AAA Working Group Pat R. Calhoun Internet-Draft Sun Microsystems, Inc. Category: Standards Track Allan C. Rubens <draft-calhoun-diameter-18.txt> Tut Systems, Inc. Haseeb Akhtar Nortel Networks Erik Guttman Sun Microsystems, Inc. February 2001 Diameter Base Protocol Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at: http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at: http://www.ietf.org/shadow.html. Distribution of this memo is unlimited. Copyright (C) The Internet Society 2001. All Rights Reserved. Calhoun et al. expires July 2001 [Page 1]
Internet-Draft February 2001 Abstract The Diameter base protocol is intended to provide a AAA framework for Mobile-IP, NASREQ and ROAMOPS. This draft specifies the message format, transport, error reporting and security services to be used by all Diameter extensions and MUST be supported by all Diameter implementations. Table of Contents 1.0 Introduction 1.1 Requirements language 1.2 Terminology 2.0 Protocol Overview 2.1 Header Format 2.2 Command Code Definitions 2.3 AVP Format 2.3.1 AVP Header 2.3.2 Optional Header Elements 2.3.3 AVP Data Formats 2.3.4 Grouped AVP Values 2.3.4.1 Example AVP with a Grouped Data type 2.3.5 Diameter Base Protocol AVPs 2.4 Mandatory AVPs 2.4.1 Host-Name AVP 2.5 State Machine 2.6 Device-Reboot-Ind (DRI) Command 2.6.1 Vendor-Id AVP 2.6.2 Firmware-Revision AVP 2.6.3 Extension-Id AVP 2.6.4 Host-IP-Address AVP 2.6 Diameter Server Discovery 3.0 "User" Sessions 3.1 State Machine 3.2 Session-Id AVP 3.3 Authorization-Lifetime AVP 3.4 Session-Timeout AVP 3.5 User-Name AVP 3.6 Session Termination 3.6.1 Session-Termination-Ind 3.6.2 Session-Termination-Request 3.6.3 Session-Termination-Answer 4.0 Reliable Transport 5.0 Error Reporting 5.1 Message-Reject-Ind (MRI) Command 5.1.1 Failed-AVP AVP 5.1.2 Failed-Command-Code Calhoun et al. expires July 2001 [Page 2]
Internet-Draft February 2001 5.2 Result-Code AVP 5.2.1 Informational 5.2.2 Success 5.2.3 Redirect Notification 5.2.4 Transient Failures 5.2.5 Permanent Failures 5.2.6 Hop-by-Hop Failures 5.3 Error-Message AVP 5.4 Error-Reporting-NAI AVP 6.0 Message Routing 6.1 Realm-Based Message Routing 6.2 Behavior of Proxy and Redirect Servers 6.2.1 Proxy and Redirect Server handling of requests 6.3 Redirect Server 6.3.1 Redirect-Host AVP 6.3.2 Redirect-Host-Address AVP 6.3.3 Redirect-Host-Port AVP 6.4 Proxy Server 6.4.1 Proxying Requests 6.4.2 Proxying Responses 6.4.3 Route-Record AVP 6.4.4 Proxy-State AVP 6.4.5 Proxy-Address AVP 6.4.6 Proxy-Info AVP 6.4.7 Routing-Realm AVP 6.5 Applying Local Policies 6.6 Hiding Network Topology 6.7 Loop Detection 6.8 Finding a Target NAS within a Domain 6.8.1 Destination-NAI AVP 7.0 Diameter Message Security 7.1 Hop-by-Hop Security 7.1.1 Integrity-Check-Value AVP 7.1.1.1 Authentication-Transform-Id AVP 7.1.1.2 Digest AVP 7.1.2 Encrypted-Payload AVP 7.1.2.1 Encryption-Transform-Id AVP 7.1.2.1.1 MD5 Payload Hiding 7.1.2.2 Plaintext-Data-Length AVP 7.1.2.3 Encrypted-Data AVP 7.2 Nonce AVP 7.3 Timestamp AVP 7.4 Key-Id AVP 8.0 IANA Considerations 8.1 AVP Attributes 8.2 Command Code AVP Values 8.3 Extension Identifier Values 8.4 Result-Code AVP Values Calhoun et al. expires July 2001 [Page 3]
Internet-Draft February 2001 8.5 Integrity-Check-Value AVP Transform Values 8.6 Encryption-Transform-Id AVP Values 8.7 Message Header Bits 8.8 AVP Header Bits 9.0 Open Issues 10.0 Diameter protocol related configurable parameters 11.0 Security Considerations 12.0 References 13.0 Acknowledgements 14.0 Authors' Addresses 15.0 Full Copyright Statement Appendix A. Diameter Service Template Calhoun et al. expires July 2001 [Page 4]
Internet-Draft February 2001 1.0 Introduction The Diameter protocol allows peers to exchange a variety of messages. The base protocol provides the following facilities: - Delivery of AVPs (attribute value pairs) - Capabilities negotiation, as required in [20] - Error notification - Extensibility, through addition of new commands and AVPs, as required in [21] All data delivered by the protocol is in the form of an AVP. Some of these AVP values are used by the Diameter protocol itself, while others deliver data associated with particular applications which employ Diameter. AVPs may be added arbitrarily to Diameter messages, so long as the required AVPs are included and AVPs which are explicitly excluded are not included. AVPs are used by base Diameter protocol to support the following required features: - Transporting of user authentication information, for the purposes of enabling the Diameter server to authenticate the user. - Transporting of service specific authorization information, between client and servers, allowing the peers to decide whether a user's access request should be granted. - Exchanging resource usage information, which MAY be used for accounting purposes, capacity planning, etc. - Proxying and Re-directing of Diameter messages through a server hierarchy. - Providing application-level security, through the use of the Integrity-Check-Value (ICV) and Encrypted-Payload AVPs. The Diameter base protocol provides the minimum requirements needed for an AAA transport protocol, as required by NASREQ [21], Mobile IP [22, 23], and ROAMOPS [20]. The base protocol is not intended to be used by itself, and must be used with an application-specific extension, such as Mobile IP [10]. The Diameter protocol was heavily inspired and builds upon the tradition of the RADIUS [1] protocol. Any node can initiate a request. In that sense, Diameter is a peer to peer protocol. In this document, a Diameter client is the device that normally initiates a request for authentication and/or authorization of a user. A Diameter server is the device that either forwards the request to another Diameter server (known as a proxy), or one that performs the actual authentication and/or authorization of the user based on some profile. Given that the server MAY send unsolicited messages to clients, it is possible for the server to initiate such messages. An example of an unsolicited message would be for a request Calhoun et al. expires July 2001 [Page 5]
Internet-Draft February 2001 that the client issue an accounting update. Diameter services require sequenced in-order reliable delivery of data, with congestion control (receiver windowing). Timely detection of failed or unresponsive peers is also required, allowing for robust operation. TCP is insufficient for this second requirement. Diameter SHOULD be transported over SCTP [26]. 1.1 Requirements language In this document, the key words "MAY", "MUST", "MUST NOT", "optional", "recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as described in [13]. 1.2 Terminology Refer to [9] for terminology used in this document. 2.0 Protocol Overview The base Diameter protocol is never used on its own. It is always extended for a particular application. Four extensions to Diameter are defined by companion documents: NASREQ [7], Mobile IP [10], Accounting Extension [15], Strong Security [11]. These options are introduced in this document but specified elsewhere. Additional extensions to Diameter may be defined in the future (see Section 8.3). The base Diameter protocol concerns itself with capabilities negotiation, and how messages are sent and how peers may eventually be abandoned. The base protocol also defines certain rules which apply to all exchanges of messages between Diameter peers. It is important to note that the base protocol provides optional application-level security AVPs (Integrity-Check-Value) which MAY be used in absence of an underlying security protocol (e.g. IP Security). Communication between Diameter peers begins with one peer sending a message to another Diameter peer. The set of AVPs included in the message is determined by a particular application of or extension to Diameter. We will refer to this as the Diameter extension. One AVP that is included to reference a user's session is the Session-Id. The initial request for authentication and/or authorization of a user would include the Session-Id. The Session-Id is then used in all Calhoun et al. expires July 2001 [Page 6]
Internet-Draft February 2001 subsequent messages to identify the user's session (see section 3.0 for more information). The communicating party may accept the request, or reject it by returning a response with Result-Code AVP set to indicate an error occurred. The specific behavior of the diameter server or client receiving a request depends on the Diameter extension employed. Session state (associated with a Session-Id) MUST be freed upon receipt of the Session-Termination-Request, Session-Termination- Answer, expiration of authorized service time in the Session-Timeout AVP, and according to rules established in a particular extension/application of Diameter. Exchanges of messages are either request/reply oriented, or in some special cases, do not require replies. All such messages that do not require replies have names ending with '-Ind' (short for Indication). The Diameter base protocol provides the Authorization-Lifetime AVP, which MAY be used by extensions to specify the duration of a specific authorized session. 2.1 Header Format The base Diameter protocol is run over SCTP [26] port TBD (for interoperability test purposes we will support 1812 until April 2001). Implementations MAY send packets from any source port, but MUST be prepared to receive packets on port TBD. When a request is received, in order to send a reply, the source and destination ports in the reply are reversed. Note that the source and destination addresses used in request and replies MAY be any of the peer's valid IP addresses. A given Diameter process SHOULD use the same port number to send all messages to aid in identifying which process sent a given message. More than one Diameter process MAY exist within a single host, so the sender's port number is needed to discriminate them. A summary of the Diameter data format is shown below. The fields are transmitted in network byte order. Calhoun et al. expires July 2001 [Page 7]
Internet-Draft February 2001 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |r r r r r r r r r r E I R| Ver | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Command-Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AVPs ... +-+-+-+-+-+-+-+-+-+-+-+-+- Flags The Message Flags field is thirteen bits. The following bits are assigned: r(eserved) MUST be zero - this flag bit is reserved for future use. E(xpected Reply) - The message solicits a response. I(nterrogation) - The message is a Query or a Reply. R(esponse) - The message is a response to another message. These flags are set depending on the command code used in a Diameter message. This enables the type of message to be interpreted, even if the specific command code is not recognized. Command Type Flags Set Indication - - - Request E - - Answer - - R Query E I - Reply - I R A Diameter node MUST NOT set these flags in any other combination. A Diameter node receiving a message in which these flags are not set appropriately SHOULD NOT reject the message for this reason, but MAY log the event for diagnosis. Version This Version field MUST be set to 1 to indicate Diameter Version 1. Message Length The Message Length field is two octets and indicates the length of the Diameter message including the header fields. Calhoun et al. expires July 2001 [Page 8]
