One document matched: draft-ietf-radext-dynamic-discovery-03.xml
<?xml version = '1.0'?>
<?rfc rfcedstyle='yes'?>
<?rfc rfcprocack='yes'?>
<?rfc toc='yes'?>
<?rfc symrefs='yes'?>
<!DOCTYPE rfc SYSTEM "../xml2rfc-1.36pre1-dev/rfc2629.dtd" [
<!ENTITY rfc2119 PUBLIC '' '../rfc-bib/reference.RFC.2119.xml'>
<!ENTITY rfc3958 PUBLIC '' '../rfc-bib/reference.RFC.3958.xml'>
<!ENTITY rfc5891 PUBLIC '' '../rfc-bib/reference.RFC.5891.xml'>
<!--ENTITY rfc4282 PUBLIC '' '../rfc-bib/reference.RFC.4282.xml'> -->
<!ENTITY radius-dtls PUBLIC '' '../i-d-bib/reference.I-D.draft-dekok-radext-dtls-03.xml'>
<!ENTITY radius-tls PUBLIC '' '../i-d-bib/reference.I-D.draft-ietf-radext-radsec-09.xml'>
]>
<rfc ipr='trust200902' docName='draft-ietf-radext-dynamic-discovery-03'
category='exp'>
<front>
<title abbrev="RADIUS Peer Discovery" >NAI-based Dynamic Peer
Discovery for RADIUS/TLS and RADIUS/DTLS</title>
<author fullname="Stefan Winter" initials="S." surname="Winter" >
<organization abbrev="RESTENA" >
Fondation RESTENA
</organization>
<address>
<postal>
<street>6, rue Richard Coudenhove-Kalergi</street>
<city>Luxembourg</city>
<code>1359</code>
<country>LUXEMBOURG</country>
</postal>
<phone>+352 424409 1</phone>
<facsimile>+352 422473</facsimile>
<email>stefan.winter@restena.lu</email>
<uri>http://www.restena.lu.</uri>
</address>
</author>
<author fullname="Mike McCauley" initials="M." surname="McCauley" >
<organization abbrev="OSC" >
Open Systems Consultants
</organization>
<address>
<postal>
<street>9 Bulbul Place</street>
<city>Currumbin Waters</city>
<code>QLD 4223</code>
<country>AUSTRALIA</country>
</postal>
<phone>+61 7 5598 7474</phone>
<facsimile>+61 7 5598 7070</facsimile>
<email>mikem@open.com.au</email>
<uri>http://www.open.com.au.</uri>
</address>
</author>
<date day="09" month="July" year="2011" />
<area>Operations and Management Area</area>
<workgroup>RADIUS Extensions Working Group</workgroup>
<keyword>RADIUS</keyword>
<keyword>AAA</keyword>
<keyword>Security</keyword>
<keyword>Reliability</keyword>
<keyword>DNS</keyword>
<abstract>
<t>This document specifies a means to find authoritative RADIUS servers
for a given realm. It can be used in conjunction with RADIUS/TLS and
RADIUS/DTLS.</t>
</abstract>
</front>
<middle>
<section title="Introduction" anchor="intro">
<section title="Requirements Language" anchor="reqlang">
<t>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.
<xref target="RFC2119" /></t>
</section>
<section title="Terminology" anchor="terms">
<t>RADIUS/TLS Client: a RADIUS/TLS <xref target="I-D.ietf-radext-radsec" />
instance which initiates a new connection.</t>
<t>RADIUS/TLS Server: a RADIUS/TLS <xref target="I-D.ietf-radext-radsec" />
instance which listens on a RADIUS/TLS port and accepts new connections</t>
<t>RADIUS/TLS node: a RADIUS/TLS client or server</t>
</section>
</section>
<section title="DNS-based NAPTR/SRV Peer Discovery" anchor="dns">
<section title="Applicability" anchor="applicability">
<t>
Dynamic server discovery as defined in this document is only
applicable for AAA transactions where a RADIUS server receives a request with a
realm for which no home RADIUS server is known. I.e. where static server
configuration does not contain a known home authentication server, or where the
server configuration explicitly states that the realm destination is to be
looked up dynamically. Furthermore, it is only applicable for 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.
