RFC 6408 PROPOSED STANDARD DIAMETER · DNS · DISCOVERY
Diameter S-NAPTR: Diameter Straightforward-Naming Authority Pointer (S-NAPTR) Usage
Lets a realm advertise, in DNS, which Diameter applications and transports each server supports.
RFC EDITOR
Jones, M., Korhonen, J., and L. Morand, "Diameter Straightforward-Naming Authority Pointer (S-NAPTR) Usage", RFC 6408, DOI 10.17487/RFC6408, November 2011, <https://www.rfc-editor.org/info/rfc6408>.
BIBTEX
@misc{rfc6408,
series = {Request for Comments},
number = 6408,
howpublished = {RFC 6408},
publisher = {RFC Editor},
doi = {10.17487/RFC6408},
url = {https://www.rfc-editor.org/info/rfc6408},
author = {M. Jones and J. Korhonen and L. Morand},
title = {{Diameter Straightforward-Naming Authority Pointer (S-NAPTR) Usage}},
pagetotal = 14,
year = 2011,
month = nov,
} LINEAGE · FROM THE RFC INDEXOpen full graph →
RFC text
Contents
Internet Engineering Task Force (IETF) M. Jones
Request for Comments: 6408 Bridgewater Systems
Updates: 3588 J. Korhonen
Category: Standards Track Nokia Siemens Networks
ISSN: 2070-1721 L. Morand
Orange Labs
November 2011
Diameter Straightforward-Naming Authority Pointer (S-NAPTR) Usage
Abstract
The Diameter base protocol specifies mechanisms whereby a given realm
may advertise Diameter nodes and the supported transport protocol.
However, these mechanisms do not reveal the Diameter applications
that each node supports. A peer outside the realm would have to
perform a Diameter capability exchange with every node until it
discovers one that supports the required application. This document
updates RFC 3588, "Diameter Base Protocol", and describes an
improvement using an extended format for the Straightforward-Naming
Authority Pointer (S-NAPTR) application service tag that allows for
discovery of the supported applications without doing Diameter
capability exchange beforehand.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6408.
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
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................2
2. Terminology .....................................................3
2.1. Requirements Language ......................................3
3. Extended NAPTR Service Field Format .............................3
3.1. IETF Standards Track Diameter Applications .................5
3.2. Vendor-Specific Diameter Applications ......................5
4. Backwards Compatibility .........................................5
5. Extended NAPTR-Based Diameter Peer Discovery ....................6
5.1. Examples ...................................................7
6. Usage Guidelines ................................................8
7. IANA Considerations .............................................9
7.1. IETF Diameter Application Service Tags .....................9
7.2. 3GPP Diameter Application Service Tags .....................9
7.3. WiMAX Forum Diameter Application Service Tags .............10
7.4. Vendor-Specific Diameter Application Service Tags .........10
7.5. Diameter Application Protocol Tags ........................11
8. Security Considerations ........................................11
9. Acknowledgments ................................................11
10. References ....................................................12
10.1. Normative References .....................................12
10.2. Informative References ...................................14
1. Introduction
The Diameter base protocol [RFC3588] specifies three mechanisms for
Diameter peer discovery. One of these involves the Diameter
implementation performing a Naming Authority Pointer (NAPTR) query
[RFC3403] for a server in a particular realm. These NAPTR records
provide a mapping from a domain to the DNS Service Locator (SRV)
record [RFC2782] or A/AAAA record [RFC1035] [RFC3596] for contacting
a server with the specific transport protocol in the NAPTR services
field.
The extended NAPTR usage for Diameter peer discovery defined by this
document is based on the Straightforward-NAPTR (S-NAPTR) Dynamic
Delegation Discovery System (DDDS) application defined in [RFC3958].
This document updates the Diameter peer discovery procedure described
in Section 5.2 of [RFC3588] and defines S-NAPTR application service
and application protocol tag values that permit the discovery of
Diameter peers that support a specific Diameter application and
transport protocol.
2. Terminology
The Diameter base protocol specification (Section 1.3 of [RFC3588])
and the Straightforward-NAPTR (S-NAPTR) DDDS application (Section 2.1
of [RFC3958]) define the terminology used in this document.
2.1. Requirements Language
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 [RFC2119].
