MBONED Working Group                                           H. Asaeda
Internet-Draft                                           Keio University                                                      NICT
Intended status: Standards Track                               T. Jinmei
Expires: July 11, 2011                                               ISC                             W. Fenner
                                                           Arastra, Inc.
                                                               S. Casner
                                                     Packet Design, Lee, Ed.
Expires: April 25, 2013                           Juniper Networks, Inc.
                                                         January 7, 2011
                                                        October 22, 2012

         Mtrace Version 2: Traceroute Facility for IP Multicast
                     draft-ietf-mboned-mtrace-v2-08
                     draft-ietf-mboned-mtrace-v2-09

Abstract

   This document describes the IP multicast traceroute facility. facility, named
   Mtrace version 2 (Mtrace2).  Unlike unicast traceroute, multicast traceroute Mtrace2
   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. an Mtrace2 client invokes a query and
   receives a reply.

Status of this Memo

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   This Internet-Draft will expire on July 11, 2011. April 25, 2013.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  6  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  8
   3.  Overview . . . .  6
     2.1.  Definitions  . . . . . . . . . . . . . . . . . . . . . . .  9
   4.  6
   3.  Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 10
     4.1.  7
     3.1.  Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . . 10
     4.2.  8
     3.2.  Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 10
   5.  8
       3.2.1.  Mtrace2 Query Header  . . . . . . . . . . . . . . . . . . . .  9
       3.2.2.  Mtrace2 Extended Query Block . . . . 12
     5.1.  # hops: 8 bits . . . . . . . . . 10
       3.2.3.  Mtrace2 Request  . . . . . . . . . . . . . . 12
     5.2.  Multicast Address . . . . . 11
       3.2.4.  Mtrace2 Reply  . . . . . . . . . . . . . . . . 13
     5.3.  Source Address . . . . 11
       3.2.5.  IPv4 Mtrace2 Standard Response Block . . . . . . . . . 12
       3.2.6.  IPv6 Mtrace2 Standard Response Block . . . . . . . . . 13
     5.4. 16
       3.2.7.  Mtrace2 Client Address Augmented Response Block . . . . . . . . . . . 19
   4.  Router Behavior  . . . . . . . 13
     5.5.  Query ID: 16 bits . . . . . . . . . . . . . . . . 20
     4.1.  Receiving Mtrace2 Query  . . . . 13
     5.6.  Client Port # . . . . . . . . . . . . . 20
       4.1.1.  Query Packet Verification  . . . . . . . . . 13
   6.  IPv4 Mtrace2 Standard Response Block . . . . . 20
       4.1.2.  Query Normal Processing  . . . . . . . . 14
     6.1.  MBZ: 8 bit . . . . . . . 21
     4.2.  Receiving Mtrace2 Request  . . . . . . . . . . . . . . . . 21
       4.2.1.  Request Packet Verification  . 14
     6.2.  Query Arrival Time: 32 bits . . . . . . . . . . . . 21
       4.2.2.  Request Normal Processing  . . . 14
     6.3.  Incoming Interface Address: 32 bits . . . . . . . . . . . 15
     6.4.  Outgoing Interface Address: 32 bits 22
     4.3.  Forwarding Mtrace2 Request . . . . . . . . . . . 15
     6.5.  Previous-Hop Router Address: 32 bits . . . . . 23
       4.3.1.  Destination Address  . . . . . . 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 . . . . 24
       4.3.2.  Source Address . . . . . . . . . . . . . . . . . . . . 24
       4.3.3.  Appending Standard Response Block  . . . 16
     6.9.  Rtg Protocol: 16 bits . . . . . . . 24
     4.4.  Sending Mtrace2 Reply  . . . . . . . . . . . 16
     6.10. Multicast Rtg Protocol: 16 bits . . . . . . . 24
       4.4.1.  Destination Address  . . . . . . 16
     6.11. Fwd TTL: 8 bits . . . . . . . . . . . 25
       4.4.2.  Source Address . . . . . . . . . . 16
     6.12. S: 1 bit . . . . . . . . . . 25
       4.4.3.  Appending Standard Response Block  . . . . . . . . . . 25
     4.5.  Proxying Mtrace2 Query . . . . . 16
     6.13. Src Mask: 7 bits . . . . . . . . . . . . . 25
     4.6.  Hiding Information . . . . . . . . 17
     6.14. Forwarding Code: 8 bits . . . . . . . . . . . . 26
   5.  Client Behavior  . . . . . 17
   7.  IPv6 Mtrace2 Standard Response Block . . . . . . . . . . . . . 19
     7.1.  MBZ: 8 bit . . . . . 26
     5.1.  Sending Mtrace2 Query  . . . . . . . . . . . . . . . . . . 26
       5.1.1.  Destination Address  . 19
     7.2.  Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 20
     7.3.  Incoming Interface ID: 32 bits . 26
       5.1.2.  Source Address . . . . . . . . . . . . . 20
     7.4.  Outgoing Interface ID: 32 bits . . . . . . . 26
     5.2.  Determining the Path . . . . . . . 20
     7.5.  Local Address . . . . . . . . . . . . 26
     5.3.  Collecting Statistics  . . . . . . . . . . 20
     7.6.  Remote Address . . . . . . . . 27
     5.4.  Last Hop Router (LHR)  . . . . . . . . . . . . . . 20
     7.7.  Input packet count on incoming interface . . . . 27
     5.5.  First Hop Router (FHR) . . . . . 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 . 27
     5.6.  Broken Intermediate Router . . . . . . . . . . . . . . . . 27
     5.7.  Non-Supported Router . 21
     7.11. Multicast Rtg Protocol: 16 bits . . . . . . . . . . . . . 21
     7.12. S: 1 bit . . . . . 28
     5.8.  Mtrace2 Termination  . . . . . . . . . . . . . . . . . . . 28
       5.8.1.  Arriving at Source . 21
     7.13. Src Prefix Len: 8 bits . . . . . . . . . . . . . . . . . 28
       5.8.2.  Fatal Error  . 21
     7.14. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 21
   8.  Mtrace2 Augmented Response Block . . . 28
       5.8.3.  No Upstream Router . . . . . . . . . . . . 22
   9.  Router Behavior . . . . . . 28
       5.8.4.  Reply Timeout  . . . . . . . . . . . . . . . . . 23
     9.1.  Receiving Mtrace2 Query . . . 28
     5.9.  Continuing after an Error  . . . . . . . . . . . . . . 23
       9.1.1.  Packet Verification . . 28
   6.  Protocol-Specific Considerations . . . . . . . . . . . . . . . 23
       9.1.2.  Normal Processing  . . . . . 29
     6.1.  PIM-SM . . . . . . . . . . . . . 23
       9.1.3.  Mtrace2 Query Received by Non-Supported Router . . . . 23
     9.2.  Receiving Mtrace2 Request . . . . . . . . . 29
     6.2.  Bi-Directional PIM . . . . . . . 24
       9.2.1.  Packet Verification . . . . . . . . . . . . . 29
     6.3.  PIM-DM . . . . 24
       9.2.2.  Normal Processing . . . . . . . . . . . . . . . . . . 24
       9.2.3.  Mtrace2 Request Received by Non-Supported Router . . . 26
     9.3.  Forwarding Mtrace2 Request . 30
     6.4.  IGMP/MLD Proxy . . . . . . . . . . . . . . . 26
       9.3.1.  Destination Address . . . . . . . 30
   7.  Problem Diagnosis  . . . . . . . . . . 26
       9.3.2.  Source Address . . . . . . . . . . . . 30
     7.1.  Forwarding Inconsistencies . . . . . . . . 26
     9.4.  Sending Mtrace2 Reply . . . . . . . . 30
     7.2.  TTL or Hop Limit Problems  . . . . . . . . . . 27
       9.4.1.  Destination Address . . . . . . 30
     7.3.  Packet Loss  . . . . . . . . . . . 27
       9.4.2.  Source Address . . . . . . . . . . . . 30
     7.4.  Link Utilization . . . . . . . . 27
     9.5.  Proxying Mtrace2 Query . . . . . . . . . . . . . 31
     7.5.  Time Delay . . . . . 27
     9.6.  Hiding Information . . . . . . . . . . . . . . . . . . . 31
   8.  IANA Considerations  . 28
   10. Client Behavior . . . . . . . . . . . . . . . . . . . . 32
     8.1.  Forwarding Codes . . . 29
     10.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 29
       10.1.1. 32
     8.2.  UDP Destination Address  . . . . . . . . . . . . . . . . . 29
       10.1.2. Source Address . . . . . . . . . . . . . . . . . . . . 29
     10.2. Determining the Path . . Port . . . . . . . . . . . . . . . . . 29
     10.3. Collecting Statistics . . 32
   9.  Security Considerations  . . . . . . . . . . . . . . . . 29
     10.4. Last Hop Router . . . 32
     9.1.  Addresses in Mtrace2 Header  . . . . . . . . . . . . . . . 32
     9.2.  Topology Discovery . . . 29
     10.5. First Hop Router . . . . . . . . . . . . . . . . . 32
     9.3.  Characteristics of Multicast Channel . . . . 30
     10.6. Broken Intermediate Router . . . . . . . 32
     9.4.  Limiting Query/Request Rates . . . . . . . . . 30
     10.7. Mtrace2 Termination . . . . . . 33
     9.5.  Limiting Reply Rates . . . . . . . . . . . . . 30
       10.7.1. Arriving at source . . . . . . 33
   10. Acknowledgements . . . . . . . . . . . . 30
       10.7.2. Fatal error . . . . . . . . . . . 33
   11. References . . . . . . . . . . 30
       10.7.3. No previous hop . . . . . . . . . . . . . . . . 33
     11.1. Normative References . . . 30
       10.7.4. Traceroute shorter than requested . . . . . . . . . . 30
     10.8. Continuing after an error . . . . . . 33
     11.2. Informative References . . . . . . . . . . 31
   11. Protocol-Specific Considerations . . . . . . . . 34
   Authors' Addresses . . . . . . . 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
     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 34

