Proxy Chaining and Policy Implementation in Roaming
RFC 2607

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Network Working Group                                           B. Aboba
Request for Comments: 2607                         Microsoft Corporation
Category: Informational                                    J. Vollbrecht
                                                    Merit Networks, Inc.
                                                               June 1999

          Proxy Chaining and Policy Implementation in Roaming

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

1.  Abstract

   This document describes how proxy chaining and policy implementation
   can be supported in roaming systems. The mechanisms described in this
   document are in current use.

   However, as noted in the security considerations section, the
   techniques outlined in this document are vulnerable to attack from
   external parties as well as susceptible to fraud perpetrated by the
   roaming partners themselves. As a result, such methods are not
   suitable for wide-scale deployment on the Internet.

2.  Terminology

   This document frequently uses the following terms:

   Network Access Server
      The Network Access Server (NAS) is the device that clients contact
      in order to get access to the network.

   RADIUS server
      This is a server which provides for authentication/authorization
      via the protocol described in [3], and for accounting as described
      in [4].

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RFC 2607          Proxy Chaining and Policy in Roaming         June 1999

   RADIUS proxy
      In order to provide for the routing of RADIUS authentication and
      accounting requests, a RADIUS proxy can be employed. To the NAS,
      the RADIUS proxy appears to act as a RADIUS server, and to the
      RADIUS server, the proxy appears to act as a RADIUS client.

   Network Access Identifier
      In order to provide for the routing of RADIUS authentication and
      accounting requests, the userID field used in PPP (known as the
      Network Access Identifier or NAI) and in the subsequent RADIUS
      authentication and accounting requests, can contain structure.
      This structure provides a means by which the RADIUS proxy will
      locate the RADIUS server that is to receive the request. The NAI
      is defined in [6].

   Roaming relationships
      Roaming relationships include relationships between companies and
      ISPs, relationships among peer ISPs within a roaming association,
      and relationships between an ISP and a roaming consortia.
      Together, the set of relationships forming a path between a local
      ISP's authentication proxy and the home authentication server is
      known as the roaming relationship path.

3.  Requirements language

   In this document, the key words "MAY", "MUST, "MUST NOT", "optional",
   "recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as
   described in [5].

4.  Introduction

   Today, as described in [1], proxy chaining is widely deployed for the
   purposes of providing roaming services. In such systems,
   authentication/authorization and accounting packets are routed
   between a NAS device and a home server through a series of proxies.
   Consultation of the home server is required for password-based
   authentication, since the home server maintains the password database
   and thus it is necessary for the NAS to communicate with the home
   authentication server in order to verify the user's identity.

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RFC 2607          Proxy Chaining and Policy in Roaming         June 1999

4.1.  Advantages of proxy chaining

   Proxies serve a number of functions in roaming, including:

   Scalability improvement
   Authentication forwarding
   Capabilities adjustment
   Policy implementation
   Accounting reliability improvement
   Atomic operation

   Scalability improvement
      In large scale roaming systems, it is necessary to provide for
      scalable management of keys used for integrity protection and
      authentication.

      Proxy chaining enables implementation of hierarchical
      forwarding within roaming systems, which improves scalability
      in roaming consortia based on authentication protocols without
      automated key management.  Since RADIUS as described in [3]
      requires a shared secret for each client-server pair, a
      consortium of 100 roaming partners would require 4950 shared
      secrets if each partner were to contact each other directly,
      one for each partner pair.  However, were the partners to
      route authentication requests through a central proxy, only
      100 shared secrets would be needed, one for each partner. The
      reduction in the number of partner pairs also brings with it