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Versions: (draft-winter-dynamic-discovery) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 7585

RADIUS Extensions Working Group                                S. Winter
Internet-Draft                                                   RESTENA
Intended status: Experimental                                M. McCauley
Expires: November 1, 2015                                      AirSpayce
                                                          April 30, 2015

    NAI-based Dynamic Peer Discovery for RADIUS/TLS and RADIUS/DTLS


   This document specifies a means to find authoritative RADIUS servers
   for a given realm.  It is used in conjunction with either RADIUS/TLS

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on November 1, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   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.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   6
     1.3.  Document Status . . . . . . . . . . . . . . . . . . . . .   6
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   7
     2.1.  DNS Resource Record (RR) definition . . . . . . . . . . .   7
       2.1.1.  S-NAPTR . . . . . . . . . . . . . . . . . . . . . . .   7
       2.1.2.  SRV . . . . . . . . . . . . . . . . . . . . . . . . .  11
       2.1.3.  Optional name mangling  . . . . . . . . . . . . . . .  12
     2.2.  Definition of the X.509 certificate property
           SubjectAltName:otherName:NAIRealm . . . . . . . . . . . .  13
   3.  DNS-based NAPTR/SRV Peer Discovery  . . . . . . . . . . . . .  15
     3.1.  Applicability . . . . . . . . . . . . . . . . . . . . . .  15
     3.2.  Configuration Variables . . . . . . . . . . . . . . . . .  16
     3.3.  Terms . . . . . . . . . . . . . . . . . . . . . . . . . .  16
     3.4.  Realm to RADIUS server resolution algorithm . . . . . . .  17
       3.4.1.  Input . . . . . . . . . . . . . . . . . . . . . . . .  17
       3.4.2.  Output  . . . . . . . . . . . . . . . . . . . . . . .  18
       3.4.3.  Algorithm . . . . . . . . . . . . . . . . . . . . . .  18
       3.4.4.  Validity of results . . . . . . . . . . . . . . . . .  19
       3.4.5.  Delay considerations  . . . . . . . . . . . . . . . .  20
       3.4.6.  Example . . . . . . . . . . . . . . . . . . . . . . .  21
   4.  Operations and Manageability Considerations . . . . . . . . .  23
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  24
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  25
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  28
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  29
   Appendix A.  Appendix A: ASN.1 Syntax of NAIRealm . . . . . . . .  30

1.  Introduction

   RADIUS in all its current transport variants (RADIUS/UDP, RADIUS/TCP,
   RADIUS/TLS, RADIUS/DTLS) requires manual configuration of all peers
   (clients, servers).

   Where more than one administrative entity collaborates for RADIUS
   authentication of their respective customers (a "roaming
   consortium"), the Network Access Identifier (NAI)
   [I-D.ietf-radext-nai] is the suggested way of differentiating users
   between those entities; the part of a username to the right of the @
   delimiter in an NAI is called the user's "realm".  Where many realms
   and RADIUS forwarding servers are in use, the number of realms to be
   forwarded and the corresponding number of servers to configure may be
   significant.  Where new realms with new servers are added or details

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   of existing servers change on a regular basis, maintaining a single
   monolithic configuration file for all these details may prove too
   cumbersome to be useful.

   Furthermore, in cases where a roaming consortium consists of
   independently working branches (e.g. departments, national
   subsidiaries), each with their own forwarding servers, and who add or
   change their realm lists at their own discretion, there is additional
   complexity in synchronising the changed data across all branches.

   Where realms can be partitioned (e.g. according to their top-level
   domain ending), forwarding of requests can be realised with a
   hierarchy of RADIUS servers, all serving their partition of the realm
   space.  Figure 1 show an example of this hierarchical routing.

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                                    |       |
                                    |   .   |
                                    |       |
                                      / | \
                    +----------------/  |  \---------------------+
                    |                   |                        |
                    |                   |                        |
                    |                   |                        |
                 +--+---+            +--+--+                +----+---+
                 |      |            |     |                |        |
                 | .edu |    . . .   | .nl |      . . .     | .ac.uk |
                 |      |            |     |                |        |
                 +--+---+            +--+--+                +----+---+
                  / | \                 | \                      |
                 /  |  \                |  \                     |
                /   |   \               |   \                    |
         +-----+    |    +-----+        |    +------+            |
         |          |          |        |           |            |
         |          |          |        |           |            |
     +---+---+ +----+---+ +----+---+ +--+---+ +-----+----+ +-----+-----+
     |       | |        | |        | |      | |          | |           |
     |utk.edu| |utah.edu| |case.edu| |hva.nl| |surfnet.nl| |soton.ac.uk|
     |       | |        | |        | |      | |          | |           |
     +----+--+ +--------+ +--------+ +------+ +----+-----+ +-----------+
          |                                        |
          |                                        |
       +--+--+                                  +--+--+
       |     |                                  |     |
     +-+-----+-+                                |     |
     |         |                                +-----+
     user: paul@surfnet.nl             surfnet.nl Authentication server

     Figure 1: RADIUS hierarchy based on Top-Level Domain partitioning

   However, such partitioning is not always possible.  As an example, in
   one real-life deployment, the administrative boundaries and RADIUS
   forwarding servers are are organised along country borders, but
   generic top-level domains such as .edu do not map to this choice of
   boundaries (see [I-D.wierenga-ietf-eduroam] for details).  These
   situations can benefit significantly from a distributed mechanism for
   storing realm and server reachability information.  This document
   describes one such mechanism: storage of realm-to-server mappings in
   DNS; realm-based request forwarding can then be realised without a
   static hierarchy such as in the following figure:

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                                   /         \
                          ---------           ------------
                         /                                \
                         |    DNS                          -
               ----------|                                  \
              /          \          surfnet.nl NAPTR?       |
        (1)  /            ----       -> radius.surfnet.nl   /
            /                 \                            /
           /                   --------           ---------
          /                            \---------/
         |   ---------------------------------------
         |  /              (2) RADIUS               \
         |  |                                       |
     +---+---+ +----+---+ +----+---+ +--+---+ +-----+----+ +-----+-----+
     |       | |        | |        | |      | |          | |           |
     |utk.edu| |utah.edu| |case.edu| |hva.nl| |surfnet.nl| |soton.ac.uk|
     |       | |        | |        | |      | |          | |           |
     +----+--+ +--------+ +--------+ +------+ +----+-----+ +-----------+
          |                                        |
          |                                        |
       +--+--+                                  +--+--+
       |     |                                  |     |
     +-+-----+-+                                |     |
     |         |                                +-----+
     user: paul@surfnet.nl             surfnet.nl Authentication server

     Figure 2: RADIUS hierarchy based on Top-Level Domain partitioning

   This document also specifies various approaches for verifying that
   server information which was retrieved from DNS was from an
   authorised party; e.g. an organisation which is not at all part of a
   given roaming consortium may alter its own DNS records to yield a
   result for its own realm.