1.  Introduction

   Given a multicast distribution tree, tracing from a multicast source
   to a receiver is difficult, since we do not know which branch of the
   multicast tree the receiver lies.  This means that we have to flood
   the whole tree to find the path from a source to a receiver.  On the
   other hand, walking up the tree from a receiver to a source is easy,
   as most existing multicast routing protocols know the upstream router
   for each source.  Tracing from a receiver to a source can involve
   only the routers on the direct path.

   This document specifies the multicast traceroute facility named
   mtrace
   Mtrace version 2 or mtrace2. Mtrace2 which allows the tracing of an IP
   multicast routing paths. path.  Mtrace2 is usually initiated from a Mtrace2
   client towards a specified source, or a Rendezvous Point (RP) if no
   source address is specified.  RP is a special router where the source
   and receiver meet in PIM-SM [1].  Moreover, Mtrace2 provides
   additional information
   about such as the packet rates and losses, or as well
   as other diagnosis information.  For
   instance, mtrace2 is  Especially, Mtrace2 can be used for
   the following purposes. purposes:

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

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

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

   Figure 1 shows a typical case on how Mtrace2 consists of the client and router programs.  The mtrace2
   client program is invoked from somewhere in used.  FHR represents
   the multicast tree, on a
   host, first-hop router, or proxy such as IGMP/MLD proxy [8].  The LHR represents the last-hop router, and the
   arrow lines represent the Mtrace2 messages that are sent from one
   node invoking to another.  The numbers before the program is called Mtrace2 messages represent
   the mtrace2 client. sequence of the messages that would happen.  Source, Receiver and
   Mtrace2 client are typically a host on the Internet.

                   2. Request                 2. Request
                     +----+                    +----+
                     |    |                    |    |
                     v    |                    v    |
    +--------+    +-----+                        +-----+    +----------+
    | Source |----| FHR |----- The mtrace2 Internet -----| LHR |----| Receiver |
    +--------+    +-----+            |           +-----+    +----------+
                      \              |             ^
                       \             |            /
                        \            |           /
                         \           |          /
                 3. Reply \          |         / 1. Query
                           \         |        /
                            \        |       /
                             \  +---------+ /
                              v | Mtrace2 |/
                                | client program creates  |
                                +---------+

                                 Figure 1

   When an Mtrace2 client initiates a multicast trace anywhere on the mtrace2
   Internet, it sends an Mtrace2 Query message, which
   includes packet to the LHR for a source and multicast address specified by
   group and a source address.  The LHR turns the client, Query packet into a
   Request, appends a standard response block containing its interface
   addresses and packet statistics to the Request packet, then forwards
   the message packet towards the source.  The Request packet is either
   unicasted to its neighbor upstream router or proxy.  This initiates
   a trace of a multicast routing path from the client toward towards the
   specified source, or multicasted
   to the group if no source the upsteam router's IP address is specified, toward a core
   router if such a router exists. not known.  In the case of PIM-SM [6], the core
   router is an RP maintaining the specified multicast address.

   When a
   similar fashion, each router or proxy receives an mtrace2 Query message and has along the
   corresponding routing state regarding path to 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 appends a
   standard response block to the query and forwards end of the Request toward the specified source or the core packet before
   forwarding it to its upstream router.  When a first-hop router or proxy (a single hop from the source
   specified in the request) or the core router FHR receives an mtrace2
   Query or the
   Request message, packet, it appends its own standard response block, turns the router or proxy invokes
   Request packet into a Reply, and unicasts the mtrace2
   router program.  The mtrace2 router program creates an mtrace2 Reply
   message. back to the
   Mtrace2 client.

   The Mtrace2 Reply message may be returned before reaching the FHR if it
   reaches the RP first, or a fatal error condition such as "no route"
   is forwarded to encountered along the mtrace2 client, thus
   completing path, or the mtrace2 Request. hop count is exceeded.

   The mtrace2 Mtrace2 client program waits for the mtrace2 Mtrace2 Reply message and displays
   the results.  When not receiving an mtrace2 Mtrace2 Reply message does not come due to
   network congestion, a broken router (see Section 10.6) 5.6), or a
   non-responding non-
   responding router (see Section 10.8), 5.7), the mtrace2 Mtrace2 client program
   can may resend an mtrace2
   another Mtrace2 Query with a lower hop count (see Section 5.1) 3.2.1), and
   repeat the process until it receives an mtrace2 Mtrace2 Reply message.  The mtrace2
   details are Mtrace2 client should also be aware that the mtrace2 Query may
   follow the control path on the routers, in specific, and it is outside the case scope of
   this document.

   Note that when a router's control plane and forwarding plane are not synchronized, e.g., a
   buggy implementation.  In this case, mtrace2 out
   of sync, the Mtrace2 Requests will might be forwarded toward the specified source or based on the core router because control
   states instead.  In which case, the
   router does traced path might not have any forwarding state for represent
   the query.

   The mtrace2 real path the data packets would follow.

   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, IPv6.  Unlike the previous version of
   Mtrace, which implements its query and response messages are
   implemented as IGMP messages [10], [8],
   all mtrace2 Mtrace2 messages are carried
   on UDP.  The UDP-based.  Although the packet formats of
   IPv4 and IPv6 mtrace2 Mtrace2 are different because of the different address families, but
   the syntax between them is similar.

2.  Terminology

   The

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL
   NOT","SHOULD", NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED","MAY", "RECOMMENDED", "MAY",
   and "OPTIONAL" in
   this document are to be interpreted as described in RFC 2119 [1]. [2],
   and indicate requirement levels for compliant Mtrace2
   implementations.

2.1.  Definitions

   Since multicast traceroutes Mtrace2 Queries and Requests flow in the opposite direction to
   the data flow, we refer to "upstream" and "downstream" with respect
   to data, unless explicitly specified.

