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Criteria for Evaluating Roaming Protocols

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 2477.
Authors Glen Zorn , Dr. Bernard D. Aboba
Last updated 2013-03-02 (Latest revision 1998-08-07)
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Network Working Group                                      Bernard Aboba
INTERNET-DRAFT                                                 Glen Zorn
Category: Informational                            Microsoft Corporation
<draft-ietf-roamops-roamreq-10.txt>                          August 1998

                   Requirements for Internet Roaming

1.  Status of this Memo

This  document  is an Internet-Draft.  Internet-Drafts are working docu-
ments of the Internet Engineering Task Force (IETF), its areas, and  its
working groups.  Note that other groups MAY also distribute working doc-
uments 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.''

To  learn  the  current  status  of any Internet-Draft, please check the
``1id-abstracts.txt'' listing contained in  the  Internet-Drafts  Shadow
Directories  on (US East Coast), (Europe), (US West Coast), or (Pacific Rim).

The distribution of this memo is unlimited.  It is filed as <draft-ietf-
roamops-roamreq-10.txt>, and expires February 7, 1999.  Please send com-
ments to the authors.

2.  Abstract

This document describes requirements for the  provisioning  of  "roaming
capability"  for dialup Internet users.  "Roaming capability" is defined
as the ability to use multiple Internet service providers (ISPs),  while
maintaining a formal, customer-vendor relationship with only one.

3.  Introduction

Operational  roaming  services are currently providing worldwide roaming
capabilities, and these services continue to  grow  in  popularity  [1].
Interested parties have included:

     Regional  Internet Service Providers (ISPs) operating within a par-
     ticular state or province, looking to combine  their  efforts  with
     those  of  other  regional providers to offer services over a wider

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     National ISPs wishing to combine their operations with those of one
     or  more  ISPs  in  another nation to provide greater coverage in a
     group of countries or on a continent.

     Businesses desiring to offer their employees a comprehensive  pack-
     age  of  dialup  services  on  a  global basis.  Those services can
     include Internet access as  well  as  secure  access  to  corporate
     intranets via a Virtual Private Network (VPN).

This  document  provides an architectural framework for the provisioning
of roaming capabilities, as well as  describing  the  requirements  that
must be met by elements of the architecture.

3.1.  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 [4].

Please  note  that the requirements specified in this document are to be
used in evaluating protocol submissions.  As such, the requirements lan-
guage  refers to capabilities of these protocols; the protocol documents
will specify  whether  these  features  are  required,  recommended,  or
optional  for  use  in  roaming.  For example, requiring that a protocol
support confidentiality is NOT the same thing as requiring that all pro-
tocol traffic be encrypted.

A  protocol  submission  is  not compliant if it fails to satisfy one or
more of the must or must not requirements for the capabilities  that  it
implements.   A  protocol  submission  that satisfies all the must, must
not, should and should not requirements for its capabilities is said  to
be "unconditionally compliant"; one that satisfies all the must and must
not requirements but not all the should or should not  requirements  for
its protocols is said to be "conditionally compliant."

3.2.  Terminology

This document frequently uses the following terms:

phone book
          This  is  a database or document containing data pertaining to
          dialup access, including  phone  numbers  and  any  associated

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phone book server
          This  is  a  server  that  maintains the latest version of the
          phone book.  Clients communicate with phone  book  servers  in
          order to keep their phone books up to date.

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

Authentication server
          This is a server which provides for  authentication/authoriza-
          tion within the roaming architecture.

Accounting server
          This  is  a  server  which  provides for accounting within the
          roaming architecture.

Authentication proxy
          Authentication proxies may  be  deployed  within  the  roaming
          architecture  for  several  purposes, including authentication
          forwarding, policy implementation, shared  secret  management,
          and  attribute  editing.  To the NAS, the authentication proxy
          appears to act as an authentication server; to the authentica-
          tion  server,  the  proxy  appears to act as an authentication

Accounting proxy
          Accounting proxies may be deployed within the  roaming  archi-
          tecture for several purposes, including accounting forwarding,
          reliability improvement, auditing, and  "pseudo-transactional"
          capability.   To  the NAS, the accounting proxy appears to act
          as an accounting server; to the accounting server,  the  proxy
          appears to act as an accounting client.

