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Versions: (draft-dekok-radext-nai) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 7542

Network Working Group                                        DeKok, Alan
INTERNET-DRAFT                                                FreeRADIUS
Obsoletes: 4282
Category: Standards Track
<draft-ietf-radext-nai-03.txt>
23 May 2013


                     The Network Access Identifier
                        draft-ietf-radext-nai-03

Abstract

   In order to provide inter-domain authentication services, it is
   necessary to have a standardized method that domains can use to
   identify each others users.  This document defines the syntax for the
   Network Access Identifier (NAI), the user identity submitted by the
   client prior to accessing network resources. This document is a
   revised version of RFC 4282 [RFC4282], which addresses issues with
   international character sets, as well as a number of other
   corrections to the previous document.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents 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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on July 8, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the



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   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008. The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.




























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Table of Contents

Appendix A - Changes from RFC4282 ............................    3
1.  Introduction .............................................    4
   1.1.  Terminology .........................................    5
   1.2.  Requirements Language ...............................    6
   1.3.  Purpose .............................................    7
   1.4.  Motivation ..........................................    7
2.  NAI Definition ...........................................    8
   2.1.  UTF-8 Syntax and Normalization ......................    8
   2.2.  Formal Syntax .......................................    9
   2.3.  NAI Length Considerations ...........................    9
   2.4.  Support for Username Privacy ........................   10
   2.5.  International Character Sets ........................   11
   2.6.  The Normalization Process ...........................   11
   2.7.  Use in Other Protocols ..............................   12
   2.8.  Routing inside of AAA Systems .......................   13
   2.9.  Compatibility with Email Usernames ..................   14
   2.10.  Compatibility with DNS .............................   14
   2.11.  Realm Construction .................................   15
      2.11.1.  Historical Practices ..........................   16
   2.12.  Examples ...........................................   17
3.  Security Considerations ..................................   17
4.  IANA Considerations ......................................   18
5.  References ...............................................   18
   5.1.  Normative References ................................   18
   5.2.  Informative References ..............................   19
Appendix A - Changes from RFC4282 ............................   21























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1.  Introduction

   Considerable interest exists for a set of features that fit within
   the general category of inter-domain authentiction, or "roaming
   capability" for network access, including dialup Internet users,
   Virtual Private Network (VPN) usage, wireless LAN authentication, and
   other applications.  Interested parties have included the following:

   *  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.

   *  Wireless LAN hotspots providing service to one or more ISPs.

   *  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 VPN, enabled by tunneling protocols such as the
      Point-to-Point Tunneling Protocol (PPTP) [RFC2637], the Layer 2
      Forwarding (L2F) protocol [RFC2341], the Layer 2 Tunneling
      Protocol (L2TP) [RFC2661], and the IPsec tunnel mode [RFC4301].

   * Other protocols which are interested in leveraging the users
      credentials in order to take advantage of an existing
      authentication framework.

   In order to enhance the interoperability of these services, it is
   necessary to have a standardized method for identifying users.  This
   document defines syntax for the Network Access Identifier (NAI).
   Examples of implementations that use the NAI, and descriptions of its
   semantics, can be found in [RFC2194].

   When the NAI was defined for network access, it had the side effect
   of defining an identifier which could be used elsewhere.  Some
   systems which required the use of an identifier did so by leveraging
   the NAI.  This process simplified the management of credentials, by
   re-using the same credential in multiple situations.  We suggest that
   this re-use is good practice.  The alternative is to have protocol-
   specific identifiers, which increases cost to both user and
   administrator.

   The goal of this document is to define the format of an identifier
   which can be used in many protocols.  A protocol may transport an



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   encoded version of the NAI (e.g. '.' as %2E).  However, the
   definition of the NAI is protocol independent.  We hope to encourage
   the wide-spread adoption of the NAI as an identifier.  This adoption
   will decrease work required to leverage identification and
   authentication in other protocols.  It will also decrease the
   complexity of systems for end users and administrators.

