A SOAP Binding for NETCONF From: http://www.ietf.org/internet-drafts/draft-goddard-netconfsoap-00.txt Date: June 19, 2003 -------------------------------------------------------------------------- Network Working Group T. Goddard Internet-Draft Wind River Systems Expires: December 18, 2003 June 19, 2003 A SOAP Binding for NETCONF draft-goddard-netconfsoap-00.txt 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. This Internet-Draft will expire on December 18, 2003. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract While the device management protocol NETCONF is generally well served by BEEP, there are environments where additional transports are desirable. The binding to SOAP described here may find application where SOAP-based tools and implementations are prevalent or where the network configuration favors HTTP. When used with multiple HTTP connections, SOAP over HTTP is sufficient for all NETCONF features except those involving asynchronous notification. Goddard Expires December 18, 2003 [Page 1] Internet-Draft A SOAP Binding for NETCONF June 2003 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. SOAP Background for NETCONF . . . . . . . . . . . . . . . . 4 2.1 Use and Storage of WSDL and XSD . . . . . . . . . . . . . . 4 2.2 SOAP over HTTP . . . . . . . . . . . . . . . . . . . . . . . 5 2.3 HTTP Drawbacks . . . . . . . . . . . . . . . . . . . . . . . 5 2.4 Important HTTP 1.1 Features . . . . . . . . . . . . . . . . 6 3. A SOAP Web Service for NETCONF . . . . . . . . . . . . . . . 7 3.1 Fundamental Use Case . . . . . . . . . . . . . . . . . . . . 7 3.2 Mapping BEEP Channels to HTTP Connections . . . . . . . . . 7 3.2.1 Asynchronous Functionality . . . . . . . . . . . . . . . . . 7 3.3 NETCONF Sessions . . . . . . . . . . . . . . . . . . . . . . 8 3.4 Capabilities Exchange . . . . . . . . . . . . . . . . . . . 9 3.5 A NETCONF/SOAP example . . . . . . . . . . . . . . . . . . . 9 3.6 Managing Multiple Devices . . . . . . . . . . . . . . . . . 10 4. Security Considerations . . . . . . . . . . . . . . . . . . 11 4.1 Integrity, Privacy, and Authentication . . . . . . . . . . . 11 4.2 Vulnerabilities . . . . . . . . . . . . . . . . . . . . . . 11 4.3 Environmental Specifics . . . . . . . . . . . . . . . . . . 11 Normative References . . . . . . . . . . . . . . . . . . . . 12 Informative References . . . . . . . . . . . . . . . . . . . 14 Author's Address . . . . . . . . . . . . . . . . . . . . . . 14 A. WSDL Definitions . . . . . . . . . . . . . . . . . . . . . . 15 A.1 NETCONF SOAP Binding . . . . . . . . . . . . . . . . . . . . 15 A.2 Sample Service Definition . . . . . . . . . . . . . . . . . 16 Intellectual Property and Copyright Statements . . . . . . . 17 Goddard Expires December 18, 2003 [Page 2] Internet-Draft A SOAP Binding for NETCONF June 2003 1. Introduction Given the use of XML [2] and the remote procedure call characteristics, it is natural to consider a binding of the NETCONF [1] operations to a SOAP [3] transport. The purpose here is to provide a concrete description of such a binding so that the technical issues can be discussed. Note that a SOAP binding for NETCONF is not necessarily intended only for managing individual devices. For instance, a server providing a SOAP interface can act as a proxy for multiple devices, possibly connecting to those devices over BEEP [16] or serial lines. In general, SOAP is a sufficient transport for NETCONF (essentially because of the remote procedure call character of both) but there are two areas of difficulty: the operation and the notification channel. The reason for this difficulty is the asynchronous aspect (from the point of view of the manager) of these features. Five basic topics are presented: points about SOAP of interest to NETCONF, specifics on implementing NETCONF as a SOAP-based web service, security considerations, and an appendix with functional WSDL. In some sense, the most important part of the document is the brief WSDL document presented in the Appendix. In theory, this WSDL combined with the NETCONF XML Schemas provide machine readable descriptions sufficient for the development of software applications using NETCONF. Goddard Expires December 18, 2003 [Page 3] Internet-Draft A SOAP Binding for NETCONF June 2003 2. SOAP Background for NETCONF Why introduce SOAP as yet another wrapper around what is already a remote procedure call message? There are, in fact, both technical and practical reasons. The technical reasons are perhaps less compelling, but let's examine them first. The use of SOAP does offer a few technical advantages. SOAP is