MBone Deployment Working Group                             Kevin Almeroth
Internet Engineering Task Force                         UC--Santa Barbara
Internet Draft                                                 Liming Wei
July 2000                                          Redback Networks, Inc.
Expires:  January 2001                                     Dino Farinacci
                                                   Procket Networks, Inc.

                  Multicast Reachability Monitor (MRM)

Status of this Memo

   This document is an Internet-Draft and is in full conformance
   with all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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   The list of current Internet-Drafts can be accessed at

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   MRM facilitates automated fault detection and fault isolation in a
   large multicast routing infrastructure. It is designed to alarm a
   network administrator of multicast reachability problems in close
   to real-time.

   There are two basic types of components in MRM, MRM manager and MRM
   testers. This document specifies the protocol with which the two MRM
   components communicate, the types of operations the testers perform,
   and information an MRM manager can obtain.

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Table of Contents

   Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   1

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   1.1 Partitioning Network Monitoring Tasks  . . . . . . . . . . . .   3

2. Functions of the MRM Mechanism . . . . . . . . . . . . . . . . . .   4
   2.1 Fault Detection  . . . . . . . . . . . . . . . . . . . . . . .   4
   2.2 Fault Isolation  . . . . . . . . . . . . . . . . . . . . . . .   5
   2.3 The Protocol . . . . . . . . . . . . . . . . . . . . . . . . .   5
      2.3.1 MRM Manager Requests  . . . . . . . . . . . . . . . . . .   6 MRM Manager Beacon Message . . . . . . . . . . . . .   7 Test Sender Requests (TSRs)  . . . . . . . . . . . .   7 Test Receiver Requests (TRRs)  . . . . . . . . . . .   8
      2.3.2 Status Reports  . . . . . . . . . . . . . . . . . . . . .  10

3. Use of MRM Well Known Addresses and Ports  . . . . . . . . . . . .  11

4. Message Formats  . . . . . . . . . . . . . . . . . . . . . . . . .  11
   4.1 MRM Message Header . . . . . . . . . . . . . . . . . . . . . .  12
   4.2 MRM Manager Beacon Message . . . . . . . . . . . . . . . . . .  13
   4.3 Test Sender Request (TSR)  . . . . . . . . . . . . . . . . . .  13
   4.4 Test Receiver Requests (TRR) . . . . . . . . . . . . . . . . .  14
   4.5 Status Report to the MRM Manager . . . . . . . . . . . . . . .  16
   4.6 MRM Test Packet  . . . . . . . . . . . . . . . . . . . . . . .  17
   4.7 MRM Request-Ack Messages . . . . . . . . . . . . . . . . . . .  17

5. Authenticating MRM Messages  . . . . . . . . . . . . . . . . . . .  17
   5.1 Generating Authenticated Messages  . . . . . . . . . . . . . .  18
   5.2 Receiving Authenticated Messages . . . . . . . . . . . . . . .  18
   5.3 Key Management . . . . . . . . . . . . . . . . . . . . . . . .  18

6. Security Considerations  . . . . . . . . . . . . . . . . . . . . .  19

7. Different Approaches to Implement MRM  . . . . . . . . . . . . . .  19

8. Example of an MRM Setup  . . . . . . . . . . . . . . . . . . . . .  19

9. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . .  21

10. Authors addresses . . . . . . . . . . . . . . . . . . . . . . . .  21

11. References  . . . . . . . . . . . . . . . . . . . . . . . . . . .  22

Appendix A - Change History . . . . . . . . . . . . . . . . . . . . .  22

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1. Introduction

   The Multicast Reachability Monitor (MRM) is a network fault detection
   and isolation mechanism for administering a multicast routing
   infrastructure. It is proposed in response to requests from network
   managers and users who need more systematic ways to get up-to-date
   multicast reachability status. For these purposes, existing tools are
   inefficient and inconvenient to use across large numbers of systems.
   The companion document [mrm-use] contains additional information on
   justification and usage guidelines for MRM.