   We note that this document only suggest that the NAI be used, but
   does not require it.  Many protocols already define their own
   identifier formats.  Some of these are incompatible with the NAI,
   while others allow the NAI in addition to non-NAI identifiers.  This
   definition of the NAI has no requirements on protocol specifications,
   implementations, or deployments.  We simply suggest that using a
   standard identifier format is preferable to using multiple
   incompatible identifier formats.

   This document is a revised version of [RFC4282], which originally
   defined internationalized NAIs.  Differences and enhancements
   compared to that document are listed in Appendix A.

1.1.  Terminology

   This document frequently uses the following terms:

   "Local" or "localized" text

      Text which is either in non-UTF-8, or in non-normalized form.  The
      character set, encoding, and locale are (in general) unknown to
      Authentication, Authorization, and Accounting (AAA) network
      protocols.  The client which "knows" the locale may have a
      different concept of this text than other AAA entities, which do
      not know the same locale.

   Network Access Identifier

      The Network Access Identifier (NAI) is the user identity submitted
      by the client during network access authentication.  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 email address or the
      user identity submitted in an application layer authentication.

   Network Access Server

      The Network Access Server (NAS) is the device that clients connect
      to in order to get access to the network.  In PPTP terminology,
      this is referred to as the PPTP Access Concentrator (PAC), and in
      L2TP terminology, it is referred to as the L2TP Access



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      Concentrator (LAC).  In IEEE 802.11, it is referred to as an
      Access Point.

   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-provided corporate network
      access support.

   Tunneling Service

      A tunneling service is any network service enabled by tunneling
      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).

1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].



























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1.3.  Purpose

   As described in [RFC2194], there are a number of providers offering
   network access services, 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
   requirements 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 initial network authentication.  It is also expected that NASes
   will use the NAI as part of the process of opening a new tunnel, in
   order to determine the tunnel endpoint.

   We also hope that other protocols can take advantage of the NAI.
   Many protocols include authentication capabilities.  The
   authentication credentials supplied in those protocols can end up
   being transported in AAA protocols.  It is therefore useful to define
   a representation of the user credentials which can be shared across
   multiple protocols.

1.4.  Motivation

   The changes from [RFC4282] are listed in detail in Appendix A.
   However, some additional discussion is appropriate to motivate those
   changes.

   The motivation to revise [RFC4282] began with internationalization
   concerns raised in the context of [EDUROAM].  Section 2.1 of
   [RFC4282] defines ABNF for realms which limits the realm grammar to
   English letters, digits, and the hyphen "-" character.  The intent
   appears to have been to encode, compare, and transport realms with
   the ToASCII operation defined in [RFC5890].  There are a number of
   problems with this approach:

   * The [RFC4282] ABNF is not aligned with internationalization of DNS.

   * The requirement in Section 2.1 that realms are ASCII conflicts
      with the Extensible Authentication Protocol (EAP) and RADIUS,
      which are both 8-bit clean, and which both recommend the use of
      UTF-8 for identitifiers.

   * Section 2.4 required mappings that are language-specific,
      and which are nearly impossible for intermediate nodes to perform
      correctly without information about that language.

   * Section 2.4 requires normalization of user names, which
      may conflict with local system or administrative requirements.



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   * The recommendations in Section 2.4 for treatment of
      bidirectional characters have proven to be unworkable.

   * The prohibition against use of unassigned code points in
      Section 2.4 effectively prohibits support for new scripts.

   * No Authentication, Authorization, and Accounting (AAA)
      client, proxy, or server has implemented any of the requirements
      in [RFC4282] Section 2.4, among other sections.

   With international roaming growing in popularity, it is important for
   these issues to be corrected in order to provide robust and inter-
   operable network services.

2.  NAI Definition


2.1.  UTF-8 Syntax and Normalization

   UTF-8 characters can be defined in terms of octets using the
   following ABNF [RFC5234], taken from [RFC3629]:

   UTF8-xtra-char  =   UTF8-2 / UTF8-3 / UTF8-4

   UTF8-2          =   %xC2-DF UTF8-tail

   UTF8-3          =   %xE0 %xA0-BF UTF8-tail /
                       %xE1-EC 2(UTF8-tail) /
                       %xED %x80-9F UTF8-tail /
                       %xEE-EF 2(UTF8-tail)

   UTF8-4          =   %xF0 %x90-BF 2( UTF8-tail ) /
                       %xF1-F3 3( UTF8-tail ) /
                       %xF4 %x80-8F 2( UTF8-tail )

   UTF8-tail       =   %x80-BF

   These are normatively defined in [RFC3629], but are repeated in this
   document for reasons of convenience.

