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Versions: (draft-kaplan-straw-sip-traceroute) 00 01 02 03 RFC 7403

STRAW Working Group                                           H. Kaplan
Internet Draft                                                   Oracle
Intended status: Standards Track                          July 10, 2014
Expires: January 10, 2015

                   A Media-based Traceroute Function for
                   the Session Initiation Protocol (SIP)


   SIP already provides the ability to perform hop-by-hop traceroute
   for SIP messages using the Max-Forwards header field to determine
   the reachability path of requests to a target.  A mechanism for
   media-loopback calls has also been defined separately, which enables
   test calls to be generated that result in media being looped back to
   the originator.  This document describes a means of performing hop-
   by-hop traceroute-style test calls using the media-loopback
   mechanism to test the media path when SIP sessions go through media-
   relaying B2BUAs.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with
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   This Internet-Draft will expire on January 10, 2015.

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Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   publication of this document.  Please review these documents
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   warranty as described in the Simplified BSD License.

Table of Contents

   1.    Introduction................................................2
   2.    Terminology.................................................3
   3.    The SIP Traceroute Mechanism................................4
      3.1.   Processing a Received Max-Forwards Header Field........4
      3.2.   Answering the INVITE...................................5
   4.    Security Considerations.....................................5
   5.    IANA Considerations.........................................6
   6.    Acknowledgments.............................................6
   7.    References..................................................6
      7.1.   Normative References...................................6
   Author's Address..................................................7

1. Introduction

   In many deployments, the media for SIP-created sessions does not
   flow directly from the originating user's UAC to the answering
   user's UAS.  Often, SIP B2BUAs in the SIP signaling path also insert
   themselves in the media plane path by manipulating SDP, either for
   injecting media such as rich ringtones or music-on-hold, or for
   relaying media in order to provide functions such as transcoding,
   IPv4-IPv6 conversion, NAT traversal, SRTP termination, media
   steering, etc.

   As more SIP domains get deployed and interconnected, the odds of a
   SIP session crossing such media-plane B2BUAs increases, as well as
   the number of such B2BUAs any given SIP session may go through.  In
   other words, any given SIP session may cross any number of B2BUA's
   both in the SIP signaling plane as well as media plane.

   When a failure or degradation occurs in the media plane, it is
   difficult to determine where in the media path they occurred.  In

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   order to aid managing and troubleshooting SIP-based sessions and
   media traversing such B2BUAs, it would be useful to progressively
   test the media path as it reaches successive B2BUAs with a test
   controlled in a single-ended way from the source UA.  A mechanism to
   perform media-loopback test sessions has been defined in [RFC6849],
   but it cannot be used directly to test B2BUAs because typically the
   B2BUAs do not have an Address of Record (AoR) to be targeted, nor is
   it known a priori which B2BUAs will be traversed for any given

   For example, suppose calls from Alice to Bob have media problems.
   Alice would like to test the media path to each B2BUA in the path to
   Bob separately, to determine which segment has the issues.  Alice
   cannot target the B2BUAs directly for each test call, because she
   doesn't know which URIs to use to target them; nor would using such
   URIs guarantee the same media path be used as a call to Bob.  A
   better solution would be to make a test call targeted to Bob, but
   with a SIP traceroute-type mechanism that makes the call terminate
   at the B2BUAs, such that she can perform test sessions to test the
   media path to each downstream B2BUA.

   This document defines how such a mechanism can be employed, using
   the [RFC6849] mechanism along with the Max-Forwards SIP header field
   such that a SIP User Agent can make multiple test calls, each
   reaching a B2BUA further downstream.  Each B2BUA in the path that
   supports the mechanism in [RFC6849] would answer the media-loopback
   call, and thus the originating SIP UA can test the media path up to
   that B2BUA.

2. Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   B2BUA: a SIP Back-to-Back User Agent, which is the logical
   combination of a User Agent Server (UAS) and User Agent Client

   UAS: a SIP User Agent Server.

   UAC: a SIP User Agent Client.

   Traceroute: a mechanism to trace a path of hops from an originator
   to a destination.  For IP, this is typically done using the TTL
   field of the IP header, starting at the value 1 and incrementing by
   1 as each IP hop responds with an ICMP error.  For SIP this can be
   done using Max-Forwards header field starting with the value 0, in a
   similar fashion to the TTL field.

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   It is assumed the reader is already familiar with media-loopback

3. The SIP Traceroute Mechanism

   The Max-Forwards header field can already be used to perform a
   simple SIP-request traceroute mechanism by generating a SIP request
   initially using a Max-Forwards value of 0, receiving a 483 Too Many
   Hops response from the next-hop, and then incrementing the value for
   subsequent SIP requests, thereby reaching SIP devices further and
   further downstream and receiving 483 from each of them.

   The mechanism described in this document uses such a Max-Forwards
   style traceroute to perform media-loopback testing.  To perform a
   SIP media-plane traceroute, the originating UAC (Alice) generates a
   SIP INVITE to a target AoR (Bob), with a Max-Forwards header field
   value of 0 and with SDP based on [RFC6849].  The SIP next-hop will
   either reject the request with a 483 Too Many Hops response, or if
   the next-hop is a B2BUA that supports this mechanism, and if the
   B2BUA allows such testing from the requesting UAC, then the B2BUA
   will answer the INVITE to establish the dialog and create a media-
   loopback session.