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

   Outgoing interface: interface
      The interface on to which traffic is forwarded data from the source or RP is expected to
      transmit for the specified source and group toward the destination. group.  It is also the
      interface on which the
   mtrace2 Query or Mtrace2 Request was will be received.

   Previous-hop router:
   The

   Upstream router that is on the link attached
      The router, connecting to the Incoming interface and of the current
      router, which is responsible for forwarding traffic data for the specified
      source and
   group.

   Last-hop router: group to the current router.

   First-hop router (FHR)
      The router that is on directly connected to the link attached source the Mtrace2
      Query specifies.

   Last-hop router (LHR)
      The router that is directly connected to the Outgoing interface and receivers.  It is
      also the router that receives the mtrace2 Mtrace2 Query from the adjacent mtrace2 an Mtrace2
      client.

   Group state: state
      It is the state in which a shared-tree protocol (e.g., protocol, such as PIM-SM [6])
   running on a router chooses [1], uses
      to choose the previous-hop upstream router toward towards the core
   router or Rendezvous Point (RP) as its parent router. RP for the specified
      group.  In this state, source-specific state is not available for
      the corresponding
   multicast group address on the router.

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

   ALL-[protocol]-ROUTERS.MCAST.NET: the specified source and group.

   ALL-[protocol]-ROUTERS.MCAST.NET
      It is a dedicated link-local multicast address for a multicast router routers to
      communicate with other their adjacent routers that are working with running the same
      routing protocol.  For instance, the address of ALL-PIM-ROUTERS.MCAST.NET [6] ALL-PIM-
      ROUTERS.MCAST.NET [1] is '224.0.0.13' for IPv4 and 'ff02::d' for
      IPv6.

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  Packet Formats

   This section describes the multicast tree details of the destination lies.  This means that
   you have to flood packet formats for Mtrace2
   messages.

   All Mtrace2 messages are encoded in TLV format (see Section 3.1).  If
   an implementation receives an unknown TLV, it SHOULD ignored and
   silently discarded the whole tree to find unknown TLV.  If the path from one source to
   one destination.  However, walking up length of a TLV exceeds
   the tree from destination to
   source is easy, as most existing multicast routing protocols know length specified in the
   previous hop for each source.  Tracing from destination to source can
   involve only routers on TLV, the direct path.

   The party requesting TLV SHOULD be accepted; however,
   any additional data after the multicast traceroute sends a traceroute TLV SHOULD be ignored.

   All Mtrace2 messages are UDP packets.  For IPv4, Mtrace2 Query and
   Request messages MUST NOT be fragmented.  For IPv6, the packet to size
   for the last-hop multicast router Mtrace2 messages MUST NOT exceed 1280 bytes, which is the
   smallest MTU for an IPv6 interface [3].  The source port is uniquely
   selected by the given multicast
   address. local host operating system.  The last-hop router turns destination port is
   the Query into IANA reserved Mtrace2 port number (see Section 8).  All Mtrace2
   messages MUST have a Request packet
   by changing the packet type valid UDP checksum.

   Additionally, Mtrace2 supports both IPv4 and adding a response data block
   containing its interface IPv6, but not mixed.
   For example, if an Mtrace2 Query or Reply message arrives in as an
   IPv4 packet, all addresses and packet statistics, and then
   forwards specified in the Request packet via unicast Mtrace2 messages MUST be
   IPv4 as well.  Same rule applies to IPv6 Mtrace2 messages.

3.1.  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

      Describes the router that the last-
   hop router believes is the proper previous hop for format of the given source
   and group.  Each hop adds its response data to Value field.  For all the end available
      types, please see Section 3.2

   Length: 16 bits

      Length of Type, Length, and Value fields in octets.  Minimum
      length required is 6 octets.  The maximum TLV length is not
      defined; however the Request
   packet, then unicast forwards it to entired Mtrace2 packet length should not
      exceeed the previous hop. available MTU.

   Value: variable length

      The first-hop
   router (the router that believes that packets from the source
   originate format is based on one of its directly connected networks) changes the
   packet type to indicate a Reply packet and sends the completed Reply
   to Type value.  The length of the mtrace2 client address specified value
      field is Length field minus 3.  All reserved fields in the Query header.  The
   Reply may Value
      field MUST be returned before reaching the first-hop router if a fatal
   error condition such transmitted as "no route" is encountered along the path zeros and ignored on receipt.

3.2.  Defined TLVs

   The following TLV Types are defined:

         Code         Type
         ====         ================================
         0x01         Mtrace2 Query
         0x02         Mtrace2 Request
         0x03         Mtrace2 Reply
         0x04         Mtrace2 Standard Response Block
         0x05         Mtrace2 Augmented Response Block
         0x06         Mtrace2 Extended Query Block

   Each Mtrace2 message MUST begin with either a Query, Request or
   hop count is exceeded.

   Multicast traceroute uses any information available to it in Reply
   TLV.  The first TLV determines the
   router to attempt to determine type of each Mtrace2 message.
   Following this TLV, there can be a previous hop to forward sequence of optional Extended
   Query Blocks.  In the trace
   towards.  Multicast routing protocols vary in case of the type Request and amount of
   state they keep; multicast traceroute endeavors to work with all of
   them by using whatever Reply message, it is available.  For example, if
   then followed by a PIM-SM sequence of Standard Response Blocks, each from a
   multicast router
   is on the (*,G) tree, it chooses the parent path towards the RP as source or the
   previous hop. RP.  In these cases, no source/group-specific state is
   available, but the path may still be traced.

4.  Packet Formats

   The mtrace2 message
   case more information is carried as needed, 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 Block can be
   followed by one or
   multicast address.  Detailed multiple Augmented Response Blocks.

   We will describe each message type in Section 9.3. details in the next few
   sections.

3.2.1.  Mtrace2 message Query

   An Mtrace2 query is encoded in TLV format.  If usually originated by an implementation
   receives a TLV whose length exceeds Mtrace2 client which
   sends an Mtrace2 Query message to the TLV length specified in LHR.  When tracing towards the
   Length field,
   source or the TLV SHOULD be accepted but any additional data
   SHOULD be ignored.  If an implementation receives a TLV whose type
   value is unknown, RP, the intermediate routers MUST NOT modify the mtrace2 Query
   message SHOULD be ignored and silently
   dropped.

4.1. except the Type field.

   An Mtrace2 TLV format Query message is shown 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |           Length              |   Value ....    # Hops     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type (8 bits)

   Length (16 bits)

   Value (variable length)

4.2.  Defined TLVs

   The following TLV Types are defined:

              Code                       Type
             ======      ======================================
               1
     |                                                               |
     |                      Multicast Address                        |
     |                                                               |
     +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
     |                                                               |
     |                        Source Address                         |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                    Mtrace2 Client Address                     |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Query ID            |        Client Port #        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 2

   # Hops: 8 bits
      This field specifies the maximum number of hops that the Mtrace2 Request
               3
      client wants to trace.  If there are some error conditions in the
      middle of the path that prevent an Mtrace2 Reply
               4             Mtrace2 Standard Response Block
               5             Mtrace2 Augmented Response Block

   An mtrace2 message MUST contain exactly one from being
      received by the client, the client MAY issues another Mtrace2
      Query header.  A
   multicast router that sends an mtrace2 Request or with the lower number of hops until it receives a 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
   multicast router that adds one mtrace2 Standard Response block to
   given mtrace2 message MAY append one from
      the FHR.

   Multicast Address: 32 bits or multiple Augmented Response
   blocks.

   The TLV type 128 bits
      This field is defined specifies an IPv4 or IPv6 address, which can be either:

      m-1:  a multicast group address to be "0x1" and "0x2" for mtrace2
   Queries and Requests, respectively.  An mtrace2 message containing traced; or,

      m-2:  all 1's in case of IPv4 or the type "0x1" is an mtrace2 Query.  It unspecified address (::) in
            case of IPv6 if no group-specific information is sent by desired.