Internet-Draft February 2001 Identifier The Identifier field is four octets, and aids in matching requests and replies. The sender MUST ensure that the identifier in a request (*-Request or *-Query) or indication (*-Ind) message is locally unique (to the sender) at any given time, and MAY attempt to ensure that the number is unique across reboots. The sender of a response (*-Answer or *-Response) MUST ensure that the Identifier field contains the same Identifier value that was found in the corresponding request. For The identifier is normally a monotonically increasing number, whose start value was randomly generated. Diameter servers should consider a message to be unique by examining the source address, source port, Session-Id and Identifier field of the message. Command-Code The Command-Code field is four octets, and is used in order to communicate the command associated with the message. The 32-bit address space is managed by IANA (see section 8.2). The following Command Codes are currently defined in the Diameter base protocol: Command-Name Abbrev. Code Reference -------------------------------------------------------- Device-Reboot-Ind DRI 257 2.6 Message-Reject-Ind MRI 259 5.1 Session-Termination-Ind STI 274 3.6.1 Session-Termination- STR 275 3.6.2 Request Session-Termination- STA 276 3.6.3 Answer Vendor-ID In the event that the Command-Code field contains a vendor specific command, the four octet Vendor-ID field contains the IANA assigned "SMI Network Management Private Enterprise Codes" [2] value. If the Command-Code field contains an IETF standard Command, the Vendor-ID field MUST be set to zero (0). AVPs AVPs are a method of encapsulating information relevant to the Diameter message. See section 2.3 for more information on AVPs. 2.2 Command Code Message Definitions All Diameter Command Code MUST include a corresponding ABNF specification, which is used to define the AVPs that MUST, MAY and MUST NOT be present. The following format is used in the definition: Calhoun et al. expires July 2001 [Page 9]
Internet-Draft February 2001 command-def = command-name "::=" diameter-message diameter-name = ALPHA *(ALPHA / DIGIT / "-") command-name = diameter-name ; The command-name has to be Command name, ; defined in the base or extended Diameter ; specifications. diameter-message = header [ *fixed] [ *required] [ *optional] [ *fixed] header = "<Diameter-Header:" command-id ">" fixed = [qual] "<" avp-spec ">" required = [qual] "{" avp-spec "}" optional = [qual] "[" avp-name "]" ; The avp-name in the 'optional' rule cannot ; evaluate to any AVP Name which is included ; in a fixed or required rule. qual = [min] "*" [max] ; See ABNF conventions, RFC 2234 section 3.6. ; The absence of any qualifiers implies that one ; and only one such AVP MUST be present. ; ; NOTE: "[" and "]" have a different meaning ; than in ABNF (see the optional rule, above). ; These braces cannot be used to express an ; optional fixed rules (such as an optional ; ICV at the end.) To do this, the convention ; is '0*1fixed'. min = 1*DIGIT ; The minimum number of times the element may ; be present. max = 1*DIGIT ; The maximum number of times the element may ; be present. avp-spec = diameter-name ; The avp-spec has to be an AVP Name, defined ; in the base or extended Diameter ; specifications. avp-name = avp-spec | "AVP" Calhoun et al. expires July 2001 [Page 10]
Internet-Draft February 2001 ; The string "AVP" stands for *any* arbitrary ; AVP Name, which does not conflict with the ; required or fixed position AVPs defined in ; the command code definition. The following is a definition of a fictitious command code: Example-Command ::= < Diameter-Header: 9999999 > { User-Name } * { Host-Name } * [ AVP ] 0*1< Integrity-Check-Vector > 2.3 AVP Format Diameter AVPs carry specific authentication, accounting and authorization information, security information as well as configuration details for the request and reply. Some AVPs MAY be listed more than once. The effect of such an AVP is specific, and is specified in each case by the AVP description. Each AVP of type OctetString MUST be padded to align on a 32 bit boundary, while other AVP types align naturally. NULL bytes are added to the end of the AVP Data field till a word boundary is reached. The length of the padding is not reflected in the AVP Length field. 2.3.1 AVP Header The fields in the AVP header MUST be sent in network byte order. The format of the header is: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AVP Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AVP Length | Reserved |P|R|V|R|M| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-ID (opt) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data ... +-+-+-+-+-+-+-+-+ AVP Code The AVP Code identifies the attribute uniquely. The first 256 AVP Calhoun et al. expires July 2001 [Page 11]
Internet-Draft February 2001 numbers are reserved for backward compatibility with RADIUS and are to be interpreted as per NASREQ [7]. AVP numbers 256 and above are used for Diameter, which are allocated by IANA (see section 8.1). AVP Length The AVP Length field is two octets, and indicates the length of this AVP including the AVP Code, AVP Length, AVP Flags, Reserved, the Vendor-ID field (if present) and the AVP data. If a message is received with an invalid attribute length, the message SHOULD be rejected. AVP Flags The AVP Flags field informs the Diameter host how each attribute must be handled. Note that subsequent Diameter extensions MAY define bits to be used within the AVP Header, and an unrecognized bit should be considered an error. The 'R' and the reserved bits are unused and should be set to 0 and ignored on receipt, while the 'P' bit is defined in [11]. The 'M' Bit, known as the Mandatory bit, indicates whether support of the AVP is required. If an AVP is received by a Home server or NAS with the 'M' bit enabled and the receiver does not support the AVP, the message MUST be rejected. If such an AVP is received by a Proxy or Redirect Server, the message MUST be forwarded to its logical destination, and MUST NOT be rejected. It is the responsibility of the originator of a message that is rejected for this purpose to correct the error. AVPs without the 'M' bit enabled are informational only and a receiver that receives a message with such an AVP that is not supported MAY simply ignore the AVP. The 'V' bit, known as the Vendor-Specific bit, indicates whether the optional Vendor-ID field is present in the AVP header. When set the AVP Code belongs to the specific vendor code address space. Unless otherwise noted, AVPs will have the following default AVP Flags field settings: The 'M' bit MUST be set. The 'V' bit MUST NOT be set. 2.3.2 Optional Header Elements The AVP Header contains one optional field. This field is only present if the respective bit-flag is enabled. Vendor-ID Calhoun et al. expires July 2001 [Page 12]
Internet-Draft February 2001 The Vendor-ID field is present if the 'V' bit is set in the AVP Flags field. The optional four octet Vendor-ID field contains the IANA assigned "SMI Network Management Private Enterprise Codes" [2] value, encoded in network byte order. Any vendor wishing to implement a Diameter extension MUST use their own Vendor-ID along with their privately managed AVP address space, guaranteeing that they will not collide with any other vendor's extensions, nor with future IETF extensions. A vendor ID value of zero (0) corresponds to the IETF adopted AVP values, as managed by the IANA. Since the absence of the vendor ID field implies that the AVP in question is not vendor specific, implementations SHOULD not use the zero (0) vendor ID. 2.3.3 AVP Data Formats The Data field is zero or more octets and contains information specific to the Attribute. The format and length of the Data field is determined by the AVP Code and AVP Length fields. The format of the Data field MAY be one of the following data types. The interpretation of the values depends on the specification of the AVP. For example, an OctetString may be used to transmit human readable string data and Unsigned32 may be used to transmit a time value. Conventions for these common interpretations are described below. OctetString The data contains arbitrary data of variable length. Unless otherwise noted, the AVP Length field MUST be set to at least 9 (13 if the 'V' bit is enabled). Data used to transmit (human readable) character string data uses the UTF-8 [24] character set and is NOT NULL-terminated. The minimum Length field MUST be 9, but can be set to any value up to 65527 bytes. AVP Values of this type that do not align on a 32-bit boundary MUST adding necessary padding. Address 32 bit (IPv4) [17] or 128 bit (IPv6) [16] address, most significant octet first. The format of the address (IPv4 or IPv6) is determined by the length. If the attribute value is an IPv4 address, the AVP Length field MUST be 12 (16 if 'V' bit is enabled), otherwise the AVP Length field MUST be set to 24 (28 if the 'V' bit is enabled) for IPv6 addresses. Integer32 32 bit signed value, in network byte order. The AVP Length Calhoun et al. expires July 2001 [Page 13]
Internet-Draft February 2001 field MUST be set to 12 (16 if the 'V' bit is enabled). Integer64 64 bit signed value, in network byte order. The AVP Length field MUST be set to 16 (20 if the 'V' bit is enabled). Unsigned32 32 bit unsigned value, in network byte order. The AVP Length field MUST be set to 12 (16 if the 'V' bit is enabled). Unsigned32 values used to transmit time data contains the four most significant octets returned from NTP [18], in network byte order. Unsigned64 32 bit unsigned value, in network byte order. The AVP Length field MUST be set to 16 (20 if the 'V' bit is enabled). Float32 This represents floating point values of single precision as described by [30]. The 32 bit value is transmitted in network byte order. The AVP Length field MUST be set to 12 (16 if the 'V' bit is enabled). Float64 This represents floating point values of double precision as described by [30]. The 64 bit value is transmitted in network byte order. The AVP Length field MUST be set to 16 (20 if the 'V' bit is enabled). Float128 This represents floating point values of quadruple precision as described by [30]. The 128 bit value is transmitted in network byte order. The AVP Length field MUST be set to 24 (28 if the 'V' bit is enabled). Grouped The Data field is specified as a sequence of AVPs. Each of these AVPs follows - in the order in which they are specified - including their headers and padding. The AVP Length field is set to 8 (12 if the 'V' bit is enabled) plus the total length of all included AVPs, including their headers. 2.3.4 Grouped AVP Values The Diameter protocol allows AVP values of type 'Grouped.' This implies that the Data field is actually a well defined sequence of AVPs. It is possible to include an AVP with a Grouped type within a Calhoun et al. expires July 2001 [Page 14]
Internet-Draft February 2001 Grouped type, that is, to nest them. AVPs within an AVP of type Grouped have the same padding requirements as non-Grouped AVPs, as defined in section 2.3. Grouped type AVP specifications include an ABNF grammar [31] specifying the required sequence of AVPs. Grouped AVP values MUST be in the specified sequence and MUST NOT include other AVP values besides those specified by the Grouped AVP grammar. 2.3.4.1 Example AVP with a Grouped Data type The Example AVP (AVP Code 999999) is of type Grouped and is used to clarify how Grouped AVP values work. The Grouped Data field has the following ABNF grammar: example-avp-val = Host-Name Host-IP-Address Host-Name = ; See Section 2.4.1 Host-IP-Address = ; See Section 2.6.4 An Example AVP with the Grouped Data Host-Name = "example.com", Host-IP-Address = "10.10.10.10" would be encoded as follows: 0 1 2 3 4 5 6 7 +-------+-------+-------+-------+-------+-------+-------+-------+ 0 | Example AVP Header (AVP Code = 999999), Length = 40 | +-------+-------+-------+-------+-------+-------+-------+-------+ 8 | Host-Name AVP Header (AVP Code = 265), Length = 19 | +-------+-------+-------+-------+-------+-------+-------+-------+ 16 | 'e' | 'x' | 'a' | 'm' | 'p' | 'l' | 'e' | '.' | +-------+-------+-------+-------+-------+-------+-------+-------+ 24 | 'c' | 'o' | 'm' |Padding| Host-IP-Addr AVP Header | +-------+-------+-------+-------+-------+-------+-------+-------+ 32 | (AVP Code = 257), Length = 12 | 0x0a | 0x0a | 0x0a | 0x0a | +-------+-------+-------+-------+-------+-------+-------+-------+ 2.3.5 Diameter Base Protocol AVPs The following table describes the Diameter AVPs defined in the base protocol, their AVP Code values, types, possible flag values and whether the AVP MAY be encrypted. Calhoun et al. expires July 2001 [Page 15]