   See [RFC5198] and section 2.6 of this specification for a discussion
   of normalization. Strings which are not in Normal Form Composed (NFC)
   are not valid NAIs and SHOULD NOT be treated as such.
   Implementations which expect to receive a NAI, but get non-normalised
   (but otherwise valid) UTF-8 strings instead SHOULD attempt to create
   a local version of the NAI, which is normalized from the input
   identifier.  This local version can then be used for local
   processing.



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   Systems MAY accept user identifiers in forms other than the NAI.
   This specification does not forbid that practice.  It only codifies
   the format and interpretation of the NAI.  Where protocols carry
   identifiers which are expected to be transported over an AAA
   protocol, it is RECOMMENDED that the identifiers be in NAI format.

2.2.  Formal Syntax

   The grammar for the NAI is given below, described in Augmented
   Backus-Naur Form (ABNF) as documented in [RFC5234].

   nai            =   utf8-username
   nai            =/  "@" utf8-realm
   nai            =/  utf8-username "@" utf8-realm

   utf8-username  =  dot-string
   dot-string     =  string
   dot-string     =/ dot-string "." string
   string         =  utf8-atext
   string         =/ string utf8-atext

   utf8-atext     =  ALPHA / DIGIT /
                     "!" / "#" /
                     "$" / "%" /
                     "&" / "'" /
                     "*" / "+" /
                     "-" / "/" /
                     "=" / "?" /
                     "^" / "_" /
                     "`" / "{" /
                     "|" / "}" /
                     "~" /
                     UTF8-xtra-char

   utf8-realm     =  1*( label "." ) label

   label          =  utf8-rtext *(ldh-str)
   ldh-str        =  *( utf8-rtext / "-" ) utf8-rtext
   utf8-rtext     =  ALPHA / DIGIT / UTF8-xtra-char

2.3.  NAI Length Considerations

   Devices handling NAIs MUST support an NAI length of at least 72
   octets.  Devices SHOULD support an NAI length of 253 octets.
   However, the following implementation issues should be considered:

   * NAI octet length constraints may impose a more severe constraint
      on the number of UTF-8 characters.



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   * NAIs are often transported in the User-Name attribute of the
      Remote Authentication Dial-In User Service (RADIUS) protocol.
      Unfortunately, RFC 2865 [RFC2865], Section 5.1, states that "the
      ability to handle at least 63 octets is recommended."  As a
      result, it may not be possible to transfer NAIs beyond 63 octets
      through all devices.  In addition, since only a single User-Name
      attribute may be included in a RADIUS message and the maximum
      attribute length is 253 octets; RADIUS is unable to support NAI
      lengths beyond 253 octets.

   * NAIs can also be transported in the User-Name attribute of
      Diameter [RFC3588], which supports content lengths up to 2^24 - 9
      octets.  As a result, NAIs processed only by Diameter nodes can be
      very long.  However, an NAI transported over Diameter may
      eventually be translated to RADIUS, in which case the above
      limitations will apply.

   * NAIs may be transported in other protocols.  Each protocol
      can have its own limitations on maximum NAI length.
   The above criteria should permit the widest use, and widest possible
   inter-operability of the NAI.

2.4.  Support for Username Privacy

   Interpretation of the username part of the NAI depends on the realm
   in question.  Therefore, the utf8-username portion SHOULD be treated
   as opaque data when processed by nodes that are not a part of the
   authoritative domain (in the sense of Section 4) for that realm.

   In some situations, NAIs are used together with a separate
   authentication method that can transfer the username part in a more
   secure manner to increase privacy.  In this case, NAIs MAY be
   provided in an abbreviated form by omitting the username part.
   Omitting the username part is RECOMMENDED over using a fixed username
   part, such as "anonymous", since it provides an unambiguous way to
   determine whether the username is intended to uniquely identify a
   single user.  However, current practice is to use the username
   "anonymous" instead of omitting the username part.  This behavior is
   also permitted.

