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RFC3004 - The User Class Option for DHCP

王朝other·作者佚名  2008-05-31
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Network Working Group G. Stump

Request for Comments: 3004 IBM

Category: Standards Track R. Droms

Cisco Systems

Y. Gu

R. Vyaghrapuri

A. Demirtjis

Microsoft

B. Beser

Pacific Broadband Communications

J. Privat

Northstream AB

November 2000

The User Class Option for DHCP

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 (2000). All Rights Reserved.

Abstract

This option is used by a Dynamic Host Configuration Protocol (DHCP)

client to optionally identify the type or category of user or

applications it represents. The information contained in this option

is an opaque field that represents the user class of which the client

is a member. Based on this class, a DHCP server selects the

appropriate address pool to assign an address to the client and the

appropriate configuration parameters. This option should be

configurable by a user.

1. IntrodUCtion

DHCP administrators may define specific user class identifiers to

convey information about a client's software configuration or about

its user's preferences. For example, the User Class option can be

used to configure all clients of people in the accounting department

with a different printer than clients of people in the marketing

department.

2. Requirements Terminology

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 [3].

3. DHCP Terminology

o "DHCP client"

A DHCP client or "client" is an Internet host using DHCP to oBTain

configuration parameters such as a network address.

o "DHCP server"

A DHCP server or "server" is an Internet host that returns

configuration parameters to DHCP clients.

o "binding"

A binding is a collection of configuration parameters, including at

least an IP address, associated with or "bound to" a DHCP client.

Bindings are managed by DHCP servers.

4. User Class option

This option is used by a DHCP client to optionally identify the type

or category of user or applications it represents. A DHCP server

uses the User Class option to choose the address pool it allocates an

address from and/or to select any other configuration option.

This option is a DHCP option [1, 2].

This option MAY carry multiple User Classes. Servers may interpret

the meanings of multiple class specifications in an implementation

dependent or configuration dependent manner, and so the use of

multiple classes by a DHCP client should be based on the specific

server implementation and configuration which will be used to process

that User class option.

The format of this option is as follows:

Code Len Value

+-----+-----+--------------------- . . . --+

77 N User Class Data ('Len' octets)

+-----+-----+--------------------- . . . --+

where Value consists of one or more instances of User Class Data.

Each instance of User Class Data is formatted as follows:

UC_Len_i User_Class_Data_i

+--------+------------------------ . . . --+

L_i Opaque-Data ('UC_Len_i' octets)

+--------+------------------------ . . . --+

Each User Class value (User_Class_Data_i) is indicated as an opaque

field. The value in UC_Len_i does not include the length field

itself and MUST be non-zero. Let m be the number of User Classes

carried in the option. The length of the option as specified in Len

must be the sum of the lengths of each of the class names plus m:

Len= UC_Len_1 + UC_Len_2 + ... + UC_Len_m + m. If any instances of

User Class Data are present, the minimum value of Len is two (Len =

UC_Len_1 + 1 = 1 + 1 = 2).

The Code for this option is 77.

A server that is not equipped to interpret any given user class

specified by a client MUST ignore it (although it may be reported).

If a server recognizes one or more user classes specified by the

client, but does not recognize one or more other user classes

specified by the client, the server MAY use the user classes it

recognizes.

DHCP clients implementing this option SHOULD allow users to enter one

or more user class values.

5. IANA Considerations

Option 77, which IANA has already assigned for this purpose, should

be used as the User Class Option for DHCP.

6. Security Considerations

DHCP currently provides no authentication or security mechanisms.

Potential eXPosures to attack are discussed is section 7 of the

protocol specification [1].

This lack of authentication mechanism means that a DHCP server cannot

check if a client or user is authorized to use a given User Class.

This introduces an obvious vulnerability when using the User Class

option. For example, if the User Class is used to give out a special

parameter (e.g., a particular database server), there is no way to

authenticate a client and it is therefore impossible to check if a

client is authorized to use this parameter.

7. References

[1] Droms, R., "Dynamic Host Configuration Protocol", RFC2131, March

1997.

[2] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor

Extensions", RFC2132, March 1997.

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

Levels", BCP 14, RFC2119, March 1997.

8. Acknowledgments

This document is based on earlier drafts by Glenn Stump, Ralph Droms,

Ye Gu, Ramesh Vyaghrapuri and Burcak Beser. Thanks to Ted Lemon,

Steve Gonczi, Kim Kinnear, Bernie Volz, Richard Jones, Barr Hibbs and

Thomas Narten for their comments and suggestions.

9. Authors' Addresses

Glenn Stump

IBM Networking Software

P.O. Box 12195

RTP, NC 27709

Phone: 919 301 4277

EMail: stumpga@us.ibm.com

Ralph Droms

Cisco Systems

300 Apollo Drive

Chelmsford, MA 01824

Phone: 978 244 4733

EMail: rdroms@cisco.com

Ye Gu

Microsoft Corporation

One Microsoft Way

Redmond, WA 98052

Phone: 425 936 8601

EMail: yegu@microsoft.com

Ramesh Vyaghrapuri

Microsoft Corporation

One Microsoft Way

Redmond, WA 98052

Phone: 425 703 9581

EMail: rameshv@microsoft.com

Burcak Beser

Pacific Broadband Communications

3103 North 1st Street

San Jose, CA 95134

Phone: 408 468 6265

Email: Burcak@pacband.com

Ann Demirtjis

Microsoft Corporation

One Microsoft Way

Redmond WA 98052

Phone: 425 705 2254

EMail: annd@microsoft.com

Jerome Privat

Northstream AB

Espace Beethoven 1

1200 Route des Lucioles

BP 302

06906 Sophia Antipolis Cedex

France

Phone: +33 4 97 23 40 45

Fax: +33 4 97 23 24 51

Mobile: +33 6 13 81 76 71

Email: jerome.privat@northstream.se

Full Copyright Statement

Copyright (C) The Internet Society (2000). 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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