1.1.  Requirements Language

   In this document, several words are used to signify the requirements
   of the specification.  The key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" in this document are to be interpreted as described in
   RFC 2119.  [RFC2119]

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1.2.  Terminology

   RADIUS/TLS Client: a RADIUS/TLS [RFC6614] instance which initiates a
   new connection.

   RADIUS/TLS Server: a RADIUS/TLS [RFC6614] instance which listens on a
   RADIUS/TLS port and accepts new connections

   RADIUS/TLS node: a RADIUS/TLS client or server

   [I-D.ietf-radext-nai] defines the terms NAI, realm, consortium.

1.3.  Document Status

   This document is an Experimental RFC.

   The communities expected to use this document are roaming consortia
   whose authentication services are based on the RADIUS protocol.

   The duration of the experiment is undetermined; as soon as enough
   experience is collected on the choice points mentioned below, it is
   expected to be obsoleted by a standards-track version of the protocol
   which trims down the choice points.

   If that removal of choice points obsoletes tags or service names as
   defined in this document and allocated by IANA, these items will be
   returned to IANA as per the provisions in [RFC6335].

   The document provides a discovery mechanism for RADIUS which is very
   similar to the approach that is taken with the Diameter protocol
   [RFC6733].  As such, the basic approach (using Naming Authority
   Pointer (NAPTR) records in DNS domains which match NAI realms) is not
   of very experimental nature.

   However, the document offers a few choice points and extensions which
   go beyond the provisions for Diameter.  The list of major additions/
   deviations is

   o  provisions for determining the authority of a server to act for
      users of a realm (declared out of scope for Diameter)

   o  much more in-depth guidance on DNS regarding timeouts, failure
      conditions, alteration of Time-To-Live (TTL) information than the
      Diameter counterpart

   o  a partially correct routing error detection during DNS lookups

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2.  Definitions

2.1.  DNS Resource Record (RR) definition

   DNS definitions of RADIUS/TLS servers can be either S-NAPTR records
   (see [RFC3958]) or Service Record (SRV) records.  When both are
   defined, the resolution algorithm prefers S-NAPTR results (see
   Section 3.4 below).

2.1.1.  S-NAPTR  Registration of Application Service and Protocol Tags

   This specification defines three S-NAPTR service tags:

   | Service Tag     | Use                                     |
   | aaa+auth        | RADIUS Authentication, i.e. traffic as  |
   |                 | defined in [RFC2865]                    |
   | - - - - - - - - | - - - - - - - - - - - - - - - - - - - - |
   | aaa+acct        | RADIUS Accounting, i.e. traffic as      |
   |                 | defined in [RFC2866]                    |
   | - - - - - - - - | - - - - - - - - - - - - - - - - - - - - |
   | aaa+dynauth     | RADIUS Dynamic Authorisation, i.e.      |
   |                 | traffic as defined in [RFC5176]         |

                      Figure 3: List of Service Tags

   This specification defines two S-NAPTR protocol tags:

   | Protocol Tag    | Use                                     |
   | radius.tls.tcp  | RADIUS transported over TLS as defined  |
   |                 | in [RFC6614]                            |
   | - - - - - - - - | - - - - - - - - - - - - - - - - - - - - |
   | radius.dtls.udp | RADIUS transported over DTLS as defined |
   |                 | in [RFC7360]                            |

                      Figure 4: List of Protocol Tags

   Note well:

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      The S-NAPTR service and protocols are unrelated to the IANA
      Service Name and Transport Protocol Number registry.

      The delimiter '.' in the protocol tags is only a separator for
      human reading convenience - not for structure or namespacing; it
      MUST NOT be parsed in any way by the querying application or

      The use of the separator '.' is common also in other protocols'
      protocol tags.  This is coincidence and does not imply a shared
      semantics with such protocols.  Definition of Conditions for Retry/Failure

   RADIUS is a time-critical protocol; RADIUS clients which do not
   receive an answer after a configurable, but short, amount of time,
   will consider the request failed.  Due to this, there is little
   leeway for extensive retries.

   As a general rule, only error conditions which generate an immediate
   response from the other end are eligible for a retry of a discovered
   target.  Any error condition involving timeouts, or the absence of a
   reply for more than one second during the connection setup phase is
   to be considered a failure; the next target in the set of discovered
   NAPTR targets is to be tried.

   Note that [RFC3958] already defines that a failure to identify the
   server as being authoritative for the realm is always considered a
   failure; so even if a discovered target returns a wrong credential
   instantly, it is not eligible for retry.

   Furthermore, the contacted RADIUS/TLS server verifies during
   connection setup whether or not it finds the connecting RADIUS/TLS
   client authorized or not.  If the connecting RADIUS/TLS client is not
   found acceptable, the server will close the TLS connection
   immediately with an appropriate alert.  Such TLS handshake failures
   are permanently fatal and not eligible for retry, unless the
   connecting client has more X.509 certificates to try; in this case, a
   retry with the remainder of its set of certificates SHOULD be
   attempted.  Not trying all available client certificates potentially
   creates a DoS for the end-user whose authentication attempt triggered
   the discovery; one of the neglected certificates might have led to a
   successful RADIUS connection and subsequent end-user authentication.

   If the TLS session setup to a discovered target does not succeed,
   that target (as identified by IP address and port number) SHOULD be
   ignored from the result set of any subsequent executions of the
   discovery algorithm at least until the target's Effective TTL (see

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   Section 3.3) has expired or until the entity which executes the
   algorithm changes its TLS context to either send a new client
   certificate or expect a different server certificate.  Server Identification and Handshake

   After the algorithm in this document has been executed, a RADIUS/TLS
   session as per [RFC6614] is established.  Since the dynamic discovery
   algorithm does not have provisions to establish confidential keying
   material between the RADIUS/TLS client (i.e. the server which
   executes the discovery algorithm) and the RADIUS/TLS server which was
   discovered, TLS-PSK ciphersuites cannot be used in the subsequent TLS
   handshake.  Only TLS ciphersuites using X.509 certificates can be
   used with this algorithm.