3. Extended NAPTR Service Field Format
The NAPTR service field format defined by the S-NAPTR DDDS
application in [RFC3958] follows this Augmented Backus-Naur Form
(ABNF) [RFC5234]:
service-parms = [ [app-service] *(":" app-protocol)]
app-service = experimental-service / iana-registered-service
app-protocol = experimental-protocol / iana-registered-protocol
experimental-service = "x-" 1*30ALPHANUMSYM
experimental-protocol = "x-" 1*30ALPHANUMSYM
iana-registered-service = ALPHA *31ALPHANUMSYM
iana-registered-protocol = ALPHA *31ALPHANUMSYM
ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
DIGIT = %x30-39 ; 0-9
SYM = %x2B / %x2D / %x2E ; "+" / "-" / "."
ALPHANUMSYM = ALPHA / DIGIT / SYM
; The app-service and app-protocol tags are limited to 32
; characters and must start with an alphabetic character.
; The service-parms are considered case-insensitive.
This specification refines the "iana-registered-service" tag
definition for the discovery of Diameter agents supporting a specific
Diameter application as defined below.
iana-registered-service =/ aaa-service
aaa-service = "aaa+ap" appln-id
appln-id = 1*10DIGIT
; Application Identifier expressed as
; a decimal integer without leading
; zeros.
The appln-id element is the Application Identifier used to identify a
specific Diameter application. The Diameter Application Identifier
is a 32-bit unsigned integer, and values are allocated by IANA as
defined in [RFC3588].
This specification also refines the "iana-registered-protocol" tag
definition for the discovery of Diameter agents supporting a specific
Diameter transport protocol as defined below.
iana-registered-protocol =/ aaa-protocol
aaa-protocol = "diameter." aaa-transport
aaa-transport = "tcp" / "sctp" / "tls.tcp"
The S-NAPTR application protocol tags defined by this specification
MUST NOT be parsed in any way by the querying application or
resolver. The delimiter (".") is present in the tag to improve
readability and does not imply a structure or namespace of any kind.
The choice of delimiter (".") for the application protocol tag
follows the format of existing S-NAPTR application protocol tag
registry entries, but this does not imply that it shares semantics
with any other specifications that create registry entries with the
same format.
The S-NAPTR application service and application protocol tags defined
by this specification are unrelated to the IANA "Service Name and
Transport Protocol Port Number Registry" (see [RFC6335]).
The maximum length of the NAPTR service field is 256 octets,
including a one-octet length field (see Section 4.1 of [RFC3403] and
Section 3.3 of [RFC1035]).
3.1. IETF Standards Track Diameter Applications
A Diameter agent MUST be capable of using the extended S-NAPTR
application service tag for dynamic discovery of a Diameter agent
supporting Standards Track applications. Therefore, every IETF
Standards Track Diameter application MUST be associated with a
"aaa-service" tag formatted as defined in this specification and
allocated in accordance with IANA policy (see Section 7).
For example, a NAPTR service field value of:
'aaa+ap6:diameter.sctp'
means that the Diameter node in the SRV or A/AAAA record supports the
Diameter Session Initiation Protocol (SIP) application ('6') and the
Stream Control Transmission Protocol (SCTP) as the transport
protocol.
3.2. Vendor-Specific Diameter Applications
S-NAPTR application service and application protocol tag values can
also be used to discover Diameter peers that support a vendor-
specific Diameter application. In this case, the vendor-specific
Diameter application MUST be associated with a "aaa-service" tag
formatted as defined in this specification and allocated in
accordance with IANA policy (see Section 7).
For example, a NAPTR service field value of:
'aaa+ap16777251:diameter.sctp'
means that the Diameter node in the SRV or A/AAAA record supports the
Diameter Third Generation Partnership Project (3GPP) S6a application
('16777251') and SCTP as the transport protocol.
4. Backwards Compatibility
Domain Name System (DNS) administrators SHOULD also provision legacy
NAPTR records [RFC3403] in the RFC 3588 style in order to guarantee
backwards compatibility with legacy Diameter peers that are RFC 3588
compliant. If the DNS administrator provisions both extended S-NAPTR
records as defined in this specification and legacy RFC 3588 NAPTR
records, then the extended S-NAPTR records MUST have higher priority
(e.g., lower order and/or preference values) than legacy NAPTR
records.
5. Extended NAPTR-Based Diameter Peer Discovery
The Diameter Peer Discovery principles are described in Section 5.2
of [RFC3588]. This specification updates the NAPTR query procedure
in the Diameter peer discovery mechanism by allowing the querying
node to determine which applications are supported by resolved
Diameter peers.