   The design goals for MRM include:

   (1) Close to real-time detection and alarm of network problems,
       independent of user input;

   (2) Good coverage over the network, both in terms of the number of
       systems to be monitored, and the types of diagnostics to be

   (3) Good extensibility and relative independence of other specific
       diagnostic tools and protocols (we borrow packet formats from
       RTPv2, but almost nothing else from the RTP protocol). This makes
       it easy to incorporate newer diagnostic tools as they become

1.1 Partitioning Network Monitoring Tasks

   Functionally, the task of monitoring a multicast domain can be
   divided into two subtasks:

   (1) Fault detection
   (2) Fault isolation

   In the fault detection phase, the participating MRM systems do not
   need much detail about the nature of the fault.  The mechanism can
   be very simple and brute force.  Data packets can be originated
   from designated locations in the network and reception conditions
   monitored from other locations.

   In the fault isolation phase, depending on the types of fault
   identified, the MRM manager can use proper tools to isolate the
   fault and hopefully pin-point the location or reasons of the fault.

   The rest of this document is organized as follows, Section 2
   describes the MRM framework and details of the MRM protocol; Section
   3 describes the usage of the well known MRM addresses and ports;
   Section 4 specifies packet formats; Sections 5 discusses the MRM
   authentication mechanisms; Section 6 discusses a few security issues;
   and Section 8 gives an example of MRM setup.

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2. Functions of the MRM Mechanism

   An MRM based fault monitoring system consists of two types of
   components: (1) an MRM manager that configures tests, collects and
   presents fault information, and (2) MRM testers that source or sink
   test traffic. These components collaborate to accomplish the two
   functions of MRM: fault detection and fault isolation.

   The MRM testers can be any routing devices or trusted end hosts.
   They provide statistics about received data packets, to be used to
   derive the network reachability status. These data packets can be
   sourced by a router acting as an MRM tester, in response to a request
   from the MRM manager. A system originating MRM data packets for
   testing purposes is also called a Test Source (TS). A configured
   set of MRM testers receiving the test traffic, and collecting
   receiver statistics are also called Test Receivers (TRs).

   An MRM manager initiates configuration requests to the MRM testers
   and assigns the roles of TSs and TRs. The MRM manager informs the TSs
   and TRs the types of monitoring or diagnostic tests to run. The MRM
   manager also specifies the type of reports the TRs should send.

   To guard against attacks on the MRM systems, IPsec Authentication
   Header (AH) [AH] is used with HMAC-MD5 transformation as the standard
   authentication algorithm.  Authentication should always be enabled,
   especially when MRM is used to monitor production services.

   Note that this document only specifies the types of information an MRM
   manager can obtain, and the protocol used to acquire such
   information. How an MRM manager processes or presents the diagnostic
   information is an implementation issue.  An MRM manager can be as
   simple as a command line wrapper of requests with simple display
   functions, it can also be more sophisticated and incorporated as part
   of a operational network monitoring tool in daily use by a network
   operation center (NOC).

2.1 Fault Detection

   Multicast routing can behave abnormally in different ways. The
   following are a few common types of faults:

   (1) Topological disconnectivity

       The network topology for multicast routing is disconnected.  For
       example when a route for a subset of the networks are not in the
       topology table.

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   (2) Black holes in forwarding path

       No multicast packets can get through to certain receivers, even
       though the network topology is perhaps intact. A possible cause
       could be disabled multicast forwarding. Another possibility is
       pruning errors,n e.g. due to inconsistent actions and timer
       values on a multi-access LAN.

   (3) Excessive/persistent Losses

       Packets flow, but with excessive losses over extended period of
       time. The possible causes include heavy congestion, line errors
       or misuse of forwarding modes, etc.

   (4) Excessive duplicates

       Packets arrive at the receivers, but with large numbers of

   (5) Others

       Other types of fault that can be detected, e.g. non-pruners
       as a failure mode. A non-pruning neighbor can be a sink for all
       multicast traffic at all times, even if no receivers exist behind
       that neighbor. This is "outlawed" by the "MBONE-community" [jhawk].
       Detecting the existence of such system in an inter-domain scenario,
       however, is not trivial.  We leave this task to the next iteration
       of MRM refinement.

2.2 Fault Isolation

   Fault isolation is initiated by the MRM manager. For different types
   of faults detected, various tools can be used to isolate the faults
   to small areas in the network. Currently, the tools available for
   this purpose includes but not limited to mtrace [MTRACE}, MIBs based
   debugging tools based, http-based status report mechanism and remote
   execution mechanisms.

   When one tool is not sufficient, a combination of tools can be
   applied.  In general, MRM is designed to be flexible about the types
   of tools it can utilize.  Integrating the functionality of other
   tools into MRM is an implementation issue for the MRM manager.