   For roaming purposes, it is typically necessary to locate the
   appropriate backend authentication server for the given NAI before
   the authentication conversation can proceed.  As a result, the realm
   portion is typically required in order for the authentication
   exchange to be routed to the appropriate server.






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2.5.  International Character Sets

   This specification allows both international usernames and realms.
   International usernames are based on the use of Unicode characters,
   encoded as UTF-8.  Internationalization of the realm portion of the
   NAI is based on "Internationalized Email Headers" [RFC5335].

   In order to ensure a canonical representation, characters of the
   username portion in an NAI MUST match the ABNF in this specification
   as well as the requirements specified in [RFC5891].  In practice,
   these requirements consist of the following item:

   * Realms MUST be of the form that can be registered as a
      Fully Qualified Domain Name (FQDN) within the DNS.

   This list is significantly shorter and simpler than the list in
   Section 2.4 of [RFC4282].  The form suggested in [RFC4282] depended
   on intermediate nodes performing canonicalizations based on
   insufficient information, which meant that the form was not
   canonical.  This document instead suggests (Section 2.10) that the
   realm owner provide a canonical form of the realm, and that all
   intermediate nodes use that form without modification.

   Specifying the realm requirement as above means that the requirements
   depend on specifications that are referenced here, rather than copied
   here.  This allows the realm definition to be updated when the
   referenced documents change, without requiring a revision of this
   specification.

   In general, the above requirement means following the requirements
   specified in [RFC5891].

2.6.  The Normalization Process

   Conversion to Unicode as well as normalization is expected to be
   performed by end systems that take "local" text as input.  Other AAA
   systems such as proxies do not have access to locale and character
   set information that is available to end systems.  Therefore, they
   are typically incapable of converting local input to Unicode.

   That is, all processing of NAIs from "local" character sets and
   locales to UTF-8 is performed by edge systems, prior to the NAIs
   entering the AAA system.  Inside of an AAA system, NAIs are sent over
   the wire in their canonical form, and this canonical form is used for
   all NAI and/or realm comparisons.

   Copying of localized text into fields that can subsequently be placed
   into the RADIUS User-Name attribute is problematic.  This practice



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   can result in a AAA proxy encountering non-UTF8 characters within
   what it expects to be an NAI.  An example of this requirement is
   [RFC3579] Section 2.1, which states:

      the NAS MUST copy the contents of the Type-Data field of the
      EAP-Response/Identity received from the peer into the User-Name
      attribute

   As a result, AAA proxies expect the contents of the EAP-
   Response/Identity sent by an EAP supplicant to consist of UTF-8
   characters, not localized text.  Using localized text in AAA username
   or identity fields means that realm routing becomes difficult or
   impossible.

   In contrast to [RFC4282] Section 2.4, we expect AAA systems to
   perform NAI comparisons, matching, and AAA routing based on the NAI
   as it is received.  This specification provides a canonical
   representation, ensures that intermediate systems such as AAA proxies
   do not need to perform translations, and can be expected to work
   through systems that are unaware of international character sets.

   For example, much of the common realm routing can be done on the
   "utf8-realm" portion of NAI, through simple checks for equality.
   This routing can be done even if the AAA proxy is unaware of
   internalized domain names.  All that is required is for the AAA proxy
   to be able to enter, store, and compare 8-bit data.

2.7.  Use in Other Protocols

   As noted earlier, the NAI MAY be used in other, non-AAA protocols.
   It is RECOMMENDED that the definition given here be used unchanged.
   Using other definitions for user identifiers may hinder
   interoperability, along with the users ability to authenticate
   successfully.  It is RECOMMENDED that protocols requiring the use of
   a user identifier reference this specification, and suggest that the
   use of an NAI is RECOMMENDED.

   We cannot require other protocols to use the NAI for user
   identifiers.  Their needs are unknown, and unknowable.  We simply
   suggest that interoperability and inter-domain authentication is
   useful, and should be encouraged.