Network Access Identifier
          In  order  to  provide  for  the routing of authentication and
          accounting packets, user name  MAY  contain  structure.   This
          structure  provides  a  means  by  which the authentication or
          accounting proxies will locate the authentication or  account-
          ing server that is to receive the request.

4.  Architectural framework

The roaming architecture consists of three major subsystems:

     Phone book Subsystem
     Authentication Subsystem

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     Accounting Subsystem

The  phone book subsystem is concerned with the maintenance and updating
of the user phone book.  The phone book provides the user with  informa-
tion on the location and phone numbers of Points of Presence (POPs) that
are roaming enabled.  The function of the authentication subsystem is to
provide  authorized  users with access to the POPs in the phonebook, and
to deny access to unauthorized users.  The goal of the  accounting  sub-
system  is  to  provide information on the resources utilized during the
user's session.

4.1.  Phone Book Subsystem

The phone book subsystem provides for the following:

     Phone number presentation
     Phone number exchange
     Phone book compilation
     Phone book update

Phone number presentation
     Phone number presentation involves the display of  available  phone
     numbers  to  the  user, and culminates in the choosing of a number.
     Since the user interface and sequence of events involved  in  phone
     number  presentation  is  a  function  of the connection management
     software being used, it is likely that individual vendors will take
     different approaches to the problem.  These differences can include
     variances  in  the  format  of  the  client  phone  books,  varying
     approaches to presentation, etc.  There is no inherent problem with
     this. As a result, phone number presentation need not be  standard-

Phone number exchange
     Phone  number exchange involves propagation of phone number changes
     between providers in a roaming association.  Current roaming imple-
     mentations do not provide for complete automation of the phone num-
     ber exchange process [1].  As a result, phone number exchange  need
     not be standardized at this time.

Phone book compilation
     Once  an  ISP's phone book server has received its updates it needs
     to compile a new phone book and propagate this phone  book  to  all
     the phone book servers operated by that ISP.  Given that the compi-
     lation process does not affect protocol interoperability,  it  need
     not be standardized.

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Phone book update
     Once  the  phone  book  is  compiled,  it needs to be propagated to
     users.  Standardization of the phone book update process allows for
     providers  to  update user phone books, independent of their client
     software or operating system.

4.2.  Authentication Subsystem

The authentication subsystem provides for the following:

     Connection management
     NAS Configuration/Authorization
     Address Assignment/Routing

Connection management
     In order to be able to use the POPs of the local  provider,  it  is
     first necessary to bring up a connection.

     Authentication  consists  of  two  parts: the claim of identity (or
     identification) and the proof of the claim (or  verification).   As
     part  of  the  authentication process, users identify themselves to
     the Network Access Server (NAS) in a manner that allows the authen-
     tication request to be routed its home destination.

     Authentication  is  typically  required prior to allowing access to
     the network.  CHAP [8] and PAP [9] are the two authentication  pro-
     tocols  most  commonly  used  within  the PPP [10] framework today.
     Some groups of users are requiring  different  forms  of  proof  of
     identity  (e.g.,  token or smart cards, Kerberos credentials, etc.)
     for  special  purposes  (such  as  acquiring  access  to  corporate
     intranets).   The  Extensible Authentication Protocol (EAP) [7] was
     created in order to provide a  general  mechanism  for  support  of
     these methods.

NAS configuration/authorization
     In order to set up the session, authorization parameters need to be
     sent to from the home authentication server to the local ISP's NAS.

Address assignment/routing
     If it is desired that the user be able to communicate with the rest
     of the Internet, then the session will be assigned  a  routable  IP
     address by the NAS.

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     In  the process of authenticating and authorizing the user session,
     it may be desirable to provide  protection  against  a  variety  of
     security threats.

4.3.  Accounting Subsystem

The  function  of the accounting subsystem is to enable the participants
in the roaming consortium to keep track of what resources are used  dur-
ing  a session. Relevant information includes how long the user was con-
nected to the service, connection speed, port type, etc.

5.  Roaming Requirements

5.1.  Phonebook requirements

5.1.1.  Phone book update protocol

     The update protocol MUST allow for updating of clients on  a  range
     of  platforms and operating systems. Therefore the update mechanism
     MUST NOT impose any operating system-specific requirements.

