One document matched: draft-ietf-radext-dynamic-discovery-03.txt
Differences from draft-ietf-radext-dynamic-discovery-02.txt
RADIUS Extensions Working Group S. Winter
Internet-Draft RESTENA
Intended status: Experimental M. McCauley
Expires: January 10, 2012 OSC
July 09, 2011
NAI-based Dynamic Peer Discovery for RADIUS/TLS and RADIUS/DTLS
draft-ietf-radext-dynamic-discovery-03
Abstract
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.
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 January 10, 2012.
Copyright Notice
Copyright (c) 2011 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
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carefully, as they describe your rights and restrictions with respect
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. DNS-based NAPTR/SRV Peer Discovery . . . . . . . . . . . . . . 3
2.1. Applicability . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. DNS RR definition . . . . . . . . . . . . . . . . . . . . . 3
2.3. Realm to AAA server resolution algorithm . . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
5. Normative References . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
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]
1.2. Terminology
RADIUS/TLS Client: a RADIUS/TLS [I-D.ietf-radext-radsec] instance
which initiates a new connection.
RADIUS/TLS Server: a RADIUS/TLS [I-D.ietf-radext-radsec] instance
which listens on a RADIUS/TLS port and accepts new connections
RADIUS/TLS node: a RADIUS/TLS client or server
2. DNS-based NAPTR/SRV Peer Discovery
2.1. Applicability
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.
2.2. DNS RR definition
DNS definitions of RADIUS/TLS servers can be either S-NAPTR records
(see [RFC3958]) or SRV records. When both are defined, the
resolution algorithm prefers S-NAPTR results (see section Section 2.3
below).
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 [I-D.ietf-radext-radsec]
and "radius.dtls" for RADIUS/DTLS [I-D.dekok-radext-dtls].
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This specification defines the SRV prefix "_radiustls._tcp" for
RADIUS over TLS [I-D.ietf-radext-radsec] and "_radiustls._udp" for
RADIUS over DTLS [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.
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.
Examples:
a. A general-purpose AAA server for realm example.com might have DNS
entries as follows:
example.com. IN NAPTR 50 50 "s" "aaa+auth:radius.tls" ""
_radiustls._tcp.foobar.example.com.
_radiustls._tcp.foobar.example.com. IN SRV 0 10 2083
radsec.example.com.
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 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:
bad.example IN NAPTR 50 50 "a" "aaa+auth:radius.dtls" ""
"very.bad.example"
c. 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:
example.org. IN NAPTR 50 50 "s" "x-eduroam:radius.tls" ""
_radiustls._tcp.eduroam.example.org.
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example.org. IN NAPTR 50 50 "s" "aaa+auth:radius.tls" ""
_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.
2.3. Realm to AAA server resolution algorithm
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.
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 @
Usage of multiple @ separators
Encoding of User-Name in local encodings
UTF-8 realms which fail the conversion rules as per [RFC5891]
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. Optional: modify R according to agreed consortium procedures
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4. 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.
5. Extract NAPTR records with service tag "aaa+auth", "aaa+acct",
"aaa+dynauth" as appropriate.
6. If no result, continue at step 9.
7. 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).
8. Terminate.
9. Generate R' = (prefix R with "_radiustls._tcp." or
"_radiustls._udp")
10. Using the host's name resolution library, perform SRV lookup
with R' as label.
11. If name resolution returns with error, O = { }. Terminate.
12. If no result, O = {}; terminate.
13. Perform subsequent lookup steps until lookup yields one or more
hostnames. O = (set of {Order/Preference, hostname} for all
hostnames). Terminate.
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:
xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s" "aaa+
auth:radius.tls" "" _radiustls._tcp.xn--tu-mnchen-t9a.example.
xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s" "fooservice:
bar.dccp" "" _abc._def.xn--tu-mnchen-t9a.example.
_radiustls._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 10 2083
radsec.xn--tu-mnchen-t9a.example.
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_radiustls._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 20 2083
backup.xn--tu-mnchen-t9a.example.
radsec.xn--tu-mnchen-t9a.example. IN AAAA 2001:0DB8::202:44ff:
fe0a:f704
radsec.xn--tu-mnchen-t9a.example. IN A 192.0.2.3
backup.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] 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. )
5. Result: 50 50 "s" "aaa+auth:radius.tls" "" _radiustls._tcp.xn--
tu-mnchen-t9a.example.
6. NOOP
7. O = {(10,radsec.xn--tu-mnchen-t9a.example.:2083),(20,backup.xn--
tu-mnchen-t9a. example.:2083)}
8. Terminate.
9. (not executed)
10. (not executed)
11. (not executed)
12. (not executed)
13. (not executed)
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
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IP stack's capabilities.
3. Security Considerations
When using DNS without DNSSEC security extensions, the replies to
NAPTR, SRV and A/AAAA requests as described in section Section 2 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.
4. IANA Considerations
This document requests IANA registration of the following S-NAPTR
parameter:
o Application Service Tags
* aaa+auth
* aaa+acct
* aaa+dynauth
o Application Protocol Tags
* radius.tls
* radius.dtls
5. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14,
RFC 2119, March 1997.
[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.
[RFC5891] Klensin, J., "Internationalized Domain
Names in Applications (IDNA): Protocol",
RFC 5891, August 2010.
[I-D.dekok-radext-dtls] DeKok, A., "DTLS as a Transport Layer for
RADIUS", draft-dekok-radext-dtls-03 (work
in progress), July 2010.
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[I-D.ietf-radext-radsec] Winter, S., McCauley, M., Venaas, S., and
K. Wierenga, "TLS encryption for RADIUS",
draft-ietf-radext-radsec-09 (work in
progress), July 2011.
Authors' 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
Open Systems Consultants
9 Bulbul Place
Currumbin Waters QLD 4223
AUSTRALIA
Phone: +61 7 5598 7474
Fax: +61 7 5598 7070
EMail: mikem@open.com.au
URI: http://www.open.com.au.
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