[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-asaeda-mboned-mtrace-v2) 00 01 02 03 04 05 06 07 08 09 10

MBONED Working Group                                           H. Asaeda
Internet-Draft                                           Keio University
Intended status: Standards Track                               T. Jinmei
Expires: July 11, 2011                                               ISC
                                                               W. Fenner
                                                           Arastra, Inc.
                                                               S. Casner
                                                     Packet Design, Inc.
                                                         January 7, 2011


         Mtrace Version 2: Traceroute Facility for IP Multicast
                     draft-ietf-mboned-mtrace-v2-08

Abstract

   This document describes the IP multicast traceroute facility.  Unlike
   unicast traceroute, multicast traceroute requires special
   implementations on the part of routers.  This specification describes
   the required functionality in multicast routers, as well as how
   management applications can use the router functionality.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on July 11, 2011.

Copyright Notice

   Copyright (c) 2011 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



Asaeda, et al.            Expires July 11, 2011                 [Page 1]

Internet-Draft                   Mtrace2                    January 2011


   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.


































Asaeda, et al.            Expires July 11, 2011                 [Page 2]

Internet-Draft                   Mtrace2                    January 2011


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  6
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  8
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   4.  Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 10
     4.1.  Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . . 10
     4.2.  Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 10
   5.  Mtrace2 Query Header . . . . . . . . . . . . . . . . . . . . . 12
     5.1.  # hops: 8 bits . . . . . . . . . . . . . . . . . . . . . . 12
     5.2.  Multicast Address  . . . . . . . . . . . . . . . . . . . . 13
     5.3.  Source Address . . . . . . . . . . . . . . . . . . . . . . 13
     5.4.  Mtrace2 Client Address . . . . . . . . . . . . . . . . . . 13
     5.5.  Query ID: 16 bits  . . . . . . . . . . . . . . . . . . . . 13
     5.6.  Client Port #  . . . . . . . . . . . . . . . . . . . . . . 13
   6.  IPv4 Mtrace2 Standard Response Block . . . . . . . . . . . . . 14
     6.1.  MBZ: 8 bit . . . . . . . . . . . . . . . . . . . . . . . . 14
     6.2.  Query Arrival Time: 32 bits  . . . . . . . . . . . . . . . 14
     6.3.  Incoming Interface Address: 32 bits  . . . . . . . . . . . 15
     6.4.  Outgoing Interface Address: 32 bits  . . . . . . . . . . . 15
     6.5.  Previous-Hop Router Address: 32 bits . . . . . . . . . . . 15
     6.6.  Input packet count on incoming interface: 64 bits  . . . . 15
     6.7.  Output packet count on outgoing interface: 64 bits . . . . 16
     6.8.  Total number of packets for this source-group pair: 64
           bits . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     6.9.  Rtg Protocol: 16 bits  . . . . . . . . . . . . . . . . . . 16
     6.10. Multicast Rtg Protocol: 16 bits  . . . . . . . . . . . . . 16
     6.11. Fwd TTL: 8 bits  . . . . . . . . . . . . . . . . . . . . . 16
     6.12. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 16
     6.13. Src Mask: 7 bits . . . . . . . . . . . . . . . . . . . . . 17
     6.14. Forwarding Code: 8 bits  . . . . . . . . . . . . . . . . . 17
   7.  IPv6 Mtrace2 Standard Response Block . . . . . . . . . . . . . 19
     7.1.  MBZ: 8 bit . . . . . . . . . . . . . . . . . . . . . . . . 19
     7.2.  Query Arrival Time: 32 bits  . . . . . . . . . . . . . . . 20
     7.3.  Incoming Interface ID: 32 bits . . . . . . . . . . . . . . 20
     7.4.  Outgoing Interface ID: 32 bits . . . . . . . . . . . . . . 20
     7.5.  Local Address  . . . . . . . . . . . . . . . . . . . . . . 20
     7.6.  Remote Address . . . . . . . . . . . . . . . . . . . . . . 20
     7.7.  Input packet count on incoming interface . . . . . . . . . 20
     7.8.  Output packet count on outgoing interface  . . . . . . . . 21
     7.9.  Total number of packets for this source-group pair . . . . 21
     7.10. Rtg Protocol: 16 bits  . . . . . . . . . . . . . . . . . . 21
     7.11. Multicast Rtg Protocol: 16 bits  . . . . . . . . . . . . . 21
     7.12. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 21
     7.13. Src Prefix Len: 8 bits . . . . . . . . . . . . . . . . . . 21
     7.14. Forwarding Code: 8 bits  . . . . . . . . . . . . . . . . . 21
   8.  Mtrace2 Augmented Response Block . . . . . . . . . . . . . . . 22
   9.  Router Behavior  . . . . . . . . . . . . . . . . . . . . . . . 23



Asaeda, et al.            Expires July 11, 2011                 [Page 3]

Internet-Draft                   Mtrace2                    January 2011


     9.1.  Receiving Mtrace2 Query  . . . . . . . . . . . . . . . . . 23
       9.1.1.  Packet Verification  . . . . . . . . . . . . . . . . . 23
       9.1.2.  Normal Processing  . . . . . . . . . . . . . . . . . . 23
       9.1.3.  Mtrace2 Query Received by Non-Supported Router . . . . 23
     9.2.  Receiving Mtrace2 Request  . . . . . . . . . . . . . . . . 24
       9.2.1.  Packet Verification  . . . . . . . . . . . . . . . . . 24
       9.2.2.  Normal Processing  . . . . . . . . . . . . . . . . . . 24
       9.2.3.  Mtrace2 Request Received by Non-Supported Router . . . 26
     9.3.  Forwarding Mtrace2 Request . . . . . . . . . . . . . . . . 26
       9.3.1.  Destination Address  . . . . . . . . . . . . . . . . . 26
       9.3.2.  Source Address . . . . . . . . . . . . . . . . . . . . 26
     9.4.  Sending Mtrace2 Reply  . . . . . . . . . . . . . . . . . . 27
       9.4.1.  Destination Address  . . . . . . . . . . . . . . . . . 27
       9.4.2.  Source Address . . . . . . . . . . . . . . . . . . . . 27
     9.5.  Proxying Mtrace2 Query . . . . . . . . . . . . . . . . . . 27
     9.6.  Hiding Information . . . . . . . . . . . . . . . . . . . . 28
   10. Client Behavior  . . . . . . . . . . . . . . . . . . . . . . . 29
     10.1. Sending Mtrace2 Query  . . . . . . . . . . . . . . . . . . 29
       10.1.1. Destination Address  . . . . . . . . . . . . . . . . . 29
       10.1.2. Source Address . . . . . . . . . . . . . . . . . . . . 29
     10.2. Determining the Path . . . . . . . . . . . . . . . . . . . 29
     10.3. Collecting Statistics  . . . . . . . . . . . . . . . . . . 29
     10.4. Last Hop Router  . . . . . . . . . . . . . . . . . . . . . 29
     10.5. First Hop Router . . . . . . . . . . . . . . . . . . . . . 30
     10.6. Broken Intermediate Router . . . . . . . . . . . . . . . . 30
     10.7. Mtrace2 Termination  . . . . . . . . . . . . . . . . . . . 30
       10.7.1. Arriving at source . . . . . . . . . . . . . . . . . . 30
       10.7.2. Fatal error  . . . . . . . . . . . . . . . . . . . . . 30
       10.7.3. No previous hop  . . . . . . . . . . . . . . . . . . . 30
       10.7.4. Traceroute shorter than requested  . . . . . . . . . . 30
     10.8. Continuing after an error  . . . . . . . . . . . . . . . . 31
   11. Protocol-Specific Considerations . . . . . . . . . . . . . . . 32
     11.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     11.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . . 32
     11.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     11.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . 32
     11.5. AMT  . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
   12. Problem Diagnosis  . . . . . . . . . . . . . . . . . . . . . . 34
     12.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . . 34
     12.2. TTL or Hop Limit Problems  . . . . . . . . . . . . . . . . 34
     12.3. Packet Loss  . . . . . . . . . . . . . . . . . . . . . . . 34
     12.4. Link Utilization . . . . . . . . . . . . . . . . . . . . . 35
     12.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . . 35
   13. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 36
     13.1. Forwarding Codes . . . . . . . . . . . . . . . . . . . . . 36
     13.2. UDP Destination Port and IPv6 Address  . . . . . . . . . . 36
   14. Security Considerations  . . . . . . . . . . . . . . . . . . . 37
     14.1. Topology Discovery . . . . . . . . . . . . . . . . . . . . 37