   Source Address: 32 bits or 128 bits
      This field specifies an mtrace2 querier
   (i.e., IPv4 or IPv6 address, which can be either:

      s-1:  an mtrace2 client).  It is changed unicast address of the source to "0x2" by be traced; or,

      s-2:  all 1's in case of IPv4 or the proper
   last-hop router.  The type field unspecified address (::) in
            case of IPv6 if no source-specific information is changed to "0x3" when desired.
            For example, the packet client is completed and sent as tracing a (*,g) group state.

      Note that it is invalid to have a source-group combination of
      (s-2, m-2).  If a router receives such combination in an mtrace2 Reply from Mtrace2
      Query, it MUST silently discard the first-hop router
   to Query.

   Mtrace2 Client Address: 32 bits or 128 bits
      This field specifies the querier.

5. Mtrace2 Query Header

   The mtrace2 supports both client's IPv4 address or IPv6
      global address.  This address MUST be a valid unicast address, and IPv6.  If the mtrace2 Query
      therefore, MUST NOT be all 1's or
   Reply arrives in an IPv4 packet, all addresses specified in the
   mtrace2 messages must be with IPv4 addresses. unspecified address.  The mtrace2 message
      Mtrace2 Reply will be sent to this address.

   Query ID: 16 bits
      This field is carried used as a UDP packet.  The UDP source port
   is uniquely selected by unique identifier for this Mtrace2 Query
      so that duplicate or delayed Reply messages may be detected.

   Client Port #: 16 bits
      This field specifies the local host operating system.  The UDP destination port is the IANA reserved mtrace2 UDP port number (see
   Section 13).  The UDP checksum MUST for receiving
      the Mtrace2 Reply packet.

3.2.2.  Mtrace2 Extended Query Block

   There may be a sequence of optional Extended Query Blocks that follow
   an Mtrace2 Query to further specify any information needed for the
   Query.  For example, an Mtrace2 client might be valid interested in mtrace2 messages.

   The mtrace2 message includes tracing
   the common mtrace2 Query header path the specified source and group would take based on a certain
   topology.  In which case, the client can pass in the multi-topology
   ID as
   follows. the Value for an Extended Query Type (see below).  The header Extended
   Query Type is only filled in by the originator of extensible and the
   mtrace2 Query; intermediate routers MUST NOT modify any behavior of the
   fields. new types will be
   addressed by seperate documents.

   The Mtrace2 Extended Query Block is formatted 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
                                                     +-+-+-+-+-+-+-+-+
                                                     |    # hops     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                      Multicast Address                        |
     |                                                               |
     +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
     |                                                               |
     |                        Source Address                         |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |           Length              |                    Mtrace2 Client Address                     |
     |                                                               |      MBZ    |T|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Extended Query ID Type      |        Client Port #           Value ....          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 1

5.1.  # hops: 8

   MBZ: 7 bits
      This field specifies the maximum number of hops that the mtrace2
   client wants to trace. must be zeroed on transmission and ignored on
      reception.

   T-bit (Transitive Attribute): 1 bit
      If there is some error condition in the
   middle of the path that prevents an mtrace2 Reply from being received TLV type is unrecognized 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.

5.2.  Multicast Address

   This field specifies the 32 bits length IPv4 or 128 bits length IPv6
   multicast address to be traced, or receiving router, then this
      TLV is filled with "all 1" in case of
   IPv4 either discarded or forwarded along with the unspecified address (::) in case Query,
      depending on the value of IPv6 if no
   group-specific information this bit.  If this bit is set, then the
      router MUST forward this TLV.  If this bit is desired.  Note that non-group-specific
   mtrace2 clear, the router
      MUST specify source address.

5.3.  Source Address send an mtrace2 Reply with an UNKNOWN_QUERY error.

   Extended Query Type: 16 bits
      This field specifies the 32 bits length IPv4 or 128 bits length IPv6
   address type of the multicast source for Extended Query Block.

   Value: 16 bits
      This field specifies the path being traced, or is
   filled with "all 1" in case value of IPv4 or with the unspecified address
   (::) in case this Extended Query.

3.2.3.  Mtrace2 Request

   The format of IPv6 if no source-specific information such as a
   trace for RPT in PIM-SM an Mtrace2 Request message is desired.  Note that non-source-specific
   traceroutes may not be possible with certain multicast routing
   protocols.

5.4. similar to an Mtrace2 Client Address

   This
   Query except the Type field specifies is 0x02.

   When a LHR receives an Mtrace2 Query message, it would turn the 32 bits length IPv4 or 128 bits length IPv6
   global address Query
   into a Request by changing the Type field of the mtrace2 client. Query from 0x01 to
   0x02.  The trace starts at this
   client address and proceeds toward LHR would then append an Mtrace2 Standard Response Block
   (see Section 3.2.5) of its own to the traffic source.

5.5. Request message before sending
   it upstream.  The upstream routers would do the same without changing
   the Type field until one of them is ready to send a Reply.

3.2.4.  Mtrace2 Reply

   The format of an Mtrace2 Reply message is similar to an Mtrace2 Query ID: 16 bits

   This
   except the Type field is used as 0x03.

   When a unique identifier for this mtrace2 FHR or a RP receives an Mtrace2 Request message which is
   destined to itself, it would append an Mtrace2 Standard Response
   Block (see Section 3.2.5) of its own to the Request message.  Next,
   it would turn the Request message into a Reply by changing the Type
   field of the Request so
   that duplicate or delayed Replies may be detected.

5.6.  Client Port #

   Mtrace2 from 0x02 to 0x03.  The Reply is sent back message would then
   be unicated to the address Mtrace2 client specified in an the Mtrace2 Client
   Address field.  This field specifies the UDP port

   There are a number the of cases an intermediate router will send Mtrace2 Reply.  This client port number MUST NOT be
   changed by any router.

6. might return a
   Reply before a Request reaches the FHR or the RP.  See Section 4.1.1,
   Section 4.2.2, Section 4.3.3, and Section 4.5 for more details.

3.2.5.  IPv4 Mtrace2 Standard Response Block

   Each intermediate IPv4 router in a trace path appends "response data
   block" to

   This section describes the forwarded trace packet. message format of an IPv4 Mtrace2 Standard
   Response Block.  The standard response data
   block looks as follows. Type field is 0x04.

     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              |      MBZ      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      Query Arrival Time                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Incoming Interface Address                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Outgoing Interface Address                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Previous-Hop                   Upstream 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 bits
      This field 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 Mtrace2 Query or Request packet at this
      router.  The 32-
   bit 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.

      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

      Note that Mtrace2 does not require synchronizing NTP timestamp among all the routers along paths on the path to
      have synchronized clocks in order to measure one-way latency.  The use of

      Additionally, Query Arrival Time is useful to measure for measuring the packets per second (PPS).
   Suppose
      packet rate.  For example, suppose that a client issues two queries Q1 and Q2,
      queries, and the corresponding requests R1 and R2 arrive at router
      X at t1 time T1 and t2, T2, then the client would be able to calculate compute the PPS at
      packet rate on router X by using the packet count results at t1 information
      stored in the R1 and t2.

6.3. R2, and the time T1 and T2.

   Incoming Interface Address: 32 bits
      This field specifies the address of the interface on which packets
      from this the source and group or the RP 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 the source and group flow or the RP are expected to transmit towards the specified destination,
      receiver, or 0 if unknown or unnumbered.

6.5.  Previous-Hop  This is also the address
      of the interface on which the Mtrace2 Query or Request arrives.

   Upstream Router Address: 32 bits
      This field specifies the address of the upstream router from which
      this router expects packets from this source.  This may be a
      multicast group (e.g.  ALL-
   [protocol]-ROUTERS.MCAST.NET)  ALL-[protocol]-ROUTERS.MCAST.NET) if the previous hop
      upstream router 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" all 1's if no
      count can be reported.  This counter may have the same value as
      ifHCInMulticastPkts from the IF-MIB [12] [9] for this interface.

6.7.

