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rfc:rfc7456

Internet Engineering Task Force (IETF) T. Mizrahi Request for Comments: 7456 Marvell Category: Standards Track T. Senevirathne ISSN: 2070-1721 S. Salam

                                                              D. Kumar
                                                                 Cisco
                                                       D. Eastlake 3rd
                                                                Huawei
                                                            March 2015
                   Loss and Delay Measurement in
        Transparent Interconnection of Lots of Links (TRILL)

Abstract

 Performance Monitoring (PM) is a key aspect of Operations,
 Administration, and Maintenance (OAM).  It allows network operators
 to verify the Service Level Agreement (SLA) provided to customers and
 to detect network anomalies.  This document specifies mechanisms for
 Loss Measurement and Delay Measurement in Transparent Interconnection
 of Lots of Links (TRILL) networks.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7456.

Mizrahi, et al. Standards Track [Page 1] RFC 7456 Loss and Delay Measurement in TRILL March 2015

Copyright Notice

 Copyright (c) 2015 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1. Introduction ....................................................3
 2. Conventions Used in this Document ...............................4
    2.1. Key Words ..................................................4
    2.2. Definitions ................................................4
    2.3. Abbreviations ..............................................5
 3. Loss and Delay Measurement in the TRILL Architecture ............6
    3.1. Performance Monitoring Granularity .........................6
    3.2. One-Way vs. Two-Way Performance Monitoring .................6
         3.2.1. One-Way Performance Monitoring ......................7
         3.2.2. Two-Way Performance Monitoring ......................7
    3.3. Point-to-Point vs. Point-to-Multipoint PM ..................8
 4. Loss Measurement ................................................8
    4.1. One-Way Loss Measurement ...................................8
         4.1.1. 1SL Message Transmission ............................9
         4.1.2. 1SL Message Reception ..............................10
    4.2. Two-Way Loss Measurement ..................................11
         4.2.1. SLM Message Transmission ...........................12
         4.2.2. SLM Message Reception ..............................12
         4.2.3. SLR Message Reception ..............................13
 5. Delay Measurement ..............................................14
    5.1. One-Way Delay Measurement .................................14
         5.1.1. 1DM Message Transmission ...........................15
         5.1.2. 1DM Message Reception ..............................16
    5.2. Two-Way Delay Measurement .................................16
         5.2.1. DMM Message Transmission ...........................17
         5.2.2. DMM Message Reception ..............................17
         5.2.3. DMR Message Reception ..............................18

Mizrahi, et al. Standards Track [Page 2] RFC 7456 Loss and Delay Measurement in TRILL March 2015

 6. Packet Formats .................................................19
    6.1. TRILL OAM Encapsulation ...................................19
    6.2. Loss Measurement Packet Formats ...........................21
         6.2.1. Counter Format .....................................21
         6.2.2. 1SL Packet Format ..................................21
         6.2.3. SLM Packet Format ..................................22
         6.2.4. SLR Packet Format ..................................23
    6.3. Delay Measurement Packet Formats ..........................24
         6.3.1. Timestamp Format ...................................24
         6.3.2. 1DM Packet Format ..................................24
         6.3.3. DMM Packet Format ..................................25
         6.3.4. DMR Packet Format ..................................26
    6.4. OpCode Values .............................................27
 7. Performance Monitoring Process .................................28
 8. Security Considerations ........................................29
 9. References .....................................................29
    9.1. Normative References ......................................29
    9.2. Informative References ....................................30
 Acknowledgments ...................................................31
 Authors' Addresses ................................................32