2.3 The Protocol

   As stated above, the task of monitoring multicast reachability is
   accomplished by letting an MRM manager configure the MRM testers to
   perform fault detection and isolation tests. The MRM manager
   summarizes or displays the collected reports for the network
   operators, in an implementation specific way.

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   The MRM manager keeps a list of tester addresses. The relevant
   routing devices are administratively configured as candidate MRM
   testers. These testers will become active TSs and TRs once they
   accept and process requests from an MRM manager.

   We chose to use RTPv2 encapsulation for the following MRM messages:
   fault report messages from TRs and optionally some test data packets.
   This is to allow re-use of existing RTP based reception mechanisms.
   Note that despite the use of the RTPv2 packet format, the design
   goals and rules for the MRM message exchange protocol are entirely
   different from those specified in RTP.

2.3.1 MRM Manager Requests

   An MRM manager sends Test Sender requests to the TSs, and Test
   Receiver requests to the TRs.

   The MRM manager optionally transmits periodic beacon requests
   to the well-known MRM multicast address MRM-ADDR (
   that all TSs and TRs listen to. This beacon mechanism has three

   (1) For the TSs and TRs to learn the liveness of the MRM manager;

   (2) As a medium to periodically refresh requests, in order for
       testers to recover lost MRM messages, configurations or state
       (e.g. across reboots).

   (3) Inform a large group of test participants that an MRM session
       has been changed or cancelled.

   The use of beacon messages by the manager is optional primarily
   because multicast connectivity between the manager and TSs and
   TRs may not exist.  As a result, while beacon messages may add
   robustness, they should not be relied on to provide critical
   functionality.  While the manager chooses whether or not to
   send beacon messages, TSs and TRs must be prepared to handle
   these messages.

   The MRM manager may send a request to either a unicast address,
   or multicast address When the message is sent via
   unreliable unicast transport (UDP), the recipient must send a
   positive acknowledgement after it has received that request.
   Unacknowledged request messages are retransmitted.

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   The MRM manager periodically transmits beacon messages to advertise its
   liveness to all MRM testers. This message is UDP-encapsulated.  The
   sender's timestamp can be used to calculate the jitters in delay
   between subsequent beacon messages.

   The recommended default Beacon message interval is 1 minute.  The MRM
   manager may piggyback the manager requests on the beacon messages.
   This potentially reduces the need to individually check and repair
   each tester's setup state, while still able to provide reliability
   through a soft-state refresh mechanism. Test Sender Requests (TSRs)

   A Test Sender request is first unicast delivered to a TS, then
   refreshed through multicast delivery via the MRM beacon mechanism.
   A Test Sender request specifies one of the following two ways to
   generate test packets:

   (1) Local packet trigger. This request includes the following

       (a) intervals between two consecutive test packets;
       (b) format and length of test packets (e.g. RTP/UDP);
       (c) multicast address for the test group.

       If a TS accepts this local packet trigger, it will start sending
       periodic test packets, at intervals specified in the MRM request
       message. The IP address of the MRM manager will be used as the ID
       for all test packets originated by the TS under this request.  To
       detect loops and packet losses, all test packets also contain a
       monotonically increasing sequence number (if encapsulated in RTP,
       this would be the RTP sequence number).

   (2) Proxy packet trigger (see Section 5 for security impacts).

       This request lets a TS send a (sequence of) MRM test packet(s),
       using the IP source address provided by the manager request
       message.  This request contains all parameters a local packet
       trigger has, plus a proxy-source address.

       This request is useful for monitoring intra-domain multicast
       connectivity for external sources.  A proxy packet trigger can be
       used to inject packets into the local domain, pretending there is
       an active source external of the local domain. Inside the domain,
       as far as forwarding is concerned, these packets are
       indistinguishable from packets originated from a real external
       source.  For security reasons, proxy packet triggers should be
       enabled very carefully.

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   TSR messages are also used to stop ongoing tests.  By re-sending
   the original TSR packet, but with a holdtime of zero, a test can
   be stopped.  NOTE:  TRR messages with a holdtime of zero should
   also be sent to each test receiver participating in the test. Test Receiver Requests (TRRs)

   An MRM status request is first addressed to a unicast address of a
   TR, and subsequently should be carried in the MRM manager beacon
   messages sent to

   Each such request carries a holdtime of the request, after which the
   TR can safely discard any information collected.  A TRR with a
   holdtime of zero implies that an ongoing test should be terminated.
   The TRR specifies how each TR should collect the reception data.