The extended-format NAPTR records provide a mapping from a domain to
the SRV record or A/AAAA record for contacting a server supporting a
specific transport protocol and Diameter application. The resource
record will contain an empty regular expression and a replacement
value, which is the SRV record or the A/AAAA record for that
particular transport protocol.
The assumption for this mechanism to work is that the DNS
administrator of the queried domain has first provisioned the DNS
with extended-format NAPTR entries. The steps below replace the
NAPTR query procedure steps in Section 5.2 of [RFC3588].
a. The Diameter implementation performs a NAPTR query for a server in
a particular realm. The Diameter implementation has to know in
advance in which realm to look for a Diameter agent, and in which
Application Identifier it is interested. For example, the realm
could be deduced from the Network Access Identifier (NAI) in the
User-Name attribute-value pair (AVP) or extracted from the
Destination-Realm AVP.
b. If the returned NAPTR service fields contain entries formatted as
"aaa+apX:Y" where "X" indicates the Application Identifier and "Y"
indicates the supported transport protocol(s), the target realm
supports the extended format for NAPTR-based Diameter peer
discovery defined in this document.
If "X" contains the required Application Identifier and "Y"
matches a supported transport protocol, the Diameter
implementation resolves the "replacement" field entry to a
target host using the lookup method appropriate for the "flags"
field.
If "X" does not contain the required Application Identifier or
"Y" does not match a supported transport protocol, the Diameter
implementation abandons the peer discovery.
c. If the returned NAPTR service fields contain entries formatted as
"aaa+apX" where "X" indicates the Application Identifier, the
target realm supports the extended format for NAPTR-based Diameter
peer discovery defined in this document.
If "X" contains the required Application Identifier, the
Diameter implementation resolves the "replacement" field entry
to a target host using the lookup method appropriate for the
"flags" field and attempts to connect using all supported
transport protocols following the order specified in
Section 2.1 of [RFC3588].
If "X" does not contain the required Application Identifier,
the Diameter implementation abandons the peer discovery.
d. If the returned NAPTR service fields contain entries formatted as
"aaa:X" where "X" indicates the supported transport protocol(s),
the target realm supports Diameter but does not support the
extended format for NAPTR-based Diameter peer discovery defined in
this document.
If "X" matches a supported transport protocol, the Diameter
implementation resolves the "replacement" field entry to a
target host using the lookup method appropriate for the "flags"
field.
e. If the returned NAPTR service fields contain entries formatted as
"aaa", the target realm supports Diameter but does not support the
extended format for NAPTR-based Diameter peer discovery defined in
this document. The Diameter implementation resolves the
"replacement" field entry to a target host using the lookup method
appropriate for the "flags" field and attempts to connect using
all supported transport protocols following the order specified in
Section 2.1 of [RFC3588].
f. If the target realm does not support NAPTR-based Diameter peer
discovery, the client proceeds with the next peer discovery
mechanism described in Section 5.2 of [RFC3588].
5.1. Examples
As an example, consider a client that wishes to discover a Diameter
server in the ex1.example.com realm that supports the Credit Control
application. The client performs a NAPTR query for that domain, and
the following NAPTR records are returned:
;; order pref flags service regexp replacement
IN NAPTR 50 50 "s" "aaa:diameter.sctp" ""
_diameter._sctp.ex1.example.com
IN NAPTR 50 50 "s" "aaa+ap1:diameter.sctp" ""
_diameter._sctp.ex1.example.com
IN NAPTR 50 50 "s" "aaa+ap4:diameter.sctp" ""
_diameter._sctp.ex1.example.com
This indicates that the server supports NASREQ (ID=1) and Credit
Control (ID=4) applications over SCTP. If the client supports SCTP,
it will be used, targeted to a host determined by an SRV lookup of
_diameter._sctp.ex1.example.com.
