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RFC3203 - DHCP reconfigure extension

王朝other·作者佚名  2008-05-31
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Network Working Group Y. T'Joens

Request for Comments: 3203 C. Hublet

Category: Standards Track Alcatel

P. De Schrijver

Mind

December 2001

DHCP reconfigure extension

Status of this Memo

This document specifies an Internet standards track protocol for the

Internet community, and requests discussion and suggestions for

improvements. Please refer to the current edition of the "Internet

Official Protocol Standards" (STD 1) for the standardization state

and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2001). All Rights Reserved.

Abstract

This document defines extensions to DHCP (Dynamic Host Configuration

Protocol) to allow dynamic reconfiguration of a single host triggered

by the DHCP server (e.g., a new IP address and/or local configuration

parameters). 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 document allow the dynamic

reconfiguration of individual hosts.

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 RFC2119 [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. Note that the usage of these procedures

are limited to the set of options that are eligible for configuration

by DHCP and should not override manually configured parameters.

Note further that usage of the FORCERENEW message to reconfigure a

client address or local configuration parameters can lead to the

interruption of active sessions, and that as such these procedures

should be used in controlled circumstances.

2.3 Example usage

2.3.1 Embedded DHCP clients

The autoconfiguration of home gateways (more generically Network

Termination equipment) for public networking purposes can be achieved

through means of DHCP, as described in [DSL_autoconf]. In order to

allow service changes or service interruption, the FORCERENEW message

can trigger the home gateway to contact the DHCP server, prior to the

expiry of the lease.

2.3.2 Hospitality service scenario

In self provisioned networks, e.g., hotel rooms, the hotel owned DHCP

server can hand out limited use IP addresses, that allows the

customer to consume local services or select external services from a

web browser interface. In order to allow external services through

other service providers, e.g., global internet services or enterprise

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

IP address.

2.3.3 Network renumbering

Under tightly controlled conditions, the FORCERENEW procedures can be

used to brute force the renumbering of entire subnets, client per

client, under control of a DHCP server.

2.4 Rationale

The approach as described in this document 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.

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 (9)

5. IANA Considerations

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

DHCPFORCERENEW message is 9.

6. Security Considerations

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

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.

6.1 Protocol vulnerabilities

The mechanism described in this document is vulnerable to a denial of

service attack through flooding a client with bogus FORCERENEW

messages. The calculations involved in authenticating the bogus

FORECERENEW messages may overwhelm the device on which the client is

running.

7. References

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

2131, March 1997.

[DHCP-AUTH] Droms, R. and W. Arbaugh, "Authentication for DHCP

Messages", RFC3118, June 2001.

[DSL_autoconf] Technical Report TR-044, "Auto-Configuration for Basic

Internet (IP-based) Services", DSL Forum, November

2001

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate

Requirement Levels", BCP 14, RFC2119, March 1997.

8. Acknowledgements

The authors would like to thank David Allan, Nortel, for the

constructive comments to these procedures.

9. Authors' Addresses

Yves T'joens

Alcatel Network Strategy Group

Francis Wellesplein 1, 2018 Antwerp, Belgium

Phone: +32 3 240 7890

EMail: yves.tjoens@alcatel.be

Peter De Schrijver

Mind NV

Vaartkom 11

3000 Leuven

EMail: p2@mind.be

Alcatel Broadband Networking Division

Veldkant 33b, 2550 Kontich, Belgium

Phone: +32 3 450 3322

EMail: Christian.Hublet@alcatel.be

10. Full Copyright Statement

Copyright (C) The Internet Society (2001). All Rights Reserved.

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 implementation 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

document itself may not be modified in any way, such as by removing

the copyright notice or references to the Internet Society or other

Internet organizations, except as needed for the purpose of

developing Internet standards in which case the procedures for

copyrights defined in the Internet Standards process must be

followed, or as required to translate it into languages other than

English.

The limited permissions granted above are perpetual and will not be

revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an

"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING

TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING

BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION

HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF

MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

Funding for the RFCEditor function is currently provided by the

Internet Society.

 
 
 
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