[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-tsirtsis-dhc-aaa-ra) 00

   DHC WG                                                G. Tsirtsis
                                                Flarion Technologies
   Internet Draft                                          J. Privat
                                                         Northstream
   Title: draft-ietf-dhc-aaa-ra-00.txt
   Expires : June 2001                                   January 2001




                   Triggering AAA from DHCP Relay Agents
                       draft-ietf-dhc-aaa-ra-00.txt


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [1].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.
   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet- Drafts as reference
   material or to cite them other than as "work in progress."
   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt
   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.



Abstract


   Recently there has been interest in using DHCP for configuring
   clients accessing the Internet through some form of high-speed access
   technology such as cable or ADSL [DHC-AGENT]. In addition, although
   DHCP was initially designed for configuring fixed hosts, proposals
   are being made to enhance DHCP to support roaming/mobile clients
   [DHC-ENHANCE]. These two trends have put in evidence the need for a
   coupling between AAA and DHCP. Some initial requirements for DHCP/AAA
   have been proposed in [DHC-AAA].

   This document proposes a different model in which AAA procedures are
   invoked not from a DHCP server but from a DHCP relay agent to make
   sure that ALL the Internet Access features supported by the PPP model
   can be replicated in a DHCP based Internet Access environment.





Tsirtsis, Privat                                                     1
Internet Draft          Triggering AAA from RA            January 2001





1. Introduction

   Traditionally DHCP has mainly been used in intranets such as
   corporate or campus networks. Recently there has been interest in
   using DHCP for configuring clients accessing the Internet through
   some form of high-speed access technology such as cable or ADSL [DHC-
   AGENT].

   In addition, although DHCP was initially designed for configuring
   fixed hosts, proposals are being made to enhance DHCP to support
   roaming/mobile clients [DHC-ENHANCE]. These two trends have put in
   evidence the need for a coupling between AAA and DHCP. Some initial
   requirements for DHCP/AAA have been proposed in [DHC-AAA].

   This document proposes a different model in which AAA procedures are
   invoked not from a DHCP server but from a DHCP relay agent. The
   reason is that if DHCP is to replace PPP in some environments, there
   will be a strong requirement to make sure that ALL the Internet
   Access features supported by the PPP model can be replicated in DHCP-
   based Internet Access scenarios.

   However, there are fundamental differences between PPP-based and
   DHCP-based Internet access.
   On the one hand, PPP terminates on the Access Router (or Network
   Access Server-NAS) which becomes the Policy Enforcement Point between
   the network and the client. Typically the NAS is at the same time a
   PPP terminator, AAA client and possibly DHCP relay agent. This is a
   very powerful model since the NAS is the most sensible point at which
   to apply services such as Accounting, Resource Allocation,
   Authentication and many others.
   On the other hand, DHCP runs from the client to the DHCP server which
   is inside the Access Network and possibly several routers away from
   the Access Router. In the absence of PPP, the Access Router, as it
   stands at the moment, does not have a way to trigger the AAA
   functions that PPP based networks have. Although, DHCP relay agents
   will typically be operating in the Access Routers, these are
   considered to be very simple, and most importantly transparent,
   devices.

   We propose in this document that DHCP relay agents be used as AAA
   triggers intercepting and conveying relevant information from clients
   to AAA servers. This allows the PPP Internet Access model to be
   replicated in a non-PPP environment.








 Tsirtsis, Privat                                                    2
Internet Draft          Triggering AAA from RA            January 2001


2. Currently proposed model: AAA from DHCP server

2.1 Description

   The currently proposed model for DHCP based roaming and mobile IP as
   described in [DHC-AAA] and [MOBILEIP-AAA] is shown in Figure 1. In
   this model the AAA procedure is invoked from the DHCP server.

                           Local Domain                  Internet
                         +-------------+              +----------------+
                         |  +------+   |              |   +------+     |
                         |  | AAAL |   | AAA Protocol |   | AAAP |     |
                         |  |      +----------------------+      |     |
                         |  +---+--+   |              |   +------+     |
                         |      |      |              |                |
                         |      |      |              +----------------+
                         |      |      |
                         |      |      |
        +--------+       |  +---+---+  |
        | DHCP   |  DHCP |  | DHCP  |  |
        | Client |-------|--| Server|  |
        +--------+       |  +-------+  |       AAAP =  Public authority
                         |             |       AAAL =  local authority
                         +-------------+

               Figure 1: DHCP/AAA Current Model

   Even with the use of a DHCP Relay Agent the above picture does not
   change fundamentally but only becomes Figure 2.

                        Local Domain                  Internet
                         +-------------+              +----------------+
                         |  +------+   |              |   +------+     |
                         |  | AAAL |   | AAA Protocol |   | AAAP |     |
                         |  |      +----------------------+      |     |
                         |  +---+--+   |              |   +------+     |
                         |      |      |              |                |
                         |      |      |              +----------------+
                         |      |      |
                         |      |      |
      +------+  +-----+  |  +---+---+  |
      |DHCP  |  |DHCP |  |  | DHCP  |  |
      |Client|--|Relay|--|--| Server|  |
      +------+  +-----+  |  +-------+  |      AAAP =  Public authority
                         |             |      AAAL =  local authority
                         +-------------+
               Figure 2: DHCP/AAA Servers Model with Relay Agent







 Tsirtsis, Privat                                                    3
Internet Draft          Triggering AAA from RA            January 2001



2.2 Limitations

   The above model is fine for traditional use of DHCP in corporate and
   other such networks were a level of trust already exists between the
   clients and the network. DHCP is, however, increasingly being used in
   other environments such as residential access over Cable modems or
   possibly xDSL and mobile networks.
   These new types of applications for DHCP have different requirements
   and characteristics in terms of security and trust. Before DHCP was
   considered in the above types of networks, PPP had been applied
   successfully providing similar functionality. PPP has a fundamental
   difference to DHCP in the way it treats new clients. All checks
   happen from the Access Point, i.e: the first point of attachment for
   the client, for example the NAS. Figure 3 shows this PPP model.


