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RFC 2485 PROPOSED STANDARD AUTHENTICATION · DHCP · CONFIGURATION

DHCP Option for The Open Group's User Authentication Protocol

DHCP option that delivers User Authentication Protocol server addresses

On rfc-editor.org ↗
PUBLISHED
January 1999
AUTHORS
S. Drach
STREAM
IETF
OPTION CODE
98
DEFAULT HTTP PATH
/uap
DEFAULT HTTP PORT
80
DEFAULT HTTPS PORT
443
DOI
10.17487/RFC2485

RFC text

Contents
Original text · RFC Editor View on rfc-editor.org ↗ 
Network Working Group                                           S. Drach
Request for Comments: 2485                              Sun Microsystems
Category: Standards Track                                   January 1999



     DHCP Option for The Open Group's User Authentication Protocol

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 (1999).  All Rights Reserved.

Abstract

   This document defines a DHCP [1] option that contains a list of
   pointers to User Authentication Protocol servers that provide user
   authentication services for clients that conform to The Open Group
   Network Computing Client Technical Standard [2].

Introduction

   The Open Group Network Computing Client Technical Standard, a product
   of The Open Group's Network Computing Working Group (NCWG), defines a
   network computing client user authentication facility named the User
   Authentication Protocol (UAP).

   UAP provides two levels of authentication, basic and secure.  Basic
   authentication uses the Basic Authentication mechanism defined in the
   HTTP 1.1 [3] specification.  Secure authentication is simply basic
   authentication encapsulated in an SSLv3 [4] session.

   In both cases, a UAP client needs to obtain the IP address and port
   of the UAP service.  Additional path information may be required,
   depending on the implementation of the service.  A URL [5] is an
   excellent mechanism for encapsulation of this information since many
   UAP servers will be implemented as components within legacy HTTP/SSL
   servers.

   Most UAP clients have no local state and are configured when booted
   through DHCP.  No existing DHCP option [6] has a data field that
   contains a URL.  Option 72 contains a list of IP addresses for WWW
   servers, but it is not adequate since a port and/or path can not be
   specified.  Hence there is a need for an option that contains a list
   of URLs.

User Authentication Protocol Option

   This option specifies a list of URLs, each pointing to a user
   authentication service that is capable of processing authentication
   requests encapsulated in the User Authentication Protocol (UAP).  UAP
   servers can accept either HTTP 1.1 or SSLv3 connections.  If the list
   includes a URL that does not contain a port component, the normal
   default port is assumed (i.e., port 80 for http and port 443 for
   https).  If the list includes a URL that does not contain a path
   component, the path /uap is assumed.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |    Length     |   URL list
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Code            98

      Length          The length of the data field (i.e., URL list) in
                      bytes.

      URL list        A list of one or more URLs separated by the ASCII
                      space character (0x20).

References

   [1]  Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
        March 1997.

   [2]  Technical Standard: Network Computing Client, The Open Group,
        Document Number C801, October 1998.

   [3]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H., and T.
        Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC
        2068, January 1997.

   [4]  Freier, A., Karlton, P., and P. Kocher, "The SSL Protocol,
        Version 3.0", Netscape Communications Corp., November 1996.
        Standards Information Base, The Open Group,
        http://www.db.opengroup.org/sib.htm#SSL_3.

   [5]  Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
        Resource Locators (URL)", RFC 1738, December 1994.

   [6]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
        Extensions", RFC 2132, March 1997.

Security Considerations

   DHCP currently provides no authentication or security mechanisms.
   Potential exposures to attack are discussed in section 7 of the DHCP
   protocol specification.

   The User Authentication Protocol does not have a means to detect
   whether or not the client is communicating with a rogue
   authentication service that the client contacted because it received
   a forged or otherwise compromised UAP option from a DHCP service
   whose security was compromised.  Even secure authentication does not
   provide relief from this type of attack.  This security exposure is
   mitigated by the environmental assumptions documented in the Network
   Computing Client Technical Standard.

Author's Address

   Steve Drach
   Sun Microsystems, Inc.
   901 San Antonio Road
   Palo Alto, CA 94303

   Phone: (650) 960-1300
   EMail: drach@sun.com

Full Copyright Statement

   Copyright (C) The Internet Society (1999).  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.

AI ELI5

On this page
PROBLEMNetwork clients need to locate User Authentication Protocol (UAP) servers when they boot, but existing DHCP options cannot specify full URLs with ports and paths.
MECHANISMDHCP option 98 carries a space-separated list of URLs pointing to UAP servers, allowing clients to find authentication services that provide basic or SSL-encrypted authentication.
ENABLES AUTOMATIC DISCOVERYClients can be configured automatically to locate the authentication servers they need without local state, supporting The Open Group's Network Computing Client model.

§1The Open Group's User Authentication Protocol

The User Authentication Protocol (UAP) is a mechanism defined by The Open Group for network clients to authenticate users. It provides two levels of authentication: basic authentication using HTTP 1.1's mechanism, and secure authentication by encapsulating basic authentication inside an SSLv3 session.

UAP clients need to obtain the address and port of the UAP service, plus any path information required by the implementation. A URL is the ideal way to encode this information, since many UAP servers are implemented within legacy HTTP/SSL servers.

A network needs a way to check that you are who you say you are. This protocol gives a standard method to do that check.

§2The User Authentication Protocol Option

DHCP option 98 contains a list of URLs separated by ASCII space (0x20). Each URL points to a UAP server capable of processing authentication requests. If a URL lacks a port component, the default port is assumed (port 80 for http, port 443 for https). If a URL lacks a path component, the path /uap is assumed.

The option structure is simple: a code field set to 98, a length field containing the byte count of the URL list, and the URL list itself. Servers may include multiple URLs, allowing clients to choose from several authentication services.

The option is just a list of web addresses where the client can find the authentication server. Each address is separated by a space, like writing down multiple phone numbers.

§3Security Considerations

DHCP itself provides no authentication or security mechanisms, and potential exposures to attack are discussed in the DHCP specification. A rogue authentication service could compromise a client if the client received a forged UAP option from a compromised DHCP server. However, the UAP specification documents environmental assumptions that mitigate this exposure.

The automatic setup process is convenient but can be tricked if someone controls the network. The system assumes your network is mostly trustworthy.

§4References

[1]RFC 2131Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.March 1997[2]RFC 2132Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor Extensions", RFC 2132, March 1997.March 1997