ROAMOPS Working Group Bernard Aboba
INTERNET-DRAFT Microsoft
Category: Standards Track Glen Zorn
<draft-ietf-roamops-roamreq-07.txt> Microsoft
1 March 1998
Roaming Requirements
1. Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working docu-
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The distribution of this memo is unlimited. It is filed as <draft-
ietf-roamops-roamreq-07.txt>, and expires September 1, 1998. Please
send comments 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
As described in [1], operational roaming services are currently pro-
viding worldwide roaming capabilities, and these services continue to
grow in popularity. Interested parties have included:
Regional Internet Service Providers (ISPs) operating within a
particular state or province, looking to combine their efforts
with those of other regional providers to offer services over a
wider area.
National ISPs wishing to combine their operations with those of
one or more ISPs in another nation to provide greater coverage in
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a group of countries or on a continent.
Businesses desiring to offer their employees a comprehensive
package 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
This document specifies a set of requirements for elements of the
roaming architecture, and uses the same words as [4] for defining the
significance of each particular requirement. These words are:
MUST This word, or the adjectives "REQUIRED" or "SHALL", means
that the definition is an absolute requirement of the speci-
fication.
MUST NOT This phrase, or the phrase "SHALL NOT", means that the defi-
nition is an absolute prohibition of the specification.
SHOULD This word, or the adjective "RECOMMENDED", means that there
may exist valid reasons in particular circumstances to
ignore a particular item, but the full implications must be
understood and carefully weighed before choosing a different
course.
SHOULD NOT
This phrase means that there may exist valid reasons in par-
ticular circumstances when the particular behavior is
acceptable or even useful, but the full implications should
be understood and the case carefully weighed before imple-
menting any behavior described with this label.
MAY This word, or the adjective "OPTIONAL", means that an item
is truly optional. One vendor may choose to include the
item because a particular marketplace requires it or because
the vendor feels that it enhances the product while another
vendor may omit the same item. An implementation which does
not include a particular option MUST be prepared to interop-
erate with another implementation which does include the
option, though perhaps with reduced functionality. In the
same vein an implementation which does include a particular
option MUST be prepared to interoperate with another imple-
mentation which does not include the option (except, of
course, for the feature the option provides).
Please note that the requirements specified in this document are to be
used in evaluating protocol submissions. As such, the requirements
language refers to capabilities of these protocols; the protocol
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documents will specify whether these features are required, recom-
mended, or optional for use in roaming. For example, requiring that a
protocol support confidentiality is NOT the same thing as requiring
that all protocol traffic be encrypted.
An 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 require-
ments 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
attributes.
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/autho-
rization 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, and to the
authentication server, the proxy appears to act as an
authentication client.
Accounting proxy
Accounting proxies may be deployed within the roaming archi-
tecture for several purposes, including accounting forward-
ing, reliability improvement, auditing, and "pseudo-transac-
tional" capability. To the NAS, the accounting proxy appears
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to act as an accounting server, and 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, the userID field used in PPP (known as
the Network Access Identifier or NAI) may contain structure.
This structure provides a means by which the authentication
or accounting proxies will locate the authentication or
accounting server that is to receive the request.
4. Architectural framework
The roaming architecture consists of three major subsystems:
Phone book Subsystem
Authentication Subsystem
Accounting Subsystem
The phone book subsystem is concerned with the maintenance and updat-
ing of the user phone book. The phone book provides the user with
information 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 subsystem 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 that Fred is using, 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 standardized.
Phone number exchange
Phone number exchange involves propagation of phone number
changes between providers in a roaming association. As described
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in [1], no current roaming implementations provide for complete
automation of the phone number exchange process. 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 com-
pilation process does not affect protocol interoperability, it
need not be standardized.
Phone book update
Once the phone book is compiled, it needs to be propagated to
customers. Standardization of the phone book update process
allows for providers to update the phone books of users, indepen-
dent of their client and operating system.
4.2. Authentication Subsystem
The authentication subsystem provides for the following:
Connection management
Authentication
NAS Configuration/Authorization
Address Assignment/Routing
Security
Connection management
In order to be able to use the POPs of the local provider, it is
first necessary to bring up a connection.
Identification
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
authentication request to be routed its home destination.
Authentication
Authentication is typically required prior to allowing access to
the network. CHAP and PAP are the two authentication protocols
used within the PPP 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 Extensi-
ble Authentication Protocol (EAP) 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.
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Address assignment/routing
If it is desired that the user be able to communicate with the
rest of the Internet, then it the session will be assigned a
routable IP address by the NAS.
Security
In the process of authenticating and authorizing Fred's 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
during a session. Relevant information includes how long the user was
connected to the service, what speed he connected at, the port type
connected to, etc.
5. Roaming Requirements
5.1. Phonebook requirements
5.1.1. Phone book update protocol
Portability
The update protocol MUST allow for updating of clients on a range
of platforms and operating systems. Therefore the update mecha-
nism MUST not impose any operating system-specific requirements.
Authentication
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.
Versioning
The update protocol MUST provide for updating of the phone book
from an arbitrary previous version to the latest available ver-
sion.
Integrity Checking
The client MUST be able to determine the integrity of the
received update before applying it, as well as the integrity of
the newly produced phone book after updating it.
Light weight transfers
Since the client machine can be a low-end PC, the update protocol
MUST be lightweight.