   The originating UAC can then end the media-loopback session,
   generate another INVITE to the same target AoR with a Max-Forwards
   header field value of 1, which will reach the second SIP next hop,
   and so on.

   A defined [RFC3326] SIP Reason header field cause value of '483'
   will be in the 200 answer from each B2BUA answering the INVITE,
   until the INVITE reaches the final UAS (Bob), which does not use the
   Reason cause value. (see Section 3.2 for details)

   Using this mechanism a SIP UAC can test the path from itself to each
   successive B2BUA on the path to a target.  Such a mechanism could
   also be useful for establishing a permanent test call between an
   Enterprise and a Service Provider across a SIP Trunk, for example,
   or for automated measurement systems to test the media path between
   domains, etc.

3.1. Processing a Received Max-Forwards Header Field

   As currently defined in [RFC3261], the UAS half of a B2BUA does not
   technically need to inspect the Max-Forwards header field value for
   received requests - only Proxies do.  This behavior was updated by
   [draft-loop-detection], such that a compliant B2BUA needs to both
   inspect the value in order to prevent loops, as well as copy and
   decrement the value as if it were a Proxy.  This document also

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   requires such behavior in order for the mechanism to succeed;
   therefore a B2BUA supporting the traceroute mechanism defined in
   this document MUST also comply with [draft-loop-detection].

3.2. Answering the INVITE

   If a SIP B2BUA receives a dialog-creating INVITE request with a Max-
   Forwards header value of 0, with SDP for media-loopback based on
   [RFC6849], and the policies of the B2BUA allow it to answer such a
   request, then it is answered as if the original target of the
   request were the local SIP B2BUA.  The normal procedures of SIP
   apply, as well as [RFC6849], as if the request had been targeted at
   the local B2BUA device as the intended destination all along.

   In the 200 response for the INVITE, the B2BUA MUST also add a Reason
   header, per [RFC3326], with a protocol field value of "SIP", a cause
   field value of "483", and a reason-text value of "Traceroute
   Response".  The purpose of the Reason header is to indicate to the
   UAC that the request is being answered due to reaching a Max-
   Forwards of 0, rather than being answered due to reaching the final
   UAS.  When the ultimate target UAS answers a loopback-based INVITE
   with a Max-Forwards greater than or equal to 0, the Reason header
   would not be added to the response and the UAC will know the
   traceroute is complete.

   If a B2BUA receives an INVITE with media-loopback SDP and a Max-
   Forwards header field value of 0 as defined in this document, and it
   does not accept the session (e.g., due to local policy), then it
   SHOULD respond with a 483 Too Many Hops response, per normal
   [RFC3261] rules as it would previously.  In other words, in such a
   case it behaves no differently than it would have if it did not
   support this document's new behavior.

4. Security Considerations

   There are security implications for the mechanism defined in this
   document.  Answering media-loopback calls in a B2BUA consumes
   resources on the B2BUA, and network bandwidth in between, and thus
   exposes a vector for denial of service attacks; therefore, B2BUAs
   should provide configuration options to control who can make such
   test calls, how many concurrent calls can be established and
   maintained, and for how long.  Entities that deploy B2BUAs should
   set these options to values that reduce the denial-of-service risk
   to an acceptable level.  A B2BUA might perform digest-challenge
   authentication with specific credentials for such calls, for
   example; or it might only allow specific sources to make such calls,
   at a specific time.  Such policies are typically vendor-specific
   based on local policies and deployment usage scenarios, and cannot
   to be explicitly defined in this document.

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   The security considerations of [RFC6849] also apply to this
   document.  Since B2BUAs are not end user devices, there is no human
   user to monitor the loopback session activity on the B2BUA as
   recommended in [RFC6849]; instead, B2BUAs should log such events, or
   provide some form of administrative notification.

5.   IANA Considerations

   This document makes no request of IANA.

6.   Acknowledgments

   The general concept of performing media-loopback on a hop-by-hop
   basis using a decrementing header traceroute style approach came out
   of discussions several years ago, between the author, Kaynam
   Hedayat, Nagarjuna Venna, and Patrick MeLampy.  Other people that
   have contributed to the topic over the years since then: Brett Tate,
   Paul Kyzivat, Peter Dawes, Zaid Ally, Dianna Stiller, Jon Boone, and
   several others whom I have lost the names of since.

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).

7.   References

7.1. Normative References

    [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
         Requirement Levels", RFC 2119, March 1997.

    [RFC3261]  Rosenberg, J., et al, "SIP: Session Initiation
         Protocol", RFC 3261, June 2002.

    [RFC3326]  Schulzrinne, H., Oran, D., and Camarillo, G., "The
         Reason Header Field for the Session Initiation Protocol
         (SIP)", RFC 3326, December 2002.

    [RFC6849]  Kaplan, H., et al, "An Extension to the Session
         Description Protocol (SDP) for Media Loopback", RFC 6849,
         February 2013.

    [draft-loop-detection] Kaplan, H., and Pascual, V., "Loop Detection
         Mechanisms for Session Initiation Protocol (SIP) Back-to-Back
         User Agents (B2BUAs)", draft-ietf-straw-b2bua-loop-detection-
         02, September 2013.

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Author's Address

   Hadriel Kaplan
   Email: hadrielk@yahoo.com

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