fundamentally an XML messaging scheme (which is capable of supporting remote procedure call) and it defines a natural message format composed of a "header" and a "body" contained within an "envelope". The "header" contains meta-information relating to the message, and can be used to indicate such things as store-and-forward behaviour or transactional characteristics. In addition, SOAP specifies an optional encoding for the "body" of the message. However, this encoding is not applicable to NETCONF as one of the goals is to have highly readable XML, and SOAP-encoding is optimized instead for ease of automated deserialization. These benefits of SOAP are message structure are simple, but worthwhile due to the fact that they are already standardized. It is the practical reasons that truly make SOAP over HTTP an interesting choice for device management. It is not difficult to invent a mechanism for exchanging XML messages over TCP, but what is difficult is getting that mechanism supported in a wide variety of tools and operating systems and having that mechanism understood by a great many developers. SOAP over HTTP (with WSDL) is seeing good success at this, and this means that a device management protocol making use of these technologies has advantages in being implemented and adopted. Admittedly, there are interoperability problems with SOAP and WSDL, but such problems have wide attention and can be expected to be resolved. 2.1 Use and Storage of WSDL and XSD One of the advantages of using machine readable formats such as Web Services Description Language (WSDL) [4] and XML Schemas [5] is that they can be used automatically in the software development process. With appropriate tools, WSDL and XSD can be used to generate classes that act as remote interfaces or application specific data structures. Other uses, such as document generation and service location, are also common. A great innovation found with many XML-based definition languages is the use of hyperlinks for referring to documents containing supporting definitions. For instance, in WSDL, the import statement Goddard Expires December 18, 2003 [Page 4] Internet-Draft A SOAP Binding for NETCONF June 2003 imports the definitions of XML types and elements from the base NETCONF schema. Ideally, the file containing that schema is hosted on a web server under the authority of the standards body that defined the schema. In this way, dependent standards can be built up over time and all are accessible to automated software tools that ensure adherence to the standards. Thus, it will gradually become as important for ietf.org to host documents like http://ietf.org/netconf/1.0/base/base.xsd as they now host documents such as http://www.ietf.org/rfc/rfc2616.txt 2.2 SOAP over HTTP While it is true that SOAP focuses on messages and can be bound to different underlying protocols such as HTTP or SMTP, most existing SOAP implementations support only HTTP or HTTP/TLS. For this discussion we will assume SOAP over HTTP or HTTP/TLS unless otherwise specified. (This also includes applications of IPSec to SOAP over HTTP.) Note that there are a number of advantages to considering SOAP over protocols other than HTTP, as HTTP is asymmetric with respect to client and server. This causes difficulties in supporting asynchronous notification (relieved in many ways by replacing HTTP with BEEP). However, it is also the case that the full potential of HTTP is not currently used by SOAP. For instance, multiple SOAP replies to a single request could be contained in a multipart MIME [7] response. This would be a similar strategy to the use of multipart/related with SOAP attachments [14]. 2.3 HTTP Drawbacks HTTP is not the ideal transport for messaging, but it is adequate for the most basic interpretation of "remote procedure call". HTTP is based on a communication pattern of the client (which initiates the TCP connection) making a "request" to the server. The server returns a "response" and this process is continued (possibly over a persistent connection, as described below). This matches the basic idea of a remote procedure call where the caller invokes a procedure on a remote server and waits for the return value. Potential criticisms of HTTP could include the following: o server-initiated data flow is awkward Goddard Expires December 18, 2003 [Page 5] Internet-Draft A SOAP Binding for NETCONF June 2003 o headers are verbose and text-based o idle connections may be closed by intermediate proxies o data encapsulation must adhere to MIME o bulk transfer relies on stream-based ordering In many ways these criticisms are directed at particular compromises in the design of HTTP. As such, they are important to consider, but it is not clear that they result in fatal drawbacks for a device management protocol. 