Internet-Draft February 2001 +---------------------+ | AVP Flag rules | |----+-----+----+-----|----+ AVP Section | | |SHLD| MUST|MAY | Attribute Name Code Defined Data Type |MUST| MAY | NOT| NOT|Encr| -----------------------------------------|----+-----+----+-----|----| Authentication- 285 7.1.1.1 Unsigned32 | | | | | N | Transform-Id | | | | | | Authorization- 291 3.3 Unsigned32 | | | | | N | Lifetime | | | | | | Destination-NAI 293 6.8 OctetString| | | | | Y | Digest 287 7.1.1.2 OctetString| | | | | N | Encrypted-Data 290 7.1.2.3 OctetString| | | | | N | Encrypted- 260 7.1.2 Grouped | M | | | | N | Payload | | | | | | Encryption- 288 7.1.2.1 Unsigned32 | | | | | N | Transform-Id | | | | | | Error-Message 281 5.3 OctetString| | | | | N | Error-Reporting- 294 5.3 OctetString| | | | | Y | NAI | | | | | | Extension-Id 258 2.6.3 Integer32 | M | | | | Y | Failed-AVP 279 5.1.1 OctetString| | | | | Y | Failed-Command- 270 5.1.2 Unsigned32 | | | | | Y | Code | | | | | | Firmware 267 2.6.2 Unsigned32 | | | | V,M | Y | -Revision | | | | | | Host-IP-Address 257 2.6.4 Address | M | | | V | N | Host-Name 264 2.4.1 OctetString| M | | | V | N | Integrity-Check 259 7.1.1 Grouped | M | | | | N | -Value | | | | | | Key-Id 286 7.4 Unsigned32 | | | | | N | Nonce 261 7.2 OctetString| | | | | N | Plaintext-Data- 289 7.1.2.2 Unsigned32 | | | | | N | Length | | | | | | Proxy-Address 280 6.4.5 Address | M | | | V | N | Proxy-Info 284 6.4.6 OctetString| M | | | V | N | Proxy-State 33 6.4.4 Grouped | M | | | V | N | Redirect-Host 292 6.3.1 Grouped | | | | | Y | Redirect-Host 278 6.3.2 Address | | | | | Y | Address | | | | | | Redirect-Host- 277 6.3.3 Unsigned32 | | | | | Y | Port | | | | | | Result-Code 268 5.2 Unsigned32 | M | | | | N | Route-Record 282 6.4.3 OctetString| M | | | V | N | Routing-Realm 283 6.4.7 OctetString| M | | | V | N | Session-Id 263 3.2 OctetString| | | | | Y | Session-Timeout 27 3.6 Unsigned32 | | | | | Y | Calhoun et al. expires July 2001 [Page 16]
Internet-Draft February 2001 +---------------------+ | AVP Flag rules | |----+-----+----+-----|----+ AVP Section | | |SHLD| MUST|MAY | Attribute Name Code Defined Data Type |MUST| MAY | NOT| NOT|Encr| -----------------------------------------|----+-----+----+-----|----| Timestamp 262 7.3 Unsigned32 | | | | | N | User-Name 1 3.5 OctetString| | | | | Y | Vendor-Id 266 2.6.1 Unsigned32 | | | | V,M | Y | -----------------------------------------|----+-----+----+-----|----| 2.4 Mandatory AVPs This section defines the Diameter AVPs that MUST be present in all Diameter messages. 2.4.1 Host-Name AVP The Host-Name AVP (AVP Code 264) [1] is of type OctetString. This AVP identifies the endpoint which originated the Diameter message, i.e. the NAS, home server, or broker. Proxy servers do not modify this AVP. All Diameter messages MUST include the Host-Name AVP, which contains the host name of the originator of the Diameter message and MUST follow the NAI [8] naming conventions. Note that the Host-Name AVP may resolve to more than one address as the Diameter peer may support more than one address. 2.5 State Machine This section contains a finite state machine, that MUST be observed by all Diameter implementations. Each Diameter node MUST follow the state machine described below when communicating with each peer. State Event Action New State ----- ----- ------ --------- Initial Local request to establish SCTP Idle communication with a Diameter Connect peer with which there is no existing transport level connection established. Initial Receive transport level Send DRI Wait-DRI connection request from a Diameter peer. Calhoun et al. expires July 2001 [Page 17]
Internet-Draft February 2001 Idle Connection Established Send DRI Wait-DRI Idle Receive DRI Send DRI Open Wait-DRI Receive DRI None Open Open Receive other messages Process Open Message Open Receive DRI Cleanup Closed Open Transport level failure Cleanup Closed Closed Diameter Entity shutdown Close Initial or close connection with peer connection The Initial and Idle states MAY be merged if the local SCTP implementation is able to implement the piggyback of data during the connection phase. When the Cleanup action is invoked, the Diameter node SHOULD attempt to forward all pending requests and replies, which haven't been acknowledged, to an alternate server (when possible). If the final destination for a specific message is the host that is no longer accessible, the message in question SHOULD be responded with the Result-Code AVP set to Diameter_UNABLE_TO_DELIVER. 2.6 Device-Reboot-Ind (DRI) Command A Diameter device sends the Device-Reboot-Ind message, by setting the Command-Code field with a value of 257, to inform a peer that a reboot has just occurred. Since SCTP [26] allows for connections to span multiple interfaces, hence multiple IP addresses, the Device- Reboot-Ind message MUST contain one Host-IP-Address AVP for each potential IP address that MAY be locally used when transmitting Diameter messages. The DRI message is also used for capabilities negotiation, such as the supported protocol version number, and the locally supported extensions. The receiver uses the extensions advertised in order to determine whether it SHOULD send certain application-specific Diameter commands. A Diameter node MUST retain the supported extensions in order to ensure that unrecognized commands and/or AVPs are not sent to a peer. Note that in a proxy environment, it is still possible that a downstream proxy has no available peer that have advertised the extension that corresponds to the Command-Code, and therefore the request cannot be forwarded any further. The Diameter Calhoun et al. expires July 2001 [Page 18]
Internet-Draft February 2001 base protocol provides this error reporting, via the Result-Code AVP. Once the transport layer connection has been established, a Diameter entity MUST issue a DRI message, regardless of whether the peer was statically configured, or dynamically discovered (see Section 2.6 for more information). If a peer is no longer reachable, a Diameter device SHOULD periodically attempt to establish a transport level connection with the peer and send a DRI message. This message does not require a reply. If a Diameter node receives a DRI message that results in an error, a Message-Reject-Ind message MUST be returned. Message Format <Device-Reboot-Ind> ::= < Diameter Header: 257 > { Host-Name } 1* { Host-IP-Address } { Vendor-Id } * { Extension-Id } [ Firmware-Revision ] * [ AVP ] 0*1< Integrity-Check-Value > 2.6.1 Vendor-Id AVP The Vendor-Id AVP (AVP Code 266) is of type Unsigned32 and contains the IANA assigned "SMI Network Management Private Enterprise Codes" [2] value of the Diameter device. This MAY be used in order to know which vendor specific attributes may be sent to the peer. It is also envisioned that the combination of the Vendor-Name and the Firmware-Revision (section 2.6.2) AVPs MAY provide very useful debugging information. 2.6.2 Firmware-Revision AVP The Firmware-Revision AVP (AVP Code 267) is of type Unsigned32 and is used to inform a Diameter peer of the firmware revision of the issuing device. For devices that do not have a firmware revision (general purpose computers running Diameter software modules, for instance), the revision of the Diameter software module may be reported instead. Calhoun et al. expires July 2001 [Page 19]
Internet-Draft February 2001 2.6.3 Extension-Id AVP The Extension-Id AVP (AVP Code 258) is of type Unsigned32 and is used in order to identify a specific Diameter extension. This AVP is used in the Device-Reboot-Ind message in order to inform the peer what extensions are locally supported. The Extension-Id MUST also be present in all messages that are defined in a separate Diameter specification and have an Extension ID assigned. Each Diameter extension draft MUST have an IANA assigned extension Identifier (see section 8.3). The base protocol does not require an Extension-Id since its support is mandatory. There MAY be more than one Extension-Id AVP within a Diameter Device-Reboot-Ind message. The following values are recognized: NASREQ 1 [7] Strong Security 2 [11] Resource Management 3 [29] Mobile-IP 4 [10] Accounting 5 [15] Furthermore, servers acting as Redirect or Proxy servers (see Section 6.0) MAY wish to advertise support for ALL possible extensions. Such servers are then responsible for finding a downstream server that supports the extension of a particular message. This is done by including the Extension-Id AVP with a value of zero (0). 2.6.4 Host-IP-Address AVP The Host-IP-Address AVP (AVP Code 257) [1] is of type Address and is used to inform a Diameter peer of the sender's IP address. All source addresses that a Diameter node expects to use with SCTP [26] MUST be advertised in the Device-Reboot-Ind message by including a Host-IP-Address AVP for each address. This AVP MUST ONLY be used in the Device-Reboot-Ind message. 2.6 Diameter Server Discovery Allowing for dynamic Diameter server discovery will make it possible for simpler and more robust deployment of AAA services. In order to promote interoperable implementations of Diameter server discovery, the following mechanisms are described. These are based on existing IETF standards. There are two cases where Diameter server discovery may be performed. Calhoun et al. expires July 2001 [Page 20]
Internet-Draft February 2001 The first is when a Diameter client needs to discover a first-hop Diameter server. The second case is when a Diameter server needs to discover another server - for further handling of a Diameter operation. In both cases, the following 'search order' is recommended: 1. The Diameter implementation consults its list of static (manual) configured Diameter server locations. These will be used if they exist and respond. 2. The Diameter implementation uses SLPv2 [28] to discover Diameter services. The Diameter service template [32] is included in Appendix A. It is recommended that SLPv2 security be deployed (this requires distributing keys to SLPv2 agents.) This is discussed further in Appendix A. SLPv2 will allow Diameter implementations to discover the location of Diameter servers in the local site, as well as their characteristics. Diameter servers with specific capabilities (say support for the Accounting extension) can be requested, and only those will be discovered. 3. The Diameter implementation uses DNS to request the SRV RR [33] for the '_diameter._sctp' server in a particular domain. The Diameter implementation has to know in advance which domain to look for an Diameter server in. This could be deduced, for example, from the 'realm' in a NAI that an Diameter implementation needed to perform an Diameter operation on. Diameter allows AAA peers to protect the integrity and privacy of communication as well as to perform end-point authentication. Still, it is prudent to employ DNS Security as a precaution when using DNS SRV RRs to look up the location of a Diameter server. [34, 35, 36] 3.0 "User" Sessions When a user requests access to the network, a Diameter client issues an authentication and authorization request to its local server. The request contains a Session-Id AVP, which is used in subsequent messages (e.g. subsequent authorization, accounting, etc) relating to the user's session. The Session-Id AVP is a means for the client and servers to correlate a Diameter message with a user session. When a Diameter server authorizes a user to use network resources, it SHOULD add the Authorization-Lifetime AVP to the response. The Authorization-Lifetime AVP defines the maximum amount of time a user Calhoun et al. expires July 2001 [Page 21]
Internet-Draft February 2001 MAY make use of the resources before another authorization request is to be transmitted to the server. If the server does not receive another authorization request before the timeout occurs, it SHOULD release any state information related to the user's session. Note that the Authorization-Lifetime AVP implies how long the Diameter server is willing to pay for the services rendered, therefore a Diameter client SHOULD NOT expect payment for services rendered past the session expiration time. The base protocol does not include any authorization request messages, since these are largely application-specific and are defined in a Diameter protocol extension document. However, the base protocol does define a set of messages that are used to terminate user sessions. These are used to allow servers that maintain state information to free resources. 3.1 State Machine This section contains a finite state machine, representing the life cycle of Diameter sessions, and MUST be observed by all Diameter implementations. The term Service-Specific below refers to a message defined in a Diameter extension (e.g. Mobile IP, NASREQ). State Event Action New State ----- ----- ------ --------- Idle Client or Device Requests send serv. Pending access specific auth req Idle Service-Specific authorization send serv. Open request received, and specific successfully processed response Pending Successful Service-Specific Grant Open Authorization response Access received Open Authorization-Lifetime expires send serv. Open specific auth req Open Successful Service-Specific Extend Open Authorization response Access received Open Failed Service-Specific Discon. Closed Authorization response user/device Calhoun et al. expires July 2001 [Page 22]