   There are numerous ways to define which certificates are acceptable
   for use in this context.  This document defines one mandatory-to-
   implement mechanism which allows to verify whether the contacted host
   is authoritative for an NAI realm or not.  It also gives one example
   of another mechanism which is currently in wide-spread deployment,
   and one possible approach based on DNSSEC which is yet unimplemented.

   For the approaches which use trust roots (see the following two
   sections), a typical deployment will use a dedicated trust store for
   RADIUS/TLS certificate authorities, particularly a trust store which
   is independent from default "browser" trust stores.  Often, this will
   be one or few CAs, and they only issue certificates for the specific
   purpose of establishing RADIUS server-to-server trust.  It is
   important not to trust a large set of CAs which operate outside the
   control of the roaming consortium, for their issuance of certificates
   with the properties important for authorisation (such as NAIRealm and
   policyOID below) is difficult to verify.  Therefore, clients SHOULD
   NOT be pre-configured with a list of known public CAs by the vendor
   or manufacturer.  Instead, the clients SHOULD start off with an empty
   CA list.  The addition of a CA SHOULD be done only when manually
   configured by an administrator.  Mandatory-to-implement mechanism: Trust Roots + NAIRealm

   Verification of authority to provide AAA services over RADIUS/TLS is
   a two-step process.

   Step 1 is the verification of certificate wellformedness and validity
   as per [RFC5280] and whether it was issued from a root certificate
   which is deemed trustworthy by the RADIUS/TLS client.

   Step 2 is to compare the value of algorithm's variable "R" after the
   execution of step 3 of the discovery algorithm in Section 3.4.3 below

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   (i.e. after a consortium name mangling, but before conversion to a
   form usable by the name resolution library) to all values of the
   contacted RADIUS/TLS server's X.509 certificate property
   "subjectAlternativeName:otherName:NAIRealm" as defined in
   Section 2.2.  Other mechanism: Trust Roots + policyOID

   Verification of authority to provide AAA services over RADIUS/TLS is
   a two-step process.

   Step 1 is the verification of certificate wellformedness and validity
   as per [RFC5280] and whether it was issued from a root certificate
   which is deemed trustworthy by the RADIUS/TLS client.

   Step 2 is to compare the values of the contacted RADIUS/TLS server's
   X.509 certificate's extensions of type "Policy OID" to a list of
   configured acceptable Policy OIDs for the roaming consortium.  If one
   of the configured OIDs is found in the certificate's Policy OID
   extensions, then the server is considered authorized; if there is no
   match, the server is considered unauthorized.

   This mechanism is inferior to the mandatory-to-implement mechanism in
   the previous section because all authorized servers are validated by
   the same OID value; the mechanism is not fine-grained enough to
   express authority for one specific realm inside the consortium.  If
   the consortium contains members which are hostile against other
   members, this weakness can be exploited by one RADIUS/TLS server
   impersonating another if DNS responses can be spoofed by the hostile

   The shortcomings in server identification can be partially mitigated
   by using the RADIUS infrastructure only with authentication payloads
   which provide mutual authentication and credential protection (i.e.
   EAP types passing the criteria of [RFC4017]): using mutual
   authentication prevents the hostile server from mimicking the real
   EAP server (it can't terminate the EAP authentication unnoticed
   because it does not have the server certificate from the real EAP
   server); protection of credentials prevents the impersonating server
   from learning usernames and passwords of the ongoing EAP conversation
   (other RADIUS attributes pertaining to the authentication, such as
   the EAP peer's Calling-Station-ID, can still be learned though).  Other mechanism: DNSSEC / DANE

   Where DNSSEC is used, the results of the algorithm can be trusted;
   i.e. the entity which executes the algorithm can be certain that the
   realm that triggered the discovery is actually served by the server

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   that was discovered via DNS.  However, this does not guarantee that
   the server is also authorized (i.e. a recognised member of the
   roaming consortium).  The server still needs to present an X.509
   certificate proving its authority to serve a particular realm.

   The authorization can be sketched using DNSSEC+DANE as follows: DANE/
   TLSA records of all authorized servers are put into a DNSSEC zone
   which contains all known and authorised realms; the zone is rooted in
   a common, consortium-agreed branch of the DNS tree.  The entity
   executing the algorithm uses the realm information from the
   authentication attempt, and then attempts to retrieve TLSA Resource
   Records (TLSA RR) for the DNS label "realm.commonroot".  It then
   verifies that the presented server certificate during the RADIUS/TLS
   handshake matches the information in the TLSA record.


      Realm = "example.com"

      Common Branch = "idp.roaming-consortium.example.

      label for TLSA query = "example.com.idp.roaming-

      result of discovery algorithm for realm "example.com" =

      ( TLS certificate of matches TLSA RR ? "PASS" :
      "FAIL" )  Client Authentication and Authorisation

   Note that RADIUS/TLS connections always mutually authenticate the
   RADIUS server and the RADIUS client.  This specification provides an
   algorithm for a RADIUS client to contact and verify authorization of
   a RADIUS server only.  During connection setup, the RADIUS server
   also needs to verify whether it considers the connecting RADIUS
   client authorized; this is outside the scope of this specification.

2.1.2.  SRV

   This specification defines two SRV prefixes (i.e. two values for the
   "_service._proto" part of an SRV RR as per [RFC2782]):

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   | SRV Label         | Use                                     |
   | _radiustls._tcp   | RADIUS transported over TLS as defined  |
   |                   | in [RFC6614]                            |
   | - - - - - - - - - | - - - - - - - - - - - - - - - - - - - - |
   | _radiusdtls._udp  | RADIUS transported over DTLS as defined |
   |                   | in [RFC7360]                            |

                       Figure 5: List of SRV Labels

   Just like NAPTR records, the lookup and subsequent follow-up of SRV
   records may yield more than one server to contact in a prioritised
   list.  [RFC2782] does not specify rules regarding "Definition of
   Conditions for Retry/Failure", nor "Server Identification and
   Handshake".  This specification defines that the rules for these two
   topics as defined in Section and Section SHALL be
   used both for targets retrieved via an initial NAPTR RR as well as
   for targets retrieved via an initial SRV RR (i.e. in the absence of
   NAPTR RRs).

