draft-ietf-radext-dynamic-discovery-06.txt		draft-ietf-radext-dynamic-discovery-07.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: August 29, 2013 OSC		Expires: January 05, 2014 OSC
	February 25, 2013		July 04, 2013
	NAI-based Dynamic Peer Discovery for RADIUS/TLS and RADIUS/DTLS		NAI-based Dynamic Peer Discovery for RADIUS/TLS and RADIUS/DTLS
	draft-ietf-radext-dynamic-discovery-06		draft-ietf-radext-dynamic-discovery-07
	Abstract		Abstract
	This document specifies a means to find authoritative RADIUS servers		This document specifies a means to find authoritative RADIUS servers
	for a given realm. It is used in conjunction with either RADIUS/TLS		for a given realm. It is used in conjunction with either RADIUS/TLS
	and RADIUS/DTLS.		and RADIUS/DTLS.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	skipping to change at page 1, line 33		skipping to change at page 1, line 33
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	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."
	This Internet-Draft will expire on August 29, 2013.		This Internet-Draft will expire on January 05, 2014.
	Copyright Notice		Copyright Notice
	Copyright (c) 2013 IETF Trust and the persons identified as the		Copyright (c) 2013 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
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 10		skipping to change at page 2, line 10
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	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. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 3		2.1. DNS RR definition . . . . . . . . . . . . . . . . . . . . 3
	2.2. DNS RR definition . . . . . . . . . . . . . . . . . . . . 3		2.1.1. S-NAPTR . . . . . . . . . . . . . . . . . . . . . . . 3
	2.3. Realm to RADIUS server resolution algorithm . . . . . . . 6		2.1.2. SRV . . . . . . . . . . . . . . . . . . . . . . . . . 8
	2.3.1. Input . . . . . . . . . . . . . . . . . . . . . . . . 6		2.1.3. Remarks . . . . . . . . . . . . . . . . . . . . . . . 8
	2.3.2. Output . . . . . . . . . . . . . . . . . . . . . . . 7		2.2. Definition of the X.509 certificate property
	2.3.3. Algorithm . . . . . . . . . . . . . . . . . . . . . . 7		SubjectAltName:otherName:NAIRealm . . . . . . . . . . . . 10
	2.3.4. Validity of results . . . . . . . . . . . . . . . . . 8		3. DNS-based NAPTR/SRV Peer Discovery . . . . . . . . . . . . . 11
	2.3.5. Delay considerations . . . . . . . . . . . . . . . . 9		3.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 11
	2.3.6. Example . . . . . . . . . . . . . . . . . . . . . . . 9		3.2. Configuration Variables . . . . . . . . . . . . . . . . . 11
	3. Security Considerations . . . . . . . . . . . . . . . . . . . 11		3.3. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 11
	4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11		3.4. Realm to RADIUS server resolution algorithm . . . . . . . 12
	5. Normative References . . . . . . . . . . . . . . . . . . . . 12		3.4.1. Input . . . . . . . . . . . . . . . . . . . . . . . . 12
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13		3.4.2. Output . . . . . . . . . . . . . . . . . . . . . . . 13
			3.4.3. Algorithm . . . . . . . . . . . . . . . . . . . . . . 13
			3.4.4. Validity of results . . . . . . . . . . . . . . . . . 15
			3.4.5. Delay considerations . . . . . . . . . . . . . . . . 16
			3.4.6. Example . . . . . . . . . . . . . . . . . . . . . . . 16
			4. Security Considerations . . . . . . . . . . . . . . . . . . . 19
			5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
			6. Normative References . . . . . . . . . . . . . . . . . . . . 20
			Appendix A. Appendix A: ASN.1 Syntax of NAIRealm . . . . . . . . 21
	1. Introduction		1. Introduction
	RADIUS in all its current transport variants (RADIUS/UDP, RADIUS/TLS,		RADIUS in all its current transport variants (RADIUS/UDP, RADIUS/TLS,
	RADIUS/DTLS) requires manual configuration of all peers (clients,		RADIUS/DTLS) requires manual configuration of all peers (clients,
	servers).		servers).
	Where RADIUS forwarding servers are in use, the number of realms to		Where RADIUS forwarding servers are in use, the number of realms to
	be forwarded and the corresponding number of servers to configure may		be forwarded and the corresponding number of servers to configure may
	be significant. Where new realms with new servers are added or		be significant. Where new realms with new servers are added or
	skipping to change at page 2, line 49		skipping to change at page 3, line 10
	independently working branches, each with their own forwarding		independently working branches, each with their own forwarding
	servers, and who add or change their realm lists at their own		servers, and who add or change their realm lists at their own
	discretion, there is additional complexity in synchronising the		discretion, there is additional complexity in synchronising the
	changed data across all branches.		changed data across all branches.