Internet-Draft February 2001 received. Open Session-Timeout Expires on send STR Discon NAS Open STI Received send STR Discon Open Session-Timeout Expires on send STI Discon home AAA server Discon STI Received ignore Discon Discon STR Received Discon. Closed user/device Discon STA Received Discon. Closed user/device Closed Transition to state Cleanup When the Cleanup action is invoked, the Diameter node MAY attempt to release all resources for the particular session. Any event not listed above MUST be considered as an error condition, and a response, if applicable, MUST be returned to the originator of the message. 3.2 Session-Id AVP The Session-Id AVP (AVP Code 263) is of type OctetString and is used to identify a specific session (see section 3.0). The Session-Id data uses the UTF-8 [24] character set. All messages pertaining to a specific session MUST include only one Session-Id AVP and the same value MUST be used throughout the life of a session. When present, the Session-Id SHOULD appear immediately following the Diameter Header (see section 2.1). For messages that do not pertain to a specific session, multiple Session-Id AVPs MAY be present as long as they are encapsulated within an AVP of type Grouped. The Session-Id MUST be globally unique at any given time since it is used by the server to identify the session (or flow). The format of the session identifier SHOULD be as follows: <Sender's Host-Name><sender's port number> <monotonically increasing 32 bit value><optional value> Calhoun et al. expires July 2001 [Page 23]
Internet-Draft February 2001 The monotonically increasing 32 bit value SHOULD NOT start at zero upon reboot, but rather start at a random value. This will minimize the possibility of overlapping Session-Ids after a reboot. Alternatively, an implementation MAY keep track of the increasing value in non-volatile memory. The optional value is implementation specific but may include a modem's device Id, a layer 2 address, timestamp, etc. The session Id is created by the Diameter device initiating the session, which in most cases is done by the client. Note that a Session-Id MAY be used by more than one extension (e.g. authentication for a specific service and accounting, both of which have separate extensions). 3.3 Authorization-Lifetime AVP The Authorization-Lifetime AVP (AVP Code 291) is of type Unsigned32 and contains the maximum number of seconds of service to be provided to the user before the user is to be re-authenticated and/or re- authorized. Great care should be taken when the Authorization- Lifetime value is determined, since a low value could create significant Diameter traffic, which could congest both the network and the servers. This AVP MAY be provided by the client as a hint of the maximum duration that it is willing to accept. However, the server DOES NOT have to observe the hint, and MAY return a value that is smaller than the hint. A value of zero means that no re-authorization is required. 3.4 Session-Timeout AVP The Session-Timeout AVP (AVP Code 27) [1] is of type Unsigned32 and contains the maximum number of seconds of service to be provided to the user before termination of the session. A value of zero means that this session has an unlimited number of seconds before termination. This AVP MAY be provided by the client as a hint of the maximum duration that it is willing to accept. However, the server DOES NOT have to observe the hint, and MAY return a value that is smaller than the hint. 3.5 User-Name AVP The User-Name AVP (AVP Code 1) [1] is of type OctetString, which Calhoun et al. expires July 2001 [Page 24]
Internet-Draft February 2001 contains the User-Name. The value is represented as a UTF-8 character encoded string in a format consistent with the NAI specification [8]. 3.6 Session Termination The Diameter Base Protocol provides a set of messages that MAY be used by any peer to explicitly request that a previously authenticated and/or authorized session be terminated. Since the Session-Id is typically tied to a particular service (i.e. Mobile IP, NASREQ, etc), the session termination messages are used to request that the service tied to the Session Id be terminated. 3.6.1 Session-Termination-Ind The Session-Termination-Ind (STI), indicated by the Command-Code set to 274, MAY be sent by any Diameter entity to the access device to request that a particular session be terminated. This message MAY be used when a server detects that a session MUST be terminated, which is typically done as a policy decision (e.g. local resources have been expended, etc). The Destination-NAI AVP MUST be present, and contain the NAI of the access device that initiated the session (see section 3.0). Upon receipt of the STI message, the access device SHOULD issue a Session-Terminate-Request message. Message Format <Session-Termination-Ind> ::= < Diameter Header: 274 > { Session-Id } { Host-Name } { User-Name } { Destination-NAI } * [ AVP ] * [ Proxy-State ] * [ Route-Record ] * [ Routing-Realm ] 0*1< Integrity-Check-Value > 3.6.2 Session-Termination-Request The Session-Termination-Request (STR), indicated by the Command-Code set to 275, is sent by the access device to inform the Home AAA that an authenticated and/or authorized session is being terminated. Calhoun et al. expires July 2001 [Page 25]
Internet-Draft February 2001 Upon receipt of the STR, the Home Diameter Server SHOULD release all resources for the session indicated by the Session-Id AVP. Any intermediate server in the Proxy-Chain MAY also release any resources, if necessary. Message Format <Session-Termination-Request> ::= < Diameter Header: 275 > { Session-Id } { Host-Name } { User-Name } * [ AVP ] * [ Proxy-State ] * [ Route-Record ] * [ Routing-Realm ] 0*1< Integrity-Check-Value > 3.6.3 Session-Termination-Answer The Session-Termination-Answer (STA), indicated by the Command-Code set to 276, is sent by the Home Diameter Server to acknowledge that the session has been terminated. The Result-Code AVP MUST be present, and MAY contain an indication that an error occurred while servicing the STR. Message Format <Session-Termination-Answer> ::= < Diameter Header: 276 > { Session-Id } { Result-Code } { Host-Name } { User-Name } * [ AVP ] * [ Proxy-State ] * [ Route-Record ] * [ Routing-Realm ] 0*1< Integrity-Check-Value > 4.0 Reliable Transport In order to provide rapid discovery of the failure of a communicating peer, aggressive retransmission and rapid transactions, Diameter peers MUST be able to send and receive messages over SCTP [26]. A Diameter peer MAY use TCP [27], as TCP does provide reliable transport, though it does not have the properties listed above. Calhoun et al. expires July 2001 [Page 26]
Internet-Draft February 2001 5.0 Error Reporting There are five different types of errors within Diameter. The first being where a Diameter message is poorly formatted and unrecognizable, indicated below by "Bad Message". This error condition applies if a received message creates a fatal error (e.g. fails transport level authentication, cannot be parsed, etc). The second case involves receiving a Command-Code that is not supported, which is shown below by "Unknown Command". The third case is where an AVP is received, marked mandatory and is unknown by the receiver, which is labeled below as "Unknown AVP". This fourth case involves receiving a message with a known AVP, yet the value is either unknown or illegal, which is shown below as "Bad AVP Value". The last case occurs when an error occurs while processing a specific extension command, which is not related to the message format and is labeled "Extension Error" below. Error Type Ignore Message Send Extension Message-Reject-Ind Response + Result-Code Bad Message X Unknown Command X Unknown AVP X Bad AVP Value X Extension Error X "Ignore Message" indicates that the message is simply dropped. The "Message-Reject-Ind" indicates that a Message-Reject-Ind message MUST be sent to the peer as described in the appropriate section. The "Extension Response + Result-Code" error has an extension-specific command code, and indicates that the appropriate Response to the message MUST be sent with the Result-Code AVP set to a value that enables the peer to understand the nature of the problem. 5.1 Message-Reject-Ind (MRI) Command The Message-Reject-Ind (MRI), indicated by the Command-Code set to 259, provides a generic means of completing transactions by indicating errors in the messages that initiated them. The Message- Reject-Ind command is sent in response: 1. An error is found in a message of type Ind, Answer and Response 2. A message that contains an unrecognized command code 3. A message was received that cannot pass the base protocol error checking. Calhoun et al. expires July 2001 [Page 27]
Internet-Draft February 2001 In the event that a request is received that causes an error defined in a Diameter extension, the appropriate response with the Result- Code AVP SHOULD be sent. The Message-Reject-Ind message MUST contain the same identification in the header and include the Session-Id if it was present in the original message that it is responding to, even if the identification is erroneous. Message Format The structure of the Message-Reject-Ind message is defined as follows: <Message-Reject-Ind message> ::= < Diameter Header: 259 > { Result-Code } { Host-Name } { Error-Reporting-NAI } [ Session-Id ] [ Failed-Command-Code ] [ Failed-AVP ] * [ AVP ] * [ Proxy-State ] * [ Route-Record ] * [ Routing-Realm ] 0*1< Integrity-Check-Value > where the Identifier value in the message header and optionally the Session-Id AVP are copied from the message being rejected. The Result-Code AVP indicate the nature of the error causing rejection, and the Failed-AVP AVP provides some minimal debugging data by indicating a specific AVP type which caused the problem. See the description of the Result-Code AVP for indication of when the Failed-AVP AVP MUST be present in the message. See [25] for more information. 5.1.1 Failed-AVP AVP The Failed-AVP AVP (AVP Code 279) is of type OctetString and provides debugging information in cases where a request is rejected or not fully processed due to erroneous information in a specific AVP. The value of the Result-Code AVP will provide information on the reason for the Failed-AVP AVP. A Diameter message MAY contain one or more Failed-AVP AVPs, each containing a complete AVP that could not be processed successfully. The possible reasons for this AVP are the presence of an improperly Calhoun et al. expires July 2001 [Page 28]
Internet-Draft February 2001 constructed AVP, an unsupported or unrecognized AVP, an invalid AVP value; or the omission of a required AVP. 5.1.2 Failed-Command-Code The Failed-Command-Code AVP (AVP Code 270) is of type Unsigned32 and contains the offending Command-Code that resulted in sending the Message-Reject-Ind message. 5.2 Result-Code AVP The Result-Code AVP (AVP Code 268) is of type Unsigned32 and indicates whether a particular request was completed successfully or whether an error occurred. All Diameter messages of type *-Response or *-Answer MUST include one Result-Code AVP, while messages of type -Ind MAY include the Result-Code AVP. A non-successful Result-Code AVP (one containing a non 2001 value) MUST include the Error- Reporting-NAI AVP. The Result Code field contains an IANA-managed 32-bit address space representing errors (see section 8.4). Diameter provides five different classes of errors, all identified by the thousands digit: - 1xxx (Informational) - 2xxx (Success) - 3xxx (Redirect Notification) - 4xxx (Transient Failures) - 5xxx (Permanent Failure) - 6xxx (Hop-by-Hop Failure) A non-recognize class (one whose first digit is not defined in this section) MUST be handled as a permanent failure. 5.2.1 Informational Errors that fall within the Informational category are used to inform a requester that the request cannot be immediately satisfied and a further response will be issued in the near future. DIAMETER_BE_PATIENT 1001 The Diameter server responsible for authentication and/or authorizing the user cannot satisfy the request at the moment, and will respond within the next 3 seconds. 5.2.2 Success Calhoun et al. expires July 2001 [Page 29]