2.1.3.  Optional name mangling

   It is expected that in most cases, the SRV and/or NAPTR label used
   for the records is the DNS A-label representation of the literal
   realm name for which the server is the authoritative RADIUS server
   (i.e. the realm name after conversion according to section 5 of

   However, arbitrary other labels or service tags may be used if, for
   example, a roaming consortium uses realm names which are not
   associated to DNS names or special-purpose consortia where a globally
   valid discovery is not a use case.  Such other labels require a
   consortium-wide agreement about the transformation from realm name to
   lookup label, and/or which service tag to use.


   a.  A general-purpose RADIUS server for realm example.com might have
       DNS entries as follows:

          example.com.  IN NAPTR 50 50 "s" "aaa+auth:radius.tls.tcp" ""

          _radiustls._tcp.foobar.example.com.  IN SRV 0 10 2083

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   b.  The consortium "foo" provides roaming services for its members
       only.  The realms used are of the form enterprise-name.example.
       The consortium operates a special purpose DNS server for the
       (private) TLD "example" which all RADIUS servers use to resolve
       realm names.  "Company, Inc." is part of the consortium.  On the
       consortium's DNS server, realm company.example might have the
       following DNS entries:

          company.example.  IN NAPTR 50 50 "a"
          "aaa+auth:radius.dtls.udp" "" roamserv.company.example.

   c.  The eduroam consortium (see [I-D.wierenga-ietf-eduroam] uses
       realms based on DNS, but provides its services to a closed
       community only.  However, a AAA domain participating in eduroam
       may also want to expose AAA services to other, general-purpose,
       applications (on the same or other RADIUS servers).  Due to that,
       the eduroam consortium uses the service tag "x-eduroam" for
       authentication purposes and eduroam RADIUS servers use this tag
       to look up other eduroam servers.  An eduroam participant
       example.org which also provides general-purpose AAA on a
       different server uses the general "aaa+auth" tag:

          example.org.  IN NAPTR 50 50 "s" "x-eduroam:radius.tls.tcp" ""

          example.org.  IN NAPTR 50 50 "s" "aaa+auth:radius.tls.tcp" ""

          _radiustls._tcp.eduroam.example.org.  IN SRV 0 10 2083 aaa-

          _radiustls._tcp.aaa.example.org.  IN SRV 0 10 2083 aaa-

2.2.  Definition of the X.509 certificate property

   This specification retrieves IP addresses and port numbers from the
   Domain Name System which are subsequently used to authenticate users
   via the RADIUS/TLS protocol.  Regardless whether the results from DNS
   discovery are trustworthy or not (e.g. DNSSEC in use), it is always
   important to verify that the server which was contacted is authorized
   to service requests for the user which triggered the discovery

   The input to the algorithm is an NAI realm as specified in
   Section 3.4.1.  As a consequence, the X.509 certificate of the server
   which is ultimately contacted for user authentication needs to be

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   able to express that it is authorized to handle requests for that

   Current subjectAltName fields do not semantically allow to express an
   NAI realm; the field subjectAltName:dNSName is syntactically a good
   match but would inappropriately conflate DNS names and NAI realm
   names.  Thus, this specification defines a new subjectAltName field
   to hold either a single NAI realm name or a wildcard name matching a
   set of NAI realms.

   The subjectAltName:otherName:sRVName field certifies that a
   certificate holder is authorized to provide a service; this can be
   compared to the target of DNS label's SRV resource record.  If the
   Domain Name System is insecure, it is required that the label of the
   SRV record itself is known-correct.  In this specification, that
   label is not known-correct; it is potentially derived from a
   (potentially untrusted) NAPTR resource record of another label.  If
   DNS is not secured with DNSSEC, the NAPTR resource record may have
   been altered by an attacker with access to the Domain Name System
   resolution, and thus the label to lookup the SRV record for may
   already be tainted.  This makes subjectAltName:otherName:sRVName not
   a trusted comparison item.

   Further to this, this specification's NAPTR entries may be of type
   "A" which do not involve resolution of any SRV records, which again
   makes subjectAltName:otherName:sRVName unsuited for this purpose.

   This section defines the NAIRealm name as a form of otherName from
   the GeneralName structure in SubjectAltName defined in [RFC5280].

      id-on-naiRealm OBJECT IDENTIFIER ::= { id-on XXX }

      ub-naiRealm-length INTEGER ::= 255

      NAIRealm ::= UTF8String (SIZE (1..ub-naiRealm-length))

   The NAIRealm, if present, MUST contain an NAI realm as defined in
   [I-D.ietf-radext-nai].  It MAY substitute the leftmost dot-separated
   label of the NAI with the single character "*" to indicate a wildcard
   match for "all labels in this part".  Further features of regular
   expressions, such as a number of characters followed by a * to
   indicate a common prefix inside the part, are not permitted.

   The comparison of an NAIRealm to the NAI realm as derived from user
   input with this algorithm is a byte-by-byte comparison, except for
   the optional leftmost dot-separated part of the value whose content
   is a single "*" character; such labels match all strings in the same
   dot-separated part of the NAI realm.  If at least one of the

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   sAN:otherName:NAIRealm values matches the NAI realm, the server is
   considered authorized; if none matches, the server is considered

   Since multiple names and multiple name forms may occur in the
   subjectAltName extension, an arbitrary number of NAIRealms can be
   specified in a certificate.


   | NAI realm (RADIUS)  | NAIRealm (cert)   | MATCH?                |
   | foo.example         | foo.example       | YES                   |
   | foo.example         | *.example         | YES                   |
   | bar.foo.example     | *.example         | NO                    |
   | bar.foo.example     | *ar.foo.example   | NO (NAIRealm invalid) |
   | bar.foo.example     | bar.*.example     | NO (NAIRealm invalid) |
   | bar.foo.example     | *.*.example       | NO (NAIRealm invalid) |
   | sub.bar.foo.example | *.*.example       | NO (NAIRealm invalid) |
   | sub.bar.foo.example | *.bar.foo.example | YES                   |

         Figure 6: Examples for NAI realm vs. certificate matching

   Appendix A contains the ASN.1 definition of the above objects.

3.  DNS-based NAPTR/SRV Peer Discovery

3.1.  Applicability

   Dynamic server discovery as defined in this document is only
   applicable for new AAA transactions and per service (i.e. distinct
   discovery is needed for Authentication, Accounting, and Dynamic
   Authorization) where a RADIUS entity which acts as a forwarding
   server for one or more realms receives a request with a realm for
   which it is not authoritative, and which no explicit next hop is
   configured.  It is only applicable for

   a.  new user sessions, i.e. for the initial Access-Request.
       Subsequent messages concerning this session, for example Access-
       Challenges and Access-Accepts use the previously-established
       communication channel between client and server.

   b.  the first accounting ticket for a user session.

   c.  the first RADIUS DynAuth packet for a user session.

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3.2.  Configuration Variables

   The algorithm contains various variables for timeouts.  These
   variables are named here and reasonable default values are provided.
   Implementations wishing to deviate from these defaults should make
   they understand the implications of changes.