   Output packet count on outgoing interface: 64 bits bit
      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" all 1's if no count can be reported.
      This counter may have the same value as ifHCOutMulticastPkts from
      the IF-
   MIB IF-MIB [9] 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 the router to the specified group, or "all 1" all 1's if no
      count can be reported.  If the S bit is set, set (see below), the count
      is for the source network, as specified by the Src Mask field. field (see
      below).  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] [10] for this
      forwarding entry.

6.9.

   Rtg Protocol: 16 bits
      This field describes the routing protocol unicast routing protocol running between
      this router and the upstream router, and it is used to decide an determine
      the RPF interface for the requested source. specified source or RP.  This value
      should have the same value as ipMcastRouteRtProtocol from the
      IPMROUTE-STD-MIB [13] [10] for this entry.  If the router is not able
      to obtain this value, "all 0" all 0's must be specified.

6.10.

   Multicast Rtg Protocol: 16 bits
      This field describes the multicast routing protocol in use between
   this
      the router and the previous-hop upstream router.  This value should have the
      same value as ipMcastRouteProtocol from the IPMROUTE-STD-MIB [13] [10]
      for this entry.  If the router does not able to cannot obtain this value, "all
   0" all 0's
      must be specified.

6.11.

   Fwd TTL: 8 bits
      This field contains the TTL that a in which an Mtrace2 Request packet is required to have before
   it will can
      be forwarded over towards the outgoing interface.

6.12. source or the RP.

   S: 1 bit

   This S
      If this bit is set, it 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.

6.13.

   Src Mask: 7 bits
      This field contains the number of 1's in the netmask this the 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 4.1 and Section 4.2 will explain how and when the forwarding code
      Forwarding Code is filled.  Defined values are as follows; 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.
                          the specified group towards the source or RP.
   0x02   PRUNE_SENT      This router has sent a prune upstream which
                          applies to the source and group in the
                            mtrace2
                          Mtrace2 Request.
   0x03   PRUNE_RCVD      This router has stopped forwarding for this
                          source and group in response to a request
                          from the next hop downstream router.
   0x04   SCOPED          The group is subject to administrative
                          scoping at this hop. router.
   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. LHR.
   0x07   NOT_FORWARDING  This router is not forwarding this source, source and
                          group out the outgoing interface for an
                          unspecified reason.
   0x08   REACHED_RP      Reached the Rendezvous Point or Core Point.
   0x09   RPF_IF          Mtrace2 Request arrived on the expected
                          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 client.
   0x0D   UNKNOWN_QUERY   A non-transitive Extended Query Type was
                          received by a router discovers there is which does 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 support
                          the
   details.

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

7.  IPv6 Mtrace2
   0x81   NO_SPACE        There was not enough room to insert another
                          Standard Response Block

   Each intermediate IPv6 router in a trace path appends "response data
   block" to the forwarded trace packet.
   0x83   ADMIN_PROHIB    Mtrace2 is administratively prohibited.

3.2.6.  IPv6 Mtrace2 Standard Response Block

   This section describes the message format of an IPv6 Mtrace2 Standard
   Response Block.  The standard response data
   block looks as follows. Type field is also 0x04.

     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              |      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 2          |S|Src Prefix Len |Forwarding Code|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

7.1.

   MBZ: 8 bit

   Must bits
      This field must be zeroed on transmission and ignored on
      reception.

7.2.

   Query Arrival Time: 32 bits
      Same definition described as in Section 6.2

7.3. IPv4.

   Incoming Interface ID: 32 bits
      This field specifies the interface ID on which packets from this the
      source and group or RP are expected to arrive, or 0 if unknown.  This ID
      should be the value taken from InterfaceIndex of the IF-MIB [12] [9]
      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 to which packets from this the
      source and group flow or RP are expected to the specified destination, transmit, or 0 if unknown.  This ID
      should be the value taken from InterfaceIndex of the IF-MIB [9]
      for this interface.  This field is carried in network byte order.

7.5. interface

   Local Address Address: 128 bits
      This field specifies a global IPv6 address that uniquely
      identifies the router.  A  An 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 link-
      local addresses, its link-local address can be specified in this
      field.

7.6.

   Remote Address Address: 128 bits
      This field specifies the address of the previous-hop upstream router, which, in
      most cases, is a link-local unicast address for the queried source
   and destination addresses. upstream
      router.

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

   This

      Note that this may be a multicast group (e.g., ALL-[protocol]-
      ROUTERS.MCAST.NET) if the previous hop upstream router is not known because of
      the workings of the a 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 interface: 64 bits
      Same definition described as in Section 6.6

7.8. IPv4.

   Output packet count on outgoing interface interface: 64 bits
      Same definition described as in Section 6.7

7.9. IPv4.

   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" pair: 64 bits
      Same definition as in IPv4, except if no
   count can be reported.  If the S bit is set, set (see
      below), 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 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 [10]
      for this forwarding entry.

7.10.

   Rtg Protocol: 16 bits
      Same definition described as in Section 6.9

7.11. IPv4.

   Multicast Rtg Protocol: 16 bits
      Same definition described as in Section 6.10

7.12. IPv4.

   MBZ 2: 15 bits
      This field must be zeroed on transmission and ignored on
      reception.

   S: 1 bit

   This S bit indicates that the packet count for the source-group pair
   is for the source network,
      Same definition as determined by masking the source
   address with in IPv4, except the Src Prefix Len field.

7.13. field is
      used to mask the source address.

   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. (0xff).

   Forwarding Code: 8 bits
      Same definition described as in Section 6.14

8. IPv4.

3.2.7.  Mtrace2 Augmented Response Block

   In addition to the standard response block, Standard Response Block, a multicast router on the
   traced path will be able to can optionally add "augumented response block" when it sends one or multiple Augmented Response
   Blocks before sending the mtrace2 Request to its upstream router or sends the Reply to the
   Mtrace2 Client Address.  This augmented response block router.

   The Augmented Response Block is flexible to
   add for various information. purposes such as
   providing diagnosis information (see Section 7) and protocol
   verification.  It's Type field is 0x05, and its format is 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
                                                     +-+-+-+-+-+-+-+-+
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |           Length              |      MBZ      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Augmented Response Type    |           Value ....          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The augmented response block is always appended to mtrace2 TLV header
   (0x04).  The

   MBZ: 8 bits
      This field must be zeroed on transmission and ignored on
      reception.

   Augmented Response Type: 16 bits Type filed of
      This field specifies the augmented response block is
   defined for type of various purposes, such responses from a
      multicast router that might need to communicate back to the
      Mtrace2 client as well as diagnosis (as in Section 12)
   and protocol verification.  The packet length of the augmented
   response block is specified in multicast routers on the augmented response block TLV
   header as seen in Section 4.1. traced
      path.

      The following augmented response block type Augmented Response Type is defined: defined as follows:

          Code    Type
        ======    =================================================
          ====    ===============================================
          0x01    # Mtrace2 of the returned Standard Response Blocks Returned

      When the NO_SPACE error occurs, occurs on a router, the router sends back the mtrace2
   Reply with contained data (i.e., all appended response blocks), and
   continues should send
      the mtrace2 Query by sending an mtrace2 original Mtrace2 Request received from the downstream router
      as will be
   described in Section 9.3. a Reply back to the Mtrace2 client, and continue with a new
      Mtrace2 Request.  In this mtrace2 the new Request, the router
   appends the augmented response block would add a
      Standard Response Block followed by an Augmented Response Block
      with 0x01 as the code "0x01" Augmented Response Type, and the number of the
      returned mtrace2 response blocks.  Every router between
   this router and Mtrace2 Standard Response Blocks as the first-hop Value.

      Each upstream router can would recognize the limit total number of hops the
      Request has been traced so far by referring adding this number and the # hops
      number of the Standard Response Block in the header. current Request
      message.

      This document only defines the above augmented response block type
   and does not define other augmented response block types.  Specifing one Augmented Response Type in the
      Augmented Response Block.  The description on how to deal with provide
      diagnosis information using the Augmented Response Block is out of
      the scope of this document, and will be also described addressed in separate
      documents.