	These situations can benefit significantly from a distributed		These situations can benefit significantly from a distributed
	mechanism for storing realm and server reachability information.		mechanism for storing realm and server reachability information.
	This document describes one such mechanism: storage of realm-to-		This document describes one such mechanism: storage of realm-to-
	server mappings in DNS.		server mappings in DNS.
	This document does not specify how to verify that server information		This document also specifies various approaches for verifying that
	which was retrieved from DNS was from an authorised party; e.g. an		server information which was retrieved from DNS was from an
	organisation which is not at all part of a given roaming consortium		authorised party; e.g. an organisation which is not at all part of a
	may alter its own DNS records to yield a result for its own realm.		given roaming consortium may alter its own DNS records to yield a
			result for its own realm.
	RADIUS/TLS and RADIUS/DTLS have their own ways how to verify that a
	contacted peer is authorised (e.g. by presenting PKIX certificates
	from a agreed-upon CA).
	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",
	and "OPTIONAL" in this document are to be interpreted as described in		and "OPTIONAL" in this document are to be interpreted as described in
	RFC 2119. [RFC2119]		RFC 2119. [RFC2119]
	1.2. Terminology		1.2. Terminology
	RADIUS/TLS Client: a RADIUS/TLS [RFC6614] instance which initiates a		RADIUS/TLS Client: a RADIUS/TLS [RFC6614] instance which initiates a
	new connection.		new connection.
	RADIUS/TLS Server: a RADIUS/TLS [RFC6614] instance which listens on a		RADIUS/TLS Server: a RADIUS/TLS [RFC6614] instance which listens on a
	RADIUS/TLS port and accepts new connections		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. Definitions
	2.1. Applicability
	Dynamic server discovery as defined in this document is only
	applicable for AAA transactions 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. 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		2.1. 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 2.3 below).		resolution algorithm prefers S-NAPTR results (see Section 3.4 below).
			2.1.1. S-NAPTR
			2.1.1.1. Registration of Application Service and Protocol Tags
	This specification defines three S-NAPTR service tags:		This specification defines three S-NAPTR service tags:
	+-----------------+-----------------------------------------+		+-----------------+-----------------------------------------+
	| Service Tag | Use |		| Service Tag | Use |
	+-----------------+-----------------------------------------+		+-----------------+-----------------------------------------+
	| aaa+auth | RADIUS Authentication, i.e. traffic as |		| aaa+auth | RADIUS Authentication, i.e. traffic as |
	| | defined in [RFC2865] |		| | defined in [RFC2865] |
	| - - - - - - - - | - - - - - - - - - - - - - - - - - - - - |		| - - - - - - - - | - - - - - - - - - - - - - - - - - - - - |
	| aaa+acct | RADIUS Accounting, i.e. traffic as |		| aaa+acct | RADIUS Accounting, i.e. traffic as |
	skipping to change at page 4, line 35		skipping to change at page 4, line 34
	| | in [I-D.ietf-radext-dtls] |		| | in [I-D.ietf-radext-dtls] |
	+-----------------+-----------------------------------------+		+-----------------+-----------------------------------------+
	Figure 2: List of Protocol Tags		Figure 2: List of Protocol Tags
	Note well:		Note well:
	The S-NAPTR service and protocols are unrelated to the IANA		The S-NAPTR service and protocols are unrelated to the IANA
	Service Name and Transport Protocol Number registry		Service Name and Transport Protocol Number registry
	The delimiter '.' in the protocol tags is only a separator for		The delimiter '.' in the protocol tags is only a separator for
	human reading convenience - not for structure or namespacing; it		human reading convenience - not for structure or namespacing; it
	MUST NOT be parsed in any way by the querying application or		MUST NOT be parsed in any way by the querying application or
	resolver.		resolver.
	The use of the separator '.' is common also in other protocols'		The use of the separator '.' is common also in other protocols'
	protocol tags. This is coincidence and does not imply a shared		protocol tags. This is coincidence and does not imply a shared
	semantics with such protocols.		semantics with such protocols.
	This specification defines two SRV prefixes (i.e. two values for the		2.1.1.2. Definition of Conditions for Retry/Failure
	"_service._proto" part of an SRV RR):
			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 time-outs, 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.
			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 algorithm does
			not allow to derive 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
			can not be used for the subsequent TLS handshake in the RADIUS/TLS
			conversation. 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 a 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.
