draft-ietf-radext-dynamic-discovery-02.txt   draft-ietf-radext-dynamic-discovery-03.txt 
RADIUS Extensions Working Group S. Winter RADIUS Extensions Working Group S. Winter
Internet-Draft RESTENA Internet-Draft RESTENA
Intended status: Experimental M. McCauley Intended status: Experimental M. McCauley
Expires: September 6, 2010 OSC Expires: January 10, 2012 OSC
March 05, 2010 July 09, 2011
NAI-based Dynamic Peer Discovery for RADIUS over TLS and DTLS NAI-based Dynamic Peer Discovery for RADIUS/TLS and RADIUS/DTLS
draft-ietf-radext-dynamic-discovery-02 draft-ietf-radext-dynamic-discovery-03
Abstract Abstract
This document specifies a means to find authoritative AAA servers for This document specifies a means to find authoritative RADIUS servers
a given NAI realm. It can be used in conjunction with RADIUS over for a given realm. It can be used in conjunction with RADIUS/TLS and
TLS and RADIUS over DTLS. RADIUS/DTLS.
Status of This Memo Status of This Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF). Note that other groups may also distribute
other groups may also distribute working documents as Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts. Drafts is at http://datatracker.ietf.org/drafts/current/.
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at This Internet-Draft will expire on January 10, 2012.
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
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This Internet-Draft will expire on September 6, 2010.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
skipping to change at page 2, line 19 skipping to change at page 2, line 14
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. DNS-based NAPTR/SRV Peer Discovery . . . . . . . . . . . . . . 3 2. DNS-based NAPTR/SRV Peer Discovery . . . . . . . . . . . . . . 3
2.1. Applicability . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Applicability . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. DNS RR definition . . . . . . . . . . . . . . . . . . . . . 3 2.2. DNS RR definition . . . . . . . . . . . . . . . . . . . . . 3
2.3. Realm to AAA server resolution algorithm . . . . . . . . . 5 2.3. Realm to AAA server resolution algorithm . . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 3. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
5. Normative References . . . . . . . . . . . . . . . . . . . . . 8 5. Normative References . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
1.1. Requirements Language 1.1. Requirements Language
In this document, several words are used to signify the requirements In this document, several words are used to signify the requirements
of the specification. The key words "MUST", "MUST NOT", "REQUIRED", of the specification. The key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
skipping to change at page 3, line 30 skipping to change at page 3, line 30
RADIUS/TLS Server: a RADIUS/TLS [I-D.ietf-radext-radsec] instance RADIUS/TLS Server: a RADIUS/TLS [I-D.ietf-radext-radsec] instance
which listens on a RADIUS/TLS port and accepts new connections which listens on a RADIUS/TLS port and accepts new connections
RADIUS/TLS node: a RADIUS/TLS client or server RADIUS/TLS node: a RADIUS/TLS client or server
2. DNS-based NAPTR/SRV Peer Discovery 2. DNS-based NAPTR/SRV Peer Discovery
2.1. Applicability 2.1. Applicability
Dynamic server discovery as defined in this document is only Dynamic server discovery as defined in this document is only
applicable for AAA transactions where a AAA server receives a request applicable for AAA transactions where a RADIUS server receives a
with a NAI realm for which no home AAA server is known. I.e. where request with a realm for which no home RADIUS server is known. I.e.
static server configuration does not contain a known home where static server configuration does not contain a known home
authentication server, or where the server configuration explicitly authentication server, or where the server configuration explicitly
states that the realm destination is to be looked up dynamically. states that the realm destination is to be looked up dynamically.
Furthermore, it is only applicable for new user sessions, i.e. for Furthermore, it is only applicable for new user sessions, i.e. for
the initial Access-Request. Subsequent messages concerning this the initial Access-Request. Subsequent messages concerning this
session, for example Access-Challenges, Access-Accepts, Accounting session, for example Access-Challenges and Access-Accepts use the
Messages or Change-of-Authorisation messages use the previously- previously-established communication channel between client and
established communication channel between client and server. server.