That SRV lookup would return:
;; Priority Weight Port Target
IN SRV 0 1 3868 server1.ex1.example.com
IN SRV 0 2 3868 server2.ex1.example.com
As an alternative example, a client wishes to discover a Diameter
server in the ex2.example.com realm that supports the NASREQ
application over SCTP. The client performs a NAPTR query for that
domain, and the following NAPTR records are returned:
;; order pref flags service regexp replacement
IN NAPTR 150 50 "a" "aaa:diameter.sctp" ""
server1.ex2.example.com
IN NAPTR 150 50 "a" "aaa:diameter.tls.tcp" ""
server2.ex2.example.com
IN NAPTR 150 50 "a" "aaa+ap1:diameter.sctp" ""
server1.ex2.example.com
IN NAPTR 150 50 "a" "aaa+ap1:diameter.tls.tcp" ""
server2.ex2.example.com
This indicates that the server supports NASREQ (ID=1) over SCTP and
Transport Layer Security (TLS)/TCP via hosts server1.ex2.example.com
and server2.ex2.example.com, respectively.
6. Usage Guidelines
Diameter is a peer-to-peer protocol, whereas most of the applications
that extend the base protocol behave like client/server applications.
The role of the peer is not advertised in the NAPTR tags and not even
communicated during Diameter capability negotiation
(Capabilities-Exchange-Request and Capabilities-Exchange-Answer
message exchange). For this reason, NAPTR-based Diameter peer
discovery for an application defining client/server roles should only
be used by a client to discover servers.
7. IANA Considerations
7.1. IETF Diameter Application Service Tags
IANA has reserved a value of "aaa" for Diameter in the "(S-NAPTR)
Application Service Tag" registry created by [RFC3958]. IANA has
also reserved the following S-NAPTR application service tags for
existing IETF Diameter applications in the same registry.
+------------------+----------------------------+
| Tag | Diameter Application |
+------------------+----------------------------+
| aaa+ap1 | NASREQ [RFC3588] |
| aaa+ap2 | Mobile IPv4 [RFC4004] |
| aaa+ap3 | Base Accounting [RFC3588] |
| aaa+ap4 | Credit Control [RFC4006] |
| aaa+ap5 | EAP [RFC4072] |
| aaa+ap6 | SIP [RFC4740] |
| aaa+ap7 | Mobile IPv6 IKE [RFC5778] |
| aaa+ap8 | Mobile IPv6 Auth [RFC5778] |
| aaa+ap9 | QoS [RFC5866] |
| aaa+ap4294967295 | Relay [RFC3588] |
+------------------+----------------------------+
Future IETF Diameter applications MUST reserve the S-NAPTR
application service tag corresponding to the allocated Diameter
Application ID as defined in Section 3.
7.2. 3GPP Diameter Application Service Tags
IANA has reserved the following S-NAPTR application service tags for
existing 3GPP Diameter applications in the "S-NAPTR Application
Service Tag" registry created by [RFC3958].
+----------------+----------------------+
| Tag | Diameter Application |
+----------------+----------------------+
| aaa+ap16777250 | 3GPP STa [TS29.273] |
| aaa+ap16777251 | 3GPP S6a [TS29.272] |
| aaa+ap16777264 | 3GPP SWm [TS29.273] |
| aaa+ap16777267 | 3GPP S9 [TS29.215] |
+----------------+----------------------+
Future 3GPP Diameter applications can reserve entries in the "S-NAPTR
Application Service Tag" registry created by [RFC3958] that
correspond to the allocated Diameter Application IDs as defined in
Section 3.
7.3. WiMAX Forum Diameter Application Service Tags
IANA has reserved the following S-NAPTR application service tags for
existing Worldwide Interoperability for Microwave Access (WiMAX)
Forum Diameter applications in the "S-NAPTR Application Service Tag"
registry created by [RFC3958].
+----------------+--------------------------------------------------+
| Tag | Diameter Application |
+----------------+--------------------------------------------------+
| aaa+ap16777281 | WiMAX Network Access Authentication and |
| | Authorization Diameter Application (WNAAADA) |
| | [WiMAX-BASE] |
| aaa+ap16777282 | WiMAX Network Accounting Diameter Application |
| | (WNADA) [WiMAX-BASE] |
| aaa+ap16777283 | WiMAX MIP4 Diameter Application (WM4DA) |
| | [WiMAX-BASE] |
| aaa+ap16777284 | WiMAX MIP6 Diameter Application (WM6DA) |
| | [WiMAX-BASE] |
| aaa+ap16777285 | WiMAX DHCP Diameter Application (WDDA) |
| | [WiMAX-BASE] |
| aaa+ap16777286 | WiMAX Location Authentication Authorization |
| | Diameter Application (WLAADA) [WiMAX-LBS] |
| aaa+ap16777287 | WiMAX Policy and Charging Control R3 Policies |
| | Diameter Application (WiMAX PCC-R3-P) |
| | [WiMAX-PCC] |
| aaa+ap16777288 | WiMAX Policy and Charging Control R3 Offline |
| | Charging Diameter Application (WiMAX PCC-R3-OFC) |
| | [WiMAX-PCC] |
| aaa+ap16777289 | WiMAX Policy and Charging Control R3 Offline |
| | Charging Prime Diameter Application (WiMAX |
| | PCC-R3-OFC-PRIME) [WiMAX-PCC] |
| aaa+ap16777290 | WiMAX Policy and Charging Control R3 Online |
| | Charging Diameter Application (WiMAX PCC-R3-OC) |
| | [WiMAX-PCC] |
+----------------+--------------------------------------------------+
Future WiMAX Forum Diameter applications can reserve entries in the
"S-NAPTR Application Service Tag" registry created by [RFC3958] that
correspond to the allocated Diameter Application IDs as defined in
Section 3.