   The following are the request types for the TRs:

   (1) Monitor multicast group. This request has the following fields:

       (a) J-bit. If set, the TR will join the specified group, as if it
           were a host with a member of that group.

           If a tester did an IGMP join at the beginning of a test, when
           the MRM request expires, the IGMP group membership should be

           When a TR is instructed to join a data group of an existing
           application (e.g. a heartbeat [heartbeat] group), it is wise
           to assess the impact on the TR system if the data rate is

           Furthermore, the use of existing groups introduces uncertainty
           as to whether the source is actually transmitting.  Because
           TRs expect a constant flow of packets, using existing group
           traffic, which may be bursty, introduces uncertainty at the
           receiver as to whether traffic is flowing but is being lost
           or not being sent.

       (b) The address of the group to be monitored;

       (c) List of source addresses to record reception quality

       (d) Threshold description for triggering fault reports.

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           This draft revision only specifies packet loss based
           threshold.  A fault is detected if the packet loss percentage
           has reached the threshold during the specified time window for
           measurement. Once set, the width of this window is fixed. But
           the starting point (or left edge) of the window keeps moving

           Reception quality data within the measurement window should be
           kept so that threshold calculations can be made continuously
           as the window moves forward in time.

       (e) Maximum and minimum delays to trigger fault report. The report
           is sent at a randomized delay between the minimum and the
           maximum value.

       (f) Type of error reports solicited. It is possible to specify an
           RTCP report (as if the test session uses RTP), or a native MRM
           report.  Currently, MRM only supports RTP-based reports.

   (2) Fault isolation request. This request is sent after a fault is
       detected and identified by the MRM manager. It specifies the tool
       and its associated parameters.

       Details about this request message will be added in a future
       revision of the MRM specification.

   (3) Poll for receiver statistics. This instructs the TR to report the
       statistics (historic data) it has collected via Status Reports.
       The TR will send Status Reports, even if the fault threshold has
       not been reached. Section 2.3.2 describes the status report
       mechanism in detail.

   When large numbers of TRs are activated, a fault in the upstream of a
   tree may result in many TRs sending reports at the same time.  To
   address the issue of possible report implosion, each TR may use one
   of the following two strategies:

   (1) Report via unicast message. The MRM manager assigns a pre-
       determined report-delay (as part of the configuration design
       task) to each TR. Each TR upon detecting a fault, will randomly
       delay the sending of its report based on the pre-set delay
       period. This would allow an MRM system to monitor networks with
       up to thousands of systems without unreasonable compromises in
       detection response times.

   (2) Each TR may be instructed to report the detected faults to the
       well-known MRM group address using the RTCP format
       [RFC1889] and does back-off or suppression when duplicate reports
       from other Testers are seen.  If using this strategy the manager
       should realize that using multicast to report a problem with
       multicast may not be particularly robust.

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       This method allows the use of existing RTP-based monitoring tools
       in the initial deployment and experiments with MRM.  However, it
       will prevent the MRM manager from learning a complete list of
       receivers affected by a specific fault. When multicast routing is
       not working correctly, these reports may not be heard by the MRM
       manager, leaving faults undetected and not alarmed by the MRM
       manager.  It is recommended that all designs include at least a
       subset of TRs that (take turns to) unicast their reports.

   There is ambiguity in MRM not hearing any fault report from a certain
   TR. It could be due to fault-free network status, the crash of the
   TR, or problems in the transport mechanism between the TR and the MRM
   manager. Requiring each TR to frequently report its liveness and to
   only do unicast fault report may work for a moderate number of
   testers, but may put undue burden on the network for larger numbers
   of testers.  A compromising solution is to only report liveness from
   a critical portion of the network and do unicast fault report from a
   subset of the testers. The periodic liveness reports serve two
   purposes: (1) it provides evidence that the tester is still alive;
   (2) it indicates the conditions of the tester functions. The
   request-ack messages are used as tester liveness reports.

   Note that the fault isolation phase does not necessarily require the
   MRM manager to send a Fault Isolation Request to a TR. E.g, in a
   typical network today, a third party mtrace issued by the MRM manager
   may be sufficient to identify the faulty hop excessively dropping
   packets if the tester is not completely blacked out.

