RADIUS Extensions Working Group                                S. WinterInternet-Draft                                                   RESTENAIntended status: Experimental                                M. McCauleyExpires: November 1, 2015                                      AirSpayce                                                          April 30, 2015    NAI-based Dynamic Peer Discovery for RADIUS/TLS and RADIUS/DTLS                 draft-ietf-radext-dynamic-discovery-15Abstract   This document specifies a means to find authoritative RADIUS servers   for a given realm.  It is used in conjunction with either RADIUS/TLS   and RADIUS/DTLS.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.Winter & McCauley       Expires November 1, 2015                [Page 1]Internet-Draft            RADIUS Peer Discovery               April 2015Table 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 . . . . . . . .  301.  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 detailsWinter & McCauley       Expires November 1, 2015                [Page 2]Internet-Draft            RADIUS Peer Discovery               April 2015   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.Winter & McCauley       Expires November 1, 2015                [Page 3]Internet-Draft            RADIUS Peer Discovery               April 2015                                    +-------+                                    |       |                                    |   .   |                                    |       |                                    +---+---+                                      / | \                    +----------------/  |  \---------------------+                    |                   |                        |                    |                   |                        |                    |                   |                        |                 +--+---+            +--+--+                +----+---+                 |      |            |     |                |        |                 | .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:Winter & McCauley       Expires November 1, 2015                [Page 4]Internet-Draft            RADIUS Peer Discovery               April 2015                                    ---------                                   /         \                          ---------           ------------                         /                                \                         |    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",   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",   and "OPTIONAL" in this document are to be interpreted as described in   RFC 2119.  [RFC2119]Winter & McCauley       Expires November 1, 2015                [Page 5]Internet-Draft            RADIUS Peer Discovery               April 20151.2.  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 lookupsWinter & McCauley       Expires November 1, 2015                [Page 6]Internet-Draft            RADIUS Peer Discovery               April 20152.  Definitions2.1.  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-NAPTR2.1.1.1.  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:Winter & McCauley       Expires November 1, 2015                [Page 7]Internet-Draft            RADIUS Peer Discovery               April 2015      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      resolver.      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.2.1.1.2.  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 (seeWinter & McCauley       Expires November 1, 2015                [Page 8]Internet-Draft            RADIUS Peer Discovery               April 2015   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.2.1.1.3.  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.2.1.1.3.1.  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 belowWinter & McCauley       Expires November 1, 2015                [Page 9]Internet-Draft            RADIUS Peer Discovery               April 2015   (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 2.2.2.1.1.3.2.  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   member.   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).2.1.1.3.3.  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 serverWinter & McCauley       Expires November 1, 2015               [Page 10]Internet-Draft            RADIUS Peer Discovery               April 2015   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.   Example:      Realm = "example.com"      Common Branch = "idp.roaming-consortium.example.      label for TLSA query = "example.com.idp.roaming-      consortium.example.      result of discovery algorithm for realm "example.com" =      192.0.2.1:2083      ( TLS certificate of 192.0.2.1:2083 matches TLSA RR ? "PASS" :      "FAIL" )2.1.1.3.4.  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]):Winter & McCauley       Expires November 1, 2015               [Page 11]Internet-Draft            RADIUS Peer Discovery               April 2015   +-------------------+-----------------------------------------+   | 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 2.1.1.2 and Section 2.1.1.3 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   [RFC5891]).   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.   Examples:   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.          _radiustls._tcp.foobar.example.com.  IN SRV 0 10 2083          radsec.example.com.Winter & McCauley       Expires November 1, 2015               [Page 12]Internet-Draft            RADIUS Peer Discovery               April 2015   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" ""          _radiustls._tcp.eduroam.example.org.          example.org.  IN NAPTR 50 50 "s" "aaa+auth:radius.tls.tcp" ""          _radiustls._tcp.aaa.example.org.          _radiustls._tcp.eduroam.example.org.  IN SRV 0 10 2083 aaa-          eduroam.example.org.          _radiustls._tcp.aaa.example.org.  IN SRV 0 10 2083 aaa-          default.example.org.2.2.  Definition of the X.509 certificate property      SubjectAltName:otherName:NAIRealm   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   process.   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 beWinter & McCauley       Expires November 1, 2015               [Page 13]Internet-Draft            RADIUS Peer Discovery               April 2015   able to express that it is authorized to handle requests for that   realm.   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 theWinter & McCauley       Expires November 1, 2015               [Page 14]Internet-Draft            RADIUS Peer Discovery               April 2015   sAN:otherName:NAIRealm values matches the NAI realm, the server is   considered authorized; if none matches, the server is considered   unauthorized.   Since multiple names and multiple name forms may occur in the   subjectAltName extension, an arbitrary number of NAIRealms can be   specified in a certificate.   