			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: compare the value of algorithm's variable "R" after the
			execution of step 3 of the discovery algorithm in Section 3.4.3 below
			(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. The comparison is a byte-by-byte comparison, except for
			dot-separated parts of the value whose content is a single "*"
			character; such labels match all strings in the same part of the NAI
			realm. If at least one of the sAN:otherName:NAIRealm values matches
			the NAI realm, the server is considered authorized; if none matches,
			the server is considered unauthorized.
			Examples:
			+-----------------+---------------------------------------------+
			| NAI realm | sAN:otherName:NAIRealm | MATCH? |
			+-----------------+---------------------------------------------+
			| foo.example | foo.example | YES |
			| foo.example | *.example | YES |
			| bar.foo.example | *.example | NO |
			| bar.foo.example | bar.*.example | YES |
			| bar.foo.example | *.*.example | YES |
			| sub.bar.foo.example | *.*.example | NO |
			| sub.bar.foo.example | sub.bar.foo.example | YES |
			+-----------------+---------------------------------------------+
			Figure 3: Examples for NAI realm vs. certificate matching
			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: 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.
			It should be noted that these shortcomings can be mitigated by using
			the RADIUS infrastructure only with authentication payloads which
			provide mutual authentication; that way, the final EAP server that
			was reached can be validated by the EAP peer, and any improper
			redirections to a different server will be detected.
			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 server
			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 authorization can be sketched using DNSSEC+DANE as follows: if
			DANE/TLSA records of all authorized servers are put into a DNSSEC
			zone with a common, consortium-specific branch of the DNS tree, then
			the entity executing the algorithm can retrieve TLSA RRs for the
			label "realm.commonroot" and verify 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. Remark
			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]):
	+-----------------+-----------------------------------------+		+-----------------+-----------------------------------------+
	| SRV Label | Use |		| SRV Label | Use |
	+-----------------+-----------------------------------------+		+-----------------+-----------------------------------------+
	| _radiustls._tcp | RADIUS transported over TLS as defined |		| _radiustls._tcp | RADIUS transported over TLS as defined |
	| | in [RFC6614] |		| | in [RFC6614] |
	| - - - - - - - - | - - - - - - - - - - - - - - - - - - - - |		| - - - - - - - - | - - - - - - - - - - - - - - - - - - - - |
	| _radiustls._udp | RADIUS transported over DTLS as defined |		| _radiustls._udp | RADIUS transported over DTLS as defined |
	| | in [I-D.ietf-radext-dtls] |		| | in [I-D.ietf-radext-dtls] |
	+-----------------+-----------------------------------------+		+-----------------+-----------------------------------------+
	Figure 3: List of SRV Labels		Figure 4: 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. Remarks
	It is expected that in most cases, the SRV and/or NAPTR label used		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		for the records is the DNS A-label representation of the literal
	realm name for which the server is the authoritative RADIUS server		realm name for which the server is the authoritative RADIUS server
	(i.e. the realm name after conversion according to section 5 of		(i.e. the realm name after conversion according to section 5 of
	[RFC5891]).		[RFC5891]).
	However, arbitrary other SRV and/or NAPTR labels may be used if, for		However, arbitrary other labels or service tags may be used if, for
	example, a roaming consortium uses realm names which are not		example, a roaming consortium uses realm names which are not
	associated to DNS names or special-purpose consortia where a globally		associated to DNS names or special-purpose consortia where a globally
	valid discovery is not a use case. Such other labels require a		valid discovery is not a use case. Such other labels require a
	consortium-wide agreement about the transformation from realm name to		consortium-wide agreement about the transformation from realm name to
	lookup label.		lookup label, and/or which service tag to use.
	Examples:		Examples:
	a. A general-purpose RADIUS server for realm example.com might have		a. A general-purpose RADIUS server for realm example.com might have
	DNS entries as follows:		DNS entries as follows:
	example.com. IN NAPTR 50 50 "s" "aaa+auth: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.foobar.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 RADIUS servers use to resolve		(private) TLD "example" which all RADIUS 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" "aaa+auth: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 RADIUS		other, general-purpose, applications (on the same or other RADIUS
	skipping to change at page 6, line 23		skipping to change at page 10, line 5
	example.org. IN NAPTR 50 50 "s" "aaa+auth: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 RADIUS server resolution algorithm		2.2. Definition of the X.509 certificate property
			SubjectAltName:otherName:NAIRealm
	This algorithm can be used to discover RADIUS servers (for RADIUS		This specification retrieves IP addresses and port numbers from the
	Authentication and RADIUS Accounting) or to discover RADIUS DynAuth		Domain Name System which are subsequently used to authenticate users
	servers.		via the RADIUS/TLS protocol. Since the Domain Name System is not
			necessarily trustworthy (e.g. if DNSSEC is not deployed for the
			queried domain name), it is important to verify that the server which
			was contacted is authorized to service requests for the user which
			triggered the discovery process.
