Submitted to DHC Working Group                      Peter De Schrijver
INTERNET DRAFT                                            Yves T'Joens
<draft-ietf-dhc-pv4-reconfigure-04.txt>               Christian Hublet
                                                            April 2001
                                               Expires September, 2001

                       DHCP reconfigure extension

Status of this memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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   Distribution of this memo is unlimited.


   This draft defines extensions to DHCP [DHCP] to allow dynamic
   reconfiguration of a single host triggered by the DHCP server (eg. a
   new IP address). This is achieved by introducing a unicast FORCERENEW
   message which forces the client to the RENEW state. The behaviour for
   hosts using the DHCP INFORM message to obtain configuration
   information is also described.

1. Introduction

   The procedures as described within this draft allow the dynamic
   reconfiguration of individual hosts.

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1.1 Conventions

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

2. DHCP force renew

   This section describes the FORCERENEW message extension.

2.1 Terminology

   DHCP client : host to be reconfigured using DHCP.

   DHCP server : server which configured the DHCP client.

2.2 Force renew procedures

   The DHCP server sends a unicast FORCERENEW message to the client.
   Upon receipt of the unicast FORCERENEW message, the client will
   change its state to the RENEW state, and will then try to renew its
   lease according to normal DHCP procedures. If the server wants to
   assign a new IP address to the client, it will reply to the DHCP
   REQUEST with a DHCP NAK. The client will then go back to the init
   state and broadcast a DHCP DISCOVER message. The server can now
   assign a new IP address to the client by replying with a DHCP OFFER.
   If the FORCERENEW message is lost, the DHCP server will not receive a
   DHCP REQUEST from the client and it should retransmit the FORCERENEW
   message using an exponential backoff algorithm. Depending on the
   bandwidth of the network between server and client, the server should
   choose a delay. This delay grows exponentially as retransmissions
   fail. The amount of retransmissions should be limited.

   The procedures described above assume the server to send a unicast
   FORCERENEW message to the client. Receipt of a multicast FORCERENEW
   message by the client should be silently discarded.

   It can be that a client has obtained a network address through some
   other means (e.g., manual configuration) and has used a DHCP INFORM
   request to obtain other local configuration parameters. Such clients
   should respond to the receipt of a unicast FORCERENEW message with a
   new DHCP INFORM request so as to obtain a potential new set of local
   configuration parameters.

2.3 Rationale

   This approach has a number of advantages. It does not require new
   states to be added to the DHCP client implementation. This minimizes

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   the amount of code to be changed. It also allows lease RENEWAL to be
   driven by the server, which can be used to optimize network usage or
   DHCP server load.

3. Extended DHCP state diagram

+--------+             +------+
| Init / |         +-->+ Init +<---------------+-------------------+
| Reboot |         |   +--+---+                |                   |
+---+----+     DHCPNAK/ -/Send DHCPDISCOVER    |                   |
    |          Restart    |     (broadcast)    |                   |
    |              |      v   v-------------+  |                   |
 -/Send DHCPREQUEST| +----+------+    DHCPOFFER/DHCPDECLINE        |
    |   (broadcast)| | Selecting |----------+  |                   |
    v              | +----+------+             |                   |
+---+----+         |   DHCPOFFER/DHCPREQUEST   |                   |
| Reboot +---------+  (broadcast)              |                   |
+---+----+                v                    |                   |
    |                +----+-------+            DHCPNAK /halt network
    |                + Requesting |            |       lease expired
   DHCPACK/          +----+-------+            |                   |
   Record lease           |                    |                   |
   set timers         DHCPACK/Record lease     |                   |
    |                     v   Set T1 & T2      |                   |
    |                  +--+----+DHCPFORCE  +---+---+          +----+---+
    +----------------->+ Bound +---------->+ Renew +--------->+ Rebind |
                       +--+-+--+T1 expires +-+-+---+T2 expires+----+---+
                          ^     /DHCPREQUEST | |    /broadcast     |
                       DHCPACK    to leasing | |    DHCPREQUEST    |
                          |        server    | |                   |

4. Message layout

   The FORCERENEW message makes use of the normal DHCP message layout
   with the introduction of a new DHCP message type. DHCP option 53
   (DHCP message type) is extended with a new value : DHCPFORCERENEW

5. IANA Considerations

   The new value for DHCP option 53 (DHCP message type) to indicate a

6. Security Considerations

   As in some network environments FORCERENEW can be used to snoop and

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   spoof traffic, the FORCERENEW message MUST be authenticated using the
   procedures as described in [DHCP-AUTH]. FORCERENEW messages failing
   the authentication should be silently discarded by the client.

7. References

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

   [DHCP-AUTH] R. Droms et al., "Authentication for DHCP Messages",
   RFCxxxx, yyyy 2001.

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

8. Acknowledgements

   The authors would like to thank David Allan, Nortel, for the
   constructive comments to these procedures.

9. Contacts

   Peter De Schrijver
   Alcatel Network Strategy Group
   Francis Wellesplein 1, 2018 Antwerp, Belgium
   Phone : +32 3 240 8569
   E-mail :

   Yves T'joens
   Alcatel Network Strategy Group
   Francis Wellesplein 1, 2018 Antwerp, Belgium
   Phone : +32 3 240 7890
   E-mail :

   Christian Hublet
   Alcatel Carrier Internetworking Division
   De Villermontstraat 28, 2550 Kontich, Belgium
   Phone : +32 3 450 3322
   E-mail :

8. Full Copyright Statement

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   included on all such copies and derivative works.  However, this

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   document itself may not be modified in any way, such as by removing
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   This document and the information contained herein is provided on an

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