Internet-Draft February 2001 Errors that fall within the Success category are used to inform a peer that a request has been successfully completed. DIAMETER_SUCCESS 2001 The Request was successfully completed. 5.2.3 Redirect Notification Errors that fall within the Redirect Notification category are used to inform a peer that the request cannot be satisfied locally and should instead be forwarded to another server. DIAMETER_REDIRECT_INDICATION 3001 A proxy or redirect server has determined that the request could not be satisfied locally and the initiator of the request should direct the request directly to the server, whose contact information has been added to the response. This error code MUST NOT be sent in a Message-Reject-Ind message. 5.2.4 Transient Failures Errors that fall within the transient failures category are used to inform a peer that the request could not be satisfied at the time it was received, but MAY be able to satisfy the request in the future. DIAMETER_AUTHENTICATION_REJECTED 4001 The authentication process for the user failed, most likely due to an invalid password used by the user. Further attempts MUST only be tried after prompting the user for a new password. DIAMETER_NO_END_2_END_SECURITY 4002 A proxy has detected that end-to-end security has been applied to portions of the Diameter message, and the proxy does not allow this security mode since it needs to alter the message by applying some local policies. 5.2.5 Permanent Failures Errors that fall within the permanent failures category are used to inform the peer that the request failed, and should not be attempted again. DIAMETER_USER_UNKNOWN 5001 A request was received for a user that is unknown, therefore authentication and/or authorization failed. Calhoun et al. expires July 2001 [Page 30]
Internet-Draft February 2001 DIAMETER_AVP_UNSUPPORTED 5002 The peer received a message that contained an AVP that is not recognized or supported and was marked with the Mandatory bit. A Diameter message with this error MUST contain one or more Failed-AVP AVP containing the AVPs that caused the failure. DIAMETER_UNKNOWN_SESSION_ID 5003 The request or response contained an unknown Session-Id. DIAMETER_AUTHORIZATION_REJECTED 5004 A request was received for which the user could not be authorized. This error could occur if the service requested is not permitted to the user. DIAMETER_INVALID_AVP_VALUE 5005 The request contained an AVP with an invalid value in its data portion. A Diameter message with this result code MUST include the offending AVPs within a Failed-AVP AVP. DIAMETER_MISSING_AVP 5006 The request did not contain an AVP that is required by the Command Code definition. If this value is sent in the Result- Code AVP, a Failed-AVP AVP SHOULD be included in the message. The data portion of the Failed-AVP MUST have its AVP Code set to the Data field of the missing AVP. DIAMETER_INVALID_CMS_DATA 5007 The Request did not contain a valid CMS-Data [11] AVP. DIAMETER_LOOP_DETECTED 5008 A Proxy or Redirect server detected a loop while trying to get the message to the Home Diameter server. Further attempts should not be attempted until the loop has been fixed. DIAMETER_AUTHORIZATION_FAILED 5009 A request was received for which the user could not be authorized at this time. This error could occur when the user has already expended allowed resources, or is only permitted to access services within a time period. DIAMETER_CONTRADICTING_AVPS 5010 The Home Diameter server has detected AVPs in the request that contradicted each other, and is not willing to provide service to the user. One or more Failed-AVP AVPs MUST be present, containing the AVPs that contradicted each other. 5.2.6 Hop-by-Hop Failures Calhoun et al. expires July 2001 [Page 31]
Internet-Draft February 2001 Proxies receiving messages with the Result-Code AVP set to an error within the Hop-by-Hop failure category SHOULD attempt to take some local action to correct the error. If no local action can be taken to correct the problem, the error MUST be forwarded towards the originator of the message. DIAMETER_INVALID_RECORD_ROUTE 6001 The last Record-Route AVP in the message is not set to the identity of the sender of the message. See Section 6.0 for more information. DIAMETER_COMMAND_UNSUPPORTED 6002 The Request contained a Command-Code that the receiver did not recognize or support. The Message-Reject-Ind message MUST also contain an Failed-Command-Code AVP containing the unrecognized Command-Code. DIAMETER_TIME_INVALID 6003 This Result-Code value is return to inform a peer that the message received contained an invalid timestamp value (in Timestamp AVP). DIAMETER_UNABLE_TO_DELIVER 6004 The request could not be delivered to a host that handles the realm requested at this time. DIAMETER_REALM_NOT_SERVED 6005 A proxy or redirect server has determined that it is unable to forward the request or provide redirect information since the realm portion of the NAI requested is unknown. DIAMETER_UNSUPPORTED_TRANSFORM 6006 A message was received that included an Integrity-Check-Value or CMS-Data AVP [11] that made use of an unsupported transform. DIAMETER_INVALID_ICV 6007 The Request did not contain a valid Integrity-Check-Value AVP. 5.3 Error-Message AVP The Error-Message AVP (AVP Code 281) is of type OctetString. It is a human readable UTF-8 character encoded string. It MAY accompany a Result-Code AVP as a human readable error message. The Error-Message AVP is not intended to be useful in real-time, and SHOULD NOT be expected to be parsed by network entities. Calhoun et al. expires July 2001 [Page 32]
Internet-Draft February 2001 5.4 Error-Reporting-NAI AVP The Error-Reporting-NAI AVP (AVP Code 294) is of type OctetString. This AVP contains the Network Access Identifier of the Diameter host that set the Result-Code AVP to a value other than 2001 (Success). This AVP is intended to be used for troubleshooting purposes, and MUST be set when the Result-Code AVP indicates a failure. 6.0 Message Routing This section describes the expected behavior of a Diameter server acting as a proxy or redirect server. 6.1 Realm-Based Message Routing Diameter Message routing is done through the use of the realm portion of the Network Access Identifier (NAI), and an associated realm routing table (see section 10.0). The NAI has a format of user@realm, and Diameter servers have a list of locally supported realms, and MAY have a list of externally supported realms. When a message is received that includes a realm that is not locally supported, the message is proxied to the Diameter entity configured in the "route" table. There are instances where the User-Name AVP is not present in authorization requests. This is typically true in networks where a request is sent to the network before the call was even answered. However, such requests MAY need to be proxied. In such cases, the first hop Diameter proxy MAY append the Routing-Realm AVP to the Diameter message, by using a DNIS or ANI to Routing-Realm association table, if it is known. If the message is forwarded to a downstream proxy, the proxy MAY add the missing Routing-Realm AVP (or replace an existing Routing-Realm AVP), if the realm associated with the DNIS or ANI is known. Figure 1 depicts an example where DIA1 receives a request to authenticate user "joe@abc.com". DIA1 looks up "abc.com" in its local realm route table and determines that the message must be proxied to DIA2. DIA2 does the same check, and proxies the message to DIA3. DIA3 checks its realm route table, and determines that the realm is locally supported, and processes the authentication request, and returns the response. How the response actually makes it back to the sender of the original request is described in the next section. Calhoun et al. expires July 2001 [Page 33]
Internet-Draft February 2001 (Request) (Request) (User-Name=joe@abc.com) (User-Name=joe@abc.com) +------+ ------> +------+ ------> +------+ | | | | | | | DIA1 +-------------------+ DIA2 +-------------------+ DIA3 | | | | | | | +------+ <------ +------+ <------ +------+ (Response) (Response) (User-Name=joe@abc.com) (User-Name=joe@abc.com) mno.net xyz.com abc.com Figure 1: Realm-Based Routing 6.2 Behavior of Proxy and Redirect Servers This section describes the behavior of Diameter proxy and redirect servers in detail. In both cases, determining the next hop for a Diameter message is done via the Routing-Realm or the User-Name AVP [1], whose syntax must comply with the Network Access Identifier (NAI) [12] specification. When present, the Routing-Realm takes precedence over the User-Name AVP for routing decisions. The Routing-Realm AVP, or the realm portion of the User-Name AVP is used to identify the next hop server the message must be forwarded to. Note the processing rules contained in this section are intended to be used as general guidelines to Diameter developers. Certain implementations MAY use different methods than the ones described here, and still be in compliance with the protocol specification. 6.2.1 Proxy and Redirect Server handling of requests Any request received by a Diameter server MUST perform a next hop lookup. Lookups are performed against what is commonly known as the Domain Routing Table (see section 10.0). A Domain Routing Table Entry contains the following fields: - Domain Name. The Domain Name is analogous to the realm portion of the NAI. This is the field that is typically used as a primary key in the routing table lookups. Note that some implementations perform their lookups based on longest-match- from-the-right on the realm rather than requiring an exact match. - Extension Id. It is possible for a routing entry to have a different destination based on the extension identifier of the message. This field is typically used as a secondary key field in routing table lookups. - Local Action. The Local Action field is used to identify how a Calhoun et al. expires July 2001 [Page 34]
Internet-Draft February 2001 message should be treated. The following actions are supported: 1. LOCAL - Diameter messages that resolve to a routing entry with the Local Action set to Local can be satisfied locally, and do not need to be forwarded to another server. 2. PROXY - All Diameter messages that fall within this category MUST be forwarded to a next hop server. The local server MAY apply its local policies to the message by including new AVPs to the message prior to forwarding. See section 6.4 for more information. 3. REDIRECT - Diameter messages that fall within this category MUST have the identity of the home Diameter server(s) appended, and returned to the sender of the message. See section 6.3 for more information. - Server Identifier - One or more servers the message is to be forwarded to. When the Local Action is set to PROXY, this field contains the identities of the server(s) the message must be forwarded to. When the Local Action field is set to REDIRECT, this field contains the Home Diameter server(s) for the realm. It is important to note that Diameter servers MUST support at least one of the PROXY, REDIRECT, or LOCAL modes of operation. Servers do not need to support all modes of operation in order to conform with the protocol specification. Servers MUST NOT reorder AVPs with the same AVP Code. 6.3 Redirect Server A Redirect Server is one that provides NAI Realm to Diameter Home Server address resolution. When a message is received by a peer, the Routing-Realm or the realm portion of the User-Name AVP is extracted from the message, and the realm portion is used to perform a lookup in the domain routing table. Implementations MAY also use the Extension Id as a secondary key in the domain routing table lookup. Successful routing table lookups will return one or more home Diameter servers that could satisfy the message. The home servers are encoded in one or more Redirect-Host-Address AVPs. If the Redirect- Host-Port is to be included (meaning that the host is not listening on the standard Diameter port), it MUST be encapsulated within the Redirect-Host AVP along with its corresponding Redirect-Host-Address AVP. Calhoun et al. expires July 2001 [Page 35]