     The client MUST be able to determine the authenticity of the server
     sending  the  phone  book  update.   The server MAY also be able to
     authenticate the client.

     The update protocol MUST provide for updating  of  the  phone  book
     from an arbitrary previous version to the latest available version.

Integrity Checking
     The client MUST be able to determine the integrity of the  received
     update  before  applying  it,  and  MUST  be  able to determine the
     integrity of the newly produced phone book after updating it.

Light weight transfers
     Since the client may be a low-end machine  or  internet  appliance,
     the update protocol MUST be lightweight.

Language support
     The phone book update mechanism MUST support the ability to request

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     that the phone book be transmitted in  a  particular  language  and
     character set.  For example, if the customer has a Russian language
     software package, then the propagation and  update  protocols  MUST
     provide  a  mechanism  for  the  user to request a Russian language
     phone book.

5.1.2.  Phone book format

Phone number attributes
     The phone book format MUST support phone number attributes commonly
     used  by Internet service providers.  These attributes are required
     in order to provide users with information on the  capabilities  of
     the available phone numbers.

Provider attributes
     In addition to providing information relating to a given phone num-
     ber, the phone book MUST  provide  information  on  the  individual
     roaming consortium members.  These attributes are required in order
     to provide users with information about the individual providers in
     the roaming consortium.

Service attributes
     In addition to providing information relating to a given phone num-
     ber, and service provider, the phone book MUST provide  information
     relevant  to  configuration  of  the service.  These attributes are
     necessary to provide the client with information  relating  to  the
     operation of the service.

     Since it will frequently be necessary to add phone book attributes,
     the phone book format MUST support the addition  of  phone  number,
     provider  and service attributes without modification to the update
     protocol.  Registration of new phone book attributes will  be  han-
     dled  by  IANA.   The attribute space MUST be sufficiently large to
     accomodate growth.

     Since phone book will typically be frequently  updated,  the  phone
     book format MUST be compact so as to minimize the bandwidth used in
     updating it.

5.2.  Authentication requirements

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5.2.1.  Connection Management

Given the current popularity and near ubiquity of PPP, a  roaming  stan-
dard MUST provide support for PPP and IP. A roaming standard MAY provide
support for other framing protocols such as SLIP.  However, SLIP support
is  expected  to prove difficult since SLIP does not support negotiation
of connection parameters and lacks support for protocols other than  IP.

A  roaming  standard MAY provide support for non-IP protocols (e.g., IPX
or AppleTalk) since these may be useful for the provision  of  corporate
intranet  access via the Internet.  Since it is intended that the client
will begin  PPP  negotiation  immediately  on  connection,  support  for
scripting SHOULD NOT be part of a roaming standard.

5.2.2.  Identification

A roaming standard MUST provide a standardized format for the userID and
realm presented to the NAS.

5.2.3.  Verification of Identity

Authentication types
     A roaming standard MUST support CHAP, and SHOULD support EAP.   Due
     to  security  concerns, PAP authentication SHOULD NOT be supported.
     A possible exception is where PAP is used to  support  a  one  time
     password or token.

     A roaming standard, once available, is likely to be widely deployed
     on the Internet.  A roaming standard MUST therefore provide  suffi-
     cient  scalability  to  allow for the formation of roaming associa-
     tions with thousands of ISP members.

RADIUS Support
     Given the current popularity and near ubiquity of RADIUS  [2,3]  as
     an authentication, authorization and accounting solution, a roaming
     standard MUST be able to incorporate RADIUS-enabled devices  within
     the  roaming  architecture. It is expected that this will be accom-
     plished by development of gateways between RADIUS and  the  roaming
     standard authentication, authorization, and accounting protocol.

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5.2.4.  NAS Configuration/Authorization

In  order  to  ensure  compatibility  with the NAS or the local network,
authentication/authorization proxies often will add, delete,  or  modify
attributes  returned  by the home authentication server. In addition, an
authentication proxy will often carry out resource management and policy
functions.   As a result, a roaming standard MUST support the ability of
proxies to perform attribute editing and implement policy.

5.2.5.  Address assignment/routing

A roaming standard MUST  support  dynamic  address  assignment.   Static
address  assignment MAY be supported, most likely via layer 2 or layer 3

Layer 2 tunneling protocols
     Layer-2 tunneling protocols, such as PPTP, L2F, or L2TP, hold great
     promise  for  the  implementation  of Virtual Private Networks as a
     means for inexpensive access to remote  networks.  Therefore  proxy
     implementations MUST NOT preclude use of layer 2 tunneling.