2.2. DNS RR definition 2.2. DNS RR definition
DNS definitions of RADIUS/TLS servers can be either S-NAPTR records DNS definitions of RADIUS/TLS servers can be either S-NAPTR records
(see [RFC3958]) or SRV records. When both are defined, the (see [RFC3958]) or SRV records. When both are defined, the
resolution algorithm prefers S-NAPTR results (see section Section 2.3 resolution algorithm prefers S-NAPTR results (see section Section 2.3
below). below).
This specification defines two S-NAPTR service tag: a general-purpose This specification defines three S-NAPTR service tags: "aaa+auth",
tag "nai-roaming" and a special-purpose tag "eduroam" for the eduroam "aaa+acct" and "aaa+dynauth". This specification defines two S-NAPTR
roaming consortium. This specification defines two S-NAPTR protocol protocol tags: "radius.tls" for RADIUS/TLS [I-D.ietf-radext-radsec]
tags: "radius.tls" for RADIUS over TLS [I-D.ietf-radext-radsec] and and "radius.dtls" for RADIUS/DTLS [I-D.dekok-radext-dtls].
"radius.dtls" for RADIUS over DTLS [I-D.dekok-radext-dtls].
This specification defines the SRV prefix "_radiustls._tcp" for This specification defines the SRV prefix "_radiustls._tcp" for
RADIUS over TLS [I-D.ietf-radext-radsec] and "_radiustls._udp" 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 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 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 (punycode) of the literal realm name for which the server is the AAA
server. server.
However, arbitrary other labels may be used if, for example, a However, arbitrary other labels may be used if, for example, a
roaming consortium uses realm names which are not associated to DNS roaming consortium uses realm names which are not associated to DNS
names or special-purpose consortia where a globally valid discovery names or special-purpose consortia where a globally valid discovery
is not a use case. Such other labels require a consortium-wide is not a use case. Such other labels require a consortium-wide
agreement about the transformation from realm name to lookup label. agreement about the transformation from realm name to lookup label.
Examples: Examples:
a. A general-purpose AAA server for realm example.com might have DNS a. A general-purpose AAA server for realm example.com might have DNS
entries as follows: entries as follows:
example.com. IN NAPTR 50 50 "s" "nai-roaming:radius.tls" "" example.com. IN NAPTR 50 50 "s" "aaa+auth:radius.tls" ""
_radiustls._tcp.foobar.example.com. _radiustls._tcp.foobar.example.com.
_radiustls._tcp.example.com. IN SRV 0 10 2083 _radiustls._tcp.foobar.example.com. IN SRV 0 10 2083
radsec.example.com. radsec.example.com.
b. The consortium "foo" provides roaming services for its members b. The consortium "foo" provides roaming services for its members
only. The realms used are of the form enterprise-name.example. only. The realms used are of the form enterprise-name.example.
The consortium operates a special purpose DNS server for the The consortium operates a special purpose DNS server for the
(private) TLD "example" which all AAA servers use to resolve (private) TLD "example" which all AAA servers use to resolve
realm names. "Bad, Inc." is part of the consortium. On the realm names. "Bad, Inc." is part of the consortium. On the
consortium's DNS server, realm bad.example might have the consortium's DNS server, realm bad.example might have the
following DNS entries: following DNS entries:
bad.example IN NAPTR 50 50 "a" "nai-roaming:radius.dtls" "" bad.example IN NAPTR 50 50 "a" "aaa+auth:radius.dtls" ""
"very.bad.example" "very.bad.example"
c. the eduroam consortium uses realms based on DNS, but provides its c. The eduroam consortium uses realms based on DNS, but provides its
services to a closed community only. However, a AAA domain services to a closed community only. However, a AAA domain
participating in eduroam may also want to expose AAA services to participating in eduroam may also want to expose AAA services to
other, general-purpose, applications (on the same or other AAA other, general-purpose, applications (on the same or other AAA
servers). Due to that, the eduroam consortium uses the service servers). Due to that, the eduroam consortium uses the service
tag "eduroam" and eduroam AAA servers use this tag to look up tag "x-eduroam" for authentication purposes and eduroam AAA
other eduroam servers. An eduroam participant example.org which servers use this tag to look up other eduroam servers. An
also provides general-purpose AAA on a different server uses the eduroam participant example.org which also provides general-
general "nai-roaming" tag: purpose AAA on a different server uses the general "aaa+auth"
tag:
example.org. IN NAPTR 50 50 "s" "eduroam:radius.tls" "" example.org. IN NAPTR 50 50 "s" "x-eduroam:radius.tls" ""
_radiustls._tcp.eduroam.example.org. _radiustls._tcp.eduroam.example.org.