1. Introduction

 TRILL [TRILL] is a protocol for transparent least-cost routing, where
 Routing Bridges (RBridges) route traffic to their destination based
 on least cost, using a TRILL encapsulation header with a hop count.
 Operations, Administration, and Maintenance [OAM] is a set of tools
 for detecting, isolating, and reporting connection failures and
 performance degradation.  Performance Monitoring (PM) is a key aspect
 of OAM.  PM allows network operators to detect and debug network
 anomalies and incorrect behavior.  PM consists of two main building
 blocks: Loss Measurement and Delay Measurement.  PM may also include
 other derived metrics such as Packet Delivery Rate, and Inter-Frame
 Delay Variation.
 The requirements of OAM in TRILL networks are defined in [OAM-REQ],
 and the TRILL OAM framework is described in [OAM-FRAMEWK].  These two
 documents also highlight the main requirements in terms of
 Performance Monitoring.
 This document defines protocols for Loss Measurement and for Delay
 Measurement in TRILL networks.  These protocols are based on the
 Performance Monitoring functionality defined in ITU-T G.8013/Y.1731
 [Y.1731-2013].

Mizrahi, et al. Standards Track [Page 3] RFC 7456 Loss and Delay Measurement in TRILL March 2015

 o  Loss Measurement: the Loss Measurement protocol measures packet
    loss between two RBridges.  The measurement is performed by
    sending a set of synthetic packets and counting the number of
    packets transmitted and received during the test.  The frame loss
    is calculated by comparing the numbers of transmitted and received
    packets.  This provides a statistical estimate of the packet loss
    between the involved RBridges, with a margin of error that can be
    controlled by varying the number of transmitted synthetic packets.
    This document does not define procedures for packet loss
    computation based on counting user data for the reasons given in
    Section 5.1 of [OAM-FRAMEWK].
 o  Delay Measurement: the Delay Measurement protocol measures the
    packet delay and packet delay variation between two RBridges.  The
    measurement is performed using timestamped OAM messages.

2. Conventions Used in this Document

2.1. Key Words

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [KEYWORDS].
 The requirement level of PM in [OAM-REQ] is 'SHOULD'.  Nevertheless,
 this memo uses the entire range of requirement levels, including
 'MUST'; the requirements in this memo are to be read as 'A MEP
 (Maintenance End Point) that implements TRILL PM
 MUST/SHOULD/MAY/...'.

2.2. Definitions

 o  One-way packet delay (based on [IPPM-1DM]) - the time elapsed from
    the start of transmission of the first bit of a packet by an
    RBridge until the reception of the last bit of the packet by the
    remote RBridge.
 o  Two-way packet delay (based on [IPPM-2DM]) - the time elapsed from
    the start of transmission of the first bit of a packet from the
    local RBridge, receipt of the packet at the remote RBridge, the
    transmission of a response packet from the remote RBridge back to
    the local RBridge, and receipt of the last bit of that response
    packet by the local RBridge.
 o  Packet loss (based on [IPPM-Loss] -  the number of packets sent by
    a source RBridge and not received by the destination RBridge.  In
    the context of this document, packet loss is measured at a
    specific probe instance and a specific observation period.  As in

Mizrahi, et al. Standards Track [Page 4] RFC 7456 Loss and Delay Measurement in TRILL March 2015

    [Y.1731-2013], this document distinguishes between near-end and
    far-end packet loss.  Note that this semantic distinction
    specifies the direction of packet loss but does not affect the
    nature of the packet loss metric, which is defined in [IPPM-Loss].
 o  Far-end packet loss - the number of packets lost on the path from
    the local RBridge to the remote RBridge in a specific probe
    instance and a specific observation period.
 o  Near-end packet loss - the number of packets lost on the path from
    the remote RBridge to the local RBridge in a specific probe
    instance and a specific observation period.