Asaeda, et al.            Expires July 11, 2011                 [Page 4]

Internet-Draft                   Mtrace2                    January 2011


     14.2. Traffic Rates  . . . . . . . . . . . . . . . . . . . . . . 37
     14.3. Limiting Query/Request Rates . . . . . . . . . . . . . . . 37
   15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 38
   16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39
     16.1. Normative References . . . . . . . . . . . . . . . . . . . 39
     16.2. Informative References . . . . . . . . . . . . . . . . . . 39
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41












































Asaeda, et al.            Expires July 11, 2011                 [Page 5]

Internet-Draft                   Mtrace2                    January 2011


1.  Introduction

   This document specifies the multicast traceroute facility named
   mtrace version 2 or mtrace2.  Mtrace2 allows the tracing of an IP
   multicast routing paths.  Mtrace2 provides additional information
   about packet rates and losses, or other diagnosis information.  For
   instance, mtrace2 is used for the following purposes.

   o  To trace the path that a packet would take from some source to
      some destination.

   o  To isolate packet loss problems (e.g., congestion).

   o  To isolate configuration problems (e.g., TTL threshold).

   Mtrace2 consists of the client and router programs.  The mtrace2
   client program is invoked from somewhere in the multicast tree, on a
   host, router, or proxy such as IGMP/MLD proxy [8].  The node invoking
   the program is called the mtrace2 client.

   The mtrace2 client program creates the mtrace2 Query message, which
   includes a source and multicast address specified by the client, and
   forwards the message to its neighbor router or proxy.  This initiates
   a trace of a multicast routing path from the client toward the
   specified source, or if no source address is specified, toward a core
   router if such a router exists.  In the case of PIM-SM [6], the core
   router is an RP maintaining the specified multicast address.

   When a router or proxy receives an mtrace2 Query message and has the
   corresponding routing state regarding the source and multicast
   addresses specified in the Query, the router or proxy invokes the
   mtrace2 router program.  The mtrace2 router program creates an
   mtrace2 Request message corresponding to the query and forwards the
   Request toward the specified source or the core router.

   When a first-hop router or proxy (a single hop from the source
   specified in the request) or the core router receives an mtrace2
   Query or Request message, the router or proxy invokes the mtrace2
   router program.  The mtrace2 router program creates an mtrace2 Reply
   message.  The Reply message is forwarded to the mtrace2 client, thus
   completing the mtrace2 Request.

   The mtrace2 client program waits for the mtrace2 Reply message and
   displays the results.  When an mtrace2 Reply message does not come
   due to network congestion, a broken router (see Section 10.6) or a
   non-responding router (see Section 10.8), the mtrace2 client program
   can resend an mtrace2 Query with a lower hop count (see Section 5.1)
   and repeat the process until it receives an mtrace2 Reply message.



Asaeda, et al.            Expires July 11, 2011                 [Page 6]

Internet-Draft                   Mtrace2                    January 2011


   The mtrace2 client should also be aware that the mtrace2 Query may
   follow the control path on the routers, in the case of a router's
   control plane and forwarding plane are not synchronized, e.g., a
   buggy implementation.  In this case, mtrace2 Requests will be
   forwarded toward the specified source or the core router because the
   router does not have any forwarding state for the query.

   The mtrace2 supports both IPv4 and IPv6 multicast traceroute
   facility.  The protocol design, concept, and program behavior are
   same between IPv4 and IPv6 mtrace2.  While the original IPv4
   multicast traceroute, mtrace, the query and response messages are
   implemented as IGMP messages [10], all mtrace2 messages are carried
   on UDP.  The packet formats of IPv4 and IPv6 mtrace2 are different
   because of the different address families, but the syntax is similar.





































Asaeda, et al.            Expires July 11, 2011                 [Page 7]

Internet-Draft                   Mtrace2                    January 2011


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 RFC 2119 [1].

   Since multicast traceroutes flow in the opposite direction to the
   data flow, we refer to "upstream" and "downstream" with respect to
   data, unless explicitly specified.

   Incoming interface:
   The interface on which traffic is expected from the specified source
   and group.

   Outgoing interface:
   The interface on which traffic is forwarded from the specified source
   and group toward the destination.  It is the interface on which the
   mtrace2 Query or Request was received.

   Previous-hop router:
   The router that is on the link attached to the Incoming interface and
   is responsible for forwarding traffic for the specified source and
   group.

   Last-hop router:
   The router that is on the link attached to the Outgoing interface and
   receives the mtrace2 Query from the adjacent mtrace2 client.

   Group state:
   It is the state in which a shared-tree protocol (e.g., PIM-SM [6])
   running on a router chooses the previous-hop router toward the core
   router or Rendezvous Point (RP) as its parent router.  In this state,
   source-specific state is not available for the corresponding
   multicast address on the router.

   Source-specific state:
   It is the state in which a routing protocol running on a router
   chooses the path that would be followed for a source-specific join.

   ALL-[protocol]-ROUTERS.MCAST.NET:
   It is a dedicated multicast address for a multicast router to
   communicate with other routers that are working with the same routing
   protocol.  For instance, the address of ALL-PIM-ROUTERS.MCAST.NET [6]
   is '224.0.0.13' for IPv4 and 'ff02::d' for IPv6.







Asaeda, et al.            Expires July 11, 2011                 [Page 8]

Internet-Draft                   Mtrace2                    January 2011


3.  Overview

   Given a multicast distribution tree, tracing from a source to a
   multicast destination is hard, since you do not know down which
   branch of the multicast tree the destination lies.  This means that
   you have to flood the whole tree to find the path from one source to
   one destination.  However, walking up the tree from destination to
   source is easy, as most existing multicast routing protocols know the
   previous hop for each source.  Tracing from destination to source can
   involve only routers on the direct path.

   The party requesting the multicast traceroute sends a traceroute
   Query packet to the last-hop multicast router for the given multicast
   address.  The last-hop router turns the Query into a Request packet
   by changing the packet type and adding a response data block
   containing its interface addresses and packet statistics, and then
   forwards the Request packet via unicast to the router that the last-
   hop router believes is the proper previous hop for the given source
   and group.  Each hop adds its response data to the end of the Request
   packet, then unicast forwards it to the previous hop.  The first-hop
   router (the router that believes that packets from the source
   originate on one of its directly connected networks) changes the
   packet type to indicate a Reply packet and sends the completed Reply
   to the mtrace2 client address specified in the Query header.  The
   Reply may be returned before reaching the first-hop router if a fatal
   error condition such as "no route" is encountered along the path or
   hop count is exceeded.

   Multicast traceroute uses any information available to it in the
   router to attempt to determine a previous hop to forward the trace
   towards.  Multicast routing protocols vary in the type and amount of
   state they keep; multicast traceroute endeavors to work with all of
   them by using whatever is available.  For example, if a PIM-SM router
   is on the (*,G) tree, it chooses the parent towards the RP as the
   previous hop.  In these cases, no source/group-specific state is
   available, but the path may still be traced.