2.3.2 Status Reports

   These reports are sent by the TRs to the MRM manager, in response to
   a status request.

   For now, we use RTP [RFC1889] "receiver report (RR)" packet format to
   carry receiver's status reports. It is expected that the MRM-native
   report format (to be defined in future draft revisions) will carry
   more useful information about the routing state and statistics.

   Please refer to RFC1889 for details on the packet formats. Here we
   define the few RTCP items used by MRM (or loosely referred to as RTP
   profile for MRM):

      SSRC (Synchronization source) of packet sender:
         IP address of the Test Sender.

      Extended highest sequence number received:
         Highest sequence number seen by the Test Receiver.

      Fraction loss:
         Percent loss of Test Sender data.

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      Cumulative number of packets lost:
         Total number of RTP data packets from SSRC lost within this
         reception window period.

      Inter-arrival Jitter:
         Set to zero when sent, ignored when received.

   When this report is UDP encapsulated and unicast addressed to the MRM
   manager, it is explicitly acknowledged. The acknowledgement packet
   contains the RTCP header portion of the original packet after the MRM

3. Use of MRM Well Known Addresses and Ports

   Once all TS and TR systems are configured, they join the well-known
   MRM control group MRM-ADDR ( and listen to the well-known

   The MRM beacon messages are periodically sent to UDP
   port 679.

4. Message Formats

   By default, MRM control messages are encapsulated inside UDP, and an
   IP authentication header (AH) [KA98], is inserted in between the IP
   header and the UDP header, as shown below:

      | IP Header |  AH  | UDP header | MRM header |  MRM payload |

   The MRM status report in RTCP format is:

      | IP Header |  AH  | UDP header | RTCP Rcvr Report | MRM header |

   The MRM ACK packet format is:

      | IP Header |  AH  | UDP header | MRM header | RTCP Header |

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   The inserted AH is reproduced below:

       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
      | Next Header   |  Payload Len  |          RESERVED             |
      |                 Security Parameters Index (SPI)               |
      |                    Sequence Number                            |
      |                                                               |
      |                Authentication Data (variable)                 |
      |                                                               |

   As specified in [KA98], the following are the default values for the
   fields above:

      Next Header: 17, the value for UDP protocol.

      Payload Len: 5, when MD5 is used (total length is 7 32-bit words).

      RESERVED: 0 when sent, ignored when received.

      SPI: 0 - 50, when using configured MD5 keys

      Sequence Number: the sequence number

      Authentication Data: message digest

4.1 MRM Message Header

   The MRM message header contains 4 32-bit words.

       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
      |Version| Type  |   Code        |           Holdtime            |
      |                    Target IP address                          |
      |M|    Reserved                 |      MRM message length       |
      |              Timestamp (in milliseconds)                      |

      Version:  4 bits
         This revision defines version 1 of MRM.

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      Type: 4 bits
         The defined message types are:

         0 = Beacon       (from MRM manager to all testers)
         1 = TS Request   (from MRM manager to Test Senders)
         2 = TR Request   (from MRM manager to Test Receivers)
         3 = Status Response  (from TR to the MRM manager)
         4 = TS Request Ack   (from TS to MRM manager)
         5 = TR request Ack   (from TR to MRM manager)
         6 = Status Response Ack  (from MRM manager to TR)

      Code: 8 bits
         Defined according to each packet type.

      Holdtime: 16 bits
         Maximum duration in seconds this message should be honored.

      Target IP address: 32 bits
         The unicast address of the intended recipient of this message.

      M: 1 bit,
         0: last MRM request message in this packet.
         1: more MRM request messages follow in the same packet.

   When multiple MRM messages are grouped into one packet, the IP/AH/UDP
   headers of the second and all subsequent MRM messages are omitted. The
   total length of the IP packet will reflect the the sum of lengths of
   all MRM messages in the packet.

4.2 MRM Manager Beacon Message

   This message is UDP encapsulated, addressed to UDP port MRM-MANAGER-
   PORT.  The outstanding Test Sender Requests and Test Receiver
   Requests are included in the beacon message. The individual MRM
   headers are included with these TSR/TRRs.

4.3 Test Sender Request (TSR)

   There are two code values for a TSR:

      0: Local packet trigger
      1: Proxy packet trigger

   NOTE:  A host-based implementation is not expected to provide
   proxy packet capability.