2.4 Important HTTP 1.1 Features HTTP 1.1 [8] includes two important features that provide for relatively efficient transport of SOAP messages. These features are "persistent connections" and "chunked transfer-coding". Persistent connections allow a single TCP connection to be used across multiple HTTP requests. This permits multiple SOAP request/ response message pairs to be exchanged without the overhead of creating a new TCP connection for each request. Given that a single stream is used for both requests and responses, it is clear that some form of framing is necessary. For messages whose length is known in advance, this is handled by the HTTP header "Content-length". For messages of dynamic length, "Chunking" is required. HTTP "Chunking" or "chunked transfer-coding" allows the sender to send an indefinite amount of binary data. This is accomplished by informing the receiver of the size of each "chunk" (substring of the data) before the chunk is transmitted. The last chunk is indicated by a chunk of zero length. Chunking can be effectively used to transfer a large XML document where the document is generated on-line from a non-XML form in memory. In terms of application to SOAP message exchanges, persistent connections are clearly important for performance reasons, and are particularly important when it is the persistence of authenticated connections that is at stake. When one considers that messages of dynamic length are the rule rather than the exception for SOAP messages, it is also clear that Chunking is very useful. In some cases it is possible to buffer a SOAP response and determine its length before sending, but the storage requirements for this are prohibitive for many devices. Together, these two features provide a good foundation for device management using SOAP over HTTP. Goddard Expires December 18, 2003 [Page 6] Internet-Draft A SOAP Binding for NETCONF June 2003 3. A SOAP Web Service for NETCONF 3.1 Fundamental Use Case The fundamental use case for NETCONF over SOAP (NETCONF/SOAP) over HTTP is that of a management console ("manager" role) managing one or more devices running NETCONF agents ("agent" role). The manager initiates one or more HTTP connections to the agent and drives the NETCONF sessions through repeated SOAP messages over HTTP requests. When the manager closes all HTTP connections associated with a session, the NETCONF session is also closed. 3.2 Mapping BEEP Channels to HTTP Connections While the transport of SOAP over BEEP [17] has been specified, the purpose of this discussion is to describe how to map the BEEP [16] semantics and performance characteristics already assumed by NETCONF onto a (possibly persistent) SOAP over HTTP connection. This configuration is chosen because it is the one that benefits most from existing SOAP tools and implementations. It is true that BEEP has many advantages over HTTP for the transport of SOAP messages, but the fact remains that HTTP is currently more widely deployed than BEEP. At some point in the future, NETCONF/SOAP over BEEP may also be of interest. It can be easily dealt with as many of the issues already discussed in this document are pertinent. There would simply be a few enhancements regarding asynchronous notification. NETCONF employs potentially three BEEP channels per session: the management channel, the operation channel, and the notification channel. In the SOAP over HTTP binding, each of these channels should be mapped to an individual HTTP connection (although the notification channel may remain in a BEEP channel in a separate TCP connection). Thus, SOAP messages on one connection (corresponding to the management channel) must be able to refer to SOAP messages on another connection (corresponding to the operation channel) as the "session" is potentially spread across multiple TCP connections. For instance, it may be necessary to abort a time-extended SOAP request on the "operation" HTTP connection by sending an "" message on the "management" HTTP connection. It would be possible to assign distinct characteristics to the "operation" and "management" HTTP connections, but the simpler option is to allow any number of connections in the same session, each capable of "management" and "operation" procedure calls. 