Network Working Group D. Wing Internet-Draft Cisco Systems Intended status: Standards Track S. Niccolini Expires: February 19, 2008 NEC H. Tschofenig Nokia Siemens Networks M. Stiemerling NEC August 18, 2007 Spam Score for SIP draft-wing-sipping-spam-score-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 February 19, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document defines a mechanism for SIP proxies to communicate a spam score to downstream SIP proxies and SIP user agents so they can provide alternate call routing or call handling. Wing, et al. Expires February 19, 2008 [Page 1] Internet-Draft SIP Spam Score August 2007 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 [RFC2119]. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Operation of Spam-Scoring Proxy . . . . . . . . . . . . . . . . 3 3. Operation of Proxy or User Agent . . . . . . . . . . . . . . . 3 4. ABNF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 9.1. Normative References . . . . . . . . . . . . . . . . . . . 6 9.2. Informational References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Intellectual Property and Copyright Statements . . . . . . . . . . 8 Wing, et al. Expires February 19, 2008 [Page 2] Internet-Draft SIP Spam Score August 2007 1. Introduction It is desirable for SIP proxies to insert a spam score so that downstream SIP proxies and downstream SIP user agents can use a high score to decide that special handling is required. For example, a score above 20 might cause one of the spam avoidance techniques, described in [I-D.ietf-sipping-spam], to be triggered for this call. This specification allows each SIP proxy to contribute spam scoring information that can be useful to downstream SIP proxies and the SIP UA. The downstream SIP proxies might ignore that information (e.g., they don't trust it) or might use it (e.g., they trust it because it was generated by a federation). From a deployment point of view it is expected that the score will most likely be benefical (and trustworthy) when inserted by a SIP proxy on the recipients side for evaluation by a SIP UA that has a direct relationship with this SIP proxy. 2. Operation of Spam-Scoring Proxy A SIP proxy generates a spam score using a local mechanism. Negative scores indicate the SIP request is not considered spam, and positive scores indicate the SIP request is considered spam. The higher the value, the more likely a message is spam or is not spam. This spam score is inserted into the "Via:" header, which is already generated by the proxy. The Via header was chosen because it the Via is already correlated with the proxy that generated the Via header. 3. Operation of Proxy or User Agent A downstream proxy MAY use the spam score or spam-detail information to change call routing or call handling. It is RECOMMENDED that only scores generated by trusted proxies be used. The behavior of the SIP proxy or user agent when the spam score is above a certain value is a local matter. Examples of behavior include: o a SIP request with a high spam score might cause a proxy or user agent to redirect the SIP request to company's main telephone extension or to the user's voicemail o a user agent might alert the user by flashing the phone (without audible ringing) Wing, et al. Expires February 19, 2008 [Page 3] Internet-Draft SIP Spam Score August 2007 o a user agent might allow calls with a spam score below a certain value during daylight hours, but deny such calls at night. o a proxy might challenge the caller to complete a Turing test. These aspects are discussed in [I-D.tschofenig-sipping-framework-spit-reduction]. 4. ABNF ABNF using the ABNF syntax of [RFC3261]: via-extension = spam-score / spam-detail spam-score = "spam" EQUAL score score = *"-" 1*4DIGIT [ "." 0*3DIGIT ] spam-detail = "spam-detail" EQUAL detail detail = QUOTE mech SEMI rule-score *(COMMA rule-score) QUOTE rule-score = rule [ "=" score ] mech = token rule = token Figure 1: ABNF Wing, et al. Expires February 19, 2008 [Page 4] Internet-Draft SIP Spam Score August 2007 5. Examples The following example shows a SIP score generated by biloxi.com and atlanta.com. In this example, atlanta.com is owned by a spammer who is trying to fool downstream systems with their low spam score (0.0). However, the biloxi.com proxies and user agents only pay attention to spam scores from Via: headers generated by biloxi.com proxies, so atlanta.com's attempts are in vain. INVITE sip:bob@biloxi.com SIP/2.0 Via: SIP/2.0/UDP biloxi.com;branch=z9hG4bKnashds8 ;received=192.0.2.1 ;spam=-5 ;spam-detail="Hormel-1.0;whitelist=-10,call_volume=5" Via: SIP/2.0/UDP sip.atlanta.com;branch=z9hG4bKfjzc ;received=192.0.3.2 ;spam=-100 ;spam-detail="Jaeger-3.3;not-a-spammer=-100" Max-Forwards: 70 To: Bob From: Alice ;tag=1928301774 Call-ID: a84b4c76e66710@pc33.atlanta.com CSeq: 314159 INVITE Contact: Content-Type: application/sdp Content-Length: 142 Figure 2: example 6. Security Considerations SIP proxies and SIP user agents need to ignore spam scores in Via headers generated by proxies that aren't trusted. Via headers have the most recent proxy on top, so parsing for spam scores should stop at the first Via header from a non-trusted proxy. 7. Acknowledgements Add your name here. 8. IANA Considerations This document will add new IANA registrations for new SIP headers. [[This section will be completed in a later version of this Wing, et al. Expires February 19, 2008 [Page 5] Internet-Draft SIP Spam Score August 2007 document.]] 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. 9.2. Informational References [I-D.ietf-sipping-spam] Rosenberg, J. and C. Jennings, "The Session Initiation Protocol (SIP) and Spam", draft-ietf-sipping-spam-05 (work in progress), July 2007. [I-D.tschofenig-sipping-framework-spit-reduction] Tschofenig, H., "A Framework to tackle Spam and Unwanted Communication for Internet Telephony", draft-tschofenig-sipping-framework-spit-reduction-01 (work in progress), July 2007. Authors' Addresses Dan Wing Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134 USA Email: dwing@cisco.com Wing, et al. Expires February 19, 2008 [Page 6] Internet-Draft SIP Spam Score August 2007 Saverio Niccolini Network Laboratories, NEC Europe Ltd. Kurfuersten-Anlage 36 Heidelberg 69115 Germany Phone: +49 (0) 6221 4342 118 Email: saverio.niccolini@netlab.nec.de URI: http://www.netlab.nec.de Hannes Tschofenig Nokia Siemens Networks Otto-Hahn-Ring 6 Munich, Bavaria 81739 Germany Email: Hannes.Tschofenig@nsn.com Martin Stiemerling Network Laboratories, NEC Europe Ltd. Kurfuersten-Anlage 36 Heidelberg 69115 Germany Phone: +49 (0) 6221 4342 113 Email: stiemerling@netlab.nec.de URI: http://www.netlab.nec.de Wing, et al. Expires February 19, 2008 [Page 7] Internet-Draft SIP Spam Score August 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. 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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Wing, et al. Expires February 19, 2008 [Page 8]