2.3. Abbreviations

 1DM      One-way Delay Measurement
 1SL      One-way Synthetic Loss Measurement
 DMM      Delay Measurement Message
 DMR      Delay Measurement Reply
 DoS      Denial of Service
 FGL      Fine-Grained Label [FGL]
 MD       Maintenance Domain
 MD-L     Maintenance Domain Level
 MEP      Maintenance End Point
 MIP      Maintenance Intermediate Point
 MP       Maintenance Point
 OAM      Operations, Administration, and Maintenance [OAM]
 PM       Performance Monitoring
 SLM      Synthetic Loss Measurement Message
 SLR      Synthetic Loss Measurement Reply
 TLV      Type-Length-Value
 TRILL    Transparent Interconnection of Lots of Links [TRILL]

Mizrahi, et al. Standards Track [Page 5] RFC 7456 Loss and Delay Measurement in TRILL March 2015

3. Loss and Delay Measurement in the TRILL Architecture

 As described in [OAM-FRAMEWK], OAM protocols in a TRILL campus
 operate over two types of Maintenance Points (MPs): Maintenance End
 Points (MEPs) and Maintenance Intermediate Points (MIPs).
            +-------+     +-------+     +-------+
            |       |     |       |     |       |
            |  RB1  |<===>|  RB3  |<===>|  RB2  |
            |       |     |       |     |       |
            +-------+     +-------+     +-------+
               MEP           MIP           MEP
          Figure 1: Maintenance Points in a TRILL Campus
 Performance Monitoring (PM) allows a MEP to perform Loss and Delay
 Measurements on any other MEP in the campus.  Performance Monitoring
 is performed in the context of a specific Maintenance Domain (MD).
 The PM functionality defined in this document is not applicable to
 MIPs.

3.1. Performance Monitoring Granularity

 As defined in [OAM-FRAMEWK], PM can be applied at three levels of
 granularity: Network, Service, and Flow.
 o  Network-level PM: the PM protocol is run over a dedicated test
    VLAN or FGL [FGL].
 o  Service-level PM: the PM protocol is used to perform measurements
    of actual user VLANs or FGLs.
 o  Flow-level PM: the PM protocol is used to perform measurements on
    a per-flow basis.  A flow, as defined in [OAM-REQ], is a set of
    packets that share the same path and per-hop behavior (such as
    priority).  As defined in [OAM-FRAMEWK], flow-based monitoring
    uses a Flow Entropy field that resides at the beginning of the OAM
    packet header (see Section 6.1) and mimics the forwarding behavior
    of the monitored flow.

3.2. One-Way vs. Two-Way Performance Monitoring

 Paths in a TRILL network are not necessarily symmetric, that is, a
 packet sent from RB1 to RB2 does not necessarily traverse the same
 set of RBridges or links as a packet sent from RB2 to RB1.  Even
 within a given flow, packets from RB1 to RB2 do not necessarily
 traverse the same path as packets from RB2 to RB1.

Mizrahi, et al. Standards Track [Page 6] RFC 7456 Loss and Delay Measurement in TRILL March 2015

3.2.1. One-Way Performance Monitoring

 In one-way PM, RB1 sends PM messages to RB2, allowing RB2 to monitor
 the performance on the path from RB1 to RB2.
 A MEP that implements TRILL PM SHOULD support one-way Performance
 Monitoring.  A MEP that implements TRILL PM SHOULD support both the
 PM functionality of the sender, RB1, and the PM functionality of the
 receiver, RB2.
 One-way PM can be applied either proactively or on-demand, although
 the more typical scenario is the proactive mode, where RB1 and RB2
 periodically transmit PM messages to each other, allowing each of
 them to monitor the performance on the incoming path from the peer
 MEP.

3.2.2. Two-Way Performance Monitoring

 In two-way PM, a sender, RB1, sends PM messages to a reflector, RB2,
 and RB2 responds to these messages, allowing RB1 to monitor the
 performance of:
 o  The path from RB1 to RB2.
 o  The path from RB2 to RB1.
 o  The two-way path from RB1 to RB2, and back to RB1.
 Note that in some cases it may be interesting for RB1 to monitor only
 the path from RB1 to RB2.  Two-way PM allows the sender, RB1, to
 monitor the path from RB1 to RB2, as opposed to one-way PM
 (Section 3.2.1), which allows the receiver, RB2, to monitor this
 path.
 A MEP that implements TRILL PM MUST support two-way PM.  A MEP that
 implements TRILL PM MUST support both the sender and the reflector PM
 functionality.
 As described in Section 3.1, flow-based PM uses the Flow Entropy
 field as one of the parameters that identify a flow.  In two-way PM,
 the Flow Entropy of the path from RB1 to RB2 is typically different
 from the Flow Entropy of the path from RB2 to RB1.  This document
 uses the Reflector Entropy TLV [TRILL-FM], which allows the sender to
 specify the Flow Entropy value to be used in the response message.
 Two-way PM can be applied either proactively or on-demand.