Asaeda, et al.            Expires July 11, 2011                 [Page 9]

Internet-Draft                   Mtrace2                    January 2011


4.  Packet Formats

   The mtrace2 message is carried as a UDP packet.  The destination
   address of mtrace2 Query messages is either the last-hop router
   unicast address or multicast address if the mtrace2 client does not
   know the proper last-hop router address.  The destination address of
   mtrace2 Report messages is the address specified in Previous-Hop
   Router Address field in the last appended mtrace2 Standard Response
   Block, which is either the previous-hop router unicast address or
   multicast address.  Detailed in Section 9.3.

   Mtrace2 message is encoded in TLV format.  If an implementation
   receives a TLV whose length exceeds the TLV length specified in the
   Length field, the TLV SHOULD be accepted but any additional data
   SHOULD be ignored.  If an implementation receives a TLV whose type
   value is unknown, the mtrace2 message SHOULD be ignored and silently
   dropped.

4.1.  Mtrace2 TLV format

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |           Length              |   Value ....  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type (8 bits)

   Length (16 bits)

   Value (variable length)

4.2.  Defined TLVs

   The following TLV Types are defined:

              Code                       Type
             ======      ======================================
               1             Mtrace2 Query
               2             Mtrace2 Request
               3             Mtrace2 Reply
               4             Mtrace2 Standard Response Block
               5             Mtrace2 Augmented Response Block

   An mtrace2 message MUST contain exactly one Mtrace2 Query header.  A
   multicast router that sends an mtrace2 Request or Reply message MUST
   add one mtrace2 Standard Response block to given mtrace2 message but
   MUST NOT add multiple mtrace2 Standard Response blocks to it.  A



Asaeda, et al.            Expires July 11, 2011                [Page 10]

Internet-Draft                   Mtrace2                    January 2011


   multicast router that adds one mtrace2 Standard Response block to
   given mtrace2 message MAY append one or multiple Augmented Response
   blocks.

   The TLV type field is defined to be "0x1" and "0x2" for mtrace2
   Queries and Requests, respectively.  An mtrace2 message containing
   the type "0x1" is an mtrace2 Query.  It is sent by an mtrace2 querier
   (i.e., an mtrace2 client).  It is changed to "0x2" by the proper
   last-hop router.  The type field is changed to "0x3" when the packet
   is completed and sent as an mtrace2 Reply from the first-hop router
   to the querier.








































Asaeda, et al.            Expires July 11, 2011                [Page 11]

Internet-Draft                   Mtrace2                    January 2011


5.  Mtrace2 Query Header

   The mtrace2 supports both IPv4 and IPv6.  If the mtrace2 Query or
   Reply arrives in an IPv4 packet, all addresses specified in the
   mtrace2 messages must be with IPv4 addresses.

   The mtrace2 message is carried as a UDP packet.  The UDP source port
   is uniquely selected by the local host operating system.  The UDP
   destination port is the IANA reserved mtrace2 port number (see
   Section 13).  The UDP checksum MUST be valid in mtrace2 messages.

   The mtrace2 message includes the common mtrace2 Query header as
   follows.  The header is only filled in by the originator of the
   mtrace2 Query; intermediate routers MUST NOT modify any of the
   fields.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                                     +-+-+-+-+-+-+-+-+
                                                     |    # hops     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                      Multicast Address                        |
     |                                                               |
     +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
     |                                                               |
     |                        Source Address                         |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                    Mtrace2 Client Address                     |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Query ID            |        Client Port #        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 1

5.1.  # hops: 8 bits

   This field specifies the maximum number of hops that the mtrace2
   client wants to trace.  If there is some error condition in the
   middle of the path that prevents an mtrace2 Reply from being received
   by the client, the client issues another mtrace2 Query with the lower
   number of hops until it receives a Reply from the first-hop router.






Asaeda, et al.            Expires July 11, 2011                [Page 12]

Internet-Draft                   Mtrace2                    January 2011


5.2.  Multicast Address

   This field specifies the 32 bits length IPv4 or 128 bits length IPv6
   multicast address to be traced, or is filled with "all 1" in case of
   IPv4 or with the unspecified address (::) in case of IPv6 if no
   group-specific information is desired.  Note that non-group-specific
   mtrace2 MUST specify source address.

5.3.  Source Address

   This field specifies the 32 bits length IPv4 or 128 bits length IPv6
   address of the multicast source for the path being traced, or is
   filled with "all 1" in case of IPv4 or with the unspecified address
   (::) in case of IPv6 if no source-specific information such as a
   trace for RPT in PIM-SM is desired.  Note that non-source-specific
   traceroutes may not be possible with certain multicast routing
   protocols.

5.4.  Mtrace2 Client Address

   This field specifies the 32 bits length IPv4 or 128 bits length IPv6
   global address of the mtrace2 client.  The trace starts at this
   client address and proceeds toward the traffic source.

5.5.  Query ID: 16 bits

   This field is used as a unique identifier for this mtrace2 Request so
   that duplicate or delayed Replies may be detected.

5.6.  Client Port #

   Mtrace2 Reply is sent back to the address specified in an Mtrace2
   Client Address field.  This field specifies the UDP port number the
   router will send Mtrace2 Reply.  This client port number MUST NOT be
   changed by any router.
















Asaeda, et al.            Expires July 11, 2011                [Page 13]

Internet-Draft                   Mtrace2                    January 2011


6.  IPv4 Mtrace2 Standard Response Block

   Each intermediate IPv4 router in a trace path appends "response data
   block" to the forwarded trace packet.  The standard response data
   block looks as follows.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                                     +-+-+-+-+-+-+-+-+
                                                     |      MBZ      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Query Arrival Time                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Incoming Interface Address                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Outgoing Interface Address                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Previous-Hop Router Address                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .           Input packet count on incoming interface            .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .           Output packet count on outgoing interface           .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .      Total number of packets for this source-group pair       .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Rtg Protocol         |    Multicast Rtg Protocol     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Fwd TTL    |      MBZ      |S|   Src Mask  |Forwarding Code|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6.1.  MBZ: 8 bit

   Must be zeroed on transmission and ignored on reception.

6.2.  Query Arrival Time: 32 bits

   The Query Arrival Time is a 32-bit NTP timestamp specifying the
   arrival time of the mtrace2 Request packet at this router.  The 32-
   bit form of an NTP timestamp consists of the middle 32 bits of the
   full 64-bit form; that is, the low 16 bits of the integer part and
   the high 16 bits of the fractional part.




Asaeda, et al.            Expires July 11, 2011                [Page 14]

Internet-Draft                   Mtrace2                    January 2011


   The following formula converts from a UNIX timeval to a 32-bit NTP
   timestamp:

      query_arrival_time
      = (tv.tv_sec + 32384) << 16 + ((tv.tv_usec << 10) / 15625)

   The constant 32384 is the number of seconds from Jan 1, 1900 to Jan
   1, 1970 truncated to 16 bits. ((tv.tv_usec << 10) / 15625) is a
   reduction of ((tv.tv_usec / 100000000) << 16).

   However, mtrace2 does not require synchronizing NTP timestamp among
   all routers along paths to measure one-way latency.  The use of Query
   Arrival Time is useful to measure the packets per second (PPS).
   Suppose that a client issues two queries Q1 and Q2, and the
   corresponding requests R1 and R2 arrive at router X at t1 and t2,
   then the client would be able to calculate the PPS at router X by
   using the packet count results at t1 and t2.

6.3.  Incoming Interface Address: 32 bits

   This field specifies the address of the interface on which packets
   from this source and group are expected to arrive, or 0 if unknown or
   unnumbered.

6.4.  Outgoing Interface Address: 32 bits

   This field specifies the address of the interface on which packets
   from this source and group flow to the specified destination, or 0 if
   unknown or unnumbered.