	2.3.1. Input		The input to the algorithm is a NAI realm as specified in
			Section 3.4.1. As a consequence, the X.509 certificate of the server
			which is ultimately contacted for user authentication needs to be
			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-nai OBJECT IDENTIFIER ::= { id-on XXX }
			NAIRealm ::= UTF8String (SIZE (1..MAX))
			The NAIRealm, if present, MUST contain an NAI realm as defined in
			[I-D.ietf-radext-nai]. It MAY substitute labels on all dot-separated
			parts 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.
			This subjectAltName MAY occur more than once in a certificate.
			Appendix A contains the ASN.1 definition of the above objects.
			3. DNS-based NAPTR/SRV Peer Discovery
			3.1. Applicability
			Dynamic server discovery as defined in this document is only
			applicable for AAA transactions 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. RADIUS DynAuth server discovery
			3.2. Configuration Variables
			The algorithm contains various variables for timeouts. These
			variables are named here and reasonable default values are provided.
			Implementations wishing to deviate from these defaults should make
			they understand the implications of changes.
			DNS_TIMEOUT: maximum amount of time to wait for the complete set
			of all DNS queries to complete: Default = 3 seconds
			MIN_EFF_TTL: minimum DNS TTL of discovered targets: Default = 60
			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 seconds
			3.3. Terms
			Positive DNS response: a response which contains the RR that was
			queried for.
			Negative DNS response: a response which does not contain the RR that
			was queried for, but contains an SOA record along with a TTL
			indicating cache duration for this negative result.
			DNS Error: Where the algorithm states "name resolution returns with
			an error", this shall mean that either the DNS request timed out, or
			a DNS response which is neither a positive nor a negative response
			(e.g. SERVFAIL).
			Effective TTL: The validity period for discovered RADIUS/TLS target
			hosts. Calculated as: Effective TTL (set of DNS TTL values) = max {
			MIN_EFF_TTL, min { DNS TTL values } }
			SRV lookup: for the purpose of this specification, SRV lookup
			procedures are defined as per [RFC2782], but excluding that RFCs "A"
			fallback as defined in its section "Usage Rules", final "else"
			clause.
			3.4. Realm to RADIUS server resolution algorithm
			3.4.1. Input
	For RADIUS Authentication and RADIUS Accounting server discovery,		For RADIUS Authentication and RADIUS Accounting server discovery,
	input I to the algorithm is the RADIUS User-Name attribute with		input I to the algorithm is the RADIUS User-Name attribute with
	content of the form "user@realm"; the literal @ sign being the		content of the form "user@realm"; the literal @ sign being the
	separator between a local user identifier within a realm and its		separator between a local user identifier within a realm and its
	realm. The use of multiple literal @ signs in a User-Name is		realm. The use of multiple literal @ signs in a User-Name is
	strongly discouraged; but if present, the last @ sign is to be		strongly discouraged; but if present, the last @ sign is to be
	considered the separator. All previous instances of the @ sign are		considered the separator. All previous instances of the @ sign are
	to be considered part of the local user identifier.		to be considered part of the local user identifier.
	skipping to change at page 7, line 25		skipping to change at page 13, line 23
	UTF-8 realms which end with a . ("dot") character.		UTF-8 realms which end with a . ("dot") character.
	For the last bullet point, "trailing dot", special precautions should		For the last bullet point, "trailing dot", special precautions should
	be taken to avoid problems when resolving servers with the algorithm		be taken to avoid problems when resolving servers with the algorithm
	below: they may resolve to a RADIUS server even if the peer RADIUS		below: they may resolve to a RADIUS server even if the peer RADIUS
	server only is configured to handle the realm without the trailing		server only is configured to handle the realm without the trailing
	dot. If that RADIUS server again uses NAI discovery to determine the		dot. If that RADIUS server again uses NAI discovery to determine the
	authoritative server, the server will forward the request to		authoritative server, the server will forward the request to
	localhost, resulting in a tight endless loop.		localhost, resulting in a tight endless loop.
	2.3.2. Output		3.4.2. Output
	Output O of the algorithm is a set of tuples {hostname; port; order/		Output O of the algorithm is a two-tuple consisting of: O-1) a set of
	preference; TTL} - the set can be empty.		tuples {hostname; port; 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).