      DNS_TIMEOUT: maximum amount of time to wait for the complete set
      of all DNS queries to complete: Default = 3 seconds

      MIN_EFF_TTL: minimum DNS TTL of discovered targets: Default = 60

      BACKOFF_TIME: if no conclusive DNS response was retrieved after
      DNS_TIMEOUT, do not attempt dynamic discovery before BACKOFF_TIME
      has elapsed.  Default = 600 seconds

3.3.  Terms

   Positive DNS response: a response which contains the RR that was
   queried for.

   Negative DNS response: a response which does not contain the RR that
   was queried for, but contains an SOA record along with a TTL
   indicating cache duration for this negative result.

   DNS Error: Where the algorithm states "name resolution returns with
   an error", this shall mean that either the DNS request timed out, or
   a DNS response which is neither a positive nor a negative response
   (e.g. SERVFAIL).

   Effective TTL: The validity period for discovered RADIUS/TLS target
   hosts.  Calculated as: Effective TTL (set of DNS TTL values) = max {
   MIN_EFF_TTL, min { DNS TTL values } }

   SRV lookup: for the purpose of this specification, SRV lookup
   procedures are defined as per [RFC2782], but excluding that RFCs "A"
   fallback as defined in its section "Usage Rules", final "else"

   Greedy result evaluation: The NAPTR to SRV/A/AAAA resolution may lead
   to a tree of results, whose leafs are the IP addresses to contact.
   The branches of the tree are ordered according to their order/
   preference DNS properties.  An implementation is executing greedy
   result evaluation if it uses a depth-first search in the tree along
   the highest order results, attempts to connect to the corresponding
   resulting IP addresses, and only backtracks to other branches if the
   higher ordered results did not end in successful connection attempts.

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3.4.  Realm to RADIUS server resolution algorithm

3.4.1.  Input

   For RADIUS Authentication and RADIUS Accounting server discovery,
   input I to the algorithm is the RADIUS User-Name attribute with
   content of the form "user@realm"; the literal @ sign being the
   separator between a local user identifier within a realm and its
   realm.  The use of multiple literal @ signs in a User-Name is
   strongly discouraged; but if present, the last @ sign is to be
   considered the separator.  All previous instances of the @ sign are
   to be considered part of the local user identifier.

   For RADIUS DynAuth Server discovery, input I to the algorithm is the
   domain name of the operator of a RADIUS realm as was communicated
   during user authentication using the Operator-Name attribute
   ([RFC5580], section 4.1).  Only Operator-Name values with the
   namespace "1" are supported by this algorithm - the input to the
   algorithm is the actual domain name, preceeded with an "@" (but
   without the "1" namespace identifier byte of that attribute).

   Note well: The attribute User-Name is defined to contain UTF-8 text.
   In practice, the content may or may not be UTF-8.  Even if UTF-8, it
   may or may not map to a domain name in the realm part.  Implementors
   MUST take possible conversion error paths into consideration when
   parsing incoming User-Name attributes.  This document describes
   server discovery only for well-formed realms mapping to DNS domain
   names in UTF-8 encoding.  The result of all other possible contents
   of User-Name is unspecified; this includes, but is not limited to:

      Usage of separators other than @.

      Encoding of User-Name in local encodings.

      UTF-8 realms which fail the conversion rules as per [RFC5891].

      UTF-8 realms which end with a . ("dot") character.

   For the last bullet point, "trailing dot", special precautions should
   be taken to avoid problems when resolving servers with the algorithm
   below: they may resolve to a RADIUS server even if the peer RADIUS
   server only is configured to handle the realm without the trailing
   dot.  If that RADIUS server again uses NAI discovery to determine the
   authoritative server, the server will forward the request to
   localhost, resulting in a tight endless loop.

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3.4.2.  Output

   Output O of the algorithm is a two-tuple consisting of: O-1) a set of
   tuples {hostname; port; protocol; order/preference; Effective TTL} -
   the set can be empty; and O-2) an integer: if the set in the first
   part of the tuple is empty, the integer contains the Effective TTL
   for backoff timeout, if the set is not empty, the integer is set to 0
   (and not used).

3.4.3.  Algorithm

   The algorithm to determine the RADIUS server to contact is as

   1.   Determine P = (position of last "@" character) in I.

   2.   generate R = (substring from P+1 to end of I)

   3.   modify R according to agreed consortium procedures if applicable

   4.   convert R to a representation usable by the name resolution
        library if needed

   5.   Initialize TIMER = 0; start TIMER.  If TIMER reaches
        DNS_TIMEOUT, continue at step 20.

   6.   Using the host's name resolution library, perform a NAPTR query
        for R (see "Delay considerations" below).  If the result is a
        negative DNS response, O-2 = Effective TTL ( TTL value of the
        SOA record ) and continue at step 13.  If name resolution
        returns with error, O-1 = { empty set }, O-2 = BACKOFF_TIME and

   7.   Extract NAPTR records with service tag "aaa+auth", "aaa+acct",
        "aaa+dynauth" as appropriate.  Keep note of the protocol tag and
        remaining TTL of each of the discovered NAPTR records.

   8.   If no records found, continue at step 13.

   9.   For the extracted NAPTRs, perform successive resolution as
        defined in [RFC3958], section 2.2.  An implementation MAY use
        greedy result evaluation according to the NAPTR order/preference
        fields (i.e. can execute the subsequent steps of this algorithm
        for the highest-order entry in the set of results, and only
        lookup the remainder of the set if necessary).

   10.  If the set of hostnames is empty, O-1 = { empty set }, O-2 =
        BACKOFF_TIME and terminate.

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   11.  O' = (set of {hostname; port; protocol; order/preference;
        Effective TTL ( all DNS TTLs that led to this hostname ) } for
        all terminal lookup results).

   12.  Proceed with step 18.

   13.  Generate R' = (prefix R with "_radiustls._tcp." and/or

   14.  Using the host's name resolution library, perform SRV lookup
        with R' as label (see "Delay considerations" below).

   15.  If name resolution returns with error, O-1 = { empty set }, O-2
        = BACKOFF_TIME and terminate.

   16.  If the result is a negative DNS response, O-1 = { empty set },
        O-2 = min { O-2, Effective TTL ( TTL value of the SOA record ) }
        and terminate.

   17.  O' = (set of {hostname; port; protocol; order/preference;
        Effective TTL ( all DNS TTLs that led to this result ) } for all

   18.  Generate O-1 by resolving hostnames in O' into corresponding A
        and/or AAAA addresses: O-1 = (set of {IP address; port;
        protocol; order/preference; Effective TTL ( all DNS TTLs that
        led to this result ) } for all hostnames ), O-2 = 0.