Internet-Draft February 2001 +------------------+ | Diameter | | Redirect Server | +------------------+ ^ | Request | | Response + joe@xyz.com | | Result Code = | | Redirect | v +----------+ Request +----------+ | abc.net |------------->| xyz.net | | Diameter | | Diameter | | Server |<-------------| Server | +----------+ Response +----------+ Figure 2: Diameter Redirect Server Lastly, the Result-Code AVP is added with the Data field of the AVP set to Diameter_REDIRECT_INDICATION [1], and the message is returned to the sender of the request. Redirect servers MAY also include the certificate of the Home server(s). These certificates are encapsulated in a CMS-Data AVP [11]. When this occurs, the server forwarding the request directly to the Home Diameter server SHOULD include its own certificate in the message. 6.3.1 Redirect-Host AVP The Redirect-Host AVP (AVP Code 292) is of type Grouped and is found in responses that include the Result-Code AVP set to Diameter_REDIRECT_REQUEST. This AVP only needs to be used if the host the message is to be redirected to is not listening on the standard Diameter port. Its Data field has the following ABNF grammar: Redirect-Host = Redirect-Host-Address Redirect-Host-Port Redirect-Host-Address = ; See Section 6.3.2 Redirect-Host-Port = ; See Section 6.3.3 The Redirect-Host-Address AVP Data field contains the IP Address of the Diameter host to which the request MUST be redirected. The Redirect-Host-Port contains the port number to which the request should be sent. Upon receipt of such a Result Code, and this AVP, the receiving host SHOULD send the request directly to the host identified by the Redirect-Host-Address AVP. Calhoun et al. expires July 2001 [Page 36]
Internet-Draft February 2001 +---------------------------------------------------------------+ | AVP Header (AVP Code = 292) | +---------------------------------------------------------------+ | Redirect-Host-Address AVP | +---------------------------------------------------------------+ | Redirect-Host-Port AVP | +---------------------------------------------------------------+ 6.3.2 Redirect-Host-Address AVP The Redirect-Host-Address AVP (AVP Code 278) is of type Address. Its use is described in Section 6.3.1. 6.3.3 Redirect-Host-Port AVP The Redirect-Host-Port AVP (AVP Code 277) is of type Unsigned32. Its use is described in Section 6.3.1. 6.4 Proxy Server This section outlines the processing rules for Diameter proxy servers. A proxy server can either be stateful or stateless. A Proxy server MAY act in a stateful manner for some requests, and be stateless for others. There are two types of states that servers MAY wish to maintain; transaction and session. Maintaining transaction state implies that a server keeps a copy of a request, which is then used when the corresponding response is received. This could be done to apply local policies to the message, or simply for auditing purposes. Maintaining session state implies that a server keeps track of all "active" users. An active user is one that has been authorized for a particular service, and the server has not received any indication that the user has relinquished access. A stateless proxy is one that does not maintain transaction, nor session state. It frees the messages sent once acknowledgements are received by the transport layer. A stateful proxy can be viewed as a Diameter Server upon receiving a request, and as a Client when forwarding the message. For all intents and purposes, stateful servers terminate an upstream "session", and initiates a downstream "session" (see Figure 3), and MAY provide the following features: - Protocol translation (e.g. RADIUS <-> Diameter) - Limiting resources authorized to a particular user Calhoun et al. expires July 2001 [Page 37]
Internet-Draft February 2001 - Per user or transaction auditing +--------+ +-----------------+ +--------+ | Client | --------> | Server | Client | -------> | Server | +--------+ +-----------------+ +--------+ Figure 3 - Example of Stateful Proxy A stateful proxy that maintains transaction state SHOULD release transaction information after a request's corresponding response has been forwarded towards the recipient, and has been acknowledged by the underlying transport. A stateful proxy that maintains session state SHOULD release the session state once it is informed that a user and/or device has relinquished access. Home servers processing requests that include the Route-Record and/or the Proxy-State AVPs MUST return these AVPs in the same order in the corresponding response. 6.4.1 Proxying Requests A proxy server MUST check for forwarding loops before proxying a message of type Request, Query or Indication. Such as message has been looped if the server finds its own address in a Route-Record AVP. A Diameter server that proxies a message or type Request, Query or Indication MUST append a Route-Record AVP, which includes its identity. Diameter Servers that receive messages MUST validate the last Route-Record AVP in the message and ensure that the host identified in the AVP is the same as the sender of the message. A Proxy Server MAY also include the Proxy-State AVP in a message of type Request or Query, which is used to encode local state information. The Proxy-State AVP is guaranteed to be present in the corresponding response. The message is then forwarded to the downstream Diameter server, as identified in the Domain Routing Table. Proxy Server MUST save the Identifier in request messages, and update the header field with a locally unique value. The saved identifier MAY be encoded in the Proxy-State AVP, and will be required in the processing of the corresponding response. Calhoun et al. expires July 2001 [Page 38]
Internet-Draft February 2001 6.4.2 Proxying Responses A proxy server MUST only process messges of type Response or Answer whose last Route-Record AVP matches one of its addresses. Any responses that do not conform to this rule MUST be dropped. The last Route-Record AVP MUST be removed from the message before it is forwarded to the next hop, which is identified by the second to last Route-Record AVP. If the last Proxy-State AVP in the message is targeted to the local Diameter server, the AVP MUST be removed. If a proxy server receives a response with a Result-Code AVP indicating a failure, it MUST NOT modify the contents of the AVP. Any additional local errors detected SHOULD be logged, but not reflected in the Result-Code AVP. Prior to forwarding the response, proxy servers MUST restore the original value of the Diameter header's Identifier field. 6.4.3 Route-Record AVP The Route-Record AVP (AVP Code 282) is of type OctetString, and contains the Fully Qualified Domain Name of the Proxy appending this AVP to a Diameter message. 6.4.4 Proxy-State AVP The Proxy-State AVP (AVP Code = 33) is of type Grouped. The Grouped Data field has the following ABNF grammar: Proxy-State = Proxy-Address Proxy-Info Proxy-Address = ; See Section 6.4.5 Proxy-Info = ; See Section 6.4.6 The Proxy-Address AVP Data field contains one of the IP addresses of the system that created the AVP. This assists hosts in determining whether a Proxy-State AVP is intended for the local host. The Proxy- Info AVP contains state information, and MUST be treated as opaque data. Calhoun et al. expires July 2001 [Page 39]
Internet-Draft February 2001 +---------------------------------------------------------------+ | AVP Header (AVP Code = 33) | +---------------------------------------------------------------+ | Proxy-Address AVP | +---------------------------------------------------------------+ | Proxy-Info AVP | +---------------------------------------------------------------+ 6.4.5 Proxy-Address AVP The Proxy-Address AVP (AVP Code = 280) is of type Address. Its use is described in Section 6.4.4. 6.4.6 Proxy-Info AVP The Proxy-Info AVP (AVP Code = 284) is of type OctetString. Its use is described in Section 6.4.4. 6.4.7 Routing-Realm AVP The Routing-Realm AVP (AVP Code 283) is of type OctetString and contains the realm portion of the Network Access Identifier. When present, the Routing-Realm AVP MAY be used to perform any message routing decisions. 6.5 Applying Local Policies Proxies MAY apply local access policies to Diameter requests, or responses, by adding, changing or deleting AVPs in the messages. Proxies that apply local policies MUST NOT allow end-to-end security on any messages that traverse through it, unless security is terminated locally. A proxy wishing to modify a Diameter message to enforce some local policy that detects that end-to-end security has been applied to the message MUST return a response to the originator with the Result-Code set to Diameter_NO_END_2_END_SECURITY. The originator of the request MAY re-issue the request with no end-to-end security if it falls within its local policy. In the event that the Home Diameter server receives a request with contradictory information (possibly due to some proxy adding a local policy), it MAY accept the latest AVP, or MAY return the response with the Result Code AVP set to Diameter_CONTRADICTING_AVPS. However, Calhoun et al. expires July 2001 [Page 40]
Internet-Draft February 2001 a NAS receiving a response that contains contradictory information SHOULD reject service to the user. 6.6 Hiding Network Topology Stateful proxies forwarding requests to servers outside of their administrative domain MAY hide the internal network topology. Servers perform this by removing all Route-Record AVPs in the message, and maintains the Route-Record AVPs to add to the corresponding response. Such stateful servers MUST still add their own Route-Record AVP to the request prior to forwarding. 6.7 Loop Detection When a Diameter Proxy or Redirect server receives a message of type Request, Query or Indication, it MUST examine all Route-Record AVPs in the message to determine whether such an AVP already exists with the local server's identity. If an AVP with the local host's identity is found in the request, it is an indication that the message is being looped through the same set of proxies. When such an event occurs, the Diameter server that detects the loop returns a response with the Result-Code AVP set to Diameter_LOOP_DETECTED. 6.8 Finding a Target NAS within a Domain The Diameter protocol supports unsolicited server initiated messages. However, when such messages are transmitted, they have a specific target Network Access Server (NAS) in mind. Unsolicited server initiated messages are unique in that they contain the Destination- NAI AVP. Routing of such messages follow the same set of guidelines described in section 6.0, with one exception. When a proxy server has determined that a message, which includes the Destination-NAI AVP, has reached its target realm, the Destination-NAI AVP is used to identify the actual NAS the message should be forwarded to. 6.8.1 Destination-NAI AVP The Destination-NAI AVP (AVP Code 293) [1] is of type OctetString, and contains the NAI [8] of the intended recipient of the message. This AVP MUST be present in all unsolicited server initiated messages. 7.0 Diameter Message Security Calhoun et al. expires July 2001 [Page 41]
