NetworkRUCUS Exploratory Working Group D. Wing Internet-Draft CiscoSystemsIntended status:Standards TrackExperimental S. Niccolini Expires:February 19,August 16, 2008 M. Stiemerling NEC H. Tschofenig Nokia Siemens NetworksM. Stiemerling NEC August 18, 2007February 13, 2008 Spam Score for SIPdraft-wing-sipping-spam-score-00.txtdraft-wing-sipping-spam-score-01 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 onFebruary 19,August 16, 2008. Copyright Notice Copyright (C) The IETF Trust(2007).(2008). Abstract This document defines a mechanism for SIP proxies to communicate a spam score to downstream SIP proxies and to SIP useragents so theyagents. This information can then be used as input to other decision making engines, for example, to provide alternate call routing or call handling.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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Operation of Spam-Scoring Proxy . . . . . . . . . . . . . . . . 33.4. Operation of Proxy or User Agent . . . . . . . . . . . . . . .3 4. ABNF .4 5. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 5.5 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 56.7. Security Considerations . . . . . . . . . . . . . . . . . . . .5 7.6 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .5 8.6 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . .5 9.6 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 69.1.10.1. Normative References . . . . . . . . . . . . . . . . . . . 69.2.10.2. Informational References . . . . . . . . . . . . . . . . .67 Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . . 7 A.1. Changes from -00 to -01 . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .67 Intellectual Property and Copyright Statements . . . . . . . . . .89 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 avoidancetechniques,techniques described in[I-D.ietf-sipping-spam],[RFC5039] 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 SIPUA.user agent (UA). The downstream SIP proxies or SIP UA might ignore that information (e.g.,they don'tit doesn't trustit)the SIP proxy that generated the spam score) or might useit (e.g., they trust it because itit. Note that this document does not make the attempt to define how the spam score wasgenerated by a federation). From a deployment point of view it is expectedderived nor to distribute information that could be used to verify the spam scorewill mostgeneration. Furthermore, this document does not attempt to cryptographically bind the identity of the entity generating the score to the value itself. Hence, its usage is likely to bebenefical (and trustworthy) when inserted by a SIP proxy on the recipients side for evaluation by a SIP UA that hasuseful only between neighboring administrative domains communicating such adirect relationship with this SIP proxy.score. 2. 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]. 3. Operation of Spam-Scoring Proxy A SIP proxy evaluates an incoming SIP request and generates a spam score using a local mechanism.Negative scores indicateThis score is between 0 (indicating theSIP requestmessage is notconsidered spam,spam) andpositive scores100 (indicating the message is spam). Values between 0 and 100 indicate the 'likelihood' that the SIP request isconsidered spam. Thespam, with higherthe value, the more likelyvalues indicating a higher likelihood the message isspam or is notspam. This spam score is inserted into the"Via:" header, whichnew "Spam-Score" header. This header field contains a summary spam score and optionally contains detail information. The detail information isalready generated by the proxy.implementation dependent. TheVia header was chosen because it the Viadetail information isalready correlated withvaluable for debugging and to provide the SIP user agent or SIP proxythat generatedwith additional information regarding how theVia header. 3.spam-scoring SIP proxy's local mechanism arrived at the summary spam score. 