</t>
</section>
<section title="DNS RR definition" anchor="rr-def">
<t>
DNS definitions of RADIUS/TLS servers can be either S-NAPTR
records (see <xref target="RFC3958" />) or SRV records. When both are defined, the resolution algorithm prefers
S-NAPTR results (see section <xref target="algo" /> below). </t>
<t>This specification defines three S-NAPTR service
tags: "aaa+auth", "aaa+acct" and "aaa+dynauth". This specification defines two S-NAPTR protocol tags: "radius.tls" for RADIUS/TLS <xref target="I-D.ietf-radext-radsec" /> and "radius.dtls" for RADIUS/DTLS
<xref target="I-D.dekok-radext-dtls" />.</t>
<t>This specification defines the SRV prefix "_radiustls._tcp" for RADIUS over TLS <xref target="I-D.ietf-radext-radsec" />
and "_radiustls._udp" for RADIUS over DTLS <xref target="I-D.dekok-radext-dtls" />. It is
expected that in most cases, the label used for the records is the DNS
representation (punycode) of the literal realm name for which the server is the
AAA server.</t>
<t>
However, arbitrary other labels 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.
</t>
<t>Examples:
<list style="letters">
<t>A general-purpose AAA server for realm
example.com might have DNS entries as follows:
<list style="empty">
<t>example.com. IN NAPTR 50 50 "s"
"aaa+auth:radius.tls" "" _radiustls._tcp.foobar.example.com.</t>
<t>_radiustls._tcp.foobar.example.com. IN SRV 0 10
2083 radsec.example.com.</t>
</list>
</t>
<t>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 AAA servers use to resolve realm names. "Bad, Inc." is
part of the consortium. On the consortium's DNS server, realm
bad.example might have the following DNS entries:
<list style="empty">
<t>bad.example IN NAPTR 50
50 "a" "aaa+auth:radius.dtls" "" "very.bad.example"</t>
</list>
</t>
<t>The eduroam consortium 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 AAA servers). Due to that,
the eduroam consortium uses the service tag "x-eduroam" for authentication purposes and eduroam AAA
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:
<list style="empty">
<t>example.org. IN NAPTR 50 50 "s" "x-eduroam:radius.tls" "" _radiustls._tcp.eduroam.example.org.</t>
<t>example.org. IN NAPTR 50 50 "s" "aaa+auth:radius.tls" "" _radiustls._tcp.aaa.example.org</t>
<t>_radiustls._tcp.eduroam.example.org. IN SRV 0 10 2083 aaa-eduroam.example.org.</t>
<t>_radiustls._tcp.aaa.example.org. IN SRV 0 10 2083 aaa-default.example.org.</t>
</list>
</t>
</list>
</t>
</section>
<section title="Realm to AAA server resolution algorithm" anchor="algo">
<t>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.
Output O of the algorithm is a set of hostname:port and an
associated order/preference; the set can be empty.</t>
<t>
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:
<list>
<t>Usage of separators other than @</t>
<t>Usage of multiple @ separators</t>
<t>Encoding of User-Name in local encodings</t>
<t>UTF-8 realms which fail the conversion rules as per <xref target="RFC5891"/></t>
</list>
</t>
<t>The algorithm to determine the RADIUS server to contact is as follows:
<list style="numbers">
<t>Determine P = (position of last "@" character) in I.</t>
<t>generate R = (substring from P+1 to end of I)</t>
<t>Optional: modify R according to agreed consortium procedures</t>
<t>Using the host's name resolution library, perform a NAPTR query for R. The name resolution library may need to convert R to a different respresentation, depending on the resolution backend used. If no result, continue at step 9. If name resolution returns with error, O = { }. Terminate.</t>
<t>Extract NAPTR records with service tag "aaa+auth", "aaa+acct", "aaa+dynauth" as appropriate.</t>
<t>If no result, continue at step 9.</t>
<t>Evaluate NAPTR result(s) for desired protocol tag, perform subsequent lookup
steps until lookup yields one or more hostnames. O = (set of {Order/Preference,
hostname:port} for all lookup results).</t>
<t>Terminate.</t>
<t>Generate R' = (prefix R with "_radiustls._tcp." or "_radiustls._udp")</t>
<t>Using the host's name resolution library, perform
SRV lookup with R' as label.</t>
<t>If name resolution returns with error, O = { }.