Mizrahi, et al. Standards Track [Page 7] RFC 7456 Loss and Delay Measurement in TRILL March 2015

3.3. Point-to-Point vs. Point-to-Multipoint PM

 PM can be applied either as a point-to-point measurement protocol, or
 as a point-to-multi-point measurement protocol.
 The point-to-point approach measures the performance between two
 RBridges using unicast PM messages.
 In the point-to-multipoint approach, an RBridge RB1 sends PM messages
 to multiple RBridges using multicast messages.  The reflectors (in
 two-way PM) respond to RB1 using unicast messages.  To protect
 against reply storms, the reflectors MUST send the response messages
 after a random delay in the range of 0 to 2 seconds.  This ensures
 that the responses are staggered in time and that the initiating
 RBridge is not overwhelmed with responses.  Moreover, an RBridge
 Scope TLV [TRILL-FM] can be used to limit the set of RBridges from
 which a response is expected, thus reducing the impact of potential
 response bursts.

4. Loss Measurement

 The Loss Measurement protocol has two modes of operation: one-way
 Loss Measurement and two-way Loss Measurement.
 Note: The terms 'one-way' and 'two-way' Loss Measurement should not
 be confused with the terms 'single-ended' and 'dual-ended' Loss
 Measurement used in [Y.1731-2013].  As defined in Section 3.2, the
 terms 'one-way' and 'two-way' specify whether the protocol monitors
 performance on one direction or on both directions.  The terms
 'single-ended' and 'dual-ended', on the other hand, describe whether
 the protocol is asymmetric or symmetric, respectively.

4.1. One-Way Loss Measurement

 One-way Loss Measurement measures the one-way packet loss from one
 MEP to another.  The loss ratio is measured using a set of One-way
 Synthetic Loss Measurement (1SL) messages.  The packet format of the
 1SL message is specified in Section 6.2.2.  Figure 2 illustrates a
 one-way Loss Measurement message exchange.

Mizrahi, et al. Standards Track [Page 8] RFC 7456 Loss and Delay Measurement in TRILL March 2015

                      TXp              TXc
        Sender    --------------------------------------
                        \                \
                         \ 1SL   . . .    \ 1SL
                          \                \
                          \/               \/
        Receiver  --------------------------------------
                          RXp              RXc
                   Figure 2: One-Way Loss Measurement
 The one-way Loss Measurement procedure uses a set of 1SL messages to
 measure the packet loss.  The figure shows two non-consecutive
 messages from the set.
 The sender maintains a counter of transmitted 1SL messages, and
 includes the value of this counter, TX, in each 1SL message it
 transmits.  The receiver maintains a counter of received 1SL
 messages, RX, and can calculate the loss by comparing its counter
 values to the counter values received in the 1SL messages.
 In Figure 2, the subscript 'c' is an abbreviation for current, and
 'p' is an abbreviation for previous.

4.1.1. 1SL Message Transmission

 One-way Loss Measurement can be applied either proactively or on-
 demand, although as mentioned in Section 3.2.1, it is more likely to
 be applied proactively.
 The term 'on-demand' in the context of one-way Loss Measurement
 implies that the sender transmits a fixed set of 1SL messages,
 allowing the receiver to perform the measurement based on this set.
 A MEP that supports one-way Loss Measurement MUST support unicast
 transmission of 1SL messages.
 A MEP that supports one-way Loss Measurement MAY support multicast
 transmission of 1SL messages.
 The sender MUST maintain a packet counter for each peer MEP and probe
 instance (test ID).  Every time the sender transmits a 1SL packet, it
 increments the corresponding counter and then integrates the value of
 the counter into the Counter TX field of the 1SL packet.
 The 1SL message MAY be sent with a variable-size Data TLV, allowing
 Loss Measurement for various packet sizes.

