draft-ietf-dhc-pv4-reconfigure-06.txt   rfc3203.txt 
Submitted to DHC Working Group Yves T'Joens Network Working Group Y. T'Joens
INTERNET DRAFT Christian Hublet Request for Comments: 3203 C. Hublet
<draft-ietf-dhc-pv4-reconfigure-06.txt> Alcatel Category: Standards Track Alcatel
Peter De Schrijver P. De Schrijver
Mind Mind
July 2001 December 2001
Expires December, 2001
DHCP reconfigure extension DHCP reconfigure extension
Status of this memo Status of this Memo
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Abstract Abstract
This draft defines extensions to DHCP [DHCP] to allow dynamic This document defines extensions to DHCP (Dynamic Host Configuration
reconfiguration of a single host triggered by the DHCP server (eg. a Protocol) to allow dynamic reconfiguration of a single host triggered
new IP address and/or local configuration parameters). This is by the DHCP server (e.g., a new IP address and/or local configuration
achieved by introducing a unicast FORCERENEW message which forces the parameters). This is achieved by introducing a unicast FORCERENEW
client to the RENEW state. The behaviour for hosts using the DHCP message which forces the client to the RENEW state. The behaviour
INFORM message to obtain configuration information is also described. for hosts using the DHCP INFORM message to obtain configuration
information is also described.
1. Introduction 1. Introduction
The procedures as described within this draft allow the dynamic The procedures as described within this document allow the dynamic
reconfiguration of individual hosts. reconfiguration of individual hosts.
1.1 Conventions 1.1 Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. DHCP force renew 2. DHCP force renew
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DHCP client : host to be reconfigured using DHCP. DHCP client : host to be reconfigured using DHCP.
DHCP server : server which configured the DHCP client. DHCP server : server which configured the DHCP client.
2.2 Force renew procedures 2.2 Force renew procedures
The DHCP server sends a unicast FORCERENEW message to the client. The DHCP server sends a unicast FORCERENEW message to the client.
Upon receipt of the unicast FORCERENEW message, the client will Upon receipt of the unicast FORCERENEW message, the client will
change its state to the RENEW state, and will then try to renew its 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 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 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 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 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. 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 If the FORCERENEW message is lost, the DHCP server will not receive a
DHCP REQUEST from the client and it should retransmit the FORCERENEW DHCP REQUEST from the client and it should retransmit the FORCERENEW
message using an exponential backoff algorithm. Depending on the message using an exponential backoff algorithm. Depending on the
bandwidth of the network between server and client, the server should bandwidth of the network between server and client, the server should
choose a delay. This delay grows exponentially as retransmissions choose a delay. This delay grows exponentially as retransmissions
fail. The amount of retransmissions should be limited. fail. The amount of retransmissions should be limited.
The procedures described above assume the server to send a unicast The procedures described above assume the server to send a unicast
FORCERENEW message to the client. Receipt of a multicast FORCERENEW FORCERENEW message to the client. Receipt of a multicast FORCERENEW
message by the client should be silently discarded. message by the client should be silently discarded.
It can be that a client has obtained a network address through some 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 other means (e.g., manual configuration) and has used a DHCP INFORM
request to obtain other local configuration parameters. Such clients request to obtain other local configuration parameters. Such clients
should respond to the receipt of a unicast FORCERENEW message with a 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 new DHCP INFORM request so as to obtain a potential new set of local
configuration parameters. Note that the usage of these procedures are configuration parameters. Note that the usage of these procedures
limited to the set of options that are eligible for configuration by are limited to the set of options that are eligible for configuration
DHCP and should not override manually configured parameters. by DHCP and should not override manually configured parameters.
Note further that usage of the FORCERENEW message to reconfigure a Note further that usage of the FORCERENEW message to reconfigure a
client address or local configuration parameters can lead to the client address or local configuration parameters can lead to the
interruption of active sessions, and that as such these procedures interruption of active sessions, and that as such these procedures
should be used in controlled circumstances. should be used in controlled circumstances.