   Where a protocol is 8-bit clean, it can likely transport the NAI as-
   is, without further modification.

   Where a protocol is not 8-bit clean, it MUST NOT affect the
   definition or handling of the NAI.  That is, if a protocol escapes
   the '.'  character as "%2E", then the protocol may have an identifier



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   transported as "fred@example%2Ecom", whereas the NAI for that user is
   "fred@example.com".  Any comparison, validation, or use of the NAI
   MUST be done on its un-escaped (i.e. utf8-clean) form.

2.8.  Routing inside of AAA Systems

   Many AAA systems use the "utf8-realm" portion of the NAI to route
   requests within a AAA proxy network.  The semantics of this operation
   involves a logical AAA routing table, where the "utf8-realm" portion
   acts as a key, and the values stored in the table are one or more
   "next hop" AAA servers.

   Intermediate nodes MUST use the "utf8-realm" portion of the NAI
   without modification to perform this lookup.  Comparisons between the
   NAI as given in a AAA packet, and as provisioned in a logical AAA
   routing table SHOULD be done as a byte-for-byte equality test.  As
   noted earlier, intermediate nodes may not have access to the same
   locale information as the system which injected the NAI into the AAA
   routing systems.  Therefore, almost all "case insensitive"
   comparisons will be wrong.  Where the "utf8-realm" is entirely ASCII,
   current systems sometimes perform case-insensitive matching on
   realms.  This practice MAY be continued, as it has been shown to work
   in practice.

   We also note that many existing systems use user identifiers which
   are similar in format to the NAI, but which are not compliant with
   this specification.  For example, they may use non-NFC form, or they
   may have multiple "@" characters in the user identifier.
   Intermediate nodes MAY normalize non-NFC identifiers to NFC, prior to
   looking up the "utf8-realm" in the logical routing table.
   Intermediate nodes MUST NOT modify the identifiers that they forward.
   The data as entered by the user is inviolate.

   The "utf8-realm" provisioned in the logical AAA routing table SHOULD
   be provisioned to the proxy prior to it receiving any AAA traffic.
   The "utf8-realm" SHOULD be supplied by the "next hop" or "home"
   system that also supplies the routing information necessary for
   packets to reach the next hop.

   This "next hop" information may be any of, or all of, the following
   information: IP address; port; RADIUS shared secret; TLS certificate;
   DNS host name; or instruction to use dyanmic DNS discovery (i.e. look
   up a record in the "utf8-realm" domain).  This list is not
   exhaustive, and my be extended by future specifications.

   It is RECOMMENDED to use the entirety of the "utf8-realm" for the
   routing decisions.  However, systems MAY use a portion of the
   "utf8-realm" portion, so long as that portion is a valid



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   "utf8-realm", and that portion is handled as above.  For example,
   routing "fred@example.com" to a "com" destination is forbidden,
   because "com" is not a valid "utf8-realm".  However, routing
   "fred@sales.example.com" to the "example.com" destination is
   permissible.

   Another reason to forbid the use of a single label (e.g.
   "fred@sales") is that many systems treat a single label as being a
   local identifier within their realm.  That is, a user logging in as
   "fred@sales" to a domain "example.com", would be treated as if the
   NAI was instead "fred@sales.example.com".  Permitting the use of a
   single label would mean changing the interpretation and meaning of a
   single label, which cannot be done.

2.9.  Compatibility with Email Usernames

   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 is based on the BNF described in [RFC5198], it has been modified
   for the purposes of Section 2.2.  It does not permit quoted text
   along with "folding" or "non-folding" whitespace that is commonly
   used in email addresses.  As such, the NAI is not necessarily
   equivalent to usernames used in e-mail.

   However, it is a common practice to use email addresses as user
   identifiers in AAA systems.  The ABNF in Section 2.2 is defined to be
   close to the "utf8-addr-spec" portion of [RFC5335], while still being
   compatible with [RFC4282].

   In contrast to [RFC4282] Section 2.5, we state that the
   internationalization requirements for NAIs and email addresses are
   substantially similar.  The NAI and email identifiers may be the
   same, and both need to be entered by the user and/or the operator
   supplying network access to that user.  There is therefore good
   reason for the internationalization requirements to be similar.