Mizrahi, et al. Standards Track [Page 9] RFC 7456 Loss and Delay Measurement in TRILL March 2015

4.1.2. 1SL Message Reception

 The receiver MUST maintain a reception counter for each peer MEP and
 probe instance (test ID).  Upon receiving a 1SL packet, the receiver
 MUST verify that:
 o  The 1SL packet is destined to the current MEP.
 o  The packet's MD level matches the MEP's MD level.
 If both conditions are satisfied, the receiver increments the
 corresponding reception counter and records the new value of the
 counter, RX1.
 A MEP that supports one-way Loss Measurement MUST support reception
 of both unicast and multicast 1SL messages.
 The receiver computes the one-way packet loss with respect to a probe
 instance measurement interval.  A probe instance measurement interval
 includes a sequence of 1SL messages with the same test ID.  The one-
 way packet loss is computed by comparing the counter values TXp and
 RXp at the beginning of the measurement interval and the counter
 values TXc and RXc at the end of the measurement interval (see
 Figure 2):
          one-way packet loss = (TXc-TXp) - (RXc-RXp)     (1)
 The calculation in Equation (1) is based on counter value
 differences, implying that the sender's counter, TX, and the
 receiver's counter, RX, are not required to be synchronized with
 respect to a common initial value.
 It is noted that if the sender or receiver resets one of the
 counters, TX or RX, the calculation in Equation (1) produces a false
 measurement result.  Hence, the sender and receiver SHOULD NOT clear
 the TX and RX counters during a measurement interval.
 When the receiver calculates the packet loss per Equation (1), it
 MUST perform a wraparound check.  If the receiver detects that one of
 the counters has wrapped around, the receiver adjusts the result of
 Equation (1) accordingly.
 A 1SL receiver MUST support reception of 1SL messages with a Data
 TLV.

Mizrahi, et al. Standards Track [Page 10] RFC 7456 Loss and Delay Measurement in TRILL March 2015

 Since synthetic one-way Loss Measurement is performed using 1SL
 messages, obviously, some 1SL messages may be dropped during a
 measurement interval.  Thus, when the receiver does not receive a
 1SL, the receiver cannot perform the calculations in Equation (1) for
 that specific 1SL message.

4.2. Two-Way Loss Measurement

 Two-way Loss Measurement allows a MEP to measure the packet loss on
 the paths to and from a peer MEP.  Two-way Loss Measurement uses a
 set of Synthetic Loss Measurement Messages (SLMs) to compute the
 packet loss.  Each SLM is answered with a Synthetic Loss Measurement
 Reply (SLR).  The packet formats of the SLM and SLR packets are
 specified in Sections 6.2.3 and 6.2.4, respectively.  Figure 3
 illustrates a two-way Loss Measurement message exchange.
                 TXp       RXp             TXc       RXc
   Sender     -----------------------------------------------
                   \       /\                \       /\
                    \      /      . . .       \      /
                 SLM \    / SLR            SLM \    / SLR
                     \/  /                     \/  /
   Reflector  -----------------------------------------------
                      TRXp                      TRXc
                   Figure 3: Two-Way Loss Measurement
 The two-way Loss Measurement procedure uses a set of SLM-SLR
 handshakes.  The figure shows two non-consecutive handshakes from the
 set.
 The sender maintains a counter of transmitted SLM messages and
 includes the value of this counter, TX, in each transmitted SLM
 message.  The reflector maintains a counter of received SLM messages,
 TRX.  The reflector generates an SLR and incorporates TRX into the
 SLR packet.  The sender maintains a counter of received SLR messages,
 RX.  Upon receiving an SLR message, the sender can calculate the loss
 by comparing the local counter values to the counter values received
 in the SLR messages.
 The subscript 'c' is an abbreviation for current, and 'p' is an
 abbreviation for previous.