6.5.  Previous-Hop Router Address: 32 bits

   This field specifies the router from which this router expects
   packets from this source.  This may be a multicast group (e.g.  ALL-
   [protocol]-ROUTERS.MCAST.NET) if the previous hop is not known
   because of the workings of the multicast routing protocol.  However,
   it should be 0 if the incoming interface address is unknown or
   unnumbered.

6.6.  Input packet count on incoming interface: 64 bits

   This field contains the number of multicast packets received for all
   groups and sources on the incoming interface, or "all 1" if no count
   can be reported.  This counter may have the same value as
   ifHCInMulticastPkts from the IF-MIB [12] for this interface.






Asaeda, et al.            Expires July 11, 2011                [Page 15]

Internet-Draft                   Mtrace2                    January 2011


6.7.  Output packet count on outgoing interface: 64 bits

   This field contains the number of multicast packets that have been
   transmitted or queued for transmission for all groups and sources on
   the outgoing interface, or "all 1" if no count can be reported.  This
   counter may have the same value as ifHCOutMulticastPkts from the IF-
   MIB for this interface.

6.8.  Total number of packets for this source-group pair: 64 bits

   This field counts the number of packets from the specified source
   forwarded by this router to the specified group, or "all 1" if no
   count can be reported.  If the S bit is set, the count is for the
   source network, as specified by the Src Mask field.  If the S bit is
   set and the Src Mask field is 63, indicating no source-specific
   state, the count is for all sources sending to this group.  This
   counter should have the same value as ipMcastRoutePkts from the
   IPMROUTE-STD-MIB [13] for this forwarding entry.

6.9.  Rtg Protocol: 16 bits

   This field describes the routing protocol used to decide an RPF
   interface for the requested source.  This value should have the same
   value as ipMcastRouteRtProtocol from the IPMROUTE-STD-MIB [13] for
   this entry.  If the router is not able to obtain this value, "all 0"
   must be specified.

6.10.  Multicast Rtg Protocol: 16 bits

   This field describes the multicast routing protocol in use between
   this router and the previous-hop router.  This value should have the
   same value as ipMcastRouteProtocol from the IPMROUTE-STD-MIB [13] for
   this entry.  If the router does not able to obtain this value, "all
   0" must be specified.

6.11.  Fwd TTL: 8 bits

   This field contains the TTL that a packet is required to have before
   it will be forwarded over the outgoing interface.

6.12.  S: 1 bit

   This S bit indicates that the packet count for the source-group pair
   is for the source network, as determined by masking the source
   address with the Src Mask field.






Asaeda, et al.            Expires July 11, 2011                [Page 16]

Internet-Draft                   Mtrace2                    January 2011


6.13.  Src Mask: 7 bits

   This field contains the number of 1's in the netmask this router has
   for the source (i.e. a value of 24 means the netmask is 0xffffff00).
   If the router is forwarding solely on group state, this field is set
   to 127 (0x7f).

6.14.  Forwarding Code: 8 bits

   This field contains a forwarding information/error code.  Section 9.2
   explains how and when the forwarding code is filled.  Defined values
   are as follows;

     Value   Name            Description

     -----  --------------  -------------------------------------------

     0x00   NO_ERROR        No error

     0x01   WRONG_IF        Mtrace2 Request arrived on an interface
                            to which this router would not forward for
                            this source, group, destination.

     0x02   PRUNE_SENT      This router has sent a prune upstream which
                            applies to the source and group in the
                            mtrace2 Request.

     0x03   PRUNE_RCVD      This router has stopped forwarding for this
                            source and group in response to a request
                            from the next hop router.

     0x04   SCOPED          The group is subject to administrative
                            scoping at this hop.

     0x05   NO_ROUTE        This router has no route for the source or
                            group and no way to determine a potential
                            route.

     0x06   WRONG_LAST_HOP  This router is not the proper last-hop
                            router.

     0x07   NOT_FORWARDING  This router is not forwarding this source,
                            group out the outgoing interface for an
                            unspecified reason.

     0x08   REACHED_RP      Reached Rendezvous Point or Core

     0x09   RPF_IF          Mtrace2 Request arrived on the expected



Asaeda, et al.            Expires July 11, 2011                [Page 17]

Internet-Draft                   Mtrace2                    January 2011


                            RPF interface for this source and group.

     0x0A   NO_MULTICAST    Mtrace2 Request arrived on an interface
                            which is not enabled for multicast.

     0x0B   INFO_HIDDEN     One or more hops have been hidden from this
                            trace.

     0x0C   REACHED_GW      Mtrace2 Request arrived on a gateway (e.g.,
                            a NAT or firewall) that hides the
                            information between this router and the
                            mtrace2 querier

     0x81   NO_SPACE        There was not enough room to insert another
                            response data block in the packet.

     0x82   ADMIN_PROHIB    Mtrace2 is administratively prohibited.

   Note that if a router discovers there is not enough room in a packet
   to insert its response, it puts the NO_SPACE code value in the
   previous router's Forwarding Code field, overwriting any error the
   previous router placed there.  After the router sends the Reply to
   the Mtrace2 Client Address in the header, the router continues the
   mtrace2 Query by sending an mtrace2 Request containing the same
   mtrace2 Query header.  Section 9.3 and Section 10.8 include the
   details.

   The 0x80 bit of the Forwarding Code is used to indicate a fatal
   error.  A fatal error is one where the router may know the previous
   hop but cannot forward the message to it.





















Asaeda, et al.            Expires July 11, 2011                [Page 18]

Internet-Draft                   Mtrace2                    January 2011


7.  IPv6 Mtrace2 Standard Response Block

   Each intermediate IPv6 router in a trace path appends "response data
   block" to the forwarded trace packet.  The standard response data
   block looks as follows.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                                     +-+-+-+-+-+-+-+-+
                                                     |      MBZ      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Query Arrival Time                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Incoming Interface ID                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Outgoing Interface ID                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     *                         Local Address                         *
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     *                         Remote Address                        *
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .           Input packet count on incoming interface            .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .           Output packet count on outgoing interface           .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .      Total number of packets for this source-group pair       .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Rtg Protocol         |    Multicast Rtg Protocol     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              MBZ            |S|Src Prefix Len |Forwarding Code|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

7.1.  MBZ: 8 bit

   Must be zeroed on transmission and ignored on reception.






Asaeda, et al.            Expires July 11, 2011                [Page 19]

Internet-Draft                   Mtrace2                    January 2011


7.2.  Query Arrival Time: 32 bits

   Same definition described in Section 6.2

7.3.  Incoming Interface ID: 32 bits

   This field specifies the interface ID on which packets from this
   source and group are expected to arrive, or 0 if unknown.  This ID
   should be the value taken from InterfaceIndex of the IF-MIB [12] for
   this interface.  This field is carried in network byte order.

7.4.  Outgoing Interface ID: 32 bits

   This field specifies the interface ID on which packets from this
   source and group flow to the specified destination, or 0 if unknown.
   This ID should be the value taken from InterfaceIndex of the IF-MIB
   for this interface.  This field is carried in network byte order.

7.5.  Local Address

   This field specifies a global IPv6 address that uniquely identifies
   the router.  A unique local unicast address [11] SHOULD NOT be used
   unless the router is only assigned link-local and unique local
   addresses.  If the router is only assigned link-local addresses, its
   link-local address can be specified in this field.

7.6.  Remote Address

   This field specifies the address of the previous-hop router, which,
   in most cases, is a link-local unicast address for the queried source
   and destination addresses.

   Although a link-local address does not have enough information to
   identify a node, it is possible to detect the previous-hop router
   with the assistance of Incoming Interface ID and the current router
   address (i.e., Local Address).

   This may be a multicast group (e.g., ALL-[protocol]-
   ROUTERS.MCAST.NET) if the previous hop is not known because of the
   workings of the multicast routing protocol.  However, it should be
   the unspecified address (::) if the incoming interface address is
   unknown.

