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12 RFC 2486
ROAMOPS Working Group Bernard Aboba
INTERNET-DRAFT Microsoft
Category: Standards Track Mark A. Beadles
<draft-ietf-roamops-nai-12.txt> WorldCom Advanced Networks
7 November 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
its working groups. Note that other groups may also distribute work-
ing documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
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rial or to cite them other than as ``work in progress.''
To learn the current status of any Internet-Draft, please check the
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Directories on ftp.ietf.org (US East Coast), nic.nordu.net (Europe),
ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim).
The distribution of this memo is unlimited. It is filed as <draft-
ietf-roamops-nai-12.txt> and expires May 1, 1999. Please send com-
ments to the authors.
2. Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
3. 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 where roaming capabilities might
be required include ISP "confederations" and ISP-provided corporate
network access support.
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4. 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
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].
4.1. 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-
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provided 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).
4.2. 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 [9].
4.3. 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.
4.4. 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.
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.
5. Formal definition of the NAI
The grammar for the NAI is given below, described in ABNF as docu-
mented in [7]. The grammar for the username is taken from [5], and
the grammar for the realm is an updated version of [4].
nai = username / ( username "@" realm )
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username = dot-string
realm = realm "." label
label = let-dig * (ldh-str)
ldh-str = *( Alpha / Digit / "-" ) let-dig
dot-string = string / ( dot-string "." string )
string = char / ( string char )
char = c / ( "\" x )
let-dig = Alpha / Digit
Alpha = %x41-5A / %x61-7A ; A-Z / a-z
Digit = %x30-39 ;0-9
c = < any one of the 128 ASCII characters, but
not any special or SP >
x = %x00-7F
; all 127 ASCII characters, no exception
SP = %x20 ; Space character
special = "<" / ">" / "(" / ")" / "[" / "]" / "\" / "."
/ "," / ";" / ":" / "@" / %x22 / Ctl
Ctl = %x00-1F / %x7F
; the control characters (ASCII codes 0 through 31
; inclusive and 127)
Examples of valid Network Access Identifiers include:
fred@3com.com
fred@foo-9.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:
fred@foo
fred@foo_9.com
@howard.edu
fred@bigco.com@smallco.com
eng:nancy@bigu.edu
eng;nancy@bigu.edu
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<nancy>@bigu.edu
6. References
[1] Aboba, B., Lu J., Alsop J.,Ding J., and W. Wang, "Review of Roam-
ing Implementations", RFC 2194, September 1997.
[2] Rigney C., Rubens A., Simpson W., and S. Willens, "Remote Authen-
tication Dial In User Service (RADIUS)", RFC 2138, April 1997.
[3] Rigney C., "RADIUS Accounting", RFC 2139, April 1997.
[4] Mockapetris, P., "Domain Names - Implementation and Specifica-
tion", RFC 1035, November 1987.
[5] Postel, J., "Simple Mail Transfer Protocol", RFC 821, August 1982.
[6] Gulbrandsen A., and P. Vixie, "A DNS RR for specifying the loca-
tion of services (DNS SRV)", RFC 2052, October 1996.
[7] Crocker, D., and P. Overrell, "Augmented BNF for Syntax Specifica-
tions: ABNF", RFC 2234, November 1997.
[8] Atkinson, R., "Security Architecture for the Internet Protocol",
RFC 1825, August 1995.
[9] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
7. Security Considerations
Since an NAI reveals the home affiliation of a user, it may assist an
attacker in further probing the username space. Typically this problem
is of most concern in protocols which transmit the user name in clear-
text across the Internet, such as in RADIUS, described in [2] and [3].
In order to prevent snooping of the user name, protocols may use con-
fidentiality services provided by IPSEC, described in [8].
8. IANA Considerations
This document defines a new namespace that will need to be adminis-
tered, namely the NAI realm namespace. In order to to avoid creating
any new administrative procedures, administration of the NAI realm
namespace will piggyback on the administration of the DNS namespace.
NAI realm names are required to be unique and the rights to use a
given NAI realm for roaming purposes are obtained coincident with
acquiring the rights to use a particular fully qualified domain name
(FQDN). Those wishing to use an NAI realm name should first acquire
the rights to use the corresponding FQDN. Using an NAI realm without
ownership of the corresponding FQDN creates the possibility of
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conflict and therefore is to be discouraged.
Note that the use of an FQDN as the realm name does not imply use of
the DNS for location of the authentication server or for authentica-
tion routing. Since to date roaming has been implemented on a rela-
tively small scale, existing implementations typically handle location
of authentication servers within a domain and perform authentication
routing based on local knowledge expressed in proxy configuration
files. The implementations 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. Note also that there is no requirement that the NAI rep-
resent a valid email address.
9. Acknowledgements
Thanks to Glen Zorn of Microsoft for many useful discussions of this
problem space.
10. Authors' Addresses
Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
Phone: 425-936-6605
EMail: bernarda@microsoft.com
Mark A. Beadles
WorldCom Advanced Networks
5000 Britton Rd.
Hilliard, OH 43026
Phone: 614-723-1941
EMail: mbeadles@wcom.net
11. Full Copyright Statement
Copyright (C) The Internet Society (1997). 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 implmentation 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 docu-
ment itself may not be modified in any way, such as by removing the
copyright notice or references to the Internet Society or other Inter-
net organizations, except as needed for the purpose of developing
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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 permis-
sions 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 WAR-
RANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY
RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE."
12. Expiration Date
This memo is filed as <draft-ietf-roamops-nai-12>, and expires May
1, 1999.
Aboba & Beadles Standards Track [Page 7]
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