   19.  For each element in O-1, test if the original request which
        triggered dynamic discovery was received on {IP address; port}.
        If yes, O-1 = { empty set }, O-2 = BACKOFF_TIME, log error,
        Terminate (see next section for a rationale).  If no, O is the
        result of dynamic discovery.  Terminate.

   20.  O-1 = { empty set }, O-2 = BACKOFF_TIME, log error, Terminate.

3.4.4.  Validity of results

   The dynamic discovery algorithm is used by servers which do not have
   sufficient configuration information to process an incoming request
   on their own.  If the discovery algorithm result contains the
   server's own listening address (IP address and port), then there is a
   potential for an endless forwarding loop.  If the listening address
   is the DNS result with the highest priorty, the server will enter a
   tight loop (the server would forward the request to itself,
   triggering dynamic discovery again in a perpetual loop).  If the
   address has a lower priority in the set of results, there is a
   potential loop with intermediate hops in between (the server could

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   forward to another host with a higher priority, which might use DNS
   itself and forward the packet back to the first server).  The
   underlying reason that enables these loops is that the server
   executing the discovery algorithm is seriously misconfigured in that
   it does not recognise the request as one that is to be processed by
   itself.  RADIUS has no built-in loop detection, so any such loops
   would remain undetected.  So, if step 18 of the algorithm discovers
   such a possible-loop situation, the algorithm should be aborted and
   an error logged.  Note that this safeguard does not provide perfect
   protection against routing loops.  One reason which might introduce a
   loop include the possiblity that a subsequent hop has a statically
   configured next-hop which leads to an earlier host in the loop.
   Another reason for occuring loops is if the algorithm was executed
   with greedy result evaluation, and the own address was in a lower-
   priority branch of the result set which was not retrieved from DNS at
   all, and thus can't be detected.

   After executing the above algorithm, the RADIUS server establishes a
   connection to a home server from the result set.  This connection can
   potentially remain open for an indefinite amount of time.  This
   conflicts with the possibility of changing device and network
   configurations on the receiving end.  Typically, TTL values for
   records in the name resolution system are used to indicate how long
   it is safe to rely on the results of the name resolution.  If these
   TTLs are very low, thrashing of connections becomes possible; the
   Effective TTL mitigates that risk.  When a connection is open and the
   smallest of the Effective TTL value which was learned during
   discovering the server has not expired, subsequent new user sessions
   for the realm which corresponds to that open connection SHOULD re-use
   the existing connection and SHOULD NOT re-execute the dynamic
   discovery algorithm nor open a new connection.  To allow for a change
   of configuration, a RADIUS server SHOULD re-execute the dynamic
   discovery algorithm after the Effective TTL that is associated with
   this connection has expired.  The server SHOULD keep the session open
   during this re-assessment to avoid closure and immediate re-opening
   of the connection should the result not have changed.

   Should the algorithm above terminate with O-1 = empty set, the RADIUS
   server SHOULD NOT attempt another execution of this algorithm for the
   same target realm before the timeout O-2 has passed.

3.4.5.  Delay considerations

   The host's name resolution library may need to contact outside
   entities to perform the name resolution (e.g. authoritative name
   servers for a domain), and since the NAI discovery algorithm is based
   on uncontrollable user input, the destination of the lookups is out
   of control of the server that performs NAI discovery.  If such

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   outside entities are misconfigured or unreachable, the algorithm
   above may need an unacceptably long time to terminate.  Many RADIUS
   implementations time out after five seconds of delay between Request
   and Response.  It is not useful to wait until the host name
   resolution library signals a timeout of its name resolution
   algorithms.  The algorithm therefore controls execution time with
   TIMER.  Execution of the NAI discovery algorithm SHOULD be non-
   blocking (i.e. allow other requests to be processed in parallel to
   the execution of the algorithm).

3.4.6.  Example


      a user from the Technical University of Munich, Germany, has a
      RADIUS User-Name of "foobar@tu-m[U+00FC]nchen.example".

      The name resolution library on the RADIUS forwarding server does
      not have the realm tu-m[U+00FC]nchen.example in its forwarding
      configuration, but uses DNS for name resolution and has configured
      the use of Dynamic Discovery to discover RADIUS servers.

      It is IPv6-enabled and prefers AAAA records over A records.

      It is listening for incoming RADIUS/TLS requests on, TCP

   May the configuration variables be

      DNS_TIMEOUT = 3 seconds

      MIN_EFF_TTL = 60 seconds

      BACKOFF_TIME = 3600 seconds

   If DNS contains the following records:

      xn--tu-mnchen-t9a.example.  IN NAPTR 50 50 "s"
      "aaa+auth:radius.tls.tcp" "" _myradius._tcp.xn--tu-mnchen-

      xn--tu-mnchen-t9a.example.  IN NAPTR 50 50 "s"
      "fooservice:bar.dccp" "" _abc123._def.xn--tu-mnchen-t9a.example.

      _myradius._tcp.xn--tu-mnchen-t9a.example.  IN SRV 0 10 2083

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      _myradius._tcp.xn--tu-mnchen-t9a.example.  IN SRV 0 20 2083

      radsecserver.xn--tu-mnchen-t9a.example.  IN AAAA

      radsecserver.xn--tu-mnchen-t9a.example.  IN A

      backupserver.xn--tu-mnchen-t9a.example.  IN A

   Then the algorithm executes as follows, with I =
   "foobar@tu-m[U+00FC]nchen.example", and no consortium name mangling
   in use:

   1.   P = 7

   2.   R = "tu-m[U+00FC]nchen.example"

   3.   NOOP

   4.   name resolution library converts R to xn--tu-mnchen-t9a.example

   5.   TIMER starts.

   6.   Result:

           (TTL = 47) 50 50 "s" "aaa+auth:radius.tls.tcp" ""

           (TTL = 522) 50 50 "s" "fooservice:bar.dccp" ""

   7.   Result:

           (TTL = 47) 50 50 "s" "aaa+auth:radius.tls.tcp" ""

   8.   NOOP

   9.   Successive resolution performs SRV query for label
        _myradius._tcp.xn--tu-mnchen-t9a.example, which results in

           (TTL 499) 0 10 2083 radsec.xn--tu-mnchen-t9a.example.

           (TTL 2200) 0 20 2083 backup.xn--tu-mnchen-t9a.example.