7.4. Vendor-Specific Diameter Application Service Tags
Vendor-Specific Diameter Application IDs are allocated by IANA
according to the "First Come First Served" policy and do not require
an IETF specification. However, the S-NAPTR application service tag
registry created by [RFC3958] defines a registration policy of
"Specification Required" with a further stipulation that the
"specification" is an RFC (of any category). If a vendor-specific
Diameter application requires the functionality defined in this
document, an RFC of any category MUST be published that reserves the
S-NAPTR Application Service Tag corresponding to the Vendor-Specific
Diameter Application ID as defined in Section 3.
7.5. Diameter Application Protocol Tags
IANA has reserved the following S-NAPTR Application Protocol Tags for
the Diameter transport protocols in the "S-NAPTR Application Protocol
Tag" registry created by [RFC3958].
+------------------+----------+
| Tag | Protocol |
+------------------+----------+
| diameter.tcp | TCP |
| diameter.sctp | SCTP |
| diameter.tls.tcp | TLS/TCP |
+------------------+----------+
Future Diameter versions that introduce new transport protocols MUST
reserve an appropriate S-NAPTR Application Protocol Tag in the
"S-NAPTR Application Protocol Tag" registry created by [RFC3958].
8. Security Considerations
This document specifies an enhancement to the NAPTR service field
format defined in RFC 3588 and also modifications to the NAPTR
processing logic defined in RFC 3588. The enhancement and
modifications are based on the S-NAPTR, which is actually a
simplification of the NAPTR, and therefore the same security
considerations described in RFC 3588 [RFC3588] are applicable to this
document. No further extensions are required beyond the security
mechanisms offered by RFC 3588. However, a malicious host doing
S-NAPTR queries learns applications supported by Diameter agents in a
certain realm faster, which might help the malicious host to scan
potential targets for an attack more efficiently when some
applications have known vulnerabilities.
9. Acknowledgments
We would like to thank Glen Zorn, Avi Lior, Itsuma Tanaka, Sebastien
Decugis, Dan Romascanu, Adrian Farrel, David Harrington, Pete
Resnick, Robert Sparks, Stephen Farrell, Wesley Eddy, Ralph Droms,
and Joe Touch for their comprehensive review comments.
10. References
10.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)",
RFC 2782, February 2000.
[RFC3403] Mealling, M., "Dynamic Delegation Discovery System
(DDDS) Part Three: The Domain Name System (DNS)
Database", RFC 3403, October 2002.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588,
September 2003.
[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", RFC 3596,
October 2003.
[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.
[RFC4004] Calhoun, P., Johansson, T., Perkins, C., Hiller, T.,
Ed., and P. McCann, "Diameter Mobile IPv4 Application",
RFC 4004, August 2005.
[RFC4006] Hakala, H., Mattila, L., Koskinen, J-P., Stura, M., and
J. Loughney, "Diameter Credit-Control Application",
RFC 4006, August 2005.
[RFC4072] Eronen, P., Ed., Hiller, T., and G. Zorn, "Diameter
Extensible Authentication Protocol (EAP) Application",
RFC 4072, August 2005.
[RFC4740] Garcia-Martin, M., Ed., Belinchon, M., Pallares-Lopez,
M., Canales-Valenzuela, C., and K. Tammi, "Diameter
Session Initiation Protocol (SIP) Application",
RFC 4740, November 2006.
[RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234,
January 2008.