7.7.  Input packet count on incoming interface

   Same definition described in Section 6.6





Asaeda, et al.            Expires July 11, 2011                [Page 20]

Internet-Draft                   Mtrace2                    January 2011


7.8.  Output packet count on outgoing interface

   Same definition described in Section 6.7

7.9.  Total number of packets for this source-group pair

   This field counts the number of packets from the specified source
   forwarded by this router to the specified group, or "all 1" if no
   count can be reported.  If the S bit is set, the count is for the
   source network, as specified by the Src Prefix Len field.  If the S
   bit is set and the Src Prefix Len field is 255, indicating no source-
   specific state, the count is for all sources sending to this group.
   This counter should have the same value as ipMcastRoutePkts from the
   IPMROUTE-STD-MIB for this forwarding entry.

7.10.  Rtg Protocol: 16 bits

   Same definition described in Section 6.9

7.11.  Multicast Rtg Protocol: 16 bits

   Same definition described in Section 6.10

7.12.  S: 1 bit

   This S bit indicates that the packet count for the source-group pair
   is for the source network, as determined by masking the source
   address with the Src Prefix Len field.

7.13.  Src Prefix Len: 8 bits

   This field contains the prefix length this router has for the source.
   If the router is forwarding solely on group state, this field is set
   to 255 (0xff)

7.14.  Forwarding Code: 8 bits

   Same definition described in Section 6.14













Asaeda, et al.            Expires July 11, 2011                [Page 21]

Internet-Draft                   Mtrace2                    January 2011


8.  Mtrace2 Augmented Response Block

   In addition to the standard response block, a multicast router on the
   path will be able to add "augumented response block" when it sends
   the mtrace2 Request to its upstream router or sends the Reply to the
   Mtrace2 Client Address.  This augmented response block is flexible to
   add various information.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                                     +-+-+-+-+-+-+-+-+
                                                     |      MBZ      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Type              |           Value ....          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The augmented response block is always appended to mtrace2 TLV header
   (0x04).  The 16 bits Type filed of the augmented response block is
   defined for various purposes, such as diagnosis (as in Section 12)
   and protocol verification.  The packet length of the augmented
   response block is specified in the augmented response block TLV
   header as seen in Section 4.1.

   The following augmented response block type is defined:

         Code                           Type
        ======    =================================================
         0x01        # Mtrace2 Standard Response Blocks Returned

   When the NO_SPACE error occurs, the router sends back the mtrace2
   Reply with contained data (i.e., all appended response blocks), and
   continues the mtrace2 Query by sending an mtrace2 Request as will be
   described in Section 9.3.  In this mtrace2 Request, the router
   appends the augmented response block with the code "0x01" and the
   number of returned mtrace2 response blocks.  Every router between
   this router and the first-hop router can recognize the limit number
   of hops by referring this number and the # hops in the header.

   This document only defines the above augmented response block type
   and does not define other augmented response block types.  Specifing
   how to deal with diagnosis information will be also described in
   separate documents.









Asaeda, et al.            Expires July 11, 2011                [Page 22]

Internet-Draft                   Mtrace2                    January 2011


9.  Router Behavior

   All of these actions are performed in addition to (NOT instead of)
   forwarding the packet, if applicable.  E.g. a multicast packet that
   has TTL or the hop limit remaining MUST be forwarded normally, as
   MUST a unicast packet that has TTL or the hop limit remaining and is
   not addressed to this router.

9.1.  Receiving Mtrace2 Query

   An mtrace2 Query message is an mtrace2 message with no response
   blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 mtrace2.

9.1.1.  Packet Verification

   Upon receiving an mtrace2 Query message, a router must examine the
   Query to see if it is the proper last-hop router for the destination
   address in the packet.  It is the proper last-hop router if it has a
   multicast-capable interface on the same subnet as the Mtrace2 Client
   Address and is the router that would forward traffic from the given
   (S,G) or (*,G) onto that subnet.

   If the router determines that it is not the proper last-hop router,
   or it cannot make that determination, it does one of two things
   depending if the Query was received via multicast or unicast.  If the
   Query was received via multicast, then it MUST be silently dropped.
   If it was received via unicast, a forwarding code of WRONG_LAST_HOP
   is noted and processing continues as in Section 9.2.

   Duplicate Query messages as identified by the tuple (Mtrace2 Client
   Address, Query ID) SHOULD be ignored.  This MAY be implemented using
   a simple 1-back cache (i.e. remembering the Mtrace2 Client Address
   and Query ID of the previous Query message that was processed, and
   ignoring future messages with the same Mtrace2 Client Address and
   Query ID).  Duplicate Request messages MUST NOT be ignored in this
   manner.

9.1.2.  Normal Processing

   When a router receives an mtrace2 Query and it determines that it is
   the proper last-hop router, it it changes the TLV type to 0x2 and
   treats it like an mtrace2 Request and performs the steps listed in
   Section 9.2.

9.1.3.  Mtrace2 Query Received by Non-Supported Router

   When a router that does not support mtrace2 receives an mtrace2 Query
   message whose destination address is multicast, the router will



Asaeda, et al.            Expires July 11, 2011                [Page 23]

Internet-Draft                   Mtrace2                    January 2011


   silently discard the message.  When the router receives an mtrace2
   Query message whose destination address is the router's interface
   address, the router returns an ICMP Port unreachable to the Mtrace2
   Client Address.

9.2.  Receiving Mtrace2 Request

   An mtrace2 Request is a traceroute message with some number of
   response blocks filled in, and uses TLV type 0x2 for IPv4 and IPv6
   mtrace2.

9.2.1.  Packet Verification

   If the mtrace2 Request does not come from an adjacent host or router,
   it MUST be silently ignored.  If the mtrace2 Request is not addressed
   to this router, or if the Request is addressed to a multicast group
   which is not a link-scoped group (i.e. 224/24 for IPv4, FFx2::/16 [3]
   for IPv6), it MUST be silently ignored.  GTSM [14] SHOULD be used by
   the router to determine whether the host or router is adjacent or
   not.

9.2.2.  Normal Processing

   When a router receives an mtrace2 Request, it performs the following
   steps.  Note that it is possible to have multiple situations covered
   by the Forwarding Codes.  The first one encountered is the one that
   is reported, i.e. all "note forwarding code N" should be interpreted
   as "if forwarding code is not already set, set forwarding code to N".

   1.   If there is room in the current buffer (or the router can
        efficiently allocate more space to use), insert a new response
        block into the packet and fill in the Query Arrival Time,
        Outgoing Interface Address (for IPv4 mtrace2) or Outgoing
        Interface ID (for IPv6 mtrace2), Output Packet Count, and Fwd
        TTL (for IPv4 mtrace2).  If there was no room, fill in the
        forwarding code "NO_SPACE" in the *previous* hop's response
        block, and forward the packet to the address specified in the
        Mtrace2 Client Address field and continue the trace as described
        in Section 9.3.

   2.   Attempt to determine the forwarding information for the source
        and group specified, using the same mechanisms as would be used
        when a packet is received from the source destined for the
        group.  A state need not be instantiated, it can be "phantom"
        state created only for the purpose of the trace, such as "dry-
        run".

        If using a shared-tree protocol and there is no source-specific



Asaeda, et al.            Expires July 11, 2011                [Page 24]

Internet-Draft                   Mtrace2                    January 2011


        state, or if no source-specific information is desired (i.e.,
        "all 1" for IPv4 or unspecified address (::) for IPv6), group
        state should be used.  If there is no group state or no group-
        specific information is desired, potential source state (i.e.,
        the path that would be followed for a source-specific Join)
        should be used.  If this router is the Core or RP and no source-
        specific state is available (e.g., this router has been
        receiving PIM Register messages from the first-hop router), note
        a code of REACHED_RP.

