ROAMOPS Working Group Bernard Aboba
INTERNET-DRAFT Microsoft
Category: Standards Track Mark A. Beadles
<draft-ietf-roamops-nai-09.txt> CompuServe, Inc.
16 February 1998
The Network Access Identifier
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
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The distribution of this memo is unlimited. It is filed as <draft-
ietf-roamops-nai-09.txt> and expires August 1, 1998. Please send
comments to the authors.
2. Abstract
In order to enhance the interoperability of roaming and tunneling ser-
vices, it is desirable to have a standardized method for identifying
users. This document proposes syntax for the Network Access Identi-
fier (NAI), the userID submitted by the client during PPP authentica-
tion. It is expected that this will be of interest for support of
roaming as well as tunneling. "Roaming capability" may be loosely
defined as the ability to use any one of multiple Internet service
providers (ISPs), while maintaining a formal, customer-vendor rela-
tionship with only one. Examples of cases where roaming capability
might be required include ISP "confederations" and ISP-provided corpo-
rate network access support.
3. Introduction
Considerable interest has arisen recently in a set of features that
fit within the general category of "roaming capability" for dialup
Internet users. Interested parties have included:
Regional Internet Service Providers (ISPs) operating within a
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particular state or province, looking to combine their efforts
with those of other regional providers to offer dialup service
over a wider area.
National ISPs wishing to combine their operations with those of
one or more ISPs in another nation to offer more comprehensive
dialup service in 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 may
include Internet access as well as secure access to corporate
intranets via a Virtual Private Network (VPN), enabled by tunnel-
ing protocols such as PPTP, L2F, L2TP, and IPSEC tunnel mode.
In order to enhance the interoperability of roaming and tunneling ser-
vices, it is desirable to have a standardized method for identifying
users. This document proposes syntax for the Network Access Identi-
fier (NAI). Examples of implementations that use the NAI, and
descriptions of its semantics, can be found in [1].
3.1. Terminology
This document frequently uses the following terms:
Network Access Identifier
The Network Access Identifier (NAI) is the userID submitted
by the client during PPP authentication. In roaming, the
purpose of the NAI is to identify the user as well as to
assist in the routing of the authentication request. Please
note that the NAI may not necessarily be the same as the
user's e-mail address or the userID submitted in an applica-
tion layer authentication.
Network Access Server
The Network Access Server (NAS) is the device that clients
dial in order to get access to the network. In PPTP termi-
nology this is referred to as the PPTP Access Concentrator
(PAC), and in L2TP terminology, it is referred to as the
L2TP Access Concentrator (LAC).
Roaming Capability
Roaming capability can be loosely defined as the ability to
use any one of multiple Internet service providers (ISPs),
while maintaining a formal, customer-vendor relationship
with only one. Examples of cases where roaming capability
might be required include ISP "confederations" and ISP-pro-
vided corporate network access support.
Tunneling Service
A tunneling service is any network service enabled by tun-
neling protocols such as PPTP, L2F, L2TP, and IPSEC tunnel
mode. One example of a tunneling service is secure access
to corporate intranets via a Virtual Private Network (VPN).
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3.2. Purpose
As described in [1], there are now a number of services implementing
dialup roaming, and the number of Internet Service Providers involved
in roaming consortia is increasing rapidly.
In order to be able to offer roaming capability, one of the require-
ments is to be able to identify the user's home authentication server.
For use in roaming, this function is accomplished via the Network
Access Identifier (NAI) submitted by the user to the NAS in the ini-
tial PPP authentication. It is also expected that NASes will use the
NAI as part of the process of opening a new tunnel, in order to deter-
mine the tunnel endpoint.
3.3. Notes for Implementors
As proposed in this document, the Network Access Identifier is of the
form user@realm. Please note that while the user portion of the NAI
conforms to the BNF described in [5], the BNF of the realm portion
allows the realm to begin with a digit, which is not permitted by the
BNF described in [4]. This change was made to reflect current prac-
tice; although not permitted by the BNF described in [4], FQDNs such
as 3com.com are commonly used, and accepted by current software.
