Internet-Draft M. Stecher Expires: December, 2002 webwasher.com June, 2002 Evaluating the ICAP protocol regarding the OPES callout protocol requirements draft-stecher-opes-icap-eval-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 in December, 2002. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document uses the requirements for OPES callout protocols [1] and evaluates whether they are fulfilled by the ICAP protocol [2]. Stecher Expires December, 2002 [Page 1] Internet-Draft Evaluating the ICAP protocol June 2002 Table of Contents 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Functional Requirements . . . . . . . . . . . . . . . . . . 3 3.1 Callout Transactions . . . . . . . . . . . . . . . . . . . . 3 3.2 Callout Channels . . . . . . . . . . . . . . . . . . . . . . 3 3.3 Reliability . . . . . . . . . . . . . . . . . . . . . . . . 4 3.4 Congestion and Flow Control . . . . . . . . . . . . . . . . 4 3.5 Support for Keep-Alive Mechanism . . . . . . . . . . . . . . 4 3.6 Operation in NAT Environments . . . . . . . . . . . . . . . 4 3.7 Multiple Callout Servers . . . . . . . . . . . . . . . . . . 4 3.8 Multiple OPES Processors . . . . . . . . . . . . . . . . . . 5 3.9 Support for Different Application Protocols . . . . . . . . 5 3.10 Capability and Parameter Negotiations . . . . . . . . . . . 5 3.11 Meta Data and Instructions . . . . . . . . . . . . . . . . . 5 3.12 Asynchronous Message Exchange . . . . . . . . . . . . . . . 5 3.13 Message Segmentation . . . . . . . . . . . . . . . . . . . . 6 4. Performance Requirements . . . . . . . . . . . . . . . . . . 6 4.1 Protocol Efficiency . . . . . . . . . . . . . . . . . . . . 6 5. Security Requirements . . . . . . . . . . . . . . . . . . . 6 5.1 Authentication, Confidentiality, and Integrity . . . . . . . 6 5.2 Hop-by-Hop Confidentiality . . . . . . . . . . . . . . . . . 6 5.3 Operation Across Un-trusted Domains . . . . . . . . . . . . 7 5.4 Privacy . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . 7 References . . . . . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 7 Full Copyright Statement . . . . . . . . . . . . . . . . . . 8 Stecher Expires December, 2002 [Page 2] Internet-Draft Evaluating the ICAP protocol June 2002 1. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [3]. 2. Introduction The Internet Content Adaption Protocol (ICAP) in its version 1.0 has been described in an Internet draft that was posted one year ago and was updated recently [2]. The OPES (Open Pluggable Edge Services) working group defined the requirements for OPES callout protocols in the Internet draft [1]. This document checks for the requirements of [1] and evaluates whether they are fulfilled by the ICAP protocol [2]. Sections 3, 4, 5 and 6 of this document are synchronized with the same sections of [1] for a convenient lookup of the referred requirements. 3. Functional Requirements 3.1 Callout Transactions fulfilled Enabling of callout transactions: fulfilled Forward complete or partial app message: fulfilled Ability to return a modified app message: fulfilled Request/Response scheme: Defined, two main methods REQMOD/RESPMOD Terminating transactions: fulfilled (can be done as in HTTP) Premature termination of transaction: Possible. ICAP server can respond and close connection (graceful shutdown) w/o handling all data. Status Code: fulfilled (first line of response contains status code) 3.2 Callout Channels fulfilled Multiple transactions: fulfilled (ICAP connections are persistent by default as in HTTP/1.1) Stecher Expires December, 2002 [Page 3] Internet-Draft Evaluating the ICAP protocol June 2002 Connect and close: fulfilled (only ICAP client connects to ICAP server, both sides can close a connection) Parameters: Parameters are negotiated with special OPTIONS requests 3.3 Reliability fulfilled "ICAP uses TCP/IP as a transport protocol" (4.1. of [2]) 3.4 Congestion and Flow Control fulfilled "ICAP uses TCP/IP as a transport protocol" (4.1. of [2]) 3.5 Support for Keep-Alive Mechanism incomplete There are no keep alive messages in the ICAP protocol. Although ICAP supports persistent connections, a normal connection itself is not an optimal method of detecting failures. As in HTTP open connections may time out and will be closed to release resources if no transactions have to be handled for some time. An ICAP client needs to implement some strategy to avoid data loss if a connection is timed out by the ICAP server as the client is sending a new request. 