9.  Router Behavior

   All

   Value: variable length
      The format is based on the Augmented Response Type value.  The
      length 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 value field is Length field minus 6.

4.  Router Behavior

   This section describes the hop limit remaining MUST be forwarded normally, as
   MUST a unicast packet that has TTL or router behavior in the hop limit remaining and is
   not addressed to this router.

9.1. context of Mtrace2
   in details.

4.1.  Receiving Mtrace2 Query

   An mtrace2 Mtrace2 Query message is an mtrace2 Mtrace2 message with no response
   blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 mtrace2.

9.1.1. of 0x01.

4.1.1.  Query Packet Verification

   Upon receiving an mtrace2 Mtrace2 Query message, a router MUST examine
   whether the Multicast Address and the Source Address are a valid
   combination as specified in Section 3.2.1, and whether the Mtrace2
   Client Address is a valid IP unicast address.  If either one is
   invalid, the Query MUST be silently ignored.

   Mtrace2 supports non-local client to the LHR.  It is up to the
   implementation to filter out such queries.

   In the case when it is a local client, the router must then examine
   the Query to see if it is the proper last-hop router LHR for the destination address
   in the packet.  It is the proper last-hop router LHR 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, LHR, or it cannot
   make that determination, it does one of two things depending if on
   whether the Query was received via multicast or unicast.  If the
   Query was received via multicast, then it MUST be silently dropped. discarded.
   If it was received via unicast, the router turns the Query into a forwarding code of WRONG_LAST_HOP
   is noted
   Reply message by changing the TLV type to 0x03 and processing continues appending a
   Standard Response Block with a Forwarding Code of WRONG_LAST_HOP.
   The rest of the fields in the Standard Response Block MUST be zeroed.
   The router then sends the Reply message to the Mtrace2 Client Address
   on the Client Port # as specified in Section 9.2. the Mtrace2 Query.

   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 of previously processed queries keyed by the Mtrace2 Client
   Address and Query ID pair.  The duration of the previous Query message that was processed, and
   ignoring future messages with the same Mtrace2 Client Address and
   Query ID). cached entries is
   implementation specific.  Duplicate Request messages MUST NOT be
   ignored in this manner.

9.1.2.

4.1.2.  Query Normal Processing

   When a router receives an mtrace2 Mtrace2 Query and it determines that it is
   the proper last-hop router, LHR, it it changes turns the Query to a Request by changing the TLV
   type from 0x01 to 0x2 and
   treats it like an mtrace2 Request 0x02, 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
   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. 4.2.

4.2.  Receiving Mtrace2 Request

   An mtrace2 Mtrace2 Request is a traceroute an Mtrace2 message with some number of
   response blocks filled in, and that uses TLV type 0x2 for IPv4 and IPv6
   mtrace2.

9.2.1. of 0x02.
   With the exception of the LHR, whose Request was just converted from
   a Query, each Request received by a router should have at least one
   Standard Response Block filled in.

4.2.1.  Request Packet Verification

   If the mtrace2 Mtrace2 Request does not come from an adjacent host or router,
   it MUST be silently ignored.  If or 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] [4] for IPv6), it MUST be silently
   ignored.  GTSM [14] [12] SHOULD be used by the router to determine whether
   the host or router is adjacent or not.

9.2.2.

   If the sum of the number of the Standard Response Blocks in the
   received Mtrace2 Request and the value of the Augmented Response Type
   of 0x01, if any, is equal or more than the # Hops in the Mtrace2
   Request, it MUST be silently ignored.

4.2.2.  Request Normal Processing

   When a router receives an mtrace2 Request, Mtrace2 Request message, 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 Forwarding
   Code N" should be interpreted as "if forwarding code Forwarding Code is not already
   set, set forwarding code Forwarding Code to N".

   1.   If there is room in the current buffer (or the router can
        efficiently allocate more space to use), insert   Prepare a new response
        block into Standard Response Block to be appended to the packet
        and fill in the Query Arrival Time, Outgoing Interface Address
        (for IPv4 mtrace2) IPv4) or Outgoing Interface ID (for IPv6 mtrace2), IPv6), 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 IPv4).  Note that the packet to Outgoing Interface
        is the address specified in one on which the Mtrace2 Client Address field and continue the trace as described
        in Section 9.3. Request message arrives.

   2.   Attempt to determine the forwarding information for the
        specified source and group specified, group, 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 a
        "phantom" state created only for the purpose of the trace, such
        as "dry-
        run". "dry-run."

        If using a shared-tree protocol and there is no source-specific
        state, or if no source-specific information is desired (i.e.,
        "all 1"
        all 1's 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 Forwarding Code of NO_ROUTE, sets the remaining fields that
        have not yet been filled in to zero, and then forwards the
        packet sends an Mtrace2
        Reply back to the mtrace2 client as described in Section 9.3. Mtrace2 client.

   4.   Fill in the Incoming Interface Address, Previous-Hop Upstream Router Address,
        Input Packet Count, Total Number of Packets, Routing Protocol,
        S, and Src Mask from (or Src Prefix Len for IPv6) using the
        forwarding information that
        was determined. determined by the step 2.

   5.   If mtrace2 Mtrace2 is administratively prohibited, note the appropriate
        forwarding code (ADMIN_PROHIB). Forwarding
        Code of ADMIN_PROHIB.  If mtrace2 Mtrace2 is administratively prohibited
        and any of the fields as filled in the 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 Outgoing interface is not enabled for multicast, note
        forwarding code
        Forwarding Code of NO_MULTICAST.  If the reception Outgoing interface is
        the interface from which the router would expect data to arrive
        from the source, note forwarding code RPF_IF.  Otherwise, if  If the
        reception Outgoing
        interface is not one to which the router would forward data from
        the source or RP to the group, a forwarding Forwarding code of WRONG_IF is
        noted.  In the above three cases, the router will return an
        Mtrace2 Reply and terminate the trace.

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

   8.   If this router is the Rendezvous Point or Core RP for the group, note a
        forwarding code Forwarding Code
        of REACHED_RP is noted. REACHED_RP.  The router will send an Mtrace2 Reply and
        terminate the trace.

   9.   If this router has sent a prune upstream which applies to the
        source and group in the mtrace2 Mtrace2 Request, it notes forwarding
        code Forwarding
        Code of PRUNE_SENT.  If the router has stopped forwarding
        downstream in response to a prune sent by the next hop downstream router,
        it notes forwarding code Forwarding Code of PRUNE_RCVD.  If the router should
        normally forward traffic downstream for this source and group downstream
        but is not, it notes forwarding code Forwarding Code of 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 Mtrace2 client, it
        notes Forwarding Code of REACHED_GW.  The router continues the
        processing as described in Section 4.5.

   11.  If the total number of the Standard Response Blocks, including
        the newly prepared one, and the value of the Augmented Response
        Type of 0x01, if any, is less than the # Hops in the Request,
        the packet is then sent on forwarded to the previous hop or the Mtrace2
        Client Address upstream router 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, 4.3; otherwise, the router will silently discard the message.  When the
   router receives an mtrace2 Request message whose destination address packet is the router's interface address, the router returns sent as an ICMP Port
   unreachable Mtrace2
        Reply to the Mtrace2 Client Address, and the mtrace2 client may
   then issue another mtrace2 Query with the lower number of # hops.

9.3. as described in Section 4.4.

4.3.  Forwarding Mtrace2 Request

9.3.1.

   This section describes how an Mtrace2 Request should be forwarded.

4.3.1.  Destination Address

   If the Previous-hop upstream router for the mtrace2 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),
   request, the
   packet Mtrace2 Request is sent to that router.  If the Incoming Interface
   interface is known but the Previous-hop upstream router is not known, not, the packet Mtrace2
   Request is sent to an appropriate multicast address on the Incoming Interface.
   interface.  The
   appropriate multicast address may SHOULD depend on the multicast
   routing protocol in use, such as ALL-[protocol]-ROUTERS.MCAST.NET.
   It MUST be a link-scoped group (i.e. 224/24 for IPv4, FF02::/16 for
   IPv6), and MUST NOT be ALL-SYSTEMS.MCAST.NET (224.0.0.1) for IPv4 and
   All Nodes Address (FF02::1) for IPv6, and IPv6.  It MAY also be ALL-ROUTERS.MCAST.NET 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. multicast address.