While the realm is typically a Fully Qualified Domain Name (FQDN), it
is not required that this be the case, and thus the NAI need not be a
valid e-mail address. As a result, use of an FQDN as the realm does
not imply use of DNS for location of the authentication server or for
authentication routing.
Since to date roaming has been implemented on a relatively small
scale, existing implementations handle location of authentication
servers within a domain and perform authentication routing based on
local knowledge expressed in proxy configuration files. The implemen-
tations described in [1] have not found a need for use of DNS for
location of the authentication server within a domain, although this
can be accomplished via use of the DNS SRV record, described in [6].
Similarly, existing implementations have not found a need for dynamic
routing protocols, or propagation of global routing information.
Please note that NAS vendors may need to modify their devices so as to
support the NAI as described in this document. Devices handling NAIs
MUST support an NAI length of at least 72 octets.
4. Formal definition of the NAI
The grammar for the NAI is given below. The grammar for the username
is taken from [5], and the grammar for the realm is a modified version
of [4].
<nai> ::= <username> | <username> "@" <realm>
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<username> ::= <dot-string>
<realm> ::= <label> | <realm> "." <label>
<label> ::= <let-dig> [ [ <ldh-str> ] <let-dig> ]
<ldh-str> ::= <let-dig-hyp> | <ldh-str> <let-dig-hyp>
<let-dig-hyp> ::= <let-dig> | "-"
<dot-string> ::= <string> | <dot-string> "." <string>
<string> ::= <char> | <string> <char>
<char> ::= <c> | "\" <x>
<let-dig> ::= <letter> | <digit>
<letter> ::= any one of the 52 alphabetic characters A through Z
in upper case and a through z in lower case
<digit> ::= any one of the ten digits 0 through 9
<c> ::= any one of the 128 ASCII characters, but not any
<special> or <SP>
<x> ::= any one of the 128 ASCII characters (no exceptions)
<SP> ::= the space character (ASCII code 32)
<special> ::= "<" | ">" | "(" | ")" | "[" | "]" | "\" | "."
| "," | ";" | ":" | "@" | """ | the control
characters (ASCII codes 0 through 31 inclusive and
127)
Examples of valid Network Access Identifiers include:
fred@3com.com
fred_smith@big-co.com
fred=?#$&*+-/^smith@bigco.com
fred@bigco.com
nancy@eng.bigu.edu
eng!nancy@bigu.edu
eng%nancy@bigu.edu
Examples of invalid Network Access Identifiers include:
@howard.edu
fred@bigco.com@smallco.com
eng:nancy@bigu.edu
eng;nancy@bigu.edu
<nancy>@bigu.edu
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5. Acknowledgements
Thanks to Glen Zorn of Microsoft for many useful discussions of this
problem space.
6. References
[1] B. Aboba, J. Lu, J. Alsop, J. Ding, W. Wang. "Review of Roaming
Implementations." RFC 2194, Microsoft, Aimnet, i-Pass Alliance, Asi-
ainfo, 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] P. Mockapetris. "Domain Names - Implementation and Specifica-
tion." RFC 1035, Information Sciences Institute, University of South-
ern California, November, 1987.
[5] Jonathan B. Postel. "Simple Mail Transfer Protocol." RFC 821,
Information Sciences Institute, University of Southern California,
August, 1982
[6] A. Gulbrandsen, P. Vixie. "A DNS RR for specifying the location
of services (DNS SRV)." RFC 2052, Troll Technologies, Vixie Enter-
prises, October 1996.
7. Authors' Addresses
Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
Phone: 425-936-6605
EMail: bernarda@microsoft.com
Mark A. Beadles
CompuServe, Inc.
5000 Britton Rd.
Hilliard, OH 43026
Phone: 614-723-1941
EMail: mbeadles@web.compuserve.com
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