[RFC5778] Korhonen, J., Ed., Tschofenig, H., Bournelle, J.,
Giaretta, G., and M. Nakhjiri, "Diameter Mobile IPv6:
Support for Home Agent to Diameter Server Interaction",
RFC 5778, February 2010.
[RFC5866] Sun, D., Ed., McCann, P., Tschofenig, H., Tsou, T.,
Doria, A., and G. Zorn, Ed., "Diameter
Quality-of-Service Application", RFC 5866, May 2010.
[TS29.215] 3rd Generation Partnership Project, "3GPP TS 29.215;
Technical Specification Group Core Network and
Terminals; Policy and Charging Control (PCC) over S9
reference point; Stage 3 (Release 8)",
<http://www.3gpp.org/ftp/Specs/html-info/29215.htm>.
[TS29.272] 3rd Generation Partnership Project, "3GPP TS 29.272;
Technical Specification Group Core Network and
Terminals; Evolved Packet System (EPS); Mobility
Management Entity (MME) and Serving GPRS Support Node
(SGSN) Related Interfaces Based on Diameter Protocol
(Release 8)",
<http://www.3gpp.org/ftp/Specs/html-info/29272.htm>.
[TS29.273] 3rd Generation Partnership Project, "3GPP TS 29.273;
Technical Specification Group Core Network and
Terminals; Evolved Packet System (EPS); 3GPP EPS AAA
interfaces (Release 8)",
<http://www.3gpp.org/ftp/Specs/html-info/29273.htm>.
[WiMAX-BASE] WiMAX Forum, "WMF-T33-001-R015v02 - WiMAX Forum(R)
Network Architecture - Detailed Protocols and
Procedures, Base Specification - Release 1.5",
<http://www.wimaxforum.org/resources/
documents/technical/T33>.
[WiMAX-LBS] WiMAX Forum, "WMF-T33-110-R015v01 - WiMAX Forum(R)
Network Architecture - Protocols and Procedures for
Location Based Services - Release 1.5",
<http://www.wimaxforum.org/resources/
documents/technical/T33>.
[WiMAX-PCC] WiMAX Forum, "WMF-T33-109-R015v02 - WiMAX Forum(R)
Network Architecture - Detailed Protocols and
Procedures, Policy and Charging Control - Release 1.5",
<http://www.wimaxforum.org/resources/
documents/technical/T33>.
10.2. Informative References
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and
S. Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, August 2011.
Authors' Addresses
Mark Jones
Bridgewater Systems
EMail: mark@azu.ca
Jouni Korhonen
Nokia Siemens Networks
EMail: jouni.nospam@gmail.com
Lionel Morand
Orange Labs
EMail: lionel.morand@orange.com
AI ELI5
On this page
PROBLEMThe Diameter base protocol lets a realm advertise nodes and transports in DNS, but not which Diameter applications they support, so a peer might have to run a capability exchange with every node until it finds a suitable one.
MECHANISMAn extended S-NAPTR service tag of the form aaa+ap followed by the Application Identifier, with an optional transport protocol tag, lets a NAPTR record say exactly which application and transport a server offers.
WHY IT MATTERSA client can pick the right server from DNS alone. The RFC updates RFC 3588 and asks DNS administrators to keep legacy records too.
§1Introduction
The Diameter base protocol (RFC 3588) defines three mechanisms for peer discovery. One is a NAPTR query for a server in a given realm, which maps a domain to an SRV record or A/AAAA record for contacting a server over a particular transport.
That mapping cannot say which Diameter applications a node supports. This RFC builds on the Straightforward-NAPTR (S-NAPTR) DDDS application of RFC 3958 and defines service and protocol tags so that a peer supporting a specific application and transport can be discovered. It updates Section 5.2 of RFC 3588.
The old directory said where the offices were, but not what each office did. The new one adds the topic.
§3The Extended Service Field
The RFC refines the S-NAPTR ABNF with two new tag forms.
- Application service:
aaa+apfollowed by anappln-idof 1 to 10 digits, the Diameter Application Identifier written as a decimal integer without leading zeros. The identifier is a 32-bit unsigned integer allocated by IANA. - Application protocol:
diameter.followed bytcp,sctportls.tcp.
For example, aaa+ap6:diameter.sctp means the node supports the Diameter SIP application (6) over SCTP. For a vendor-specific case, aaa+ap16777251:diameter.sctp means the 3GPP S6a application over SCTP.