   10.  NOOP

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   11.  O' = {

           (radsec.xn--tu-mnchen-t9a.example.; 2083; RADIUS/TLS; 10;

           (backup.xn--tu-mnchen-t9a.example.; 2083; RADIUS/TLS; 20; 60)

        } // minimum TTL is 47, up'ed to MIN_EFF_TTL

   12.  Continuing at 18.

   13.  (not executed)

   14.  (not executed)

   15.  (not executed)

   16.  (not executed)

   17.  (not executed)

   18.  O-1 = {

           (2001:0DB8::202:44ff:fe0a:f704; 2083; RADIUS/TLS; 10; 60),

           (; 2083; RADIUS/TLS; 20; 60)

        }; O-2 = 0

   19.  No match with own listening address; terminate with tuple (O-1,
        O-2) from previous step.

   The implementation will then attempt to connect to two servers, with
   preference to [2001:0DB8::202:44ff:fe0a:f704]:2083 using the RADIUS/
   TLS protocol.

4.  Operations and Manageability Considerations

   The discovery algorithm as defined in this document contains several
   options; the major ones being use of NAPTR vs. SRV; how to determine
   the authorization status of a contacted server for a given realm;
   which trust anchors to consider trustworthy for the RADIUS
   conversation setup.

   Random parties which do not agree on the same set of options may not
   be able to interoperate.  However, such a global interoperability is
   not intended by this document.

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   Discovery as per this document becomes important inside a roaming
   consortium, which has set up roaming agreements with the other
   partners.  Such roaming agreements require much more than a technical
   means of server discovery; there are administrative and contractual
   considerations at play (service contracts, backoffice compensations,
   procedures, ...).

   A roaming consortium's roaming agreement must include a profile of
   which choice points of this document to use.  So long as the roaming
   consortium can settle on one deployment profile, they will be able to
   interoperate based on that choice; this per-consortium
   interoperability is the intended scope of this document.

5.  Security Considerations

   When using DNS without DNSSEC security extensions and validation for
   all of the replies to NAPTR, SRV and A/AAAA requests as described in
   section Section 3, the result of the discovery process can not be
   trusted.  Even if it can be trusted (i.e. DNSSEC is in use), actual
   authorization of the discovered server to provide service for the
   given realm needs to be verified.  A mechanism from section
   Section or equivalent MUST be used to verify authorization.

   The algorithm has a configurable completion timeout DNS_TIMEOUT
   defaulting to three seconds for RADIUS' operational reasons.  The
   lookup of DNS resource records based on unverified user input is an
   attack vector for DoS attacks: an attacker might intentionally craft
   bogus DNS zones which take a very long time to reply (e.g. due to a
   particularly byzantine tree structure, or artificial delays in

   To mitigate this DoS vector, implementations SHOULD consider rate-
   limiting either their amount of new executions of the dynamic
   discovery algorithm as a whole, or the amount of intermediate
   responses to track, or at least the number of pending DNS queries.
   Implementations MAY choose lower values than the default for
   DNS_TIMEOUT to limit the impact of DoS attacks via that vector.  They
   MAY also continue their attempt to resolve DNS records even after
   DNS_TIMEOUT has passed; a subsequent request for the same realm might
   benefit from retrieving the results anyway.  The amount of time to
   spent waiting for a result will influence the impact of a possible
   DoS attack; the waiting time value is implementation dependent and
   outside the scope of this specification.

   With Dynamic Discovery being enabled for a RADIUS Server, and
   depending on the deployment scenario, the server may need to open up
   its target IP address and port for the entire internet, because
   arbitrary clients may discover it as a target for their

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   authentication requests.  If such clients are not part of the roaming
   consortium, the RADIUS/TLS connection setup phase will fail (which is
   intended) but the computational cost for the connection attempt is
   significant.  With the port for a TLS-based service open, the RADIUS
   server shares all the typical attack vectors for services based on
   TLS (such as HTTPS, SMTPS, ...).  Deployments of RADIUS/TLS with
   Dynamic Discovery should consider these attack vectors and take
   appropriate counter-measures (e.g. blacklisting known-bad IPs on a
   firewall, rate-limiting new connection attempts, etc.).

6.  Privacy Considerations

   The classic RADIUS operational model (known, pre-configured peers,
   shared secret security, mostly plaintext communication) and this new
   RADIUS dynamic discovery model (peer discovery with DNS, PKI security
   and packet confidentiality) differ significantly in their impact on
   the privacy of end users trying to authenticate to a RADIUS server.

   With classic RADIUS, traffic in large environments gets aggregated by
   statically configured clearinghouses.  The packets sent to those
   clearinghouses and their responses are mostly unprotected.  As a

   o  All intermediate IP hops can inspect most of the packet payload in
      clear text, including the User-Name and Calling-Station-Id
      attributes, and can observe which client sent the packet to which
      clearinghouse.  This allows the creation of mobility profiles for
      any passive observer on the IP path.

   o  The existence of a central clearinghouse creates an opportunity
      for the clearinghouse to trivially create the same mobility
      profiles.  The clearinghouse may or may not be trusted not to do
      this, e.g. by sufficiently threatening contractual obligations.

   o  In addition to that, with the clearinghouse being a RADIUS
      intermediate in possession of a valid shared secret, the
      clearinghouse can observe and record even the security-critical
      RADIUS attributes such as User-Password.  This risk may be
      mitigated by choosing authentication payloads which are
      cryptographically secured and do not use the attribute User-
      Password - such as certain EAP types.

   o  There is no additional information disclosure to parties outside
      the IP path between the RADIUS client and server (in particular,
      no DNS servers learn about realms of current ongoing

   With RADIUS and dynamic discovery,

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   o  This protocol allows for RADIUS clients to identify and directly
      connect to the RADIUS home server.  This can eliminate the use of
      clearinghouses to do forwarding of requests, and it also
      eliminates the ability of the clearinghouse to then aggregate the
      user information that flows through it.  However, there exist
      reasons why clearinghouses might still be used.  One reason to
      keep a clearinghouse is to act as a gateway for multiple backends
      in a company; another reason may be a requirement to sanitise
      RADIUS datagrams (filter attributes, tag requests with new
      attributes, ... ).

   o  Even where intermediate proxies continue to be used for reasons
      unrelated to dynamic discovery, the number of such intermediates
      may be reduced by removing those proxies which are only deployed
      for pure request routing reasons.  This reduces the number of
      entities which can inspect the RADIUS traffic.

   o  RADIUS clients which make use of dynamic discovery will need to
      query the Domain Name System, and use a user's realm name as the
      query label.  A passive observer on the IP path between the RADIUS
      client and the DNS server(s) being queried can learn that a user
      of that specific realm was trying to authenticate at that RADIUS
      client at a certain point in time.  This may or may not be
      sufficient for the passive observer to create a mobility profile.
      During the recursive DNS resolution, a fair number of DNS servers
      and the IP hops in between those get to learn that information.
      Not every single authentication triggers DNS lookups, so there is
      no one-to-one relation of leaked realm information and the number
      of authentications for that realm.

   o  Since dynamic discovery operates on a RADIUS hop-by-hop basis,
      there is no guarantee that the RADIUS payload is not transmitted
      between RADIUS systems which do not make use of this algorithm,
      and possibly using other transports such as RADIUS/UDP.  On such
      hops, the enhanced privacy is jeopardized.