Examples:   +---------------------+-------------------+-----------------------+   | 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 Discovery3.1.  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.Winter & McCauley       Expires November 1, 2015               [Page 15]Internet-Draft            RADIUS Peer Discovery               April 20153.2.  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      seconds      BACKOFF_TIME: if no conclusive DNS response was retrieved after      DNS_TIMEOUT, do not attempt dynamic discovery before BACKOFF_TIME      has elapsed.  Default = 600 seconds3.3.  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"   clause.   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.Winter & McCauley       Expires November 1, 2015               [Page 16]Internet-Draft            RADIUS Peer Discovery               April 20153.4.  Realm to RADIUS server resolution algorithm3.4.1.  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.Winter & McCauley       Expires November 1, 2015               [Page 17]Internet-Draft            RADIUS Peer Discovery               April 20153.4.2.  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   follows:   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        terminate.   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.Winter & McCauley       Expires November 1, 2015               [Page 18]Internet-Draft            RADIUS Peer Discovery               April 2015   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        "_radiustls._udp.")   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        hostnames).   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 couldWinter & McCauley       Expires November 1, 2015               [Page 19]Internet-Draft            RADIUS Peer Discovery               April 2015   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 suchWinter & McCauley       Expires November 1, 2015               [Page 20]Internet-Draft            RADIUS Peer Discovery               April 2015   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   Assume      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 192.0.2.1, TCP      /2083.   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-      t9a.example.      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      radsecserver.xn--tu-mnchen-t9a.example.Winter & McCauley       Expires November 1, 2015               [Page 21]Internet-Draft            RADIUS Peer Discovery               April 2015      _myradius._tcp.xn--tu-mnchen-t9a.example.  IN SRV 0 20 2083      backupserver.xn--tu-mnchen-t9a.example.      radsecserver.xn--tu-mnchen-t9a.example.  IN AAAA      2001:0DB8::202:44ff:fe0a:f704      radsecserver.xn--tu-mnchen-t9a.example.  IN A 192.0.2.3      backupserver.xn--tu-mnchen-t9a.example.  IN A 192.0.2.7   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" ""           _myradius._tcp.xn--tu-mnchen-t9a.example.           (TTL = 522) 50 50 "s" "fooservice:bar.dccp" ""           _abc123._def.xn--tu-mnchen-t9a.example.   7.   Result:           (TTL = 47) 50 50 "s" "aaa+auth:radius.tls.tcp" ""           _myradius._tcp.xn--tu-mnchen-t9a.example.   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.  NOOPWinter & McCauley       Expires November 1, 2015               [Page 22]Internet-Draft            RADIUS Peer Discovery               April 2015   11.  O' = {           (radsec.xn--tu-mnchen-t9a.example.; 2083; RADIUS/TLS; 10;           60),           (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),           (192.0.2.7; 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.Winter & McCauley       Expires November 1, 2015               [Page 23]Internet-Draft            RADIUS Peer Discovery               April 2015   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 2.1.1.3 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   responses).   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 theirWinter & McCauley       Expires November 1, 2015               [Page 24]Internet-Draft            RADIUS Peer Discovery               April 2015   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   consequence,   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      authentications).   With RADIUS and dynamic discovery,Winter & McCauley       Expires November 1, 2015               [Page 25]Internet-Draft            RADIUS Peer Discovery               April 2015   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 registryWinter & McCauley       Expires November 1, 2015               [Page 26]Internet-Draft            RADIUS Peer Discovery               April 2015      *  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-      realm-08.Winter & McCauley       Expires November 1, 2015               [Page 27]Internet-Draft            RADIUS Peer Discovery               April 2015      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.  References8.1.  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.Winter & McCauley       Expires November 1, 2015               [Page 28]Internet-Draft            RADIUS Peer Discovery               April 2015   [RFC7360]  DeKok, A., "Datagram Transport Layer Security (DTLS) as a              Transport Layer for RADIUS", RFC 7360, September 2014.   [I-D.ietf-radext-nai]              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.   [I-D.wierenga-ietf-eduroam]              Wierenga, K., Winter, S., and T. Wolniewicz, "The eduroam              architecture for network roaming", draft-wierenga-ietf-              eduroam-05 (work in progress), March 2015.Winter & McCauley       Expires November 1, 2015               [Page 29]Internet-Draft            RADIUS Peer Discovery               April 2015Appendix A.  Appendix A: ASN.1 Syntax of NAIRealmWinter & McCauley       Expires November 1, 2015               [Page 30]Internet-Draft            RADIUS Peer Discovery               April 2015PKIXNaiRealm08 {iso(1) identified-organization(3) dod(6)     internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)     id-mod-nai-realm-08 (TBD99) } DEFINITIONS EXPLICIT TAGS ::= BEGIN -- EXPORTS ALL -- IMPORTS    id-pkix    FROM PKIX1Explicit-2009        {iso(1) identified-organization(3) dod(6) internet(1)         security(5) mechanisms(5) pkix(7) id-mod(0)         id-mod-pkix1-explicit-02(51)}           -- from RFC 5280, RFC 5912    OTHER-NAME    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)) ENDWinter & McCauley       Expires November 1, 2015               [Page 31]Internet-Draft            RADIUS Peer Discovery               April 2015Authors' Addresses   Stefan Winter   Fondation RESTENA   6, rue Richard Coudenhove-Kalergi   Luxembourg  1359   LUXEMBOURG   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   AUSTRALIA   Phone: +61 7 5598 7474   EMail: mikem@airspayce.com   URI:   http://www.airspayce.comWinter & McCauley       Expires November 1, 2015               [Page 32]