INTERNET-DRAFT                                               Luyuan Fang
Intended Status: Standards Track                                    eBay
Expires: June 7, 2017                                      Deepak Bansal
Expires: November 13, 2016
                                                           Fabio Chiussi

                                                            May 12,

                                                        December 4, 2016

            Forcerenew Reconfiguration Extensions for DHCPv4


   This document extends the definition of the DHCPFORCERENEW message
   for parameter reconfiguration in DHCPv4. This extension makes the
   DHCPFORCERENEW message more suitable to reconfigure configuration
   parameters other than IP addresses, and aligns the behavior of the
   reconfiguration procedure in DHCPv4 to the corresponding behavior in

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Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . .  4
   2. Extended DHCPFORCERENEW Message for DHCPv4  . . . . . . . . . .  4
     2.1 DHCPFORCERENEW Procedure . . . . . . . . . . . . . . . . . .  4
     2.2 DHCPFORCEINFORENEW: Extended DHCPFORCERENEW Message  . . . .  5
     2.3 DHCPFORCEINFORENEW Client Decline  . . . . . . . . . . . . .  5
   3.  Security Considerations  . . . . . . . . . . . . . . . . . . .  6
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  6
   5.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  6
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     6.1  Normative References  . . . . . . . . . . . . . . . . . . .  6
     6.2  Informative References  . . . . . . . . . . . . . . . . . .  7
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  7

1. Introduction

   Network and cloud operators increasingly use DHCP to distribute not
   just IP addresses, but also a variety of other configuration
   parameters to the clients. The DHCP servers may need to reconfigure
   such other configuration parameters in the clients in isolation,
   i.e., without reconfiguring IP addresses. In the case of
   reconfiguration of only configuration parameters other than IP
   addresses, it is especially important that service interruptions be
   avoided. Towards this goal, it is desirable for a DHCP client, when
   receiving a reconfiguration request from the DHCP server, to be made
   aware of whether such a request includes reconfiguration of IP
   addresses or only pertains to other configuration parameters, and
   have the client adapt its behavior to each situation. Currently, this
   is achieved in DHCPv6, but not in DHCPv4. This draft proposes an
   extension of the FORCERENEW message in DHCPv4 to provide this
   additional desired client behavior.

   For historical reasons, the procedure for server-initiated
   reconfiguration of configuration parameters uses a different
   mechanism and produces a different behavior in DHCPv4 and in DHCPv6.
   This is especially noticeable in the case of reconfiguration of
   parameters other than IP addresses.

   In DHCPv6 [RFC3315] [I-D. draft-ietf-dhc-rfc3315bis], the DHCP server
   sends a Reconfigure message to a client to inform the client that the
   server has new or updated configuration parameters. The Reconfigure
   message allows the client to distinguish whether the reconfiguration
   pertains to the IP addresses, in which case the client initiates a
   Renew/Reply, or it pertains to other parameters, in which case the
   client initiates an Information-request/Reply. In addition, the
   DHCPv6 reconfiguration procedure includes a way for the client to
   decline the reconfiguration attempt.

   In DHCPv4 [RFC2131], the server-initiated reconfiguration procedure
   relies on the use of the DHCPFORCERENEW message [RFC3203] and is less
   granular than its IPv6 counterpart, which can result in service
   interruptions that could be otherwise avoided when the
   reconfiguration only involves parameters other than IP addresses.

   This is the consequence of two differences with respect to the
   reconfiguration procedure in DHCPv6.

   1. The DHCPFORCERENEW message does not contain any indication for the
      client to distinguish a reconfiguration of IP addresses from a
      reconfiguration of some other configuration information. As a
      result, the client always initiates a Renew/Reply transaction with
      the server, which typically lead to service interruptions.

   2. In DHCPv4, there is no easy way for the client to decline a
      server-initiated reconfiguration request. The ability for a client
      to decline server-initiated reconfiguration may turn useful in the
      case of configuration information reconfiguration.

   It should be noted that [RFC7341] specifies DHCPv4 over DHCPv6, thus
   making it possible to use the DHCPv6 reconfigure function to
   reconfigure parameters in DHCPv4. However, [RFC7341] is only
   applicable to a IPv6 core network. Thus, achieving similar
   reconfiguration behavior as DHCPv6 on a IPv4 network requires an
   extension to the DHCPFORCERENEW message.

   In this document, we extend the DHCPFORCERENEW message used in DHCPv4
   by introducing a new Message Type DHCPFORCEINFORENEW to distinguish
   reconfiguration of IP addresses from reconfiguration of other
   information. In the latter case, we use the usual option mechanism to
   distribute new or updated parameters to the client.

   We also introduce a way for the client to decline the reconfiguration

   Any server-initiated reconfiguration requires authentication. The
   extended DHCPFORCERENEW message must be used with the security
   mechanisms described in [RFC6704], which aligns DHCPv4 authentication
   with DHCPv6 authentication described in [I-D. draft-ietf-dhc-

   The extended DHCPFORCENEW message described in this document aligns
   the behavior of server-initiated reconfiguration in DHCPv4 with the
   corresponding behavior in DHCPv6.

1.1. Terminology

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

   In this document, we use the terminology defined in [RFC3203] and in
   [I-D. draft-ietf-dhc-rfc3315bis].