Layer 3 tunneling protocols
     Layer-3  tunneling  protocols  as  embodied  in Mobile IP [5], hold
     great promise for providing "live",  transparent  mobility  on  the
     part  of  mobile nodes on the Internet.  Therefore, a roaming stan-
     dard MUST NOT preclude the provisioning of Mobile IP Foreign Agents
     or  other Mobile IP functionality on the part of service providers.

5.2.6.  Security

Security analysis
     A roaming standard  MUST  include  a  thorough  security  analysis,
     including  a  description  of security threats and countermeasures.
     This includes specification of mechanisms for fraud prevention  and

Hop by hop security
     A roaming standard MUST provide for hop-by-hop integrity protection
     and confidentiality.  This MAY be accomplished through  support  of
     network layer security (IPSEC) [6].

End-to-end security
     As  policy implementation and attribute editing are common in roam-
     ing systems, proxies may need to modify packets in transit  between
     a  local  NAS  and  the  home server. In order to permit authorized

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     modifications while at the same time guarding  against  attacks  by
     rogue  proxies,  it  is necessary for a roaming standard to support
     data object security.  As a result, a roaming standard MUST provide
     end-to-end   confidentiality   and   integrity   protection  on  an
     attribute-by-attribute basis.  However, non-repudiation  is  NOT  a
     requirement for a roaming standard.

5.3.  Accounting requirements

Real-time accounting
     In today's roaming implementations, real-time accounting is a prac-
     tical necessity in order to support fraud detection and  risk  man-
     agement.   As a result, a roaming standard MUST provide support for
     real-time accounting.

Accounting record formats
     Today there is no proposed standard for NAS accounting,  and  there
     is wide variation in the protocols used by providers to communicate
     accounting information within their own organizations.   Therefore,
     a  roaming  standard  MUST  prescribe  a  standardized  format  for
     accounting records.  For the sake of efficiency, the record  format
     MUST be compact.

     A  standard accounting record format MUST be able to encode metrics
     commonly used to determine the user's bill.   Since  these  metrics
     change  over  time, the accounting record format MUST be extensible
     so as to be able to add future metrics as  they  come  along.   The
     record format MUST support both standard metrics as well as vendor-
     specific metrics.

6.  References

[1]  Aboba, B., Lu, J., Alsop, J., Ding, J., Wang, W.  "Review of  Roam-
     ing Implementations", RFC 2194, September 1997

[2]  Rigney, C., Rubens, A., Simpson, W., Willens, S., "Remote Authenti-
     cation Dial In User Service (RADIUS)", RFC 2138, April 1997.

[3]  Rigney, C., "RADIUS Accounting", RFC 2139, April 1997

[4]  Bradner, S., "Key words for use in  RFCs  to  Indicate  Requirement
     Levels", RFC 2119, March 1997

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[5]  Perkins, C., "IP Mobility Support", RFC 2002, October 1996

[6]  Atkinson,  R.,  "Security  Architecture for the Internet Protocol",
     RFC 1825, August 1995

[7]  Blunk, L. and Vollbrecht, J., "PPP Extensible Authentication Proto-
     col (EAP)", RFC 2284, March 1998

[8]  Simpson,  W.,  "PPP  Challenge  Handshake  Authentication  Protocol
     (CHAP)", RFC 1994, August 1996

[9]  Lloyd, B. and Simpson,  W.,  "PPP  Authentication  Protocols",  RFC
     1334, October 1992

[10] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC 1661,
     July 1994

7.  Security considerations

This document, being a requirements document, does not have any security
concerns.   The security requirements on protocols to be evaluated using
this document are mainly described in section 5.2

8.  Acknowledgements

Thanks   to   Pat   Calhoun    (,    Butch    Anton
(  and  John  Vollbrecht ( for many useful
discussions of this problem space.

9.  Authors' Addresses

Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052

Phone: 425-936-6605

Glen Zorn
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052

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Phone: 425-703-1559

10.  Expiration Date

This memo is filed as <draft-ietf-roamops-roamreq-10.txt>,  and  expires
February 7, 1999.

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