example.org. IN NAPTR 50 50 "s" "nai-roaming:radius.tls" "" example.org. IN NAPTR 50 50 "s" "aaa+auth:radius.tls" ""
_radiustls._tcp.aaa.example.org _radiustls._tcp.aaa.example.org
_radiustls._tcp.eduroam.example.org. IN SRV 0 10 2083 aaa- _radiustls._tcp.eduroam.example.org. IN SRV 0 10 2083 aaa-
eduroam.example.org. eduroam.example.org.
_radiustls._tcp.aaa.example.org. IN SRV 0 10 2083 aaa- _radiustls._tcp.aaa.example.org. IN SRV 0 10 2083 aaa-
default.example.org. default.example.org.
2.3. Realm to AAA server resolution algorithm 2.3. Realm to AAA server resolution algorithm
Input I to the algorithm is a User-Name in the form of a NAI as Input I to the algorithm is the RADIUS User-Name attribute with
defined in [RFC4282] as extracted from the User-Name attribute in an content of the form "user@realm"; the literal @ sign being the
Access-Request. Output O of the algorithm is a set of hostname:port separator between a local user identifier within a realm and its
and an associated order/preference; the set can be empty. 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 does not necessarily contain well- Note well: The attribute User-Name is defined to contain UTF-8 text.
formed NAIs and may not even contain well-formed UTF-8 strings. This In practice, the content may or may not be UTF-8. Even if UTF-8, it
document describes server discovery only for well-formed NAIs in may or may not map to a domain name in the realm part. Implementors
UTF-8 encoding. The result of all other possible contents of User- MUST take possible conversion error paths into consideration when
Name is unspecified; this includes, but is not limited to: 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 separators other than @
Usage of multiple @ separators Usage of multiple @ separators
Encoding of User-Name in local encodings Encoding of User-Name in local encodings
The algorithm to determine the AAA server to contact is as follows: UTF-8 realms which fail the conversion rules as per [RFC5891]
1. Determine P = (position of first "@" character) in I. 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) 2. generate R = (substring from P+1 to end of I)
3. Optional: modify R according to agreed consortium procedures 3. Optional: modify R according to agreed consortium procedures
4. Using the host's name resolution library, perform a NAPTR query 4. Using the host's name resolution library, perform a NAPTR query
for R. If no result, continue at step 9. If name resolution 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. returns with error, O = { }. Terminate.
5. Extract NAPTR records with service tag "nai-roaming" (replace 5. Extract NAPTR records with service tag "aaa+auth", "aaa+acct",
with other service tags where applicable). "aaa+dynauth" as appropriate.
6. If no result, continue at step 9. 6. If no result, continue at step 9.
7. Evaluate NAPTR result(s) for desired protocol tag, perform 7. Evaluate NAPTR result(s) for desired protocol tag, perform
subsequent lookup steps until lookup yields one or more subsequent lookup steps until lookup yields one or more
hostnames. O = (set of {Order/Preference, hostname:port} for hostnames. O = (set of {Order/Preference, hostname:port} for
all lookup results). all lookup results).
8. Terminate. 8. Terminate.
skipping to change at page 6, line 24 skipping to change at page 6, line 38
11. If name resolution returns with error, O = { }. Terminate. 11. If name resolution returns with error, O = { }. Terminate.