3.6 Operation in NAT Environments fulfilled (Not frequently implemented but we once encountered an ICAP server behind a firewall running NAT.) 3.7 Multiple Callout Servers fulfilled (There is nothing explicitly in the specs but it works the same way as a data processor communicates with different HTTP servers). Stecher Expires December, 2002 [Page 4] Internet-Draft Evaluating the ICAP protocol June 2002 3.8 Multiple Data Processors fulfilled (As in HTTP, an ICAP server can be contacted by any number of clients. Multiple services on one server are also planned) 3.9 Support for Different Application Protocols incomplete ICAP is designed for HTTP only. "Though transformations may be possible on other non-HTTP content, they are beyond the scope of this document." (chapter 1 of [2]). There are implementations that use ICAP for other protocols like FTP and SMTP. 3.10 Capability and Parameter Negotiations fulfilled (A basic form of these negotiations is implemented by the ICAP OTPIONS request/response. (4.10 of [2])) 3.11 Meta Data and Instructions fulfilled Meta data can be transferred in ICAP message headers (4.3 of [2]). Information about the parts of the application message through Encapsulation header (4.4.1 of [2]). Service is specified through ICAP URI (4.2 of [2]) Cache-Control header for cacheability (4.3.1 of [2]). Keeping of local copy signaled by "Allow: 204" header (4.6 of [2]) Tracing through via headers (4.4.2 of [2]). 3.12 Asynchronous Message Exchange fulfilled Many TCP connections possible, as well as parallel requests on parallel connections. Stecher Expires December, 2002 [Page 5] Internet-Draft Evaluating the ICAP protocol June 2002 Preview feature to get an additional decision point (4.5 of [2]) Asynchronous data handling of ICAP traffic is not a MUST but a SHOULD. This information is missing in the current ICAP draft. 3.13 Message Segmentation fulfilled Segmentation through chunked transfer encoding (6.3 of [2]) 4. Performance Requirements 4.1 Protocol Efficiency fulfilled Easy encapsulation of HTTP messages, little overhead. Implementations are possible with little additional latency but this depends on the algorithms used by the ICAP services (whether data handling chunk by chunk is possible); some algorithms have restrictions that are independent of the callout protocol being used. 5. Security Requirements incomplete If ICAP can be compared with HTTP, the ICAP counterpart to HTTPS (ICAPS) is missing. The ICAP protocol itself and even more current implementations are designed for usage in a trusted environment where authentication and encryption of data between ICAP client and server are not necessary. 5.1 Authentication, Confidentiality, and Integrity incomplete Authentication can be done as in HTTP (7.1 of [2]). But ICAP is designed for usage in single trust domain 5.2 Hop-by-Hop Confidentiality incomplete There is a section about principle encryption methods (7.2 of [2]) but there are no real specs for this. Stecher Expires December, 2002 [Page 6] Internet-Draft Evaluating the ICAP protocol June 2002 5.3 Operation Across Un-trusted Domains incomplete Although there is nothing in the specs, this could be implemented by a VPN solution providing a secure TCP tunnel across the untrusted domains. 5.4 Privacy failed Encryption of information relevant to privacy policies is not a MUST in ICAP. 6. Summary The ICAP protocol fulfills most of the requirements. ICAP is incomplete with respect to support for multiple application protocols, does not have keep alive messages and it lacks some security requirements. 7. Security Considerations The security requirements for the OPES callout protocol are discussed in Section 5. References [1] Beck, A., et al., "Requirements for OPES Callout Protocols", Internet Draft draft-ietf-opes-protocol-reqs-01.txt, 18-Jun-02 [2] J. Elson, A. Cerpa: ICAP - the Internet Content Adaptation Protocol, Internet Draft draft-elson-icap-01.txt, June 2002 [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. Authors' Address Martin Stecher webwasher.com AG Vattmannstr. 3 33100 Paderborn Germany EMail: martin.stecher@webwasher.com Stecher Expires December, 2002 [Page 7] Internet-Draft Evaluating the ICAP protocol June 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. 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