2. Extended DHCPFORCERENEW Message for DHCPv4


   This is the DHCPFORCERENEW procedure defined in [RFC3203].

   The DHCP server sends a unicast DHCPFORCERENEW message to the client.
   Upon receipt of the unicast DHCPFORCERENEW message, the client enters
   a Renew/Reply transaction with the server to try to renew its lease
   according to normal DHCP procedures.  If the server wants to assign a
   new IP address to the client, it replies to the DHCPREQUEST with a
   DHCPNAK. The client then goes back to the init state and broadcasts a
   DHCPDISCOVER message. The server can now assign a new IP address to
   the client by replying with a DHCPOFFER. If the DHCPFORCERENEW
   message is lost, the DHCP server does not receive a DHCPREQUEST from
   the client and retransmits the DHCPFORCERENEW message using an
   exponential backoff algorithm.

   The DHCPFORCERENEW message makes use of the normal DHCP message
   format with DHCP option 53 (DHCP message type) value equal to

   As recognized in [RFC3203], usage of the DHCPFORCERENEW message to
   reconfigure local configuration parameters other than IP addresses
   can lead to the unnecessary interruption of active sessions. Thus, a
   modification of the DHCPFORCERENEW message is desirable to avoid
   service interruptions in such increasingly common situations.


   The extended FORCERENEW message makes use of the normal DHCP message
   format with DHCP option 53 (message type) value equal to
   DHCPFORCEINFORENEW (TBD, see IANA considerations below).

   Upon receipt of a DHCPFORCEINFORENEW, the client sends a DHCPINFORM
   message to the server to request and obtain new configuration

   If the DHCPFORCEINFORENEW message is lost, the DHCP server does not
   receive a DHCPINFORM from the client and retransmits the
   DHCPFORCEINFORENEW message using an exponential backoff algorithm.

   In order to assure backward compatibility with DHCP clients not
   supporting the extended DHCPFORCERENEW message, if no DHCPINFORM is
   received once the backoff expires, the DHCP server SHOULD send a
   DHCPFORCERENEW message to brute force the reconfiguration by
   reverting to the conventional DHCPv4 reconfiguration mechanism.

   The fact that the DHCP server ultimately reverts to the
   DHCPFORCERENEW message, however, complicates the ability of the
   client to decline the FORCEINFORENEW message, as discussed in the
   next section.


   It is desirable to introduce a way to allow the client to decline the
   DHCPFORCEINFORENEW request from the server. This further aligns the
   client behavior in DHCPv4 server-initiated reconfiguration with the
   corresponding behavior in DHCPv6.

   Because of the server behavior defined in the previous section,
   motivated by the objective of achieving backward compatibility with
   clients not supporting the extended DHCPFORCERENEW message, the DHCP
   client can't simply ignore the request, since that would eventually
   result in a DHCPFORCERENEW message to be sent by the server.

   One obvious solution is to forego backward compatibility and have the
   DHCP server simply abandon the reconfiguration procedure at the end
   of the DHCPINFOFORCERENEW reconfiguration procedure.

   Alternatively, a mechanism for the client to explicit inform the
   server that it is declining the server-initiated DHCPINFOFORCERENEW
   reconfiguration procedure needs to be devised.

3.  Security Considerations

   The reconfiguration procedure using extended DHCPFORCERENEW message
   described in this draft MUST be authenticated with the procedures
   described in [RFC3118] or [RFC6704].

   The security considerations relating to the DHCPFORCEINFORENEW
   message are the same as for DHCPFORCERENEW message discussed in
   [RFC3203] and [RFC6704].

4.  IANA Considerations

   IANA is requested to assign a new value for DHCP option 53 (DHCP
   message type) [RFC2939] for the DHCPFORCEINFORENEW message from the
   registry "DHCP Message Type 53 Values" maintained at

5.  Acknowledgments

   We would like to acknowledge Tomek Mrugalski, Christian Huitema and
   Bernie Volz for their comments and review of the first version of this draft. reviews.

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.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.

   [RFC2939]  Droms, R., "Procedures and IANA Guidelines for Definition
              of New DHCP Options and Message Types", BCP 43, RFC 2939,
              September 2000.

   [RFC3203]  T'Joens, Y., Hublet, C., and P. De Schrijver, "DHCP
              reconfigure extension", RFC 3203, December 2001.

   [RFC3118]  Droms, R., Ed., and W. Arbaugh, Ed., "Authentication for
              DHCP Messages", RFC 3118, June 2001.

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

   [RFC6704]  D. Miles et al., "Forcerenew Nonce Authentication",
              RFC 6704, August 2012.

   [RFC7341]  Q. Sun et al., "DHCPv4-over-DHCPv6 (DHCP 4o6) Transport",
              RFC 7341, August 2012.

6.2  Informative References

   [I-D. draft-ietf-dhc-rfc3315bis]  T. Mrugalski et al., "Dynamic Host
              Configuration Protocol for IPv6 (DHCPv6) bis",  draft-
              ietf-dhc-rfc3315bis-06 (work in progress), July 2015. October 201.

Authors' Addresses

   Luyuan Fang
   5600 148th
   411 108th Ave NE
   Bellevue, WA 98052 98004

   Deepak Bansal
   15590 NE 31st St.
   Redmond, WA 98052

   Fabio Chiussi
   Seattle, WA 98116