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Language support
The phone book update mechanism MUST support the ability to
request that the phone book be transmitted in a particular lan-
guage and character set. For example, if the customer has a Rus-
sian language software package, then the propagation and update
protocols MUST provide a mechanism for the user to request a Rus-
sian language phone book.
5.1.2. Phone book format
Phone number attributes
The phone book format MUST support phone number attributes com-
monly used by Internet service providers. These attributes are
required in order to provide users with information on the capa-
bilities of the available phone numbers.
Provider attributes
In addition to providing information relating to a given phone
number, 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 roviding information relating to a given phone
number, and service provider, the phone book MUST provide infor-
mation relevant to configuration of the service. These attributes
are necessary to provide the client with information relating to
the operation of the service.
Extensibility
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 modifica-
tion to the update protocol. Registration of new phone book
attributes will be handled by IANA. The attribute space MUST be
sufficiently large to accomodate growth.
Compactness
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
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 pro-
vide support for other framing protocols such as SLIP, However, SLIP
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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 pro-
tocols (e.g., IPX or AppleTalk) since these will 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 will not be part of a roaming stan-
dard.
5.2.2. Identification
A roaming standard MUST provide a standardized format for the userID
and realm presented to the NAS. This userID is also commonly known as
the Network Access Identifier (NAI).
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 sup-
ported. A possible exception is where PAP is used to support a
one time password or token.
Scalability
A roaming standard, once available, is likely to be widely
deployed on the Internet. A roaming standard MUST therefore pro-
vide sufficient scalability to allow for the formation of roaming
associations with thousands of ISP members.
RADIUS Support
Given the current popularity and near ubiquity of RADIUS 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
accomplished by development of gateways between RADIUS and the
roaming standard authentication, authorization, and accounting
protocol.
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 pol-
icy functions. As a result, a roaming standard MUST support the abil-
ity of proxies to perform attribute editing and implement policy.
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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 tunneling.
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, described
in [8], hold great promise for providing "live", transparent
mobility on the part of mobile nodes on the Internet. Therefore,
proxy implementations MUST NOT preclude the provision 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 detection.
Hop by hop security
A roaming standard MUST provide for hop-by-hop integrity protec-
tion and confidentiality. This can be accomplished through sup-
port of network layer (IPSEC) or transport layer security (TLS).
End-to-end security
As policy implementation and attribute editing are common in
roaming systems, it is often necessary for proxies to modify
packets in transit between a local NAS and the home server. In
order to permit authorized 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
practical necessity in order to support fraud detection and risk
management. As a result, a roaming standard MUST provide support
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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 communi-
cate accounting information within their own organizations. As a
result, a roaming standard MUST prescribe a standardized format
for accounting records. For the sake of efficiency, the record
format MUST be compact.
Extensibility
A standard accounting record format MUST be able to encode met-
rics commonly used by Internet Service Providers to determine the
user's bill. Since these metrics change over time, the account-
ing 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. Evaluation of the RADIUS protocol
The RADIUS protocol does not satisfy the requirements for a roaming
standard authentication, authorization, and accounting protocol. These
include lack of support for hop-by-hop confidentiality, as well as
end-to-end confidentiality and integrity protection.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Requirement | Level | RADIUS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| PPP | MUST | YES |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| CHAP | MUST | YES |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| EAP | SHOULD | YES |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| RADIUS | MUST | YES |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Tunnels | MUST | YES |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| H-H | | |
| Integrity | MUST | YES |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| | | |
| H-H | | |
| Confidentiality | MUST | NO |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| E-E | | |
| Integrity | MUST | NO |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| E-E | | |
| Confidentiality | MUST | NO |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7. Acknowledgements
Thanks to Pat Calhoun of Sun Microsystems and John Vollbrecht of MERIT
for many useful discussions of this problem space.
8. References
[1] B. Aboba, J. Lu, J. Alsop, J. Ding, W. Wang. "Review of Roaming
Implementations." Internet draft (work in progress), RFC 2194,
Microsoft, Aimnet, i-Pass Alliance, Asiainfo, Merit, September 1997.
[2] C. Rigney, A. Rubens, W. Simpson, S. Willens. "Remote Authenti-
cation Dial In User Service (RADIUS)." RFC 2138, Livingston, Merit,
Daydreamer, April 1997.
[3] C. Rigney. "RADIUS Accounting." RFC 2139, Livingston, April
1997.
[4] S. Bradner. "Key words for use in RFCs to Indicate Requirement
Levels." RFC 2119, Harvard University, March, 1997.
[5] G. Zorn. "RADIUS Attributes for Tunnel Protocol Support." Inter-
net draft (work in progress), draft-ietf-radius-tunnel-auth-04.txt,
Microsoft, November 1997.
[6] B. Aboba. "Implementation of PPTP/L2TP Mandatory Tunneling via
RADIUS." Internet draft (work in progress), draft-ietf-radius-tunnel-
imp-03.txt, Microsoft, September 1997.
[7] C. Rigney, W. Willats. "RADIUS Extensions." Internet draft (work
in progress), draft-ietf-radius-ext-01.txt, Livingston, December 1997.
[8] C. Perkins. "IP Mobility Support." RFC 2002, IBM October 1996.
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9. Authors' Addresses
Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
Phone: 425-936-6605
EMail: bernarda@microsoft.com
Glen Zorn
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
Phone: 425-703-1559
EMail: glennz@microsoft.com
p
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