4.3.2.  Source Address

   An mtrace2 Mtrace2 Request should be sent with the address of the router's
   reception Incoming
   interface.  However, if the router's Incoming interface address is unnumbered, the
   router can use one of its numbered interface address as the source
   address.

   When

4.3.3.  Appending Standard Response Block

   An Mtrace2 Request MUST be sent upstream towards the source or the RP
   after appending a Standard Response Block to the end of the received
   Mtrace2 Request.  The Standard Response Block includes the multicast
   states and statistics information of the router described in
   Section 3.2.5.

   If appending the Standard Response Block would make the Mtrace2
   Request packet longer than the MTU of the Incoming Interface, or, in
   the case of IPv6, longer than 1280 bytes, the router MUST change the
   Forwarding Code in the REACHED_GW code is noted, last Standard Response Block of the received
   Mtrace2 Request into NO_SPACE.  The router then turns the Request
   into a Reply, and sends back the mtrace2 Reply as described in Section 9.4.  In addition to that, it must 4.4.

   The router will continue the
   mtrace2 Query with a new Request by proxying the original querier as in Section 9.5.

   When copying from the NO_SPACE error occurs, old
   Request excluding all the router sends back response blocks, followed by the mtrace2
   Reply previously
   prepared Standard Response Block, and an Augmented Response Block
   with contained data Augmented Response Type of 0x01 and the NO_SPACE error code number of the returned
   Standard Response Blocks as in
   Section 9.4, and continues the mtrace2 Query by sending an mtrace2 value.  The new Request containing is then
   forwarded upstream.

4.4.  Sending Mtrace2 Reply

   An Mtrace2 Reply MUST be returned to the same mtrace2 Query header and its standard and
   augmented response blocks. client by a router if the
   total number of the traced routers is equal to the # Hops in the
   Request.  The corresponding augmented response
   block type total number of the traced routers is "# Mtrace2 the sum of the
   Standard Response Blocks Returned" described in
   Section 8.

9.4.  Sending Mtrace2 Reply

9.4.1. the Request (including the one just
   added) and the number of the returned blocks, if any.

4.4.1.  Destination Address

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

9.4.2. Mtrace2 Request.

4.4.2.  Source Address

   An mtrace2 Mtrace2 Reply should SHOULD be sent with the address of the router's
   reception
   Outgoing interface.  However, if the router's Outgoing interface address is
   unnumbered, the router can use one of its numbered interface address
   as the source address.

9.5.

4.4.3.  Appending Standard Response Block

   An Mtrace2 Reply MUST be sent with the prepared Standard Response
   Block appended at the end of the received Mtrace2 Request except in
   the case of NO_SPACE forwarding code.

4.5.  Proxying Mtrace2 Query

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

   At the same time, the gateway prepares originates a new mtrace2 Mtrace2 Query message.
   The gateway uses message
   by copying the original mtrace2 Query Mtrace2 header as (the Query or Request without
   any of the base for response blocks), and makes the new mtrace2 Query; it changes as follows:

   o  sets the Mtrace2 Client Address to its
   Incoming Interface RPF interface's address and as the Mtrace2 Client Port # to Address;

   o  uses its own port
   (which may be the same as the mtrace2 port number as the gateway is
   listening on that port), and Client Port #; and,

   o  decreases # hops according to Hops by the number of standard response blocks in the Standard Response Block that
      was just returned mtrace2 Reply from the
   gateway. as a Reply.

   The mtrace2 new Mtrace2 Query message is then sent to the previous-hop upstream router or
   to an appropriate multicast address on the Incoming
   Interface. RPF interface.

   When the gateway receives the mtrace2 an Mtrace2 Reply from whose Query ID matches the first-hop router
   or any intermediate router,
   one in the original Mtrace2 header, it MUST forward relay the mtrace2 Mtrace2 Reply
   back to the mtrace2 querier Mtrace2 client by replacing the Reply's header with the
   original mtrace2 Query Mtrace2 header.

9.6.  If the gateway does not receive the
   corresponding Mtrace2 Reply within the [Mtrace Reply Timeout] period
   (see Section 5.8.4), then it silently discards the original Mtrace2
   Query or Request message, and terminates the trace.

4.6.  Hiding Information

   Information about a domain's topology and connectivity may be hidden
   from mtrace2 the Mtrace2 Requests.  The Forwarding Code of INFO_HIDDEN forwarding code may be
   used to note that, for that.  For example, the incoming interface address and
   packet count are for the entrance to on the domain ingress router of a domain, and the outgoing
   interface address and packet count are on the exit from egress router of the domain by specifying
   "all 1".  The
   can be specified as all 1's.  Additionally, the source-group packet
   count (Section 6.8 (see Section 3.2.5 and Section 7.9)
   is from router, but 3.2.6) within the domain may be "all 1"
   all 1's if it is hidden.

10.

5.  Client Behavior

10.1.

   This section describes the behavior of an Mtrace2 client in details.

5.1.  Sending Mtrace2 Query

10.1.1.

   An Mtrace2 client initiates an Mtrace2 Query by sending the Query to
   the LHR of interest.

5.1.1.  Destination Address

   If an Mtrace2 client knows the proper LHR, it unicasts an Mtrace2
   Query packet to that router; otherwise, it MAY send the 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 LHR 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 5.4 on determining the last-hop router.

10.1.2. LHR.

5.1.2.  Source Address

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

10.2.

5.2.  Determining the Path

   The

   An Mtrace2 client could send a small number of an initial query Query messages with a large "# hops" field, #
   Hops, 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" # 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 non-responding hop,
   in the hopes that further hops may respond.  These attempts should
   continue until a user-defined the [Mtrace Reply Timeout] timeout has occurred.

   See also Section 10.6 5.6 on receiving the results of a trace.

10.3.

5.3.  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), 5.8), 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 7.3 and Section 12.4.

10.4. 7.4.

5.4.  Last Hop Router (LHR)

   The mtrace2 querier Mtrace2 client 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 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
   last-hop router SHOULD ignore any mtrace2 Mtrace2 Request received via
   multicast.

10.5.

5.5.  First Hop Router (FHR)

   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 clients that are not unicast reachable from the
   first-hop first-
   hop router.  However, mtrace2  Mtrace2, however, does not reserve require any IPv4/IPv6
   multicast addresses for mtrace2 the Mtrace2 Replies.  Every mtrace2 Mtrace2 Reply is
   sent to the unicast address specified in unicast address specified in the Mtrace2 Client Address
   field of the Mtrace2 Reply.

5.6.  Broken Intermediate Router

   A broken intermediate router might simply not understand Mtrace2
   packets, and drop them.  The Mtrace2 client will get no Reply at all
   as a result.  It should then perform a hop-by-hop search by setting
   the # Hops field until it gets an Mtrace2 Reply.  The client may use
   linear or binary search; however, the latter is likely to be slower
   because a failure requires waiting for the [Mtrace Reply Timeout]
   period.

5.7.  Non-Supported Router

   When a non-supported router receives an Mtrace2 Query or Request
   message whose destination address is a multicast address, the router
   will silently discard the message.

   When the router receives an Mtrace2 Query which is destined to
   itself, the router would return an ICMP port unreachable to the
   Mtrace2 client.  On the other hand, when the router receives an
   Mtrace2 Request which is destined to itself, the router would return
   an ICMP port unreachable to its adjacent router from which the
   Request receives.  Therefore, the Mtrace2 Client Address field
   of client needs to terminate
   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 trace when the [Mtrace Reply at all
   from its mtrace2 Requests.  It should Timeout] timeout has occurred, and
   may then perform issue another Query with a hop-by-hop
   search by setting the lower 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. # Hops.