	2.3.3. Algorithm		3.4.3. Algorithm
	The algorithm to determine the RADIUS server to contact is as		The algorithm to determine the RADIUS server to contact is as
	follows:		follows:
	1. Determine P = (position of last "@" character) in I.		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. modify R according to agreed consortium procedures if applicable
	4. Using the host's name resolution library, perform a NAPTR query		4. convert R to a representation usable by the name resolution
	for R (see "Delay considerations" below). The name resolution		library if needed
	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 =
	{ empty set } and terminate.
	5. Extract NAPTR records with service tag "aaa+auth", "aaa+acct",		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 remaining TTL of		"aaa+dynauth" as appropriate. Keep note of the remaining TTL of
	each of the discovered NAPTR records.		each of the discovered NAPTR records.
	6. If no records found, continue at step 9.		8. If no records found, continue at step 13.
	7. Evaluate NAPTR result(s) for desired protocol tag, perform		9. For the extracted NAPTRs, perform successive resolution as
	subsequent lookup steps until lookup yields one or more		defined in [RFC3958], section 2.2.4, with the additional
	hostnames. O' = (set of {hostname; port; order/preference;		reservation that all records are to be immediately pursued
	min{all TTLs that led to this result} } for all lookup results).		through terminal lookup, i.e. have resulted in hostnames.
	Keep note of the remaining TTL of each of the discovered records		Failure to achieve terminal lookup for individual records is
	(e.g. SRV and AAAA).		non-fatal.
	8. Proceed with step 15.		10. If the set of hostnames is empty, O-1 = { empty set }, O-2 =
			BACKOFF_TIME and terminate.
	9. Generate R' = (prefix R with "_radiustls._tcp." or		11. O' = (set of {hostname; port; order/preference; Effective TTL (
	"_radiustls._udp")		all DNS TTLs that led to this hostname ) } for all terminal
			lookup results).
	10. Using the host's name resolution library, perform SRV lookup		12. Proceed with step 18.
	with R' as label (see "Delay considerations" below). Keep note
	of the TTL of each of the discovered SRV records.
	11. If name resolution returns with error, O = { empty set } and		13. Generate R' = (prefix R with "_radiustls._tcp." or
	terminate.		"_radiustls._udp.")
	12. If no result, O = { empty set } and terminate.		14. Using the host's name resolution library, perform SRV lookup
			with R' as label (see "Delay considerations" below).
	13. O' = (set of {hostname; port; order/preference; min{all TTLs		15. If name resolution returns with error, O-1 = { empty set }, O-2
	that led to this result} } for all hostnames).		= BACKOFF_TIME and terminate.
	14. Generate O by resoving hostnames to corresponding A and/or AAAA		16. If the result is a negative DNS response, O-1 = { empty set },
	addresses: O = (set of {IP address; port; order/preference;		O-2 = min { O-2, Effective TTL ( TTL value of the SOA record ) }
	min{all TTLs that led to this result}} for all hostnames ).		and terminate.
	15. For each element in O, test if the original request which		17. O' = (set of {hostname; port; 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; 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}.		triggered dynamic discovery was received on {IP address; port}.
	If yes, O = { empty set }, log error, Terminate. If no, O is		If yes, O-1 = { empty set }, O-2 = BACKOFF_TIME, log error,
	the result of dynamic discovery. Terminate.		Terminate (see next section for a rationale). If no, O is the
			result of dynamic discovery. Terminate.
	2.3.4. Validity of results		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 this will
			either lead to a tight loop (if that DNS entry has topmost priority,
			the server would forward the request to itself, triggering dynamic
			discovery again in a perpetual loop), or lead to a potential loop
			with intermediate hops in between (the server could 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.