                           Local Domain                  Internet
                         +-------------+              +----------------+
                         |  +------+   |              |   +------+     |
                         |  | AAAL |   | AAA Protocol |   | AAAP |     |
                         |  |      +----------------------+      |     |
                         |  +---+--+   |              |   +------+     |
                         |      |      |              |                |
                         |      |      |              +----------------+
                         |      |      |
                         |      |      |
        +--------+       |  +---+---+  |
        | PPP    |  PPP  |  |NAS/AAA|  |
        | Client |-------|--| Client|  |
        +--------+       |  +-------+  |       AAAP =  Public authority
                         |             |       AAAL =  local authority
                         +-------------+

               Figure 3: PPP Model


3 New model: AAA from DHCP Relay Agent

3.1 Description

   If DHCP is to replace PPP in some environments, a similar model is
   needed so the client details are checked on the first node of
   attachment (CMTS, DSLAM, etc...). This would produce the layout of
   Figure 4. This is consistent with the approach followed in [DHC-
   AGENT] in that the access point is the first trusted point in the
   provider network.







 Tsirtsis, Privat                                                    4
Internet Draft          Triggering AAA from RA            January 2001



                           Local Domain                  Internet
                         +-------------+              +----------------+
                         |  +------+   |              |   +------+     |
                         |  | AAAL |   | AAA Protocol |   | AAAP |     |
                         |  |      +----------------------+      |     |
                         |  +---+--+   |              |   +------+     |
                         |      |      |              |                |
                         |      |      |              +----------------+
                         |      |      |
                         |      |      +----------------+
        +--------+       |  +---+---+       +--------+  |
        | DHCP   |  DHCP |  | DHCP  |       | DHCP   |  |
        | Client |-------|--| Relay |-------| Server |  |
        +--------+       |  +-------+       +--------+  |
                         |                              |
                         +------------------------------+

               Figure 4: DHCP Relay Agent Model


3.2 Advantages

   The major benefit from this new model is the ability to enforce
   policy. In Figure 2, the DHCP server can only Authenticate the client
   details but not much else. In the PPP model, because the AAA check
   takes place at the NAS, it is possible to get detailed, customized
   configuration for the client and dynamically configure an access list
   on the NAS's interface to restrict/allow certain functions and
   resources.
   It could be argued that this customization is also possible in the
   currently proposed model (AAA from DHCP server). Once a user identity
   has been established using AAA, looking up access control lists and
   storing usage information could be done using LDAP or other existing
   means to communicate with databases/directories. However there is
   value for a provider in reusing as much as possible the same existing
   AAA mechanisms as currently deployed.


4. Impact on DHCP

4.1 Authenticating a user

   Discussion:
   In order to authenticate a user, a AAA server needs to be passed some
   information of the form username/password. How does the AAA client
   get this information? Does it get it through DHCP (either through
   existing options or through a new one) or does it get it through a
   separate challenge sent by the access point?
   Note that once an access point gets the username/password
   information, it can use it for the Agent Remote ID sub-option
   proposed in [DHC-AGENT].


 Tsirtsis, Privat                                                    5
Internet Draft          Triggering AAA from RA            January 2001


4.2 Relay Agent behavior

   Discussion:
   Clearly, the relay agent behavior needs to be specified when
   triggering AAA from DHCP messages.
   The relay agent needs to know:
   Which DHCP message triggers a AAA check.
   Which DHCP message triggers the download of policies (such as an
   access list) on the access point? Note that in order to install
   access lists, some information is required such as the IP address
   given to the client.
   What action to take if no response is received from the AAA server
   (timer, notification sent back to client).

   The Relay agent must be able to terminate service to a client if not
   authorized by a AAA server.


5 Security considerations

   Authentication is presently being added to the DHCP protocol [DHC-
   AUTH]. This allows DHCP clients and servers to authenticate each
   other. Our purpose differs in that we want to authenticate and
   authorize a user before he accesses a provider network, to apply
   policy to customize this access connection and to account for the
   service. However it may be possible to re-use some elements of this
   authentication framework when coupling AAA to DHCP.


6. Acknowledgements

   The authors would like to thank Alan O'Neill, who initiated this
   work.


7. References

   [DHC-AAA] draft-ietf-dhc-aaa-requirements-00.txt
   [MOBILEIP-AAA] RFC 2977, Mobile IP Authentication, Authorization and
   Accounting Requirements
   [DHC-AGENT] draft-ietf-dhc-agent-options-12.txt
   [DHC-ENHANCE] draft-ietf-dhc-enhance-requirements-00.txt
   [DHC-AUTH] draft-ietf-dhc-authentication-15.txt


8. Authors

   George Tsirtsis
   Flarion Technologies
   Phone: +44 20 88260073
   Email: G.Tsirtsis@Flarion.com



 Tsirtsis, Privat                                                    6
Internet Draft          Triggering AAA from RA            January 2001


   Jerome Privat
   Northstream
   Phone: +33 4 97 23 40 45
   Email: jerome.privat@northstream.se




   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.








 Tsirtsis, Privat                                                    7


Html markup produced by rfcmarkup 1.129b, available from https://tools.ietf.org/tools/rfcmarkup/