   3.   If no forwarding information can be determined, the router notes
        a forwarding code of NO_ROUTE, sets the remaining fields that
        have not yet been filled in to zero, and then forwards the
        packet to the mtrace2 client as described in Section 9.3.

   4.   Fill in the Incoming Interface Address, Previous-Hop Router
        Address, Input Packet Count, Total Number of Packets, Routing
        Protocol, S, and Src Mask from the forwarding information that
        was determined.

   5.   If mtrace2 is administratively prohibited, note the appropriate
        forwarding code (ADMIN_PROHIB).  If mtrace2 is administratively
        prohibited and any of the fields as filled in step 4 are
        considered private information, zero out the applicable fields.
        Then the packet is forwarded to the mtrace2 client as described
        in Section 9.3.

   6.   If the reception interface is not enabled for multicast, note
        forwarding code NO_MULTICAST.  If the reception interface is the
        interface from which the router would expect data to arrive from
        the source, note forwarding code RPF_IF.  Otherwise, if the
        reception interface is not one to which the router would forward
        data from the source to the group, a forwarding code of WRONG_IF
        is noted.

   7.   If the group is subject to administrative scoping on either the
        Outgoing or Incoming interfaces, a forwarding code of SCOPED is
        noted.

   8.   If this router is the Rendezvous Point or Core for the group, a
        forwarding code of REACHED_RP is noted.

   9.   If this router has sent a prune upstream which applies to the
        source and group in the mtrace2 Request, it notes forwarding
        code PRUNE_SENT.  If the router has stopped forwarding
        downstream in response to a prune sent by the next hop router,
        it notes forwarding code PRUNE_RCVD.  If the router should
        normally forward traffic for this source and group downstream



Asaeda, et al.            Expires July 11, 2011                [Page 25]

Internet-Draft                   Mtrace2                    January 2011


        but is not, it notes forwarding code NOT_FORWARDING.

   10.  If this router is a gateway (e.g., a NAT or firewall) that hides
        the information between this router and the mtrace2 querier, it
        notes forwarding code REACHED_GW.

   11.  The packet is then sent on to the previous hop or the Mtrace2
        Client Address as described in Section 9.3.

9.2.3.  Mtrace2 Request Received by Non-Supported Router

   When a router that does not understand mtrace2 Request messages
   receives an mtrace2 Request message whose destination address is
   multicast, the router will silently discard the message.  When the
   router receives an mtrace2 Request message whose destination address
   is the router's interface address, the router returns an ICMP Port
   unreachable to the Mtrace2 Client Address, and the mtrace2 client may
   then issue another mtrace2 Query with the lower number of # hops.

9.3.  Forwarding Mtrace2 Request

9.3.1.  Destination Address

   If the Previous-hop router for the mtrace2 Request is known for this
   request and the number of response blocks is less than the number
   requested (i.e., the "# hops" field in the mtrace2 Query header), the
   packet is sent to that router.  If the Incoming Interface is known
   but the Previous-hop router is not known, the packet is sent to an
   appropriate multicast address on the Incoming Interface.  The
   appropriate multicast address may depend on the routing protocol in
   use, MUST be a link-scoped group (i.e. 224/24 for IPv4, FF02::/16 for
   IPv6), MUST NOT be ALL-SYSTEMS.MCAST.NET (224.0.0.1) for IPv4 and All
   Nodes Address (FF02::1) for IPv6, and MAY be ALL-ROUTERS.MCAST.NET
   (224.0.0.2) for IPv4 or All Routers Address (FF02::2) for IPv6 if the
   routing protocol in use does not define a more appropriate group.
   Otherwise, it is sent to the Mtrace2 Client Address in the header.

9.3.2.  Source Address

   An mtrace2 Request should be sent with the address of the router's
   reception interface.  However, if the router's interface address is
   unnumbered, the router can use one of its numbered interface address
   as the source address.

   When the REACHED_GW code is noted, the router sends back the mtrace2
   Reply as in Section 9.4.  In addition to that, it must continue the
   mtrace2 Query by proxying the original querier as in Section 9.5.




Asaeda, et al.            Expires July 11, 2011                [Page 26]

Internet-Draft                   Mtrace2                    January 2011


   When the NO_SPACE error occurs, the router sends back the mtrace2
   Reply with contained data and the NO_SPACE error code as in
   Section 9.4, and continues the mtrace2 Query by sending an mtrace2
   Request containing the same mtrace2 Query header and its standard and
   augmented response blocks.  The corresponding augmented response
   block type is "# Mtrace2 Response Blocks Returned" described in
   Section 8.

9.4.  Sending Mtrace2 Reply

9.4.1.  Destination Address

   An mtrace2 Reply must be sent to the address specified in the Mtrace2
   Client Address field in the mtrace2 Query header.

9.4.2.  Source Address

   An mtrace2 Reply should be sent with the address of the router's
   reception interface.  However, if the router's interface address is
   unnumbered, the router can use one of its numbered interface address
   as the source address.

9.5.  Proxying Mtrace2 Query

   When a gateway (e.g., a NAT or firewall) that needs to block unicast
   packets to the mtrace2 querier or hide information between the
   gateway and the mtrace2 querier receives mtrace2 Query from an
   adjacent host or mtrace2 Request from an adjacent router, it sends
   back the mtrace2 Reply with contained data and the REACHED_GW code to
   the address specified in the Mtrace2 Client Address field in the
   mtrace2 Query header.

   At the same time, the gateway prepares a new mtrace2 Query message.
   The gateway uses the original mtrace2 Query header as the base for
   the new mtrace2 Query; it sets the Mtrace2 Client Address to its
   Incoming Interface address and the Client Port # to its own port
   (which may be the same as the mtrace2 port as the gateway is
   listening on that port), and decreases # hops according to the number
   of standard response blocks in the returned mtrace2 Reply from the
   gateway.  The mtrace2 Query message is sent to the previous-hop
   router or to an appropriate multicast address on the Incoming
   Interface.

   When the gateway receives the mtrace2 Reply from the first-hop router
   or any intermediate router, it MUST forward the mtrace2 Reply back to
   the mtrace2 querier with the original mtrace2 Query header.





Asaeda, et al.            Expires July 11, 2011                [Page 27]

Internet-Draft                   Mtrace2                    January 2011


9.6.  Hiding Information

   Information about a domain's topology and connectivity may be hidden
   from mtrace2 Requests.  The INFO_HIDDEN forwarding code may be used
   to note that, for example, the incoming interface address and packet
   count are for the entrance to the domain and the outgoing interface
   address and packet count are the exit from the domain by specifying
   "all 1".  The source-group packet count (Section 6.8 and Section 7.9)
   is from router, but may be "all 1" if it is hidden.










































Asaeda, et al.            Expires July 11, 2011                [Page 28]

Internet-Draft                   Mtrace2                    January 2011


10.  Client Behavior

10.1.  Sending Mtrace2 Query

10.1.1.  Destination Address

   Mtrace2 Query packet can be sent to the ALL-ROUTERS.MCAST.NET
   (224.0.0.2) for IPv4 or All Routers Address (FF02::2) for IPv6.  This
   will ensure that the packet is received by the last-hop router on the
   subnet.  Otherwise, if the proper last-hop router is known for the
   mtrace2 destination, the Query is unicasted to that router.

   See also Section 10.4 on determining the last-hop router.

10.1.2.  Source Address

   An mtrace2 Query must be sent with the address of the mtrace2
   querier's reception interface, which would be the Mtrace2 Client
   Address.

