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Submitted to DHC Working Group                      Peter De Schrijver
INTERNET DRAFT                                            Yves T'Joens
<draft-ietf-dhc-pv4-reconfigure-03.txt>               Christian Hublet
                                                               Alcatel
                                                            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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
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   Distribution of this memo is unlimited.

Abstract

   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 DHCP
   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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Internet Draft   draft-ietf-dhc-pv4-reconfigure-03.txt        April 2001


1.1 Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2. DHCP force renew

   This section describes the DHCP force renew 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 force renew message to the client. The client
   will change its state to the RENEW state. The client 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 force renew message is lost, the DHCP server will not receive
   a DHCP REQUEST from the client and it should retransmit the DHCP
   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.

   It can be that a client has obtained a network address through some
   other means (e.g., manual configuration) and has used a DHCPINFORM
   request to obtain other local configuration parameters. Such clients
   should respond to the receipt of DHCP 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
   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.




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Internet Draft   draft-ietf-dhc-pv4-reconfigure-03.txt        April 2001


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

   Field      DHCPFORCERENEW
   -----      ---------------
   'op'       BOOTREPLY
   'htype'    (From "Assigned Numbers" RFC)
   'hlen'     (Hardware address length in octets)
   'hops'     0
   'xid'      selected by server
   'secs'     0
   'ciaddr'   0
   'yiaddr'   0
   'siaddr'   0
   'flags'    0
   'giaddr'   0
   'chaddr'   client's hardware address
   'sname'    0
   'file'     0
   'options'  options



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Internet Draft   draft-ietf-dhc-pv4-reconfigure-03.txt        April 2001


   DHCP option 53 (DHCP message type) is extended with a new value :
   DHCPFORCERENEW (TBD)

5. IANA Considerations

   The new value for DHCP option 53 (DHCP message type) to indicate a
   DHCPFORCERENEW message is TBD.

6. Security Considerations

   As in some network environments DHCPFORCERENEW can be used to snoop
   and spoof traffic, the DHCPFORCERENEW message MUST be authenticated
   using the procedures as described in [DHCP-AUTH].

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 Allen, Nortel, for the
   contribution 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 : peter.de_schrijver@alcatel.be

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

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



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Internet Draft   draft-ietf-dhc-pv4-reconfigure-03.txt        April 2001


   E-mail : Christian.Hublet@alcatel.be

8. Full Copyright Statement

   This document and translations of it may be copied and furnished to
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   provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.''

























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