Mizrahi, et al. Standards Track [Page 11] RFC 7456 Loss and Delay Measurement in TRILL March 2015

4.2.1. SLM Message Transmission

 Two-way Loss Measurement can be applied either proactively or on-
 demand.
 A MEP that supports two-way Loss Measurement MUST support unicast
 transmission of SLM messages.
 A MEP that supports two-way Loss Measurement MAY support multicast
 transmission of SLM messages.
 The sender MUST maintain a counter of transmitted SLM packets for
 each peer MEP and probe instance (test ID).  Every time the sender
 transmits an SLM packet, it increments the corresponding counter and
 then integrates the value of the counter into the Counter TX field of
 the SLM packet.
 A sender MAY include a Reflector Entropy TLV in an SLM message.  The
 Reflector Entropy TLV format is specified in [TRILL-FM].
 An SLM message MAY be sent with a Data TLV, allowing Loss Measurement
 for various packet sizes.

4.2.2. SLM Message Reception

 The reflector MUST maintain a reception counter, TRX, for each peer
 MEP and probe instance (test ID).
 Upon receiving an SLM packet, the reflector MUST verify that:
 o  The SLM packet is destined to the current MEP.
 o  The packet's MD level matches the MEP's MD level.
 If both conditions are satisfied, the reflector increments the
 corresponding packet counter and records the value of the new
 counter, TRX.  The reflector then generates an SLR message that is
 identical to the received SLM, except for the following
 modifications:
 o  The reflector incorporates TRX into the Counter TRX field of the
    SLR.
 o  The OpCode field in the OAM header is set to the SLR OpCode.
 o  The reflector assigns its MEP ID in the Reflector MEP ID field.

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 o  If the received SLM includes a Reflector Entropy TLV [TRILL-FM],
    the reflector copies the value of the Flow Entropy from the TLV
    into the Flow Entropy field of the SLR message.  The outgoing SLR
    message does not include a Reflector Entropy TLV.
 o  The TRILL Header and transport header are modified to reflect the
    source and destination of the SLR packet.  The SLR is always a
    unicast message.
 A MEP that supports two-way Loss Measurement MUST support reception
 of both unicast and multicast SLM messages.
 A reflector MUST support reception of SLM packets with a Data TLV.
 When receiving an SLM with a Data TLV, the reflector includes the
 unmodified TLV in the SLR.

4.2.3. SLR Message Reception

 The sender MUST maintain a reception counter, RX, for each peer MEP
 and probe instance (test ID).
 Upon receiving an SLR message, the sender MUST verify that:
 o  The SLR packet is destined to the current MEP.
 o  The Sender MEP ID field in the SLR packet matches the current MEP.
 o  The packet's MD level matches the MEP's MD level.
 If the conditions above are met, the sender increments the
 corresponding reception counter, and records the new value, RX.
 The sender computes the packet loss with respect to a probe instance
 measurement interval.  A probe instance measurement interval includes
 a sequence of SLM messages and their corresponding SLR messages, all
 with the same test ID.  The packet loss is computed by comparing the
 counters at the beginning of the measurement interval, denoted with a
 subscript 'p', and the counters at the end of the measurement
 interval, denoted with a subscript 'c' (as illustrated in Figure 3).
          far-end packet loss = (TXc-TXp) - (TRXc-TRXp)     (2)
          near-end packet loss = (TRXc-TRXp) - (RXc-RXp)     (3)
 Note: The total two-way packet loss is the sum of the far-end and
 near-end packet losses, that is (TXc-TXp) - (RXc-RXp).