	After executing the above algorithm, the RADIUS server establishes a		After executing the above algorithm, the RADIUS server establishes a
	connection to a home server from the result set. This connection can		connection to a home server from the result set. This connection can
	potentially remain open for an indefinite amount of time. This		potentially remain open for an indefinite amount of time. This
	conflicts with the possibility of changing device and network		conflicts with the possibility of changing device and network
	configurations on the receiving end. Typically, TTL values for		configurations on the receiving end. Typically, TTL values for
	records in the name resolution system are used to indicate how long		records in the name resolution system are used to indicate how long
	it is safe to rely on the results of the name resolution. When a		it is safe to rely on the results of the name resolution. If these
	connection is open and the smallest of the TTL values which were used		TTLs are very low, thrashing of connections becomes possible; the
	for discovering the server has not expired, subsequent new user		Effective TTL mitigates that risk. When a connection is open and the
	sessions for the realm which corresponds to that open connection		smallest of the Effective TTL value which was learned during
	SHOULD re-use the existing connection and SHOULD NOT re-execute the		discovering the server has not expired, subsequent new user sessions
	dynamic discovery algorithm nor open a new connection. To allow for		for the realm which corresponds to that open connection SHOULD re-use
	a change of configuration, a RADIUS server SHOULD re-execute the		the existing connection and SHOULD NOT re-execute the dynamic
	dynamic discovery algorithm after the lowest of the TTL values that		discovery algorithm nor open a new connection. To allow for a change
	are associated with this connection have expired. The server MAY		of configuration, a RADIUS server SHOULD re-execute the dynamic
	keep the session open during this re-assessment to avoid closure and		discovery algorithm after the Effective TTL that is associated with
	immediate re-opening of the connection should the result not have		this connection has expired. The server MAY keep the session open
	changed.		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 an empty set (but no
	error), the RADIUS server SHOULD NOT attempt another execution of
	this algorithm for the same target realm before the negative TTL has
	expired.
	Should the algorithm above terminate due to an error with no TTL		Should the algorithm above terminate with O-1 = empty set, the RADIUS
	value known (e.g. DNS SERVFAIL), the RADIUS server SHOULD NOT		server SHOULD NOT attempt another execution of this algorithm for the
	attempt another execution of this algorithm for the same target realm		same target realm before the timeout O-2 has passed.
	before a configurable timeout interval has passed.
	2.3.5. Delay considerations		3.4.5. Delay considerations
	The host's name resolution library may need to contact outside		The host's name resolution library may need to contact outside
	entities to perform the name resolution (e.g. authoritative name		entities to perform the name resolution (e.g. authoritative name
	servers for a domain), and since the NAI discovery algorithm is based		servers for a domain), and since the NAI discovery algorithm is based
	on uncontrollable user input, the destination of the lookups is out		on uncontrollable user input, the destination of the lookups is out
	of control of the server that performs NAI discovery. If such		of control of the server that performs NAI discovery. If such
	outside entities are misconfigured or unreachable, the algorithm		outside entities are misconfigured or unreachable, the algorithm
	above may need an unacceptably long time to terminate. Many RADIUS		above may need an unacceptably long time to terminate. Many RADIUS
	implementations time out after five seconds of delay between Request		implementations time out after five seconds of delay between Request
	and Response. It is not useful to wait until the host name		and Response. It is not useful to wait until the host name
	resolution library signals a time-out of its name resolution		resolution library signals a time-out of its name resolution
	algorithms; instead, implementations of NAI discovery SHOULD		algorithms. The algorithm therefore control execution time with
	terminate the algorithm after the fixed upper bound of time of three		TIMER. Execution of the NAI discovery algorithm SHOULD be non-
	seconds. If no final output of the algorithm is available after this		blocking (i.e. allow other requests to be processed in parallel to
	timeout, the RADIUS server MUST assume the empty set as a result and		the execution of the algorithm).
	treat the pending request according to its static configuration
	(e.g., fallback to a default route to a home server). 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).
	2.3.6. Example		3.4.6. Example
	Example: Assume		Assume
	a user from the Technical University of Munich, Germany, has a		a user from the Technical University of Munich, Germany, has a
	RADIUS User-Name of "foobar@tu-m[U+00FC]nchen.example".		RADIUS User-Name of "foobar@tu-m[U+00FC]nchen.example".
	The name resolution library on the RADIUS forwarding server does		The name resolution library on the RADIUS forwarding server does
	not have the realm tu-m[U+00FC]nchen.example in its forwarding		not have the realm tu-m[U+00FC]nchen.example in its forwarding
	configuration, but uses DNS for name resolution and has configured		configuration, but uses DNS for name resolution and has configured
	the use of Dynamic Discovery to discover RADIUS servers.		the use of Dynamic Discovery to discover RADIUS servers.
	It is IPv6-enabled and prefers AAAA records over A records.		It is IPv6-enabled and prefers AAAA records over A records.
	It is listening for incoming RADIUS/TLS requests on 192.37.5.1,		It is listening for incoming RADIUS/TLS requests on 192.0.2.1, TCP
	TCP/2083.		/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:		If DNS contains the following records:
	xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s"		xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s"
	"aaa+auth:radius.tls" "" _radiustls._tcp.xn--tu-mnchen-		"aaa+auth:radius.tls" "" _myradius._tcp.xn--tu-mnchen-t9a.example.
	t9a.example.
	xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s"		xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s"
	"fooservice:bar.dccp" "" _abc._def.xn--tu-mnchen-t9a.example.		"fooservice:bar.dccp" "" _abc123._def.xn--tu-mnchen-t9a.example.