3.2.1 Asynchronous Functionality NETCONF uses two types of asynchronous functionality and the mapping Goddard Expires December 18, 2003 [Page 7] Internet-Draft A SOAP Binding for NETCONF June 2003 of these onto SOAP over HTTP is somewhat problematic. The two asynchronous functions are and notifications on the notification channel. For it is recommended that a polling mechanism be supported by NETCONF. With this, a client could periodically poll on a secondary HTTP connection to obtain progress information on any outstanding operations on other HTTP connections in the same session. The notification mechanism for NETCONF is specified in an existing standard for reliable syslog [13] and it is suggested that the same mechanism be used with the SOAP binding (it is simply external). If notifications via SOAP over HTTP are desired, it is probably most effective if an HTTP connection is established from the agent to the management console. Such a connection could be established in response to the manager connecting to the device. More sophisticated functionality, such as multiple SOAP replies to a single request, would require enhancements to the SOAP over HTTP specification. 3.3 NETCONF Sessions NETCONF sessions are persistent for both performance and semantic reasons. NETCONF session state contains the following: 1. Authentication Information 2. Capability Information 3. Locks 4. Pending Operations 5. Operation Sequence Numbers Authentication must be maintained throughout a session due to the fact that it is expensive to establish. Capability Information is maintained so that appropriate operations can be applied during a session. Locks are released upon termination of a session as this makes the protocol more robust. Pending operations come and go from existence during the normal course of RPC operations. Operation sequence numbers provide the small but necessary state information to refer to operations during the session. Since it is generally not possible to support a full NETCONF session with a single HTTP connection, it is necessary to identify the NETCONF session in a way that can span multiple HTTP connections. This can be performed with the SOAPAction HTTP header, as in: POST /netconf HTTP/1.0 Goddard Expires December 18, 2003 [Page 8] Internet-Draft A SOAP Binding for NETCONF June 2003 Content-Type: text/xml; charset=utf-8 SOAPAction: "netconfsession:123" Content-Length: 470 Note that the session identifier must either be known by the manager (in order to attach to an existing session) or be communicated from the agent to the manager prior to the exchange of any significant NETCONF messages. It is recommended that the session identifier be generated and placed in a SOAP header in the reply to the first SOAP request with an empty SOAPAction. It may not be an error to continue to perform operations without specifying a NETCONF session, but the user must be aware that the only way to abort such operations is to close the HTTP connection. Thus, in the case of SOAP over HTTP, a NETCONF "session" is a collection of HTTP connections with common authenticated users and a common session identifier as indicated in the SOAPAction HTTP header. To support automated cleanup, a NETCONF session is closed when all connections associated with that session are closed. 3.4 Capabilities Exchange Capabilities exchange, if defined through a NETCONF RPC operation, can easily be accommodated in the SOAP binding. 3.5 A NETCONF/SOAP example Since the proposed WSDL (in Appendix A.1) uses document/literal encoding, the use of a SOAP header and body has little impact on the representation of a NETCONF operation. This example shows HTTP/1.0 for simplicity. POST /netconf HTTP/1.0 Content-Type: text/xml; charset=utf-8 Accept: application/soap+xml, text/* Cache-Control: no-cache Pragma: no-cache SOAPAction: "netconfsession:123" Content-Length: 470 Goddard Expires December 18, 2003 [Page 9] Internet-Draft A SOAP Binding for NETCONF June 2003 xml The HTTP/1.0 response is also straightforward: HTTP/1.0 200 OK Content-Type: text/xml; charset=utf-8 root superuser fred admin barney admin 3.6 Managing Multiple Devices When a server is acting as a proxy for multiple devices, the URL for the HTTP POST can be used to indicate which device is the target. It may also be desirable to use the HTTP POST URL as a means for selecting from multiple virtual devices on a single device. Goddard Expires December 18, 2003 [Page 10] Internet-Draft A SOAP Binding for NETCONF June 2003 4. Security Considerations 4.1 Integrity, Privacy, and Authentication The NETCONF SOAP binding relies on an underlying secure transport for integrity and privacy. Such transports are expected to include TLS [11] and IPSec. There are a number of options for authentication (some of which are deployment-specific): o within the transport (such as with TLS client certificates) o within HTTP (such as Digest Access Authentication [9]) o within SOAP (such as a digital signature in the header [15]) HTTP and SOAP level authentication can be integrated with RADIUS [12] to support remote authentication databases. 