2.10.  Compatibility with DNS

   The "utf8-realm" portion of the NAI is intended to be compatible with
   Internationalized Domain Names (IDNs) [RFC5890].  As defined above,
   the "utf8-realm" portion as transported within an 8-bit clean
   protocol such as RADIUS and EAP can contain any valid UTF8 character.
   There is therefore no reason for a NAS to apply the ToAscii function
   to the "utf8-realm" portion of an NAI, prior to placing the NAI into
   a RADIUS User-Name attribute.  Unlike DNS, the NAI does not make a
   distinction between A-labels and U-labels.  Is instead an IDNA-valid
   label, as per Section 2.3.2.1 of [RFC5890].




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   When the realm portion of the NAI is used as the basis for name
   resolution, it may be necessary to convert internationalized realm
   names to ASCII using the ToASCII operation defined in [RFC5890].  As
   noted in [RFC6055] Section 2, resolver Application Programming
   Interfaces (APIs) are not necessarily DNS-specific, so that the
   ToASCII operation needs to be applied carefully:

   Applications which convert an IDN to A-label form before calling (for
   example) getaddrinfo() will result in name resolution failures if the
   Punycode name is directly used in such protocols.  Having libraries
   or protocols to convert from A-labels to the encoding scheme defined
   by the protocol (e.g., UTF-8) would require changes to APIs and/or
   servers, which IDNA was intended to avoid.

   As a result, applications SHOULD NOT assume that non-ASCII names are
   resolved using the public DNS and blindly convert them to A-labels
   without knowledge of what protocol will be selected by the name
   resolution library.

   There is, however, a problem with this approach.  A AAA proxy may not
   have sufficient information in order to perform the ToAscii
   conversion properly.  We therefore RECOMMEND that only the owner of
   the realm perform the ToAscii conversion.  We RECOMMEND that the
   owner of the realm pre-provision all proxies with the "utf8-realm"
   portion of the NAI, along with the value returned from passing the
   "utf8-realm" to the ToAscii function.  This key-value pair can then
   be placed into the logical AAA routing table discussed above.  Having
   only one entity perform the ToAscii function ensures that the result
   returned by that function are considered as canonical by all other
   participants in a AAA network.

   The paragraph above does not negate all of the benefits of using DNS
   to automatically discover the location of a "next hop" AAA server.
   Many AAA proxies require a business or legal relationship prior to
   routing any traffic.  This relationship can be leveraged to bootstrap
   the DNS information located in the logical AAA routing table.

2.11.  Realm Construction

   The home realm usually appears in the "utf8-realm" portion of the
   NAI, but in some cases a different realm can be used.  This may be
   useful, for instance, when the home realm is reachable only via
   intermediate proxies.

   Such usage may prevent interoperability unless the parties involved
   have a mutual agreement that the usage is allowed.  In particular,
   NAIs MUST NOT use a different realm than the home realm unless the
   sender has explicit knowledge that (a) the specified other realm is



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   available and (b) the other realm supports such usage.  The sender
   may determine the fulfillment of these conditions through a database,
   dynamic discovery, or other means not specified here.  Note that the
   first condition is affected by roaming, as the availability of the
   other realm may depend on the user's location or the desired
   application.

   The use of the home realm MUST be the default unless otherwise
   configured.

2.11.1.  Historical Practices

   Some systems have historically used NAI modifications with multiple
   "prefix" and "suffix" decorations to perform explicit routing through
   multiple proxies inside of a AAA network.  This practice is NOT
   RECOMMENDED for the following reasons:

   *  Using explicit routing paths is fragile, and is unresponsive to
      changes in the network due to servers going up or down, or to
      changing business relationships.

   *  There is no RADIUS routing protocol, meaning that routing paths
      have to be communicated "out of band" to all intermediate AAA
      nodes, and also to all end-user systems (supplicants) expecting to
      obtain network access.

   *  Using explicit routing paths requires thousands, if not
      millions of end-user systems to be updated with new path
      information when a AAA routing path changes.  This adds huge
      expense for updates that would be better done at only a few AAA
      systems in the network.