Internet-Draft February 2001 The Diameter Base protocol MAY be secured in one of three ways. The first method does not involve any security mechanisms in the Diameter protocol, but relies on an underlying security mechanism, such as IP Security. The second method is hop-by-hop security, which SHOULD be supported by all Diameter implementations. The third method is optional and requires a Public Key Infrastructure [14], and is documented in [11]. 7.1 Hop-by-Hop Security Diameter Hop-by-Hop security provides message integrity and per AVP encryption, and requires that the communicating entities have a pre- configured shared secret. Hop-by-Hop security is very difficult to deploy and administer in large scale networks and involves symmetric trust, unlike security based on a public key infrastructure (PKI). PKI is used for Diameter End-to-End security, and is defined in [11]. Hop-by-Hop security may be desirable in environments where symmetric cryptography is sufficient or when a PKI is not available. Figure 4 below provides an example of hop-by-hop security in a proxy chain. Assuming that the packet was received by DIA2 from DIA1, and was to be proxied to DIA3, the following steps would be taken: 1. Validating the message's integrity using the shared secret with DIA1, and removing the authenticated security AVPs. 2. Decrypting any encrypted AVPs using the secret shared with DIA1. 3. Re-encrypting AVPs using the secret shared with DIA3. 4. Computing the message hash using the secret shared with DIA3, and adding it to the ICV AVP in the Diameter message. (Shared-Secret-1) (Shared-Secret-2) +------+ -----> +------+ ------> +------+ | | |1 3| | | | DIA1 +------------------>+ DIA2 +------------------>+ DIA3 | | | |2 4| | | +------+ +------+ +------+ Figure 4: Hop-by-Hop Security in Proxy Environments The above steps that each proxy MUST perform in a proxy chain clearly describes the security issues associated with hop-by-hop security in a proxy environment. Since the message integrity is re-computed at each node in the chain, it is not possible to detect if a proxy modified information in the message (e.g. session time). Furthermore, any sensitive information would be known to all proxies in the chain, Calhoun et al. expires July 2001 [Page 42]
Internet-Draft February 2001 since each node must decrypt AVPs. Therefore, Any AVPs that contain data that MUST NOT be seen by intermediate Diameter nodes MUST be protected via the mechanism described in the strong security extension [11]. It is highly recommended that the size of the shared secrets used be sufficiently long (e.g. 128 bits), and that different shared secrets be used for both authentication and encryption. 7.1.1 Integrity-Check-Value AVP The Integrity-Check-Value AVP (AVP Code 259) is of type Grouped and is used for hop-by-hop message authentication and integrity. The Diameter header as well as all AVPs (including padding) up to the Digest AVP is protected by the Integrity-Check-Value AVP. Note that the Message Length field in the Diameter header MUST be set to zero (0) prior to the ICV calculation. The Timestamp AVP provides replay protection and the Nonce AVP provides randomness. If present, any AVPs in a message that is not succeeded by the Integrity-Check-Value AVP MUST be ignored. All Diameter implementations SHOULD support this AVP. The Integrity-Check-Value AVP (AVP Code = 259) is of type Grouped. The grammar for the grouped Data field is defined is: Integrity-Check-Value = Nonce Time Auth-Trans-Id Key-ID Digest Nonce = ; Nonce, See Section 7.2 Timestamp = ; Timestamp, See Section 7.3 Auth-Trans-Id = ; Authentication-Transform-Id, / ; See Section 7.1.1.1 Key-ID = ; Key-ID, See Section 7.4 Digest = ; Digest, See Section 7.1.1.2 Calhoun et al. expires July 2001 [Page 43]
Internet-Draft February 2001 +---------------------------------------------------------------+ | AVP Header (AVP Code = 259) | +---------------------------------------------------------------+ | Nonce AVP | +---------------------------------------------------------------+ | Timestamp AVP | +---------------------------------------------------------------+ | Authentication-Transform-Id AVP | +---------------------------------------------------------------+ | Key-ID AVP | +---------------------------------------------------------------+ | Digest AVP | +---------------------------------------------------------------+ 7.1.1.1 Authentication-Transform-Id AVP The Transform-Id AVP (AVP Code = 285) is of type Unsigned32. This value identifies the transform that was used to compute the ICV. The following values are defined in this document: HMAC-MD5-96[6] 1 The ICV is computed using the HMAC-MD5 algorithm, and the first 12 bytes of the hash output is included in the Digest AVP. All Diameter implementations supporting this AVP MUST support this transform. Using the example code provided in [6], the following call would be used to generate the Digest AVP: hmac_md5(DiameterMessage, MessageLength, Secret, Secretlength, Output) where the DiameterMessage is the complete message up to the Digest AVP. 7.1.1.2 Digest AVP The Digest AVP (AVP Code = 287) is of type OctetString. This value contains the output from the hashing algorithm, covering all AVPs in the message, including all AVPs in the Integrity-Check-Value AVP up to, but not including, the Digest AVP. 7.1.2 Encrypted-Payload AVP The Encrypted-Payload AVP (AVP Code 260) is of type Grouped and is used to encapsulate encrypted AVPs for privacy during transmission. Calhoun et al. expires July 2001 [Page 44]
Internet-Draft February 2001 Hop-by-Hop confidentiality is achieved by encapsulating all AVPs which are to be encrypted into an Encrypted-Payload AVP. This feature SHOULD be supported by Diameter implementations. The grammar for the grouped Data field is defined is: Encrypted-Payload = Enc-Trans-Id Key-ID ptextlen data Enc-Trans-Id = ; Encryption-Transform-Id, / ; See Section 7.1.2.1 Key-ID = ; See Section 7.4 ptextlen = ; Plaintext-Data-Length, See Section 7.1.2.2 data = ; Encrypted-Data, See Section 7.1.2.3 +---------------------------------------------------------------+ | AVP Header (AVP Code = 260) | +---------------------------------------------------------------+ | Encryption-Transform-Id AVP | +---------------------------------------------------------------+ | Key-ID AVP | +---------------------------------------------------------------+ | Plaintext-Data-Length AVP | +---------------------------------------------------------------+ | Encrypted-Data AVP | +---------------------------------------------------------------+ 7.1.2.1 Encryption-Transform-Id AVP The Encryption-Transform-Id AVP (AVP Code = 288) is of type Unsigned32. This AVP identifies the transform that was used to encrypt the data contained in the Encrypted-Data AVP. The following values are defined in this document: MD5 1 See section 7.1.2.4 for more information. 7.1.2.1.1 MD5 Payload Hiding The plain text (which is a buffer containing one or more AVPs) is first padded to a sixteen (16) byte boundary with 0 bytes. Since the encapsulated AVPs have length fields, it is possible to detect their boundaries, whether or not padding has been done. One or more Nonce AVPs MUST precede an Encrypted-Payload AVP. An MD5 hash is performed on the: - last Nonce AVP which precedes the Encrypted-Payload AVP Calhoun et al. expires July 2001 [Page 45]
Internet-Draft February 2001 - the shared authentication secret This MD5 hash value is then XORed with the first 16 octet segment of the buffer to encrypt. The resulting 16 octet result is saved as the first 16 octets of the encrypted buffer. The result is also used to calculate a new value using MD5: - the shared authentication secret - the 16 byte result of the previous XOR This value is then XORed with the next 16 bytes. This is done for each 16 bytes successively in the buffer to encrypt, producing an equal sized encrypted buffer. The receiver of a Diameter message with an Encrypted-Payload AVP MUST first check the integrity of the message, either through the ICV, or the CMS-Data AVP [11] if it protects the Encrypted-Payload AVP. Then the Encrypted-Payload AVP is decrypted, by reversing the above procedure, which applied to the buffer will reproduce the plain text version. The decapsulated AVPs are then used to process the Diameter message in the normal manner. 7.1.2.2 Plaintext-Data-Length AVP The Plaintext-Data-Length AVP (AVP Code = 289) is of type Unsigned32, and contains the length of the plaintext data. This AVP is necessary in order to not treat any possible padded data, added as part of the encryption transform, as part of the plaintext. 7.1.2.3 Encrypted-Data AVP The Encrypted-Data AVP (AVP Code = 290) is of type OctetString. This AVP contains the encrypted AVPs. 7.2 Nonce AVP The Nonce AVP (AVP Code 261) is of type OctetString and is present in the Integrity-Check-Value AVP and is used to ensure randomness within a message. The content of this AVP MUST be a random value of at least 128 bits. 7.3 Timestamp AVP The Timestamp AVP (AVP Code 262) is of type Unsigned32 and is used to Calhoun et al. expires July 2001 [Page 46]
Internet-Draft February 2001 add replay protection to the Diameter protocol. The Data field of this AVP is the most significant four octets returned from an NTP [18] server that indicates the number of seconds expired since Jan. 1, 1900. Messages that are older than a configurable maximum age SHOULD be rejected (see section 10.0) and a response SHOULD be returned with the Result-Code AVP Data field set to Diameter_TIMEOUT. Note that the larger the configurable value, the more susceptible one is to a replay attack. However, one does have to take into account the possibility for clock drift, and the latency involved in the transmission of the message over the network. The timestamp AVP SHOULD be updated prior to retransmission. A Diameter node that receives a message with the Result-Code AVP set to Diameter-TIMEOUT MAY use the time found in the Timestamp AVP within the reply in order to synchronize its clock with its peer. When time synchronization is done, the sender MUST NOT change its local time, but SHOULD adjust the time delta for all outgoing messages to the peer, and require that its local time be used in received messages. Implementations must be prepared to wrap at the epochal 2038 where Time values are used, and 0,1,... MUST be considered greater than 2^32-1 at that time. 7.4 Key-Id AVP The Key-Id AVP (AVP Code = 286) is of type Unsigned32. This value contains a key identifier, which is used to identify the keying information used to generate the Digest AVP or the Encrypted-Data AVP. 8.0 IANA Considerations This document defines a number of assigned numbers to be maintained by the IANA. This section explains the criteria to be used by the IANA to assign additional numbers in each of these lists. The following subsections describe the assignment policy for the namespaces defined elsewhere in this document. 8.1 AVP Attributes As defined in section 2.3, AVPs contain vendor ID, attribute and Data fields. For vendor ID value of 0, IANA will maintain a registry of Calhoun et al. expires July 2001 [Page 47]
Internet-Draft February 2001 assigned AVP codes and in some case also values. Attribute 0-254 are assigned from the RADIUS protocol [1], whose attributes are also maintained through IANA. AVP Codes 256-280 are assigned within this document. The remaining values are available for assignment through Designated Expert [12]. 8.2 Command Code Values As defined in section 2.1, the Command Code field has an associated value maintained by IANA. Values 0-255 are reserved for backward RADIUS compatibility, and values 257, 259, 274, 275 and 276 are defined in this specification. The remaining values are available for assignment via Designated Expert [12]. 8.3 Extension Identifier Values As defined in section 2.6.5, the Extension Identifier is used to identify a specific Diameter Extension. All values, other than zero (0) are available for assignment via Standards Action [12]. Note that the Diameter protocol is not inteded to be extended for any purpose. Any extensions added to the protocol MUST ensure that they fit within the existing framework, and that no changes to the base protocol are required. 8.4 Result-Code AVP Values As defined in Section 5.2, the Result Code AVP (AVP Code 268) defines the values 1001, 2001, 3001, 4001-4002, 5001-5010 and 6001-6007. All remaining values are available for assignment via IETF Consensus [12]. 8.5 Authentication-Transform-Id AVP Values Section 7.1.1.1 defines the Authentication-Transform-Id AVP (AVP Code 285) which is used to identify the authentication algorithm used to generate the contents of the Digest AVP. This document reserves the value 1. All remaining values are available for assignment via Designated Expert [12]. 8.6 Encryption-Transform-Id AVP Values Section 7.1.2.1 defines the Encryption-Transform-Id AVP (AVP Code Calhoun et al. expires July 2001 [Page 48]