12. If no result, O = {}; terminate. 12. If no result, O = {}; terminate.
13. Perform subsequent lookup steps until lookup yields one or more 13. Perform subsequent lookup steps until lookup yields one or more
hostnames. O = (set of {Order/Preference, hostname} for all hostnames. O = (set of {Order/Preference, hostname} for all
hostnames). Terminate. hostnames). Terminate.
Example: Assume a user from the Technical University of Munich, Example: Assume a user from the Technical University of Munich,
Germany, has a RADIUS User-Name of Germany, has a RADIUS User-Name of
"foobar@tu-m[U+00FC]nchen.example". If DNS contains the following "foobar@tu-m[U+00FC]nchen.example". The name resolution library on
records: the RADIUS client uses DNS for name resolution. If DNS contains the
following records:
xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s" "nai- xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s" "aaa+
roaming:radius.tls" "" _radiustls._tcp.xn--tu-mnchen-t9a.example. auth:radius.tls" "" _radiustls._tcp.xn--tu-mnchen-t9a.example.
xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s" "fooservice: xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s" "fooservice:
bar.dccp" "" _abc._def.xn--tu-mnchen-t9a.example. bar.dccp" "" _abc._def.xn--tu-mnchen-t9a.example.
_radiustls._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 10 2083 _radiustls._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 10 2083
radsec.xn--tu-mnchen-t9a.example. radsec.xn--tu-mnchen-t9a.example.
_radiustls._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 20 2083 _radiustls._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 20 2083
backup.xn--tu-mnchen-t9a.example. backup.xn--tu-mnchen-t9a.example.
skipping to change at page 7, line 4 skipping to change at page 7, line 20
radsec.xn--tu-mnchen-t9a.example. IN A 192.0.2.3 radsec.xn--tu-mnchen-t9a.example. IN A 192.0.2.3
backup.xn--tu-mnchen-t9a.example. IN A 192.0.2.7 backup.xn--tu-mnchen-t9a.example. IN A 192.0.2.7
Then the algorithm executes as follows, with I = Then the algorithm executes as follows, with I =
"foobar@tu-m[U+00FC]nchen.example", and no consortium name mangling "foobar@tu-m[U+00FC]nchen.example", and no consortium name mangling
in use: in use:
1. P = 7 1. P = 7
2. R = "tu-m[U+00FC]nchen.example" 2. R = "tu-m[U+00FC]nchen.example"
3. NOOP 3. NOOP
4. Query result: ( 50 50 "s" "nai-roaming:radius.tls" "" 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" _radiustls._tcp.xn--tu-mnchen-t9a.example. ; 50 50 "s"
"fooservice:bar.dccp" "" _abc._def.xn--tu-mnchen-t9a.example. ) "fooservice:bar.dccp" "" _abc._def.xn--tu-mnchen-t9a.example. )
5. Result: 50 50 "s" "nai-roaming:radius.tls" "" 5. Result: 50 50 "s" "aaa+auth:radius.tls" "" _radiustls._tcp.xn--
_radiustls._tcp.xn--tu-mnchen-t9a.example. tu-mnchen-t9a.example.
6. NOOP 6. NOOP
7. O = {(10,radsec.xn--tu-mnchen-t9a.example.:2083),(20,backup.xn-- 7. O = {(10,radsec.xn--tu-mnchen-t9a.example.:2083),(20,backup.xn--
tu-mnchen-t9a. example.:2083)} tu-mnchen-t9a. example.:2083)}
8. Terminate. 8. Terminate.
9. (not executed) 9. (not executed)
skipping to change at page 7, line 39 skipping to change at page 8, line 8
13. (not executed) 13. (not executed)
The implementation will then attempt to connect to two servers, with The implementation will then attempt to connect to two servers, with
preference to radsec.xn--tu-mnchen-t9a.example.:2083, using either preference to radsec.xn--tu-mnchen-t9a.example.:2083, using either
the AAAA or A addresses depending on the host configuration and its the AAAA or A addresses depending on the host configuration and its
IP stack's capabilities. IP stack's capabilities.