4. Operation of Proxy or User Agent A downstream proxy or the SIP user agent MAY use the spam score or spam-detail information to change call routing or call handling. It isRECOMMENDEDenvisioned thatonly scores generated bysome form of policies indicate the trusted proxiesbe used.in order to decide which spam scores to consider for special call treatment. In some jurisdictions, the end user needs to authorize call handling, including rejection of a call based on a spam score. Mechanisms to allow users to influence such policies are, however, out of scope of this document. The behavior of the SIP proxy or user agent when the spam score is above a certain value is a local policy 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) 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. ABNF5. Grammar ABNF using the ABNF syntax of [RFC3261]:via-extensionextension-header = spam-score/[ SP ";" spam-detail ] spam-score ="spam" EQUALscore SP "by" SP hostname score =*"-" 1*4DIGIT1*3DIGIT [ "." 0*3DIGIT ] spam-detail ="spam-detail""detail" EQUAL detail detail = QUOTE mech SEMI rule-score *(COMMA rule-score) QUOTE ; mathematical average of the rule-scores ; MUST be same as spam-score rule-score = rule [ "=" score ] mech = token rule = token Figure 1: ABNF5.6. Examples The following example shows a SIP score generated and inserted bybiloxi.comtwo SIP proxies, sip.example.com andatlanta.com.sip.example.net. In this example,atlanta.comsip.example.com is owned by a spammer who is trying to fool downstream systems with their low spam score(0.0).(0). However, thebiloxi.comexample.net proxies and user agents only pay attention to spam scores fromVia:Spam-Score headers generated bybiloxi.comexample.net proxies, soatlanta.com'sexample.com's attempts to fool the downstream proxies (with its low spam score) are in vain. INVITEsip:bob@biloxi.comsip:bob@example.net SIP/2.0 Via: SIP/2.0/UDPbiloxi.com;branch=z9hG4bKnashds8sip.example.net;branch=z9hG4bKnashds8 ;received=192.0.2.1;spam=-5 ;spam-detail="Hormel-1.0;whitelist=-10,call_volume=5"Spam-Score: 75 by sip.example.net ;detail="SIPfilter-1.0;call_volume=75" Via: SIP/2.0/UDPsip.atlanta.com;branch=z9hG4bKfjzc ;received=192.0.3.2 ;spam=-100 ;spam-detail="Jaeger-3.3;not-a-spammer=-100"sip.example.com;branch=z9hG4bKfjzc ;received=192.0.2.127 Max-Forwards: 70 To: Bob<sip:bob@biloxi.com><sip:bob@example.net> From: Alice<sip:alice@atlanta.com>;tag=1928301774<sip:alice@example.com>;tag=1928301774 Call-ID:a84b4c76e66710@pc33.atlanta.coma84b4c76e66710@pc33.example.com CSeq: 314159 INVITE Contact:<sip:alice@pc33.atlanta.com><sip:alice@pc33.example.com> Content-Type: application/sdp Content-Length: 142 [... SDP elided from this example...] Figure 2:example 6.Example with spam scores 7. Security Considerations SIP proxies and SIP user agents need to ignore spam scoresin Via headersgenerated 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[[This section will be completed in anon-trusted proxy. 7. Acknowledgements Add your name here.later version of this document.]] 8. Acknowledgements Thanks to Joachim Charzinski, Daniel Quinlan, and S. Moonesamy for their suggestions to improve this document. 9. IANA ConsiderationsThis document will add new IANA registrations for new SIP headers.[[This section will be completed in a later version of this document.]]9.10. References9.1.10.1. 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 2002.9.2.10.2. Informational References[I-D.ietf-sipping-spam][RFC5039] 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 FrameworkRFC 5039, January 2008. Appendix A. Changes Note totackle Spam and Unwanted Communication for Internet Telephony", draft-tschofenig-sipping-framework-spit-reduction-01 (work in progress), July 2007.RFC Editor: please remove this section prior to publication. A.1. Changes from -00 to -01 o Changed scoring from positive/negative to 0-100 range. o Moved score from a "Via:" extension to a new header "Spam-Score:". o Changed from Standards Track to Experimental. Authors' Addresses Dan Wing Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134 USA Email: dwing@cisco.com 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.deHannes Tschofenig Nokia Siemens Networks Otto-Hahn-Ring 6 Munich, Bavaria 81739 Germany Email: Hannes.Tschofenig@nsn.comMartin 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 Hannes Tschofenig Nokia Siemens Networks Linnoitustie 6 Espoo 02600 Finland Phone: +358 (50) 4871445 Email: Hannes.Tschofenig@nsn.com URI: http://www.tschofenig.com Full Copyright Statement Copyright (C) The IETF Trust(2007).(2008). 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. 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