   *  Manual updates to RADIUS paths are expensive, time-consuming,
      and prone to error.

   *  Creating compatible formats for the NAI is difficult
      when locally-defined "prefixes" and "suffixes" conflict with
      similar practices elsewhere in the network.  These conflicts mean
      that connecting two networks may be impossible in some cases, as
      there is no way for packets to be routed properly in a way that
      meets all requirements at all intermediate proxies.

   *  Leveraging the DNS name system for realm names establishes
      a globally unique name space for realms.

   In summary, network practices and capabilities have changed
   significantly since NAIs were first overloaded to define AAA routes
   through a network.  While explicit path routing was once useful, the



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   time has come for better methods to be used.

2.12.  Examples

   Examples of valid Network Access Identifiers include the following:

           bob
           joe@example.com
           fred@foo-9.example.com
           jack@3rd.depts.example.com
           fred.smith@example.com
           fred_smith@example.com
           fred$@example.com
           fred=?#$&*+-/^smith@example.com
           nancy@eng.example.net
           eng.example.net!nancy@example.net
           eng%nancy@example.net
           @privatecorp.example.net
           \(user\)@example.net

   Examples of invalid Network Access Identifiers include the following:

           fred@example
           fred@example_9.com
           fred@example.net@example.net
           fred.@example.net
           eng:nancy@example.net
           eng;nancy@example.net
           (user)@example.net
           <nancy>@example.net

   One example given in [RFC4282] is still permitted by the ABNF, but it
   is NOT RECOMMMENDED because of the use of the ToAscii function to
   create an ASCII encoding from what is now a valid UTF-8 string.

           alice@xn--tmonesimerkki-bfbb.example.net

3.  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 that transmit the username in
   clear-text across the Internet, such as in RADIUS, described in
   [RFC2865] and [RFC2866].  In order to prevent snooping of the
   username, protocols may use confidentiality services provided by
   protocols transporting them, such as RADIUS protected by IPsec
   [RFC3579] or Diameter protected by TLS [RFC3588].




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   This specification adds the possibility of hiding the username part
   in the NAI, by omitting it.  As discussed in Section 2.4, this is
   possible only when NAIs are used together with a separate
   authentication method that can transfer the username in a secure
   manner.  In some cases, application-specific privacy mechanism have
   also been used with NAIs.  For instance, some EAP methods apply
   method-specific pseudonyms in the username part of the NAI [RFC3748].
   While neither of these approaches can protect the realm part, their
   advantage over transport protection is that privacy of the username
   is protected, even through intermediate nodes such as NASes.

4.  IANA Considerations

   In order to avoid creating any new administrative procedures,
   administration of the NAI realm namespace piggybacks 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
   conflict and is therefore discouraged.

   Note that the use of an FQDN as the realm name does not require use
   of the DNS for location of the authentication server.  While Diameter
   [RFC3588] supports the use of DNS for location of authentication
   servers, existing RADIUS implementations typically use proxy
   configuration files in order to locate authentication servers within
   a domain and perform authentication routing.  The implementations
   described in [RFC2194] did not use DNS for location of the
   authentication server within a domain.  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 represent a valid email address.

5.  References

5.1.  Normative References

[RFC2119]
     Bradner, S., "Key words for use in RFCs to Indicate Requirement
     Levels", RFC 2119, March, 1997.

[RFC3629]
     Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63,
     RFC 3629, November 2003.



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[RFC5198]
     Klensin J., and Padlipsky M., "Unicode Format for Network
     Interchange", RFC 5198, March 2008

[RFC5234]
     Crocker, D. and P. Overell, "Augmented BNF for Syntax
     Specifications: ABNF", RFC 5234, January 2008.

[RFC5890]
     Faltstrom, P., Hoffman, P., and A. Costello, "Internationalizing
     Domain Names in Applications (IDNA)", RFC 5890

5.2.  Informative References

[RFC2194]
     Aboba, B., Lu, J., Alsop, J., Ding, J., and W. Wang, "Review of
     Roaming Implementations", RFC 2194, September 1997.

[RFC2341]
     Valencia, A., Littlewood, M., and T. Kolar, "Cisco Layer Two
     Forwarding (Protocol) "L2F"", RFC 2341, May 1998.