   Following the MRM message header are the fields for the source
   specification request:

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       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
      |   UDP port of test packets    |R| S | LEN |     Reserved      |
      |              Test group address                               |
      |              Inter-packet delay (millisecond)                 |
      |      Proxy source IP address (for proxy packet trigger)       |

      UDP port of test packets: 16 bits
         UDP port of test packets.

      R: 1 bit
         0: Tester will originate RTP/UDP encapsulated test packets
         1: Tester will originate another kind of packet (not used)

      S: 2 bits
         00: send on the targeted interface only
         01: send on all the multicast enabled interfaces
         10: send on test-send enabled interfaces
         11: Unused

      LEN: 3 bits (optional)
         Size of the packets to be sourced.  The length field represents
         a multiple of 16 bytes.  The range of possible packet sizes is
         16 bytes to 2048 bytes (2^7)*(16 bytes).  The LEN field is
         optional.  If ignored, test senders should send 16 byte packets.

      Reserved: 10 bits
         Set to zero when sent. Ignored with received.

      Inter-packet delay: 32 bits
         Number of milliseconds between consecutive test packets.

      Test group address: 32 bits
         Multicast address of the test group.

      Proxy source IP address: 32 bits
         IP address of the source to proxy packet for. This field
         exists only for a proxy packet trigger request.

4.4 Test Receiver Requests (TRR)

   The following are code values for status request messages:

      0: Monitor multicast group (Monitor request)
      1: Poll for receiver statistics (Poll request)
      2: Fault isolation request (not used in this revision)

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   Message format for monitor and poll requests:

       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
      |J|R|     Reserved              | Number of sources to monitor  |
      |Thres index (0)|  Pkt loss (%) | Reception window (seconds)    |
      |  Min report delay (seconds)   | Max report delay (seconds)    |
      |  Max startup delay (seconds)  |            Reserved           |
      |  UDP port of test packets     |  UDP port for status reports  |
      /          Threshold description block                          /
      |              Test group address                               |
      |              IP address of Source 1                           |
      |             Inter-Packet delay interval from source 1         |
      /                     ...                                       /
      |              IP address of Source n                           |
      |             Inter-Packet delay from source n                  |

      J: 1 bit
         0: Don't join the multicast group to be monitored.
         1: Join the multicast group to be monitored.

      R: 1 bit
         0: Fault report should be sent in RTCP format
         1: Fault report should be sent in native MRM format (not used).

         Zeroed when sent, ignored when received.

      Number of sources to monitor: 16 bit
         The number of sources this target tester should monitor. When
         all sources for the test group are monitored, this field is
         set to 1, and the corresponding source address field is set

      Thres index: 8 bits
         Always 0. Index of the criteria for determining a threshold
         for a fault.  The value of this index determines the content
         for the "Threshold description Block".

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      Pkt loss (%): 8 bits
         Percentage of packet loss. A criteria to determine whether a
         fault has occurred.

      Max report delay (seconds): 16 bits
         Maximum number of seconds within which a fault report must be
         sent after it is detected.

      Min report delay (seconds): 16 bits
         Minimum number of seconds a fault report needs to be sent after
         it is detected. A report should not be sent in less than this

      Max startup delay (seconds): 16 bits
         Max number of seconds the TR can wait before the start of the
         test. The test is considered started if a test packet is
         received, or the "max startup delay" has passed after the
         receipt of this request.

      Reception window (seconds): 16 bits
         Number of seconds used for calculating packet loss percentage.

      UDP port of data packets: 16 bits
         UDP port test data packets use.

      UDP port of status report packets: 16 bits
         UDP port of status report packets.

      Threshold description block: 0 bit
         Variable length, depending on "Thres index". This revision only
         defines threshold index 0, with no threshold description block.

      Test group address: 32 bits
         The IP multicast address for the test group.

      IP address of source 1 .. n: 32 bits
         The IP address of the sources the targeted tester should monitor.
         When the address is, all sources to this group will be

      Inter-packet delay from source 1 .. n: 32 bits
         Intervals between consecutive packets from the source

4.5 Status Report to the MRM Manager

   This MRM revision uses the reception report (RTCP) format based on
   Section 2.3.2. Future revisions will define MRM specific report

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4.6 MRM Test Packet

   MRM test packets are RTPv2/UDP encapsulated. The RTPv2 packet header
   is replicated below for easy of description.