   In summary, with classic RADIUS, few intermediate entities learn very
   detailed data about every ongoing authentications, while with dynamic
   discovery, many entities learn only very little about recently
   authenticated realms.

7.  IANA Considerations

   This document requests IANA registration of the following entries in
   existing registries:

   o  S-NAPTR Application Service Tags registry

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      *  aaa+auth

      *  aaa+acct

      *  aaa+dynauth

   o  S-NAPTR Application Protocol Tags registry

      *  radius.tls.tcp

      *  radius.dtls.udp

   This document reserves the use of the "radiustls" and "radiusdtls"
   service names.  Registration information as per [RFC6335] section
   8.1.1 is as follows:

      Service Name: radiustls; radiusdtls

      Transport Protocols: TCP (for radiustls), UDP (for radiusdtls)

      Assignee: IESG <iesg@ietf.org>

      Contact: IETF Chair <chair@ietf.org>

      Description: Authentication, Accounting and Dynamic authorization
      via the RADIUS protocol.  These service names are used to
      construct the SRV service labels "_radiustls" and "_radiusdtls"
      for discovery of RADIUS/TLS and RADIUS/DTLS servers, respectively.

      Reference: RFC Editor Note: please insert the RFC number of this
      document.  The protocol does not use broadcast, multicast or
      anycast communication.

   This specification makes use of the SRV Protocol identifiers "_tcp"
   and "_udp" which are mentioned as early as [RFC2782] but do not
   appear to be assigned in an actual registry.  Since they are in wide-
   spread use in other protocols, this specification refrains from
   requesting a new registry "RADIUS/TLS SRV Protocol Registry" and
   continues to make use of these tags implicitly.

   This document requires that a number of Object Identifiers be
   assigned.  They are now under the control of IANA following [RFC7299]

   IANA is requested to assign the following identifiers:

      TBD99 is to be assigned from the "SMI Security for PKIX Module
      Identifier Registry".  The suggested description is id-mod-nai-

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      TBD98 is to be assigned from the "SMI Security for PKIX Other Name
      Forms Registry."  The suggested description is id-on-naiRealm.

   RFC Editor Note: please replace the occurences of TBD98 and TBD99 in
   Appendix A of the document with the actually assigned numbers.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              February 2000.

   [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.

   [RFC3958]  Daigle, L. and A. Newton, "Domain-Based Application
              Service Location Using SRV RRs and the Dynamic Delegation
              Discovery Service (DDDS)", RFC 3958, January 2005.

   [RFC5176]  Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
              Aboba, "Dynamic Authorization Extensions to Remote
              Authentication Dial In User Service (RADIUS)", RFC 5176,
              January 2008.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5580]  Tschofenig, H., Adrangi, F., Jones, M., Lior, A., and B.
              Aboba, "Carrying Location Objects in RADIUS and Diameter",
              RFC 5580, August 2009.

   [RFC5891]  Klensin, J., "Internationalized Domain Names in
              Applications (IDNA): Protocol", RFC 5891, August 2010.

   [RFC6614]  Winter, S., McCauley, M., Venaas, S., and K. Wierenga,
              "Transport Layer Security (TLS) Encryption for RADIUS",
              RFC 6614, May 2012.

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   [RFC7360]  DeKok, A., "Datagram Transport Layer Security (DTLS) as a
              Transport Layer for RADIUS", RFC 7360, September 2014.

              DeKok, A., "The Network Access Identifier", draft-ietf-
              radext-nai-15 (work in progress), December 2014.

8.2.  Informative References

   [RFC4017]  Stanley, D., Walker, J., and B. Aboba, "Extensible
              Authentication Protocol (EAP) Method Requirements for
              Wireless LANs", RFC 4017, March 2005.

   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165, RFC
              6335, August 2011.

   [RFC6733]  Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
              "Diameter Base Protocol", RFC 6733, October 2012.

   [RFC7299]  Housley, R., "Object Identifier Registry for the PKIX
              Working Group", RFC 7299, July 2014.

              Wierenga, K., Winter, S., and T. Wolniewicz, "The eduroam
              architecture for network roaming", draft-wierenga-ietf-
              eduroam-05 (work in progress), March 2015.

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Appendix A.  Appendix A: ASN.1 Syntax of NAIRealm

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PKIXNaiRealm08 {iso(1) identified-organization(3) dod(6)
     internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
     id-mod-nai-realm-08 (TBD99) }





    FROM PKIX1Explicit-2009
        {iso(1) identified-organization(3) dod(6) internet(1)
         security(5) mechanisms(5) pkix(7) id-mod(0)
           -- from RFC 5280, RFC 5912

    FROM PKIX1Implicit-2009
       {iso(1) identified-organization(3) dod(6) internet(1) security(5)
       mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-implicit-02(59)}
             -- from RFC 5280, RFC 5912

 -- Service Name Object Identifier

 id-on   OBJECT IDENTIFIER ::= { id-pkix 8 }

 id-on-naiRealm OBJECT IDENTIFIER ::= { id-on TBD98 }

 -- Service Name

 naiRealm OTHER-NAME ::= { NAIRealm IDENTIFIED BY { id-on-naiRealm }}

 ub-naiRealm-length INTEGER ::= 255

 NAIRealm ::= UTF8String (SIZE (1..ub-naiRealm-length))


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Authors' Addresses

   Stefan Winter
   Fondation RESTENA
   6, rue Richard Coudenhove-Kalergi
   Luxembourg  1359

   Phone: +352 424409 1
   Fax:   +352 422473
   EMail: stefan.winter@restena.lu
   URI:   http://www.restena.lu.

   Mike McCauley
   AirSpayce Pty Ltd
   9 Bulbul Place
   Currumbin Waters  QLD 4223

   Phone: +61 7 5598 7474
   EMail: mikem@airspayce.com
   URI:   http://www.airspayce.com

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