[RFC2637]
     Hamzeh, K., Pall, G., Verthein, W., Taarud, J., Little, W., and G.
     Zorn, "Point-to-Point Tunneling Protocol", RFC 2637, July 1999.

[RFC2661]
     Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn, G., and B.
     Palter, "Layer Two Tunneling Protocol "L2TP"", RFC 2661, August
     1999.

[RFC2865]
     Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote
     Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000.

[RFC2866]
     Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.

[RFC3579]
     Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial In
     User Service) Support For Extensible Authentication Protocol
     (EAP)", RFC 3579, September 2003.

[RFC3588]
     Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko,
     "Diameter Base Protocol", RFC 3588, September 2003.





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[RFC3748]
     Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
     Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748,
     June 2004.

[RFC4282]
     Aboba, B. et al., "The Network Access Identifier", RFC 4282,
     December 2005.

[RFC4301]
     Kent, S. and S. Keo, "Security Architecture for the Internet
     Protocol", RFC 4301, December 2005.

[RFC5335]
     Y. Abel, Ed., "Internationalized Email Headers", RFC 5335,
     September 2008.

[EDUROAM]
     http://eduroam.org, "eduroam (EDUcational ROAMing)"

[RFC5891]
     Klensin, J., "Internationalized Domain Names in Applications
     (IDNA): Protocol", RFC 5891

[RFC6055]
     Thaler, D., et al, "IAB Thoughts on Encodings for Internationalized
     Domain Names", RFC 6055, February 2011.

Acknowledgments

   The initial text for this document was [RFC4282], which was then
   heavily edited.  The original authors of [RFC4282] were Bernard
   Aboba, Mark A. Beadles, Jari Arkko, and Pasi Eronen.

   The ABNF validator at http://www.apps.ietf.org/abnf.html was used to
   verify the syntactic correctness of the ABNF in Section 2.















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Appendix A - Changes from RFC4282

   This document contains the following updates with respect to the
   previous NAI definition in RFC 4282 [RFC4282]:

   *  The formal syntax in Section 2.1 has been updated to forbid
      non-UTF8 characters.  e.g. characters with the "high bit" set.

   *  The formal syntax in Section 2.1 has been updated to allow
      UTF-8 in the "realm" portion of the NAI.

   *  The formal syntax in [RFC4282] Section 2.1 applied to the
      NAI after it was "internationalized" via the ToAscii function.
      The contents of the NAI before it was "internationalized" were
      left indeterminate.  This document updates the formal syntax to
      define an internationalized form of the NAI, and forbids the use
      of the ToAscii function for NAI "internationalization".

   * The grammar for the user and realm portion is based on a
   combination
      of the "nai" defined in [RFC4282] Section 2.1, and the "utf8-addr-
      spec" defined in [RFC5335] Section 4.4.

   *  All use of the ToAscii function has been moved to normal
      requirements on DNS implementations when realms are used as the
      basis for DNS lookups.  This involves no changes to the existing
      DNS infrastructure.

   *  The discussions on internationalized character sets in Section 2.4
      have been updated.  The suggestion to use the ToAscii function for
      realm comparisons has been removed.  No AAA system has implemented
      these suggestions, so this change should have no operational
      impact.

   * The section "Routing inside of AAA Systems" section is new in this
      document.  The concept of a "local AAA routing table" is also new,
      although it accurately describes the functionality of wide-spread
      implementations.

   *  The "Compatibility with EMail Usernames" and "Compatibility
      with DNS" sections have been revised and updated.  We now note
      that the ToAscii function is suggested to be used only when a
      realm name is used for DNS lookups, and even then the function is
      only used by a resolving API on the local system, and even then we
      recommend that only the home network perform this conversion.

   * The "Realm Construction" section has been updated to note
      that editing of the NAI is NOT RECOMMENDED.



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   * The "Examples" section has been updated to remove the instance
      of the IDN being converted to ASCII.  This behavior is now
      forbidden.

Authors' Addresses

   Alan DeKok
   The FreeRADIUS Server Project

   Email: aland@freeradius.org









































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