4.2 Vulnerabilities The above protocols may have various vulnerabilities, and these may be inherited by NETCONF/SOAP. NETCONF itself may have vulnerabilities due to the fact that an authorization model is not currently specified. It is important that device capabilities and authorization remain constant for the duration of any outstanding NETCONF session. In the case of NETCONF/SOAP, this constancy must be given particular attention as a session may span multiple HTTP connections. 4.3 Environmental Specifics Some deployments of NETCONF/SOAP may choose to use HTTP without encryption. This presents vulnerabilities but is reasonable for closed networks or debugging scenarios. A device managed by NETCONF may interact (over protocols other than NETCONF) with devices managed by other protocols, all of differing security. Each point of entry brings with it a potential vulnerability. Goddard Expires December 18, 2003 [Page 11] Internet-Draft A SOAP Binding for NETCONF June 2003 Normative References [1] Enns, R., "XMLCONF Configuration Protocol", draft-enns-xmlconf-spec-00 (work in progress), Feb 2003, . [2] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler, "Extensible Markup Language (XML) 1.0 (Second Edition)", W3C REC REC-xml-20001006, October 2000, . [3] Box, D., Ehnebuske, D., Kakivaya, G., Layman, A., Mendelsohn, N., Nielsen, H., Thatte, S. and D. Winer, "Simple Object Access Protocol (SOAP) 1.1", W3C Note NOTE-SOAP-20000508, May 2000, . [4] Christensen, E., Curbera, F., Meredith, G. and S. Weerawarana, "Web Services Description Language (WSDL) 1.1", W3C Note NOTE-wsdl-20010315, March 2001, . [5] Thompson, H., Beech, D., Maloney, M. and N. Mendelsohn, "XML Schema Part 1: Structures", W3C Recommendation REC-xmlschema-1-20010502, May 2001, . [6] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996, . [7] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996, . [8] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999, . [9] Franks, J., Hallam-Baker, P., Hostetler, J., Leach, P., Luotonen, A., Sink, E. and L. Stewart, "An Extension to HTTP: Digest Access Authentication", RFC 2069, January 1997, . [10] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997, . Goddard Expires December 18, 2003 [Page 12] Internet-Draft A SOAP Binding for NETCONF June 2003 [11] Dierks, T., Allen, C., Treese, W., Karlton, P., Freier, A. and P. Kocher, "The TLS Protocol Version 1.0", RFC 2246, January 1999, . [12] Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000, . [13] Rose, M. and D. New, "Reliable Delivery for syslog", RFC 3195, November 2001, . Goddard Expires December 18, 2003 [Page 13] Internet-Draft A SOAP Binding for NETCONF June 2003 Informative References [14] Barton, J., Nielsen, H. and S. Thatte, "SOAP Messages with Attachments", W3C Note NOTE-SOAP-attachments-20001211, Dec 2000, . [15] Brown, A., Fox, B., Hada, S., LaMacchia, B. and H. Maruyama, "SOAP Security Extensions: Digital Signature", W3C Note NOTE-SOAP-dsig-20010206, Feb 2001, . [16] Rose, M., "The Blocks Extensible Exchange Protocol Core", RFC 3080, March 2001, . [17] O'Tuathail, E. and M. Rose, "Using the Simple Object Access Protocol (SOAP) in Blocks Extensible Exchange Protocol (BEEP)", RFC 3288, June 2002, . Author's Address Ted Goddard Wind River Systems #180, 6815-8th Street NE Calgary, AB T2E 7H7 Canada Phone: (403) 730-7590 EMail: ted.goddard@windriver.com URI: http://www.windriver.com Goddard Expires December 18, 2003 [Page 14] Internet-Draft A SOAP Binding for NETCONF June 2003 Appendix A. WSDL Definitions A.1 NETCONF SOAP Binding The following WSDL document assumes a hypothetical location for the NETCONF schema. Goddard Expires December 18, 2003 [Page 15] Internet-Draft A SOAP Binding for NETCONF June 2003 A.2 Sample Service Definition The following WSDL document assumes a hypothetical location for the NETCONF/SOAP WSDL definitions. A typical deployment of a device manageable via NETCONF/SOAP would provide a service definition similar to the following to identify the address of the device. Goddard Expires December 18, 2003 [Page 16] Internet-Draft A SOAP Binding for NETCONF June 2003 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. 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