	_radiustls._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 10 2083		_myradius._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 10 2083
	radsec.xn--tu-mnchen-t9a.example.		radsecserver.xn--tu-mnchen-t9a.example.
	_radiustls._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 20 2083		_myradius._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 20 2083
	backup.xn--tu-mnchen-t9a.example.		backupserver.xn--tu-mnchen-t9a.example.
	radsec.xn--tu-mnchen-t9a.example. IN AAAA		radsecserver.xn--tu-mnchen-t9a.example. IN AAAA
	2001:0DB8::202:44ff:fe0a:f704		2001:0DB8::202:44ff:fe0a:f704
	radsec.xn--tu-mnchen-t9a.example. IN A 192.0.2.3		radsecserver.xn--tu-mnchen-t9a.example. IN A 192.0.2.3
	backup.xn--tu-mnchen-t9a.example. IN A 192.0.2.7		backupserver.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. [name resolution library converts R to xn--tu-mnchen-		4. name resolution library converts R to xn--tu-mnchen-t9a.example
	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		5. TIMER starts.
	--tu-mnchen-t9a.example.
	6. NOOP		6. Result:
	7. O' = {(radsec.xn--tu-mnchen-t9a.example.; 2083; 10; TTL		(TTL = 47) 50 50 "s" "aaa+auth:radius.tls" ""
	A),(backup.xn--tu-mnchen-t9a. example.;2083; 20; TTL B)}		_myradius._tcp.xn--tu-mnchen-t9a.example.
	8. Go to step 15.		(TTL = 522) 50 50 "s" "fooservice:bar.dccp" ""
			_abc123._def.xn--tu-mnchen-t9a.example.
	9. (not executed)		7. Result:
	10. (not executed)		(TTL = 47) 50 50 "s" "aaa+auth:radius.tls" ""
			_myradius._tcp.xn--tu-mnchen-t9a.example.
	11. (not executed)		8. NOOP
			9. Successive resolution performs SRV query for label
			_myradius._tcp.xn--tu-mnchen-t9a.example, which results in
	12. (not executed)		(TTL 499) 0 10 2083 radsec.xn--tu-mnchen-t9a.example.
			(TTL 2200) 0 20 2083 backup.xn--tu-mnchen-t9a.example.
			10. NOOP
			11. O' = {
			(radsec.xn--tu-mnchen-t9a.example.; 2083; 10; 60),
			(backup.xn--tu-mnchen-t9a.example.; 2083; 20; 60)
			} // minimum TTL is 47, up'ed to MIN_EFF_TTL
			12. Continuing at 18.
	13. (not executed)		13. (not executed)
	14. O = {(2001:0DB8::202:44ff:fe0a:f704; 2083; 10; TTL		14. (not executed)
	A),(192.0.2.7; 2083; 20; TTL B)}
	15. O = {(2001:0DB8::202:44ff:fe0a:f704; 2083; 10; TTL		15. (not executed)
	A),(192.0.2.7; 2083; 20; TTL B)}. Terminate.
			16. (not executed)
			17. (not executed)
			18. O-1 = {
			(2001:0DB8::202:44ff:fe0a:f704; 2083; 10; 60),
			(192.0.2.7; 2083; 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		The implementation will then attempt to connect to two servers, with
	preference to radsec.xn--tu-mnchen-t9a.example.:2083, using either		preference to [2001:0DB8::202:44ff:fe0a:f704]:2083.
	the AAAA or A addresses depending on the host configuration and its
	IP stack's capabilities.
	3. Security Considerations		4. Security Considerations
	When using DNS without DNSSEC security extensions, the replies to		The results from the execution of this algorithm are only trustworthy
	NAPTR, SRV and A/AAAA requests as described in section Section 2 can		if each of the lookup steps by the name resolution library were
	not be trusted. RADIUS transports have an out-of-DNS-band means to		cryptographically secured; i.e. if DNSSEC validation was turned on
	verify that the discovery attempt led to the intended target:		during the resolution AND all of the records were in a DNSSEC signed
	certificate verification or TLS-PSK keys.		zone AND validation of all those records was successful.
	4. IANA Considerations		When using DNS without DNSSEC security extensions for at least one of
			the replies to NAPTR, SRV and A/AAAA requests as described in section
			Section 3, the result O 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 time-out 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.