2.3 Example usage 2.3 Example usage
2.3.1 Embedded DHCP clients 2.3.1 Embedded DHCP clients
The autoconfiguration of home gateways (more generically Network The autoconfiguration of home gateways (more generically Network
Termination equipment) for public networking purposes can be achieved Termination equipment) for public networking purposes can be achieved
through means of DHCP, as described in [DSL_autoconf]. In order to through means of DHCP, as described in [DSL_autoconf]. In order to
allow service changes or service interruption, the FORCERENEW message allow service changes or service interruption, the FORCERENEW message
can trigger the home gateway to contact the DHCP server, prior to the can trigger the home gateway to contact the DHCP server, prior to the
expiry of the lease. expiry of the lease.
2.3.2 Hospitality service scenario 2.3.2 Hospitality service scenario
In self provisioned networks, e.g., hotel rooms, the hotel owned DHCP In self provisioned networks, e.g., hotel rooms, the hotel owned DHCP
server can hand out limited use IP addresses, that allows the server can hand out limited use IP addresses, that allows the
customer to consume local services or select external services from a customer to consume local services or select external services from a
web browser interface. In order to allow external services through web browser interface. In order to allow external services through
other service providers, e.g., global internet services or enterprise other service providers, e.g., global internet services or enterprise
VPN services, the DHCP server can trigger the client to ask for a new VPN services, the DHCP server can trigger the client to ask for a new
DHCP initialization session so as to obtain e.g., a globally routed DHCP initialization session so as to obtain e.g., a globally routed
IP address. IP address.
2.3.3 Network renumbering 2.3.3 Network renumbering
Under tightly controlled conditions, the FORCERENEW procedures can be Under tightly controlled conditions, the FORCERENEW procedures can be
used to brute force the renumbering of entire subnets, client per used to brute force the renumbering of entire subnets, client per
client, under control of a DHCP server. client, under control of a DHCP server.
2.4 Rationale 2.4 Rationale
The approach as described in this document has a number of The approach as described in this document has a number of
advantages. It does not require new states to be added to the DHCP advantages. It does not require new states to be added to the DHCP
client implementation. This minimizes the amount of code to be client implementation. This minimizes the amount of code to be
changed. It also allows lease RENEWAL to be driven by the server, changed. It also allows lease RENEWAL to be driven by the server,
which can be used to optimize network usage or DHCP server load. which can be used to optimize network usage or DHCP server load.
3. Extended DHCP state diagram 3. Extended DHCP state diagram
+--------+ +------+ +--------+ +------+
| Init / | +-->+ Init +<---------------+-------------------+ | Init / | +-->+ Init +<---------------+-------------------+
| Reboot | | +--+---+ | | | Reboot | | +--+---+ | |
+---+----+ DHCPNAK/ -/Send DHCPDISCOVER | | +---+----+ DHCPNAK/ -/Send DHCPDISCOVER | |
| Restart | (broadcast) | | | Restart | (broadcast) | |
| | v v-------------+ | | | | v v-------------+ | |
-/Send DHCPREQUEST| +----+------+ DHCPOFFER/DHCPDECLINE | -/Send DHCPREQUEST| +----+------+ DHCPOFFER/DHCPDECLINE |
| (broadcast)| | Selecting |----------+ | | | (broadcast)| | Selecting |----------+ | |
v | +----+------+ | | v | +----+------+ | |
+---+----+ | DHCPOFFER/DHCPREQUEST | | +---+----+ | DHCPOFFER/DHCPREQUEST | |
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+----------------->+ Bound +---------->+ Renew +--------->+ Rebind | +----------------->+ Bound +---------->+ Renew +--------->+ Rebind |
+--+-+--+T1 expires +-+-+---+T2 expires+----+---+ +--+-+--+T1 expires +-+-+---+T2 expires+----+---+
^ /DHCPREQUEST | | /broadcast | ^ /DHCPREQUEST | | /broadcast |
DHCPACK to leasing | | DHCPREQUEST | DHCPACK to leasing | | DHCPREQUEST |
| server | | | | server | | |
+----------------------------------------+ +----------------------------------------+
4. Message layout 4. Message layout
The FORCERENEW message makes use of the normal DHCP 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 with the introduction of a new DHCP message type. DHCP option 53
(DHCP message type) is extended with a new value : DHCPFORCERENEW (DHCP message type) is extended with a new value: DHCPFORCERENEW (9)
(TBD)
5. IANA Considerations 5. IANA Considerations
The new value for DHCP option 53 (DHCP message type) to indicate a The new value for DHCP option 53 (DHCP message type) to indicate a
DHCPFORCERENEW message is TBD. DHCPFORCERENEW message is 9.
