Submitted to DHC Working Group Peter De Schrijver
INTERNET DRAFT Yves T'Joens
<draft-ietf-dhc-pv4-reconfigure-04.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.
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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 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",
"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 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
(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 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 : 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
E-mail : Christian.Hublet@alcatel.be
8. Full Copyright Statement
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implmentation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are
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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