Internet-Draft February 2001 288) which is used to identify the encryption algorithm used to generate the contents of the Encrypted-Data AVP. This document reserves the value 1. All remaining values are available for assignment via Designated Expert [12]. 8.7 Message Header Bits There are thirteen bits in the Flags field of the Diameter header. This document assigns bit 1 ('R'esponse), bit 2 ('I'nterrogation) and bit 3 ('E'xpected Reply). Bits 4 through 13 should only be assigned via a Standards Action [12]. 8.8 AVP Header Bits There are 16 bits in the Flags field of the AVP Header. This document assigns bit 1 ('M'andatory), bit 3 ('V'endor Specific) and bit 5 ('P'rotected). The remaining bits should only be assigned via a Standards Action [12]. 9.0 Open Issues The following are the open issues that SHOULD be addressed in future versions of the Diameter protocol: - AVPs with time values are represented by Unsigned32 type data. This value is a timestamp consistent with NTP [18]. This field is expected to expire sometime in 2038. Future investigation SHOULD be done to determine if a 64 bit time format could be used. - The fact that the Sender's IP Address is used in the construction of the Session-Id means that the introduction of Network Address Translation MAY cause two hosts to represent the same Session Identifier. This area needs to be investigated further to be able to support Diameter hosts on a private network. 10.0 Diameter protocol related configurable parameters This section contains the configurable parameters that are found throughout this document: Diameter Peer A Diameter entity MAY communicate with peers that are Calhoun et al. expires July 2001 [Page 49]
Internet-Draft February 2001 statically configured. A statically configured Diameter peer would require that either the IP address or the fully qualified domain name (FQDN) be supplied, which would then be used to resolve through DNS. Realm Routing Table A Diameter Proxy server routes messages based on the realm portion of a Network Access Identifier (NAI). The server MUST have a table of Realms Names, and the address of the peer to which the message must be forwarded to. The routing table MAY also include a "default route", which is typically used for all messages that cannot be locally processed. Maximum Age of an outstanding message Messages older than the maximum age SHOULD be rejected, as described in section 7.3. The recommended value is 4 seconds. Shared Secret The shared secret is a value that is known by two communicating peers, and is used to generate the Integrity-Check-Value and the Encryption-Payload AVP. There is no default. 11.0 Security Considerations The Diameter base protocol requires that two communicating peers exchange messages in a secure fashion. This document describes two security methods that can be used. The first requires no security at the application layer, but rather relies on an underlying security mechanism, such as IP Security. When IP Security is not available, or desirable, the Diameter protocol MAY use hop-by-hop security, which requires communicating peers to negotiate a symmetric key through some out of band mechanism. Hop-by-Hop security provides replay protection by requiring that the communicating peers share a time source, such as an NTP server. Information of a sensitive nature, which MUST NOT be seen by any intermediate Diameter node MUST NOT be encrypted using hop-by-hop encryption. When the Diameter protocol is used in an inter-domain network, strong application level security MAY be required, such as non-repudiation. When the communicating peers do require this level of security either for legal or business purposes, the extension defined in [11] MAY be used. This security model provides AVP-level authentication, and the encryption mechanism is designed such that only the target host has the keying information required to decrypt the information. Calhoun et al. expires July 2001 [Page 50]
Internet-Draft February 2001 12.0 References [1] Rigney, et alia, "RADIUS", RFC-2138, April 1997 [2] Reynolds, Postel, "Assigned Numbers", RFC 1700, October 1994. [3] Postel, "User Datagram Protocol", RFC 768, August 1980. [4] Rivest, "The MD5 Message-Digest Algorithm", RFC 1321, April 1992. [5] Kaufman, Perlman, Speciner, "Network Security: Private Communi- cations in a Public World", Prentice Hall, March 1995, ISBN 0- 13-061466-1. [6] Krawczyk, Bellare, Canetti, "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, January 1997. [7] P. Calhoun, W. Bulley, A. Rubens, J. Haag, "Diameter NASREQ Extension", draft-calhoun-diameter-nasreq-06.txt, IETF work in progress, January 2001. [8] Aboba, Beadles "The Network Access Identifier." RFC 2486. Janu- ary 1999. [9] Calhoun, Zorn, Pan, Akhtar, "Diameter Framework", draft- calhoun-diameter-framework-09.txt, IETF work in progress, Janu- ary 2001. [10] P. Calhoun, C. Perkins, "Diameter Mobile IP Extensions", draft- calhoun-diameter-mobileip-12.txt, IETF work in progress, January 2001. [11] P. Calhoun, W. Bulley, S. Farrell, "Diameter Strong Security Extension", draft-calhoun-diameter-strong-crypto-06.txt (work in progress), January 2001. [12] Narten, Alvestrand,"Guidelines for Writing an IANA Considera- tions Section in RFCs", BCP 26, RFC 2434, October 1998 [13] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [14] Myers, Ankney, Malpani, Galperin, Adams, "X.509 Internet Public Key Infrastructure Online Certificate Status Protocol (OCSP)", RFC 2560, June 1999. Calhoun et al. expires July 2001 [Page 51]
Internet-Draft February 2001 [15] Arkko, Calhoun, Patel, Zorn, "Diameter Accounting Extension", draft-calhoun-diameter-accounting-09.txt, IETF work in progress, January 2001. [16] Hinden, Deering, "IP Version 6 Addressing Architecture", RFC 2373, July 1998. [17] ISI, "Internet Protocol", RFC 791, September 1981. [18] Mills, "Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI, RFC 2030, October 1996. [19] Housley, Ford, Polk, Solo, "Internet X.509 Public Key Infras- tructure Certificate and CRL Profile", RFC 2459, January 1999. [20] B. Aboba, G. Zorn, "Criteria for Evaluating Roaming Protocols", RFC 2477, January 1999. [21] M. Beadles, D. Mitton, "Criteria for Evaluating Network Access Server Protocols", draft-ietf-nasreq-criteria-05.txt, IETF work in progress, June 2000. [22] T. Hiller and al, "CDMA2000 Wireless Data Requirements for AAA", draft-hiller-cdma2000-aaa-02.txt, IETF work in progress, Sep- tember 2000. [23] S. Glass, S. Jacobs, C. Perkins, "Mobile IP Authentication, Authorization, and Accounting Requirements". RFC 2977. October 2000. [24] F. Yergeau, "UTF-8, a transformation format of ISO 10646", RFC 2279, January 1998. [25] P. Calhoun, A. Rubens, H. Akhtar, E. Guttman, W. Bulley, J. Haag, "Diameter Implementation Guidelines", draft-calhoun- diameter-impl-guide-04.txt, IETF work in progress, June 2000. [26] R. Stewart et al., "Simple Control Transmission Protocol". RFC 2960. October 2000. [27] Postel, J. "Transmission Control Protocol", RFC 793, January 1981. [28] E. Guttman, C. Perkins, J. Veizades, M. Day. "Service Location Protocol, Version 2", RFC 2165, June 1999. [29] P. Calhoun, "Diameter Resource Management", draft-calhoun- diameter-res-mgmt-06.txt, IETF Work in Progress, January 2001. Calhoun et al. expires July 2001 [Page 52]
Internet-Draft February 2001 [30] Institute of Electrical and Electronics Engineers, "IEEE Stan- dard for Binary Floating-Point Arithmetic", ANSI/IEEE Standard 754-1985, August 1985. [31] D. Crocker, P. Overell, "Augmented BNF for Syntax Specifica- tions: ABNF", RFC 2234, November 1997. [32] E. Guttman, C. Perkins, J. Kempf, "Service Templates and Ser- vice: Schemes", RFC 2609, June 1999. [33] A. Gulbrandsen, P. Vixie, L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, February 2000. [34] D. Eastlake, "Domain Name System Security Extensions", RFC 2535, March 1999. [35] D. Eastlake, "DNS Security Operational Considerations", RFC 2541, March 1999. [36] D. Eastlake, "DNS Request and Transaction Signatures ( SIG(0)s )", RFC 2931, September 2000. 13.0 Acknowledgements The authors would like to thank Nenad Trifunovic, Tony Johansson and Pankaj Patel for their participation in the Document Reading Party. The authors would also like to acknowledge the following people for their contribution in the development of the Diameter protocol: Bernard Aboba, Jari Arkko, William Bulley, Daniel C. Fox, Lol Grant, Ignacio Goyret, Nancy Greene, Peter Heitman, Paul Krumviede, Fergal Ladley, Ryan Moats, Victor Muslin, Kenneth Peirce, Stephen Farrell, Sumit Vakil, John R. Vollbrecht, Jeff Weisberg, Jon Wood and Glen Zorn 14.0 Authors' Addresses Questions about this memo can be directed to: Pat R. Calhoun Network and Security Research Center, Sun Laboratories Sun Microsystems, Inc. 15 Network Circle Menlo Park, California, 94025 USA Calhoun et al. expires July 2001 [Page 53]
Internet-Draft February 2001 Phone: +1 650-786-7733 Fax: +1 650-786-6445 E-mail: pcalhoun@eng.sun.com Allan C. Rubens Tut Systems, Inc. 220 E. Huron, Suite 260 Ann Arbor, MI 48104 USA Phone: +1 734-995-1697 E-Mail: arubens@tutsys.com Haseeb Akhtar Wireless Technology Labs Nortel Networks 2221 Lakeside Blvd. Richardson, TX 75082-4399 USA Phone: +1 972-684-8850 E-Mail: haseeb@nortelnetworks.com Erik Guttman Solaris Advanced Development Sun Microsystems, Inc. Eichhoelzelstr. 7 74915 Waibstadt Germany Phone: +49-7263-911-701 E-mail: , 15.0 Full Copyright Statement Copyright (C) The Internet Society (2001). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this docu- ment itself may not be modified in any way, such as by removing the Calhoun et al. expires July 2001 [Page 54]
Internet-Draft February 2001 copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of develop- ing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The lim- ited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DIS- CLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 16.0 Expiration Date This memo is filed as <draft-calhoun-diameter-18.txt> and expires in July 2001. Calhoun et al. expires July 2001 [Page 55]
Internet-Draft February 2001 Appendix A. Diameter Service Template The following service template describes the attributes used by Diam- eter servers to advertise themselves. This simplifies the process of selecting an appropriate server to communicate with. A Diameter client can request specific Diameter servers based on characteristics of the Diameter service desired (for example, an AAA server to use for accounting.) Name of submitter: "Erik Guttman" <Erik.Guttman@sun.com> Language of service template: en Security Considerations: Diameter clients and servers use various cryptographic mechanisms to protect communication integrity, confidentiality as well as perform end-point authentication. It would thus be difficult if not impossible for an attacker to advertise itself using SLPv2 and pose as a legitimate Diameter peer without proper preconfigured secrets or cryptographic keys. Still, as Diameter services are vital for network operation it is important to use SLPv2 authenti- cation to prevent an attacker from modifying or eliminating ser- vice advertisements for legitimate Diameter servers. Template text: -------------------------template begins here----------------------- template-type=service:diameter template-version=0.0 template-description= The Diameter protocol is defined by draft-calhoun-diameter-18.txt template-url-syntax= url-path= ; The standard service URL syntax is used. ; For example: 'service:diameter://aaa.example.com:1812 Calhoun et al. expires July 2001 [Page 56]
Internet-Draft February 2001 supported-extensions= string L M # This attribute lists the Diameter extensions supported by the # AAA implementation. The extensions currently defined are: # Extension Name Defined by # --------------- ----------------------------------- # NASREQ draft-calhoun-diameter-nasreq-05.txt # MobileIP draft-calhoun-diameter-mobileip-11.txt # Accounting draft-calhoun-diameter-accounting-08.txt # Strong Security draft-calhoun-diameter-strong-crypto-05.txt # Resource Management draft-calhoun-diameter-res-mgmt-06.txt # # Notes: # . Diameter implementations support one or more extensions. # . Additional extensions may be defined in the future. # An updated service template will be created at that time. # NASREQ,MobileIP,Accounting,Strong Security,Resource Management supported-transports= string L M SCTP # This attribute lists the supported transports that the Diameter # implementation accepts. Note that a compliant Diameter # implementation MUST support SCTP, though it MAY support other # transports, too. SCTP,TCP -------------------------template ends here----------------------- Calhoun et al. expires July 2001 [Page 57]