       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
      |V=2|P|X|  CC   |M|     PT      |       sequence number         |
      |                           timestamp                           |
      |           synchronization source (SSRC) identifier            |
      |                   IP address of MRM manager                   |

         Set to 0 when sent, ignored when received.

         Set to 0 when sent, ignored when received.

         Set to 0 when sent, ignored when received.

      Sequence number:
         Sequence number. Set to 0, when a tester is activated.

         System timestamp, in milliseconds.

         IP address of the tester, or a configured 32-bit number that
         uniquely identifies the tester.

4.7 MRM Request-Ack Messages

   The Acknowledgement messages for the Test Sender Request and the
   Status Request provide guarantees that the requests are indeed
   received by the testers, instead of being lost.  The acknowledgement
   packets contain the MRM header and trailer for the respective
   messages, except that the message length and authentication data
   fields are recalculated.

5. Authenticating MRM Messages

   All MRM messages should be authenticated with the MD5 mechanism
   specified here. The fields in the messages are transmitted in the
   clear. Packets that fail the authentication check are discarded by
   the receivers.

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5.1 Generating Authenticated Messages

   The sender of the MRM message decides which authentication key
   is used.

   (1) The MRM message length field is filled with the number of
       bytes in the message;

   (2) The rest of the message is composed;

   (3) The IPSEC AH is constructed;

   (4) The "authentication data" field is zeroed;

   (5) The MRM authentication Key (16 byte long) is appended
       to the MRM message.

   (6) The pad for the key is added. The digest is calculated and
       written into the "authentication data" field.

   The part with the MD5 secret is not transmitted.

5.2 Receiving Authenticated Messages

   The receiver follows the following steps when processing an incoming

   (1) The digest is stored away and the "authentication data"
       field zeroed;

   (2) It finds the key according to the value of "Key ID", and
       the key is appended and the packet properly padded;

   (3) A new digest is calculated.

   A message is discarded if the new digest is different from the one
   carried in the packet.

5.3 Key Management

   We expect to rely on manual key distribution in the initial stages.
   And MRM should be able to utilize the standard secure key management
   mechanism when it becomes available.

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6. Security Considerations

   The strength of the security mechanism here depends on the strength
   of the key and the MD5 algorithm.

   Insufficiently protected TSs and TRs (e.g. by weak keys) can be
   subject to attacks that can cause the TSs and TRs to take actions
   causing harm to the network.

7. Different Approaches to Implement MRM

   MRM is originally targeted at two types of users: network operation
   centers that provide production quality services; and network
   administrators who oversee semi-production or experimental multicast
   services. The former often rely on SNMP-based tools for management
   tasks and typically desire all types of monitoring functionalities to
   be wrapped into the same set of tools. While the later, who usually
   set the stage for production quality offerings, do not normally rely
   on SNMP-based tools and favor task-oriented tools.

   For this reason, this document specifies the native MRM messages and
   operations. A companion document will define the MRM MIB that can
   accomplish the majority of the native MRM tasks.

8. Example of an MRM Setup

   The example shown in this section is for illustration purpose only,
   and does not cover all possible functionalities of the MRM framework.
          .                                                .
  Neighbor.    T1                                T2        . Neighbor
  Domain  .  +----+           +----+           +-----+     . Domain
         ----| BR1|-----------| R2 |-----------| BR3 |--------
          .  +----+           +----+           +-----+     .
          .    |   .                              |        .
               |    .                             |
               |     .-----------------------.    |
               |                              .   |
             +----+                            +-----+
             | R4 |                            | R5  |
             +----+                            +-----+
                 .                              /
                  .           T3               /
                   .        +----+            /
                    --------| R6 |-----------/
                        | MRM Manager |

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   The above is a simple topology used to demonstrate the use of various
   MRM features. Border routers BR1, BR3 and an internal router R6 are
   administratively configured as candidate MRM Testers. The MRM manager
   configures T1 to be a TS, and T2,T3 to be TRs. The following are the
   messages sent by the MRM components.

   (1) MRM manager sends Test Sender request (TSR) to T1.
       Req1 = {Local packet trigger,
               test packet interval = 60,000 (ms),
               RTP/UDP test packet  = TRUE,
               Test group           =}

       T1 acknowledges receipt of Req1.