Terminate.</t>
<t>If no result, O = {}; terminate.</t>
<t>Perform subsequent lookup steps until lookup
yields one or more hostnames. O = (set of {Order/Preference, hostname} for all
hostnames). Terminate.</t>
</list>
</t>
<t>
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 client uses DNS for name resolution. If DNS
contains the following records:
<list style="empty">
<t>xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s"
"aaa+auth:radius.tls" "" _radiustls._tcp.xn--tu-mnchen-t9a.example.</t>
<t>xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s"
"fooservice:bar.dccp" "" _abc._def.xn--tu-mnchen-t9a.example.</t>
<t>_radiustls._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 10 2083
radsec.xn--tu-mnchen-t9a.example.</t>
<t>_radiustls._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 20 2083
backup.xn--tu-mnchen-t9a.example.</t>
<t>radsec.xn--tu-mnchen-t9a.example. IN AAAA
2001:0DB8::202:44ff:fe0a:f704</t>
<t>radsec.xn--tu-mnchen-t9a.example. IN A 192.0.2.3</t>
<t>backup.xn--tu-mnchen-t9a.example. IN A 192.0.2.7</t>
</list>
Then the algorithm executes as follows, with I =
"foobar@tu-m[U+00FC]nchen.example", and no consortium name mangling in use:
<list style="numbers">
<t>P = 7</t>
<t>R = "tu-m[U+00FC]nchen.example"</t>
<t>NOOP</t>
<t>[name resolution library converts R to xn--tu-mnchen-t9a.example] Query result: ( 50 50 "s" "aaa+auth:radius.tls" "" _radiustls._tcp.xn--tu-mnchen-t9a.example. ; 50 50 "s"
"fooservice:bar.dccp" "" _abc._def.xn--tu-mnchen-t9a.example. )</t>
<t>Result: 50 50 "s" "aaa+auth:radius.tls" "" _radiustls._tcp.xn--tu-mnchen-t9a.example.</t>
<t>NOOP</t>
<t>O =
{(10,radsec.xn--tu-mnchen-t9a.example.:2083),(20,backup.xn--tu-mnchen-t9a.
example.:2083)}</t>
<t>Terminate.</t>
<t>(not executed)</t>
<t>(not executed)</t>
<t>(not executed)</t>
<t>(not executed)</t>
<t>(not executed)</t>
</list>
The implementation will then attempt to connect to two
servers, with preference to radsec.xn--tu-mnchen-t9a.example.:2083, using either
the AAAA or A addresses depending on the host configuration and its IP stack's
capabilities.</t>
</section>
</section>
<section title="Security Considerations" anchor="sec">
<t>
When using DNS without DNSSEC security extensions, the replies to NAPTR, SRV and
A/AAAA requests as described in section <xref target="dns" /> can not be
trusted. RADIUS transports have an out-of-DNS-band means to verify that the
discovery attempt led to the intended target: certificate verification
or TLS-PSK keys.
</t>
</section>
<section title="IANA Considerations" anchor="iana">
<t>
This document requests IANA registration of the following S-NAPTR parameter:
<list style="symbols">
<t>Application Service Tags
<list style="symbols">
<t>aaa+auth</t>
<t>aaa+acct</t>
<t>aaa+dynauth</t>
</list>
</t>
<t>Application Protocol Tags
<list style="symbols">
<t>radius.tls</t>
<t>radius.dtls</t>
</list>
</t>
</list>
</t>
</section>
</middle>
<back>
<references title="Normative References">
&rfc2119;
&rfc3958;
<!-- &rfc4282; -->
&rfc5891;
&radius-dtls;
&radius-tls;
</references>
<!-- <references title="Informative References">
<reference anchor="radiator-manual"
target="http://www.open.com.au/radiator/ref.html">
<front>
<title>Radiator Radius Server - Installation and
Reference Manual</title>
<author>
<organization abbrev="OSC">Open System
Consultants</organization>
</author>
<date year="2006"/>
</front>
<format type="TXT"
target="http://www.open.com.au/radiator/ref.html"/>
</reference>
</references> -->
</back>
</rfc>
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