5.8.  Mtrace2 Termination

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

10.7.1.

5.8.1.  Arriving at source 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 Upstream Router is zero.

10.7.2.

5.8.2.  Fatal error Error

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

10.7.3.

5.8.3.  No previous hop Upstream Router

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

10.7.4.  Traceroute shorter than requested

   If

5.8.4.  Reply Timeout

   This document defines the trace that is returned [Mtrace Reply Timeout] value, which is shorter than requested (i.e. the
   number of response blocks used
   to time out an Mtrace2 Reply as seen in Section 4.5, Section 5.2, and
   Section 5.7.  The default [Mtrace Reply Timeout] value is smaller than the "# hops" field), 10
   (seconds), and can be manually changed on the
   trace encountered an error Mtrace2 client and could not continue.

10.8.
   routers.

5.9.  Continuing after an error Error

   When the NO_SPACE error occurs, as described in Section 9.3, the
   multicast routers sends 4.2, a router
   will send back the mtrace2 an Mtrace2 Reply to the address
   specified in the Mtrace2 Client Address field in the mtrace2 Query
   header. client, and continue
   with a new Request (see Section 4.3.3).  In this which case, the mtrace2 Mtrace2
   client may receive multiple
   mtrace2 Mtrace2 Replies from different routers (along
   along the path).  After path.  When this happens, the client receives multiple mtrace2 Reply messages, it integrates (i.e.
   constructs) MUST treat them as a
   single mtrace2 Mtrace2 Reply message.

   If a trace times out, it is very likely to be because that a router in the middle
   of the path does not support mtrace2. Mtrace2.  That router's address will be
   in the Previous-hop router Upstream Router field of the last entry Standard Response Block in
   the last response packet received. received Reply.  A client may be able to determine (via
   mrinfo or SNMP [11][13]) [11][10]) a list of neighbors of the non-
   responding 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 an upstream router
   is.  However, if all paths but one flow back towards the non-responding non-
   responding router, it is possible to be sure that this is the correct
   path.

11.

6.  Protocol-Specific Considerations

11.1.

   This section describes the Mtrace2 behavior with the present of
   different multicast protocols.

6.1.  PIM-SM

   When an mtrace2 Mtrace2 reaches a PIM-SM RP 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 Mtrace2 Query
   may be unicasted to the RP.

11.2.

6.2.  Bi-Directional PIM

   Bi-directional PIM [7] [5] 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 the sources to the RPA (Rendezvous Rendezvous Point Address) Link (RPL), and
   from
   the RPA which, to receivers without requiring source-specific state.  In
   contrast to PIM-SM, RP Bi-directional PIM always has the state to trace.

   A Designated Forwarder (DF) for a given RPA Rendezvous Point Address
   (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 Mtrace2 Reply reports DF addresses or RPA
   along the path.

11.3.

6.3.  PIM-DM

   Routers running PIM Dense Mode [15] [13] 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 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
   upstream router is known, but the last-hop router LHR 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 LHR for the link (because they won or lost an Assert
   battle) and know who the previous hop upstream router is (because it won an Assert
   battle).  Therefore, mtrace2 Mtrace2 is always able to follow the proper path
   when traffic is flowing.

11.4.

6.4.  IGMP/MLD Proxy

   When an mtrace2 IGMP/MLD Proxy [6] receives an Mtrace2 Query packet reaches on an
   incoming interface of IGMP/
   MLD Proxy [8], interface, it puts notes a WRONG_IF (0x01) value in the Forwarding Code of
   mtrace2 standard response block (as in the
   last Standard Response Block (see Section 6.14) 3.2.5), and sends the
   mtrace2
   Mtrace2 Reply back to the Mtrace2 Client Address.  When client.  On the other hand, when an mtrace2
   Mtrace2 Query packet reaches an outgoing interface of the IGMP/MLD
   proxy, it is forwarded through onto 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

7.  Problem Diagnosis

   This section describes different scenarios Mtrace2 can be used to
   diagnose the
   appropriate multicast router.

12.  Problem Diagnosis

12.1. problems.

7.1.  Forwarding Inconsistencies

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

12.2.

7.2.  TTL or Hop Limit Problems

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

12.3.

7.3.  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 Mtrace2 Request 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 Standard Response Block
   includes a count of the packets forwarded by a node for the specified source-
   group
   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 Standard Response Block
   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.

12.4.

7.4.  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.

7.5.  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.

13.

8.  IANA Considerations

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

13.1. [7].

8.1.  Forwarding Codes

   New Forwarding codes Codes must only be created by an RFC that modifies
   this document's Section 10, 3.2.5 and Section 3.2.6, fully describing the
   conditions under which the new forwarding code Forwarding Code is used.  The IANA may
   act as a central repository so that there is a single place to look
   up forwarding
   codes Forwarding Codes and the document in which they are defined.

13.2.

8.2.  UDP Destination Port and IPv6 Address

   The IANA should allocate UDP destination port for multicast
   traceroute version 2 Mtrace2 upon
   publication of the first RFC.

14.

9.  Security Considerations

14.1.

   This section addresses some of the security considerations related to
   Mtrace2.

9.1.  Addresses in Mtrace2 Header

   An Mtrace2 header includes three addresses, source address, multicast
   address, and Mtrace2 client address.  These addresses MUST be
   congruent with the definition defined in Section 3.2.1 and forwarding
   Mtrace2 messages having invalid addresses MUST be prohibited.  For
   instance, if Mtrace2 Client Address specified in an Mtrace header is
   a multicast address, then a router that receives the Mtrace2 message
   MUST silently discard it.

9.2.  Topology Discovery

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

14.2.  Traffic Rates

9.3.  Characteristics of Multicast Channel

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

14.3.

9.4.  Limiting Query/Request Rates

   Routers should

   A router may limit mtrace2 Mtrace2 Queries and Requests by ignoring some of
   the
   received consecutive messages.  Routers  The router MAY randomly ignore the
   received messages to minimize the processing overhead, i.e., to keep
   fairness in processing queries. queries, or prevent traffic amplification.
   The rate limit is left to the router's implementation.

9.5.  Limiting Reply Rates

   The proxying and NO_SPACE behaviors may result in one Query returning
   multiple Reply messages.  In order to prevent abuse, the routers in
   the traced MAY need to rate-limit the Replies.  The rate limit
   function is left to the router's implementation.

15.

10.  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 Mtrace version 2 specification, the authors would like to
   give special thanks to Tatsuya Jinmei, Bill Fenner, and Steve Casner.
   Also, extensive comments were received from David L. Black, Ronald
   Bonica, Yiqun Cai, Liu Hui, Bharat Joshi, Robert W. Kebler, Heidi Ou,
   Pekka Savola, Shinsuke Suzuki, Dave Thaler, Achmad Husni Thamrin, and
   Cao Wei.

16.

11.  References

16.1.

11.1.  Normative References

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

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

   [2]

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

   [3]

   [4]   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 4291, February 2006.

   [7]

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

   [8]

   [6]   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

   [7]   Narten, T.
         Pusateri, "Automatic IP Multicast Without Explicit Tunnels
         (AMT)", draft-ietf-mboned-auto-multicast-08.txt (work and H. Alvestrand, "Guidelines for Writing an IANA
         Considerations Section in
         progress), October 2007.

16.2. RFCs", RFC 5226, May 2008.

11.2.  Informative References

   [10]

   [8]   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]

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

   [13]

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

   [14]

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

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

   [15]

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

Authors' Addresses

   Hitoshi Asaeda
   Keio University
   Graduate School of Media and Governance
   Fujisawa, Kanagawa  252-0882
   National Institute of Information and Communications Technology
   4-2-1 Nukui-Kitamachi
   Koganei, Tokyo  184-8795
   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, asaeda@nict.go.jp

   WeeSan Lee (editor)
   Juniper Networks, Inc.
   Palo Alto,
   1194 North Mathilda Avenue
   Sunnyvale, CA  94304  94089-1206
   US

   Email: casner@packetdesign.com weesan@juniper.net