   (2) MRM manager sends TR request Req2 to T2. Req2 has the following

          J-bit                         = TRUE,
          list of source addresses      = {T1's IP address},
          threshold for fault detection = {20% loss over 10 minutes},
          max delay for fault report    = 10 seconds,
          min delay for fault report    = 0 seconds,
          Test group                    =,

       T2 acknowledges receipt of Req2. Req2 is retransmitted if the
       retransmission timer expires.

   (3) MRM manager sends TR request Req3 to T3. Similar to Req2,
       except the target is T3, and,

          max delay for fault report    = 20 seconds,
          min delay for fault report    = 10 seconds

       By using different (min, max) report times, it can avoid report
       implosion at the MRM manager, when a fault is detected by T2 and T3
       at the same time.

   (4) MRM manager periodically sends beacon messages, carrying Req1 and
       Req2, Req3. The holdtime is set to the remaining lifetime of the
       original request.

   Assume T1 has a fault such that it can only forward 1% of all
   multicast packets, the fault is detected by T2 and T3. T2 randomly
   delays between 0-10 seconds, and sends a fault report to the MRM
   manager.  The MRM manager acknowledges this report. T3 randomly
   delays between 10-20 seconds, and sends its fault report to the MRM
   manager, which is also acknowledged. This concludes the fault
   detection phase.

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   In the fault isolation phase, assume the MRM manager sends a third
   party mtrace request to T2 or T3, and isolates the fault to between
   T1, R2 and T1, R4. The MRM manager can then issue an an alarm to the
   network operator, with proper descriptions of the problem.

   The operation for fault isolation phase might be more complicated for
   other types of fault, e.g. if T1 has lost the ability to forward
   multicast packets completely, T2 and T3 wouldn't have any multicast
   routing state or statistics for mtrace to work, some other mechanisms
   would have to be put in use.

9. Acknowledgment

   We'd like to thank John Meylor, Beau Williamson, Stephen Deering,
   Ishan Wu, Louis Mamakos, Manoj Leelanivas, David Meyer, Bill Fenner
   and Dave Thaler for their comments and suggestions.  We'd like to
   especially TY Lin and Kamil Sarac for filling in missing details from
   the previous version of the specification.

10. Authors addresses

   Kevin Almeroth
   Department of Computer Science
   University of California
   Santa Barbara, CA 93106-5110

   Liming Wei
   Redback Networks, Inc.
   1195 Borregas Avenue
   Sunnyvale, California 94089

   Dino Farinacci
   Procket Networks, Inc.
   3850 North First Street
   San Jose, CA 95134

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11. References

   [mtrace] Steven Casner, Bill Fenner et al. The mtrace tool.

   [mrm-use]Kevin Almeroth, Liming Wei, "Justification and Use of MRM",
            draft, Jan 15, 1999.

   [aboba]  Bernard Aboba, "The Use of SNTP as a Multicast Heartbeat",
            Draft, draft-ietf-mboned-sntp-heart-02.txt.

   [ping]   Jon Postel, "Internet Control Message Protocol", RFC792,
            Information Sciences Institute, 1981.

   [UDP]    Jon Postel, "User Datagram Protocol", RFC768. Information
            Sciences Institute.

   [scope]  Dave Meyer, "Administratively Scoped IP Multicast",
            Draft, draft-ietf-mboned-admin-ip-space-03.txt.

   [MD5]    R. Rivest, "The MD5 Message-Digest Algorithm", RFC1321,
            April, 1992

   [KA98]   Kent Stephen, Randall Atkinson, "IP Authentication Header",
            "draft-ietf-ipsec-auth-header-07.txt", July 1998

Appendix A - Change History

   July 2000 -- revisions since draft-ietf-mboned-mrm-00.txt

   None -- simple resubmission

   October 1999 -- revisions since pre-draft

   (1) Added a TS length field to allow test send packets to be
       specified between 16 bytes and 2048 bytes in 16 byte

   (2) Made usage of beacon messages by the manager optional.
       Test agents are required to be able to process beacon

   (3) Monitoring existing groups is relegated to a later version
       because of the difficulty in monitoring the source to
       determine if it is sending a packet.  When an MRM Test
       Source is used, Test Receivers know when, how many, and
       for how long packets will be sent.  If no packets are
       received the test receiver knows to report 100% loss.
       This assumption is not possible when monitoring existing

   (4) Added additional detail about packet formats and packet
       handling procedures to reduce ambiguity.

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