10.2.  Determining the Path

   The client could send a small number of initial query messages with a
   large "# hops" field, in order to try to trace the full path.  If
   this attempt fails, one strategy is to perform a linear search (as
   the traditional unicast traceroute program does); set the "# hops"
   field to 1 and try to get a Reply, then 2, and so on.  If no Reply is
   received at a certain hop, the hop count can continue past the non-
   responding hop, in the hopes that further hops may respond.  These
   attempts should continue until a user-defined timeout has occurred.

   See also Section 10.6 on receiving the results of a trace.

10.3.  Collecting Statistics

   After a client has determined that it has traced the whole path or as
   much as it can expect to (see Section 10.7), it might collect
   statistics by waiting a short time and performing a second trace.  If
   the path is the same in the two traces, statistics can be displayed
   as described in Section 12.3 and Section 12.4.

10.4.  Last Hop Router

   The mtrace2 querier may not know which is the last-hop router, or
   that router may be behind a firewall that blocks unicast packets but
   passes multicast packets.  In these cases, the mtrace2 Request should
   be multicasted to ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All
   Routers Address (FF02::2) for IPv6.  All routers except the correct



Asaeda, et al.            Expires July 11, 2011                [Page 29]

Internet-Draft                   Mtrace2                    January 2011


   last-hop router SHOULD ignore any mtrace2 Request received via
   multicast.

10.5.  First Hop Router

   The IANA assigned 224.0.1.32, MTRACE.MCAST.NET as the default
   multicast group for old IPv4 mtrace (v1) responses, in order to
   support mtrace queriers that are not unicast reachable from the
   first-hop router.  However, mtrace2 does not reserve any IPv4/IPv6
   multicast addresses for mtrace2 Replies.  Every mtrace2 Reply is sent
   to the unicast address specified in the Mtrace2 Client Address field
   of the mtrace2 Query header.

10.6.  Broken Intermediate Router

   A broken intermediate router might simply not understand mtrace2
   packets, and drop them.  The querier would then get no Reply at all
   from its mtrace2 Requests.  It should then perform a hop-by-hop
   search by setting the number of hops field until it gets a Reply
   (both linear and binary search are options, but binary is likely to
   be slower because a failure requires waiting for a timeout).

10.7.  Mtrace2 Termination

   When performing an expanding hop-by-hop trace, it is necessary to
   determine when to stop expanding.

10.7.1.  Arriving at source

   A trace can be determined to have arrived at the source if the
   Incoming Interface of the last router in the trace is non-zero, but
   the Previous-hop router is zero.

10.7.2.  Fatal error

   A trace has encountered a fatal error if the last Forwarding Error in
   the trace has the 0x80 bit set.

10.7.3.  No previous hop

   A trace can not continue if the last Previous-hop in the trace is set
   to 0.

10.7.4.  Traceroute shorter than requested

   If the trace that is returned is shorter than requested (i.e. the
   number of response blocks is smaller than the "# hops" field), the
   trace encountered an error and could not continue.



Asaeda, et al.            Expires July 11, 2011                [Page 30]

Internet-Draft                   Mtrace2                    January 2011


10.8.  Continuing after an error

   When the NO_SPACE error occurs, as described in Section 9.3, the
   multicast routers sends back the mtrace2 Reply to the address
   specified in the Mtrace2 Client Address field in the mtrace2 Query
   header.  In this case, the mtrace2 client may receive multiple
   mtrace2 Replies from different routers (along the path).  After the
   client receives multiple mtrace2 Reply messages, it integrates (i.e.
   constructs) them as a single mtrace2 Reply message.

   If a trace times out, it is likely to be because a router in the
   middle of the path does not support mtrace2.  That router's address
   will be in the Previous-hop router field of the last entry in the
   last response packet received.  A client may be able to determine
   (via mrinfo or SNMP [11][13]) a list of neighbors of the non-
   responding router.  If desired, each of those neighbors could be
   probed to determine the remainder of the path.  Unfortunately, this
   heuristic may end up with multiple paths, since there is no way of
   knowing what the non-responding router's algorithm for choosing a
   previous-hop router is.  However, if all paths but one flow back
   towards the non-responding router, it is possible to be sure that
   this is the correct path.





























Asaeda, et al.            Expires July 11, 2011                [Page 31]

Internet-Draft                   Mtrace2                    January 2011


11.  Protocol-Specific Considerations

11.1.  PIM-SM

   When an mtrace2 reaches a PIM-SM RP and the RP does not forward the
   trace on, it means that the RP has not performed a source-specific
   join so there is no more state to trace.  However, the path that
   traffic would use if the RP did perform a source-specific join can be
   traced by setting the trace destination to the RP, the trace source
   to the traffic source, and the trace group to 0.  This trace Query
   may be unicasted to the RP.

11.2.  Bi-Directional PIM

   Bi-directional PIM [7] is a variant of PIM-SM that builds bi-
   directional shared trees connecting multicast sources and receivers.
   Along the bi-directional shared trees, multicast data is natively
   forwarded from sources to the RPA (Rendezvous Point Address) and from
   the RPA to receivers without requiring source-specific state.  In
   contrast to PIM-SM, RP always has the state to trace.

   A Designated Forwarder (DF) for a given RPA is in charge of
   forwarding downstream traffic onto its link, and forwarding upstream
   traffic from its link towards the RPL (Rendezvous Point Link) that
   the RPA belongs to.  Hence mtrace2 reports DF addresses or RPA along
   the path.

11.3.  PIM-DM

   Routers running PIM Dense Mode [15] do not know the path packets
   would take unless traffic is flowing.  Without some extra protocol
   mechanism, this means that in an environment with multiple possible
   paths with branch points on shared media, mtrace2 can only trace
   existing paths, not potential paths.  When there are multiple
   possible paths but the branch points are not on shared media, the
   previous hop router is known, but the last-hop router may not know
   that it is the appropriate last hop.

   When traffic is flowing, PIM Dense Mode routers know whether or not
   they are the last-hop forwarder for the link (because they won or
   lost an Assert battle) and know who the previous hop is (because it
   won an Assert battle).  Therefore, mtrace2 is always able to follow
   the proper path when traffic is flowing.

11.4.  IGMP/MLD Proxy

   When an mtrace2 Query packet reaches an incoming interface of IGMP/
   MLD Proxy [8], it puts a WRONG_IF (0x01) value in Forwarding Code of



Asaeda, et al.            Expires July 11, 2011                [Page 32]

Internet-Draft                   Mtrace2                    January 2011


   mtrace2 standard response block (as in Section 6.14) and sends the
   mtrace2 Reply back to the Mtrace2 Client Address.  When an mtrace2
   Query packet reaches an outgoing interface of IGMP/MLD proxy, it is
   forwarded through its incoming interface towards the upstream router.

11.5.  AMT

   AMT [9] provides the multicast connectivity to the unicast-only
   inter-network.  To do this, multicast packets being sent to or from a
   site are encapsulated in unicast packets.  When an mtrace2 Query
   packet reaches an AMT pseudo-interface of an AMT gateway, the AMT
   gateway encapsulats it to a particular AMT relay reachable across the
   unicast-only infrastructure.  Then the AMT relay decapsulates the
   mtrace2 Query packet and forwards the mtrace2 Request to the
   appropriate multicast router.




































Asaeda, et al.            Expires July 11, 2011                [Page 33]

Internet-Draft                   Mtrace2                    January 2011


12.  Problem Diagnosis

12.1.  Forwarding Inconsistencies

   The forwarding error code can tell if a group is unexpectedly pruned
   or administratively scoped.

12.2.  TTL or Hop Limit Problems

   By taking the maximum of hops (from source + forwarding TTL (or hop
   limit) threshold) over all hops, it is possible to discover the TTL
   or hop limit required for the source to reach the destination.