Querying applications MUST NOT parse the protocol tags. The dot is only for readability and implies no structure. The tags are unrelated to the IANA Service Name and Transport Protocol Port Number Registry. The NAPTR service field is at most 256 octets, including a one-octet length field.
Each record gets a short label like a name tag: the topic number, then how to reach the office. The label is read as a whole, not taken apart.
§4Backwards Compatibility
DNS administrators SHOULD also provision legacy NAPTR records in the RFC 3588 style, so peers that only follow RFC 3588 still work. When both kinds exist, the extended S-NAPTR records MUST have higher priority than the legacy ones, for example through a lower order or preference value.
Every IETF Standards Track Diameter application MUST be associated with an aaa-service tag, and a Diameter agent MUST be able to use the extended tag to find an agent for such applications.
Keep the old signs up for visitors who only read those, but put the new, more detailed signs first.
§5Peer Discovery Procedure
The querying node must know the realm and the Application Identifier it wants. The realm could come from the Network Access Identifier in the User-Name AVP or from the Destination-Realm AVP. This RFC replaces the NAPTR query steps of RFC 3588 Section 5.2 with the following, depending on what the returned service fields look like.
aaa+apX:Y: the realm supports the extended format. If X is the needed application and Y a supported transport, resolve the replacement field. Otherwise abandon discovery.aaa+apX: if X is the needed application, resolve it and try all supported transports in the order given in Section 2.1 of RFC 3588. Otherwise abandon discovery.aaa:X: Diameter is supported without the extended format. If X is a supported transport, resolve the replacement field.aaa: likewise legacy, try all supported transports.- No NAPTR-based discovery at all: move on to the next mechanism in RFC 3588.
The RFC's example realm ex1.example.com publishes records for NASREQ (ID 1) and Credit Control (ID 4) over SCTP, and an SRV lookup of _diameter._sctp.ex1.example.com returns two servers on port 3868.
Diameter is peer-to-peer, but many applications behave as client and server, and the role is not advertised in NAPTR tags or in capability exchange. Such discovery should therefore only be used by a client to find servers.
The visitor reads each sign. If it names the right topic and a way they can travel, they go there. If not, they give up on this directory and try another way.
Credit Control over SCTP
;; order pref flags service regexp replacement
IN NAPTR 50 50 "s" "aaa+ap4:diameter.sctp" ""
_diameter._sctp.ex1.example.com§7IANA Registrations
IANA reserved aaa for Diameter in the S-NAPTR Application Service Tag registry of RFC 3958, plus tags for existing IETF applications.
aaa+ap1NASREQ,aaa+ap2Mobile IPv4,aaa+ap3Base Accounting,aaa+ap4Credit Control,aaa+ap5EAP,aaa+ap6SIP,aaa+ap7Mobile IPv6 IKE,aaa+ap8Mobile IPv6 Auth,aaa+ap9QoS, andaaa+ap4294967295Relay.- Four 3GPP tags (STa, S6a, SWm and S9) and ten WiMAX Forum tags.
- Protocol tags
diameter.tcp,diameter.sctpanddiameter.tls.tcp.
Future IETF Diameter applications MUST reserve their tag. Vendor-specific application IDs are allocated First Come First Served, but the tag registry requires a specification that is an RFC of any category, so such an application needing this functionality MUST have an RFC reserving its tag.
There is an official list of topic numbers and travel methods, and new ones have to be added to it properly.
§8Security Considerations
The change is based on S-NAPTR, a simplification of NAPTR, so the security considerations of RFC 3588 apply and no extra mechanisms are needed. The RFC adds one caution: a malicious host doing S-NAPTR queries learns the applications supported by a realm's Diameter agents faster, which could help it pick targets if some applications have known vulnerabilities.
A public directory also helps a troublemaker find the right door faster.
§7References
[RFC3588]RFC 3588Calhoun, P., et al., "Diameter Base Protocol", RFC 3588, September 2003.September 2003[RFC3958]RFC 3958Daigle, L. and A. Newton, "Domain-Based Application Service Location Using SRV RRs and the Dynamic Delegation Discovery Service (DDDS)", RFC 3958, January 2005.January 2005[RFC3403]RFC 3403Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part Three: The Domain Name System (DNS) Database", RFC 3403, October 2002.October 2002[RFC2782]RFC 2782Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, February 2000.February 2000[RFC5234]RFC 5234Crocker, D., Ed., and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008.January 2008