assigned to service particular buckets.

   Load balancing is not the same as failover, as load balancing is not
   attempting to address any redundancy concerns [RFC6853].  Load
   balancing does not attempt to address the issues of configuration or
   data synchronization between DHCPv6 servers.  However, load balancing

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   may be desirable in a failover set of servers in order to reduce the
   load on the servers in normal operations, and certain desirable
   behaviors can occur if load balancing is aware that data
   synchronization is occurring.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Background and External Requirements

   The requirements for DHCPv6 are substantially the same as for DHCPv4,
   CONFIRM, RENEW, or REBIND (as appropriate), etc.

3.  Operation

   A DHCPv6 server performing this load balancing will operate in
   substantially the same manner as if it were a DHCPv4 server load
   balancing an incoming DHCPv4/BOOTP packet with the following

   Load balancing only applies to incoming client-originated UDP DHCPv6
   messages.  RELAY-FORWs are processed based on the content of the most
   encapsulated packet (ie: the client-originated DHCPv6 message).
   Future message types will have to be considered as they are proposed
   as to how they may be load balanced.

   LEASEQUERY [RFC5007] messages MUST NOT be load balanced.  Devices
   which are sending LEASEQUERY packets will have to be sending those
   packets to all of the load balanced DHCPv6 servers, and the
   LEASEQUERY specification already considers what the device should do
   when it receives responses to the LEASEQUERY from multiple sources.

   DHCPV4-QUERY [I-D.ietf-dhc-dhcpv4-over-dhcpv6] messages SHOULD NOT be
   load balanced, but SHOULD be subject to DHCPv4 load balancing, if the
   server supports it.

   [RFC6977] are messages which should not be received by a DHCPv6
   server and thus are not considered in this document.

3.1.  Messages with a Server Identifier

   Messages which contain a Server Identifier to direct that message to
   a specific server SHOULD be processed as if load balancing were not
   in play, with the exception of RENEWs.

3.2.  RENEWs with the DHCPv6 servers sharing lease information

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   A DHCPv6 server receiving a RENEW with the server's Server Identifier
   specified MAY choose to ignore the request if the load balancing
   algorithm decides that this server should not process this message.
   Let us assume the following sequence of events:

   1.  There is a pair of DHCPv6 servers that are known to be exchanging
       lease information with each other

   2.  The first server fails and is no longer servicing DHCPv6 clients

   3.  Some number of DHCPv6 clients are bound to the second DHCPv6
       server (whether by performing a SOLCIT-ADVERTISE-REQUEST-REPLY
       sequence, or by REBINDing to the second server)

   4.  The first server is restored to service and is able to service
       DHCPv6 clients

   At this point, a disproportionate set of DHCPv6 clients are now bound
   to the second DHCPv6 server.  If the second DHCPv6 server is
   permitted to ignore the RENEW even though the Server Identifier would
   indicate that it should respond, then the clients which should be
   answered by the first server will get no response to the RENEW that
   contains the second server's Server Identifier and will perform the
   normal retry mechanisms.  At some point the client will transition
   into the REBIND state and will attempt to REBIND.  That REBIND will
   not have a Server Identifier and will be received by both DHCPv6
   servers.  Since the servers were exchanging lease information, the
   first DHCPv6 server would have sufficient information to be able to
   REPLY to the client to extend the lease and those clients would now
   be bound to the first DHCPv6 server again.  Over time this would
   result in the DHCPv6 population being rebalanced.

3.3.  RENEWs with the DHCPv6 servers not sharing lease information

   A DHCPv6 server receiving a RENEW with the server's Server Identifier
   specified SHOULD be processed as if load balancing were not in play.
   If the server ignored these RENEWs, the requesting device would
   eventually transition to REBIND, and the other servers may not have
   any lease information to answer the REBIND with, forcing the client
   to eventually drop its lease and start again from SOLICIT.

3.4.  Selecting the STID

   DHCPv6 servers MUST use the client's DUID in its entirety as the
   STID.  This is different than RFC 3074 which limited the STID to 16

   An INFORMATION-REQUEST may have no client DUID in the message.
   Calculate the hash as if a 0-length DUID were supplied, effectively
   assigning those messages to hash bucket 0.

3.5.  Replacing the secs field

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   A DHCPv6 server providing the capability of Delayed Service SHOULD
   use the value in the OPTION_ELAPSED_TIME wherever RFC 3074 makes
   reference to the secs field.

4.  Acknowledgements

   Thanks to Bernie Volz, Steve Gonczi, Ted Lemon, and Rob Stevens as
   this document heavily borrows from their previous work on RFC 3074,
   as well as Bernie and Tomek Mrugalski's additional comments during
   the discussions.

5.  IANA Considerations

   This memo includes no request to IANA.

6.  Security Considerations

   This proposal in and by itself provides no security, nor does it
   impact existing security.  Servers using this algorithm are
   responsible for ensuring that if the contents of the hash bucket
   assignments are transmitted over the network as part of the process
   of configuring any server, that message be secured against tampering,
   since tampering with the HBA could result in denial of service for
   some or all clients.

   If the hash bucket assignments are not configured such that each
   bucket is assigned to one and only one DHCP server, this results in
   some clients that will be either completely ignored by the DHCP
   servers (if no server is configured to answer that hash bucket), or
   get multiple responses (if more than one server is configured to
   answer that hash bucket).

7.  References

7.1.  Normative References

              Sun, Q., Cui, Y., Siodelski, M., Krishnan, S. and I.
              Farrer, "DHCPv4 over DHCPv6 Transport", Internet-Draft
              draft-ietf-dhc-dhcpv4-over-dhcpv6-05, February 2014.

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

   [RFC3074]  Volz, B., Gonczi, S., Lemon, T. and R. Stevens, "DHC Load
              Balancing Algorithm", RFC 3074, February 2001.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and
              M. Carney, "Dynamic Host Configuration Protocol for IPv6
              (DHCPv6)", RFC 3315, July 2003.

   [RFC5007]  Brzozowski, J., Kinnear, K., Volz, B. and S. Zeng, "DHCPv6
              Leasequery", RFC 5007, September 2007.

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   [RFC6977]  Boucadair, M. and X. Pougnard, "Triggering DHCPv6
              Reconfiguration from Relay Agents", RFC 6977, July 2013.

7.2.  Informative References

   [RFC6853]  Brzozowski, J., Tremblay, J., Chen, J. and T. Mrugalski,
              "DHCPv6 Redundancy Deployment Considerations", BCP 180,
              RFC 6853, February 2013.

Author's Address

   Andre Kostur
   Incognito Software Inc.
   Suite 500 - 375 Water St.
   Vancouver, BC V6B 5C6

   Phone: +1 604 678 2864
   Email: akostur@incognito.com

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