TOC 
Individual SubmissionM. Jones
Internet-DraftBridgewater Systems
Updates: 3588 (if approved)J. Korhonen
Intended status: Standards TrackNokia Siemens Networks
Expires: June 12, 2010December 09, 2009


Diameter Extended NAPTR
draft-jones-dime-extended-naptr-01

Abstract

This document describes an extended format for the NAPTR service fields used in dynamic Diameter agent discovery. The extended format allows NAPTR queries to contain Diameter Application-Id information.

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] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

Status of this Memo

This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79.

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Table of Contents

1.  Introduction
2.  Terminology
3.  Extended NAPTR Service Field
4.  Extended NAPTR-based Diameter Peer Discovery
5.  IANA Considerations
6.  Security Considerations
7.  Normative References
§  Authors' Addresses




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1.  Introduction

The Diameter base protocol [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.) specifies three mechanisms for the Diameter peer discovery. One of these involves the Diameter implementation performing a NAPTR query [RFC3403] (Mealling, M., “Dynamic Delegation Discovery System (DDDS) Part Three: The Domain Name System (DNS) Database,” October 2002.) for a server in a particular realm. These NAPTR records provide a mapping from a domain, to the SRV record [RFC2782] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.) for contacting a server with the specific transport protocol in the NAPTR services field.

Section 11.6 of RFC 3588 defines the following NAPTR service fields:

      Services Field               Protocol
      AAA+D2T                       TCP
      AAA+D2S                       SCTP

However, foreseen network topologies require border AAA nodes that will be specialized by Diameter application and the NAPTR service field does not allow a Diameter implementation to determine the application supported by the AAA node. Without this information, a Diameter implementation must connect and perform a capability negotiation with each candidate AAA node. This document addresses this problem by specifying an extended NAPTR service field format that permits discovery of Diameter peers that support a specific Diameter application.



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2.  Terminology

The Diameter base protocol specification (Section 1.4 of RFC 3588) defines most of the terminology used in this document.



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3.  Extended NAPTR Service Field

The Extended NAPTR service field ABNF specification for the discovery of Diameter agents supporting a specific Diameter application is show below.

      naptr-svc-field     = "AAA+D2" < protocol> [ *appln-list ]

      protocol            = "T" / "S"
                            ; "T" for TCP and "S" for SCTP.

      appln-list          = "+AP:" appln-id [ *( "," appln-id ) ]
                            ; Comma separated list of application
                            ; identifiers prefixed by "+AP:".

      appln-id            = *DIGIT
                            ; Application identifier expressed as a
                            ; decimal integer.

For example, a NAPTR service field value of:

'AAA+D2S+AP:6'

Means that the Diameter node in the SRV record supports the Diameter Session Initiation Protocol (SIP) Application ('6') and SCTP as the transport protocol.
'AAA+D2S+AP:6,1,5,4294967295'

Means that the Diameter node in the SRV record supports the Diameter Session Initiation Protocol (SIP) Application ('6'), NASREQ Application ('1'), EAP Application ('5') and SCTP as the transport protocol. The Diameter node also provides Relay functionality ('4294967295').

The maximum length of the NAPTR service field is 256 octets including one octet length field (see Section 4.1 of RFC 3403 and Section 3.3 of [RFC1035] (Mockapetris, P., “Domain names - implementation and specification,” November 1987.)). The DNS administrator of some domain SHOULD also provision base RFC 3588 style NAPTR records in order to guarantee backwards compatibility with legacy RFC 3588 compliant Diameter peers. If the DNS administrator provisions both extended NAPTR records as defined in this specification and legacy RFC 3588 NAPTR records, then the extended NAPTR records MUST have higher priority (e.g. lower order and/or preference values) than legacy NAPTR records.



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4.  Extended NAPTR-based Diameter Peer Discovery

The basic Diameter Peer Discover principles are described in Section 5.2 of [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.). This specification extends 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 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 for that particular transport protocol. If the server supports multiple transport protocols, there will be multiple NAPTR records, each with a different Services Field value and potentially different list of supported Diameter applications.

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] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.).

a.
The Diameter implementation performs a NAPTR query for a server in a particular realm. The Diameter implementation has to know in advance which realm to look for a Diameter agent in and which Application Identifier it is interested in. The realm could be deduced, for example, from the 'realm' in a NAI that a Diameter implementation needed to perform a Diameter operation on.
b.
If the returned NAPTR service fields contain entries formatted as "AAA+D2X+AP:Y" where "X" indicates the transport protocol and "Y" is a comma-separated list of Application Identifiers, the target realm supports the extended format for NAPTR-based Diameter peer discovery defined in this document.
If "X" matches a transport protocol supported by the client and "Y" contains the required Application Identifier, the client resolves the "replacement" field entry to a target host using the lookup method appropriate for the "flags" field.
If "X" does not match a transport protocol supported by the client or "Y" does not contain the required Application Identifier, the peer discovery is abandoned.
c.
If the returned NAPTR service fields contain entries formatted as "AAA+D2X" where "X" indicates the transport protocol, the target realm supports the NAPTR-based Diameter peer discovery defined in [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.).
If "X" matches a transport protocol supported by the client, the client resolves the "replacement" field entry to a target host using the lookup method appropriate for the "flags" field.
If "X" does not match a transport protocol supported by the client, the peer discovery is abandoned.
d.
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] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.).



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5.  IANA Considerations

Section 11.6 of [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.) defines a IANA registry for the NAPTR Services Field entries. Although this document does not define a new transport protocol, it is proposed to add the following entries to the existing registry to reflect the extended format of the NAPTR Services Field:

      Services Field               Protocol
      AAA+D2T+AP:x                  TCP
      AAA+D2S+AP:x                  SCTP

Editor's Note: IANA is currently missing the registry for the NAPTR Service Fields defined in [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.). This oversight will need to be resolved for this document to proceed.



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6.  Security Considerations

This document specifies an enhancement to the NAPTR service field format defined in the Diameter base protocol and the same security considerations described in RFC 3588 are applicable to this document. No further extensions are required beyond the security mechanisms offered by RFC 3588. However, a malicious host doing 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.



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7. Normative References

[RFC1035] Mockapetris, P., “Domain names - implementation and specification,” STD 13, RFC 1035, November 1987 (TXT).
[RFC2119] Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML).
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” RFC 2782, February 2000 (TXT).
[RFC3403] Mealling, M., “Dynamic Delegation Discovery System (DDDS) Part Three: The Domain Name System (DNS) Database,” RFC 3403, October 2002 (TXT).
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” RFC 3588, September 2003 (TXT).


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Authors' Addresses

  Mark Jones
  Bridgewater Systems
Email:  mark.jones@bridgewatersystems.com
  
  Jouni Korhonen
  Nokia Siemens Networks
Email:  jouni.nospam@gmail.com