6. Security Considerations 6. Security Considerations
As in some network environments FORCERENEW can be used to snoop and As in some network environments FORCERENEW can be used to snoop and
spoof traffic, the FORCERENEW message MUST be authenticated using the spoof traffic, the FORCERENEW message MUST be authenticated using the
procedures as described in [DHCP-AUTH]. FORCERENEW messages failing procedures as described in [DHCP-AUTH]. FORCERENEW messages failing
the authentication should be silently discarded by the client. the authentication should be silently discarded by the client.
6.1 Protocol vulnerabilities 6.1 Protocol vulnerabilities
The mechanism described in this document is vulnerable to a denial of The mechanism described in this document is vulnerable to a denial of
service attack through flooding a client with bogus FORCERENEW service attack through flooding a client with bogus FORCERENEW
messages. The calculations involved in authenticating the bogus messages. The calculations involved in authenticating the bogus
FORECERENEW messages may overwhelm the device on which the client is FORECERENEW messages may overwhelm the device on which the client is
running. running.
7. References 7. References
[DHCP] R.Droms, "Dynamic Host Configuration Protocol", RFC 2131, [DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC
March 1997. 2131, March 1997.
[DHCP-AUTH] R. Droms et al., "Authentication for DHCP Messages", [DHCP-AUTH] Droms, R. and W. Arbaugh, "Authentication for DHCP
RFC3118, Standards Track, June 2001. Messages", RFC 3118, June 2001.
[DSL_autoconf] Working Text WT-059, "Auto-configuration for Basic [DSL_autoconf] Technical Report TR-044, "Auto-Configuration for Basic
Internet (IP-Based) Services", DSL Forum, May 2001 Internet (IP-based) Services", DSL Forum, November
2001
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
8. Acknowledgements 8. Acknowledgements
The authors would like to thank David Allan, Nortel, for the The authors would like to thank David Allan, Nortel, for the
constructive comments to these procedures. constructive comments to these procedures.
9. Contacts 9. Authors' Addresses
Yves T'joens Yves T'joens
Alcatel Network Strategy Group Alcatel Network Strategy Group
Francis Wellesplein 1, 2018 Antwerp, Belgium Francis Wellesplein 1, 2018 Antwerp, Belgium
Phone : +32 3 240 7890 Phone: +32 3 240 7890
E-mail : yves.tjoens@alcatel.be EMail: yves.tjoens@alcatel.be
Peter De Schrijver Peter De Schrijver
Mind NV Mind NV
Vaartkom 11 Vaartkom 11
3000 Leuven 3000 Leuven
E-mail : p2@mind.be EMail: p2@mind.be
Christian Hublet Alcatel Broadband Networking Division
Alcatel Carrier Internetworking Division Veldkant 33b, 2550 Kontich, Belgium
De Villermontstraat 28, 2550 Kontich, Belgium Phone: +32 3 450 3322
Phone : +32 3 450 3322 EMail: Christian.Hublet@alcatel.be
E-mail : Christian.Hublet@alcatel.be
8. Full Copyright Statement 10. Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved.
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
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