			5. IANA Considerations
	This document requests IANA registration of the following entries in		This document requests IANA registration of the following entries in
	existing registries:		existing registries:
	o S-NAPTR Application Service Tags registry		o S-NAPTR Application Service Tags registry
	* aaa+auth		* aaa+auth
	* aaa+acct
			* aaa+acct
	* aaa+dynauth		* aaa+dynauth
	o S-NAPTR Application Protocol Tags registry		o S-NAPTR Application Protocol Tags registry
	* radius.tls		* radius.tls
	* radius.dtls		* radius.dtls
	This document reserves the use of the "_radiustls" and "_radiusdtls"		This document reserves the use of the "_radiustls" and "_radiusdtls"
	Service labels.		Service labels.
	This document requests the creation of a new IANA registry named		This document requests the creation of a new IANA registry named
	"RADIUS/TLS SRV Protocol Registry" with the following initial		"RADIUS/TLS SRV Protocol Registry" with the following initial
	entries:		entries:
	o _tcp		o _tcp
	o _udp		o _udp
	5. Normative References		6. Normative References
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.		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,		[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
	"Remote Authentication Dial In User Service (RADIUS)", RFC		"Remote Authentication Dial In User Service (RADIUS)", RFC
	2865, June 2000.		2865, June 2000.
	[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.		[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
	[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application		[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application
	Service Location Using SRV RRs and the Dynamic Delegation		Service Location Using SRV RRs and the Dynamic Delegation
	Discovery Service (DDDS)", RFC 3958, January 2005.		Discovery Service (DDDS)", RFC 3958, January 2005.
	[RFC5176] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.		[RFC5176] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
	Aboba, "Dynamic Authorization Extensions to Remote		Aboba, "Dynamic Authorization Extensions to Remote
	Authentication Dial In User Service (RADIUS)", RFC 5176,		Authentication Dial In User Service (RADIUS)", RFC 5176,
	January 2008.		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.		[RFC5580] Tschofenig, H., Adrangi, F., Jones, M., Lior, A., and B.
	Aboba, "Carrying Location Objects in RADIUS and Diameter",		Aboba, "Carrying Location Objects in RADIUS and Diameter",
	RFC 5580, August 2009.		RFC 5580, August 2009.
	[RFC5891] Klensin, J., "Internationalized Domain Names in		[RFC5891] Klensin, J., "Internationalized Domain Names in
	Applications (IDNA): Protocol", RFC 5891, August 2010.		Applications (IDNA): Protocol", RFC 5891, August 2010.
	[I-D.ietf-radext-dtls]		[I-D.ietf-radext-dtls]
	DeKok, A., "DTLS as a Transport Layer for RADIUS", draft-		DeKok, A., "DTLS as a Transport Layer for RADIUS", draft-
	ietf-radext-dtls-02 (work in progress), July 2012.		ietf-radext-dtls-05 (work in progress), April 2013.
	[RFC6614] Winter, S., McCauley, M., Venaas, S., and K. Wierenga,		[RFC6614] Winter, S., McCauley, M., Venaas, S., and K. Wierenga,
	"Transport Layer Security (TLS) Encryption for RADIUS",		"Transport Layer Security (TLS) Encryption for RADIUS",
	RFC 6614, May 2012.		RFC 6614, May 2012.
			[I-D.ietf-radext-nai]
			DeKok, A., "The Network Access Identifier", draft-ietf-
			radext-nai-03 (work in progress), May 2013.
			Appendix A. Appendix A: ASN.1 Syntax of NAIRealm
			PKIXServiceNameSAN93 {iso(1) identified-organization(3) dod(6)
			internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
			id-mod-dns-srv-name-93(40) }
			DEFINITIONS EXPLICIT TAGS ::=
			BEGIN
			-- EXPORTS ALL --
			IMPORTS
			id-pkix
			FROM PKIX1Explicit88 { iso(1) identified-organization(3)
			dod(6) internet(1) security(5) mechanisms(5) pkix(7)
			id-mod(0) id-pkix1-explicit(18) } ;
			-- from RFC 5280
			-- In the GeneralName definition using the 1993 ASN.1 syntax
			-- includes:
			OTHER-NAME ::= TYPE-IDENTIFIER
			-- Service Name Object Identifier
			id-on OBJECT IDENTIFIER ::= { id-pkix 8 }
			id-on-nai OBJECT IDENTIFIER ::= { id-on XXX }
			-- Service Name
			naiRealm OTHER-NAME ::= { NAIRealm IDENTIFIED BY { id-on-nai }}
			NAIRealm ::= UTF8String (SIZE (1..MAX))
			END
	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
	Fax: +352 422473		Fax: +352 422473
End of changes. 74 change blocks.
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