12.3.  Packet Loss

   By taking two traces, it is possible to find packet loss information
   by comparing the difference in input packet counts to the difference
   in output packet counts for the specified source-group address pair
   at the previous hop.  On a point-to-point link, any difference in
   these numbers implies packet loss.  Since the packet counts may be
   changing as the mtrace2 Query is propagating, there may be small
   errors (off by 1 or 2 or more) in these statistics.  However, these
   errors will not accumulate if multiple traces are taken to expand the
   measurement period.  On a shared link, the count of input packets can
   be larger than the number of output packets at the previous hop, due
   to other routers or hosts on the link injecting packets.  This
   appears as "negative loss" which may mask real packet loss.

   In addition to the counts of input and output packets for all
   multicast traffic on the interfaces, the response data includes a
   count of the packets forwarded by a node for the specified source-
   group pair.  Taking the difference in this count between two traces
   and then comparing those differences between two hops gives a measure
   of packet loss just for traffic from the specified source to the
   specified receiver via the specified group.  This measure is not
   affected by shared links.

   On a point-to-point link that is a multicast tunnel, packet loss is
   usually due to congestion in unicast routers along the path of that
   tunnel.  On native multicast links, loss is more likely in the output
   queue of one hop, perhaps due to priority dropping, or in the input
   queue at the next hop.  The counters in the response data do not
   allow these cases to be distinguished.  Differences in packet counts
   between the incoming and outgoing interfaces on one node cannot
   generally be used to measure queue overflow in the node.






Asaeda, et al.            Expires July 11, 2011                [Page 34]

Internet-Draft                   Mtrace2                    January 2011


12.4.  Link Utilization

   Again, with two traces, you can divide the difference in the input or
   output packet counts at some hop by the difference in time stamps
   from the same hop to obtain the packet rate over the link.  If the
   average packet size is known, then the link utilization can also be
   estimated to see whether packet loss may be due to the rate limit or
   the physical capacity on a particular link being exceeded.

12.5.  Time Delay

   If the routers have synchronized clocks, it is possible to estimate
   propagation and queuing delay from the differences between the
   timestamps at successive hops.  However, this delay includes control
   processing overhead, so is not necessarily indicative of the delay
   that data traffic would experience.



































Asaeda, et al.            Expires July 11, 2011                [Page 35]

Internet-Draft                   Mtrace2                    January 2011


13.  IANA Considerations

   The following new assignments can only be made via a Standards Action
   as specified in [4].

13.1.  Forwarding Codes

   New Forwarding codes must only be created by an RFC that modifies
   this document's Section 10, fully describing the conditions under
   which the new forwarding code is used.  The IANA may act as a central
   repository so that there is a single place to look up forwarding
   codes and the document in which they are defined.

13.2.  UDP Destination Port and IPv6 Address

   The IANA should allocate UDP destination port for multicast
   traceroute version 2 upon publication of the first RFC.


































Asaeda, et al.            Expires July 11, 2011                [Page 36]

Internet-Draft                   Mtrace2                    January 2011


14.  Security Considerations

14.1.  Topology Discovery

   Mtrace2 can be used to discover any actively-used topology.  If your
   network topology is a secret, mtrace2 may be restricted at the border
   of your domain, using the ADMIN_PROHIB forwarding code.

14.2.  Traffic Rates

   Mtrace2 can be used to discover what sources are sending to what
   groups and at what rates.  If this information is a secret, mtrace2
   may be restricted at the border of your domain, using the
   ADMIN_PROHIB forwarding code.

14.3.  Limiting Query/Request Rates

   Routers should limit mtrace2 Queries and Requests by ignoring the
   received messages.  Routers MAY randomly ignore the received messages
   to minimize the processing overhead, i.e., to keep fairness in
   processing queries.  The rate limit is left to the router's
   implementation.





























Asaeda, et al.            Expires July 11, 2011                [Page 37]

Internet-Draft                   Mtrace2                    January 2011


15.  Acknowledgements

   This specification started largely as a transcription of Van
   Jacobson's slides from the 30th IETF, and the implementation in
   mrouted 3.3 by Ajit Thyagarajan.  Van's original slides credit Steve
   Casner, Steve Deering, Dino Farinacci and Deb Agrawal.  The original
   multicast traceroute client, mtrace (version 1), has been implemented
   by Ajit Thyagarajan, Steve Casner and Bill Fenner.  The idea of the
   "S" bit to allow statistics for a source subnet is due to Tom
   Pusateri.

   For the mtrace version 2 specification, extensive comments were
   received from Ronald Bonica, Yiqun Cai, Liu Hui, Bharat Joshi, Pekka
   Savola, Shinsuke Suzuki, Dave Thaler, Achmad Husni Thamrin, and Cao
   Wei.




































Asaeda, et al.            Expires July 11, 2011                [Page 38]

Internet-Draft                   Mtrace2                    January 2011


16.  References

16.1.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to indicate requirement
         levels", RFC 2119, March 1997.

   [2]   Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
         Specification", RFC 2460, December 1998.

   [3]   Hinden, R. and S. Deering, "IP Version 6 Addressing
         Architecture", RFC 2373, July 1998.

   [4]   Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
         Considerations Section in RFCs", RFC 2434, October 1998.

   [5]   Braden, B., Borman, D., and C. Partridge, "Computing the
         Internet Checksum", RFC 1071, September 1988.

   [6]   Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
         "Protocol Independent Multicast - Sparse Mode (PIM-SM):
         Protocol Specification (Revised)", RFC 4601, August 2006.

   [7]   Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
         "Bidirectional Protocol Independent Multicast (BIDIR-PIM)",
         RFC 5015, October 2007.

   [8]   Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet
         Group Management Protocol (IGMP) / Multicast Listener Discovery
         (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")",
         RFC 4605, August 2006.

   [9]   Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and T.
         Pusateri, "Automatic IP Multicast Without Explicit Tunnels
         (AMT)", draft-ietf-mboned-auto-multicast-08.txt (work in
         progress), October 2007.

16.2.  Informative References

   [10]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
         Thyagarajan, "Internet Group Management Protocol, Version 3",
         RFC 3376, October 2002.

   [11]  Draves, R. and D. Thaler, "Default Router Preferences and More-
         Specific Routes", RFC 4191, November 2005.

   [12]  McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB",
         RFC 2863, June 2000.



Asaeda, et al.            Expires July 11, 2011                [Page 39]

Internet-Draft                   Mtrace2                    January 2011


   [13]  McWalter, D., Thaler, D., and A. Kessler, "IP Multicast MIB",
         RFC 5132, December 2007.

   [14]  Gill, V., Heasley, J., Meyer, D., Savola, P., and C. Pignataro,
         "The Generalized TTL Security Mechanism (GTSM)", RFC 5082,
         October 2007.

   [15]  Adams, A., Nicholas, J., and W. Siadak, "Protocol Independent
         Multicast - Dense Mode (PIM-DM): Protocol Specification
         (Revised)", RFC 3973, January 2005.









































Asaeda, et al.            Expires July 11, 2011                [Page 40]

Internet-Draft                   Mtrace2                    January 2011


Authors' Addresses

   Hitoshi Asaeda
   Keio University
   Graduate School of Media and Governance
   Fujisawa, Kanagawa  252-0882
   Japan

   Email: asaeda@wide.ad.jp
   URI:   http://www.sfc.wide.ad.jp/~asaeda/


   Tatuya Jinmei
   Internet Systems Consortium
   Redwood City, CA  94063
   US

   Email: Jinmei_Tatuya@isc.org


   William C. Fenner
   Arastra, Inc.
   Menlo Park, CA  94025
   US

   Email: fenner@fenron.net


   Stephen L. Casner
   Packet Design, Inc.
   Palo Alto, CA  94304
   US

   Email: casner@packetdesign.com

















Asaeda, et al.            Expires July 11, 2011                [Page 41]


Html markup produced by rfcmarkup 1.108, available from http://tools.ietf.org/tools/rfcmarkup/