3. Security Considerations 3. Security Considerations
When using DNS without security, the replies to NAPTR, SRV and A/AAAA When using DNS without DNSSEC security extensions, the replies to
requests as described in section Section 2 can not be trusted. NAPTR, SRV and A/AAAA requests as described in section Section 2 can
RADIUS transports have an out-of-DNS-band means to verify that the not be trusted. RADIUS transports have an out-of-DNS-band means to
discovery attempt led to the intended target (TLS/DTLS: ceritifcate verify that the discovery attempt led to the intended target:
verification or TLS shared secret ciphers; UDP/TCP: the RADIUS shared certificate verification or TLS-PSK keys.
secret) and are safe from DNS-based redirection attacks. [Note:
assuming here that a hypothetical RADIUS/UDP SRV discovery will NOT
deliver the shared secret in the DNS response!]
The discovery process is always susceptible to bidding down attacks
if a realm has SRV records for RADIUS/UDP and/or RADIUS/TCP as well
as for RADIUS/TLS and/or RADIUS/DTLS. While the SRV query will
expose both transports, an attacker in the routing path might
suppress the subsequent A/AAAA results for the TLS or DTLS peer and
trick the initiating peer into using the weakly protected UDP or TCP
transports. The use of DNSSEC can not fully mitigate this attack,
since it does not provide a means to detect packet suppression. The
only way to disable such bidding down attacks is by intiating
connections only to the peer(s) which match or exceed a configured
minimum security level. All implementations SHOULD provide a means
to configure the administratively desired minimum security level.
4. IANA Considerations 4. IANA Considerations
This document requests IANA registration of the following S-NAPTR This document requests IANA registration of the following S-NAPTR
parameters: parameter:
o Application Service Tags o Application Service Tags
* nai-roaming * aaa+auth
* eduroam * aaa+acct
* aaa+dynauth
o Application Protocol Tags o Application Protocol Tags
* radius.tls * radius.tls
* radius.dtls * radius.dtls
5. Normative References 5. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to [RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, Indicate Requirement Levels", BCP 14,
RFC 2119, March 1997. RFC 2119, March 1997.
[RFC3958] Daigle, L. and A. Newton, "Domain-Based [RFC3958] Daigle, L. and A. Newton, "Domain-Based
Application Service Location Using SRV RRs Application Service Location Using SRV RRs
and the Dynamic Delegation Discovery and the Dynamic Delegation Discovery
Service (DDDS)", RFC 3958, January 2005. Service (DDDS)", RFC 3958, January 2005.
[RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. [RFC5891] Klensin, J., "Internationalized Domain
Eronen, "The Network Access Identifier", Names in Applications (IDNA): Protocol",
RFC 4282, December 2005. RFC 5891, August 2010.
[I-D.dekok-radext-dtls] DeKok, A., "DTLS as a Transport Layer for [I-D.dekok-radext-dtls] DeKok, A., "DTLS as a Transport Layer for
RADIUS", draft-dekok-radext-dtls-01 (work RADIUS", draft-dekok-radext-dtls-03 (work
in progress), June 2009. in progress), July 2010.
[I-D.ietf-radext-radsec] Winter, S., McCauley, M., Venaas, S., and [I-D.ietf-radext-radsec] Winter, S., McCauley, M., Venaas, S., and
K. Wierenga, "TLS encryption for RADIUS K. Wierenga, "TLS encryption for RADIUS",
over TCP", draft-ietf-radext-radsec-06 draft-ietf-radext-radsec-09 (work in
(work in progress), March 2010. progress), July 2011.
Authors' Addresses Authors' Addresses
Stefan Winter Stefan Winter
Fondation RESTENA Fondation RESTENA
6, rue Richard Coudenhove-Kalergi 6, rue Richard Coudenhove-Kalergi
Luxembourg 1359 Luxembourg 1359
LUXEMBOURG LUXEMBOURG
Phone: +352 424409 1 Phone: +352 424409 1
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