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 The calculations in the two equations above are based on counter
 value differences, implying that the sender's counters, TX and RX,
 and the reflector's counter, TRX, are not required to be synchronized
 with respect to a common initial value.
 It is noted that if the sender or reflector resets one of the
 counters, TX, TRX, or RX, the calculation in Equations (2) and (3)
 produces a false measurement result.  Hence, the sender and reflector
 SHOULD NOT clear the TX, TRX, and RX counters during a measurement
 interval.
 When the sender calculates the packet loss per Equations (2) and (3),
 it MUST perform a wraparound check.  If the reflector detects that
 one of the counters has wrapped around, the reflector adjusts the
 result of Equations (2) and (3) accordingly.
 Since synthetic two-way Loss Measurement is performed using SLM and
 SLR messages, obviously, some SLM and SLR messages may be dropped
 during a measurement interval.  When an SLM or an SLR is dropped, the
 corresponding two-way handshake (Figure 3) is not completed
 successfully; thus, the reflector does not perform the calculations
 in Equations (2) and (3) for that specific message exchange.
 A sender MAY choose to monitor only the far-end packet loss, that is,
 perform the computation in Equation (2), and ignore the computation
 in Equation (3).  Note that, in this case, the sender can run flow-
 based PM of the path to the peer MEP without using the Reflector
 Entropy TLV.

5. Delay Measurement

 The Delay Measurement protocol has two modes of operation: one-way
 Delay Measurement and two-way Delay Measurement.

5.1. One-Way Delay Measurement

 One-way Delay Measurement is used for computing the one-way packet
 delay from one MEP to another.  The packet format used in one-way
 Delay Measurement is referred to as 1DM and is specified in Section
 6.3.2.  The one-way Delay Measurement message exchange is illustrated
 in Figure 4.

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                             T1
              Sender    -------------------         ----> time
                              \
                               \ 1DM
                                \
                                \/
              Receiver  -------------------
                                T2
            Figure 4: One-Way Delay Measurement
 The sender transmits a 1DM message incorporating its time of
 transmission, T1.  The receiver then receives the message at time T2,
 and calculates the one-way delay as:
          one-way delay = T2-T1       (4)
 Equation (4) implies that T2 and T1 are measured with respect to a
 common reference time.  Hence, two MEPs running a one-way Delay
 Measurement protocol MUST be time-synchronized.  The method used for
 synchronizing the clocks associated with the two MEPs is outside the
 scope of this document.

5.1.1. 1DM Message Transmission

 1DM packets can be transmitted proactively or on-demand, although, as
 mentioned in Section 3.2.1, they are typically transmitted
 proactively.
 A MEP that supports one-way Delay Measurement MUST support unicast
 transmission of 1DM messages.
 A MEP that supports one-way Delay Measurement MAY support multicast
 transmission of 1DM messages.
 A 1DM message MAY be sent with a variable size Data TLV, allowing
 packet Delay Measurement for various packet sizes.
 The sender incorporates the 1DM packet's time of transmission into
 the Timestamp T1 field.

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5.1.2. 1DM Message Reception

 Upon receiving a 1DM packet, the receiver records its time of
 reception, T2.  The receiver MUST verify two conditions:
 o  The 1DM packet is destined to the current MEP.
 o  The packet's MD level matches the MEP's MD level.
 If both conditions are satisfied, the receiver terminates the packet
 and calculates the one-way delay as specified in Equation (4).
 A MEP that supports one-way Delay Measurement MUST support reception
 of both unicast and multicast 1DM messages.
 A 1DM receiver MUST support reception of 1DM messages with a Data
 TLV.
 When one-way Delay Measurement packets are received periodically, the
 receiver MAY compute the packet delay variation based on multiple
 measurements.  Note that packet delay variation can be computed even
 when the two peer MEPs are not time-synchronized.

5.2. Two-Way Delay Measurement

 Two-way Delay Measurement uses a two-way handshake for computing the
 two-way packet delay between two MEPs.  The handshake includes two
 packets: a Delay Measurement Message (DMM) and a Delay Measurement
 Reply (DMR).  The DMM and DMR packet formats are specified in
 Sections 6.3.3 and 6.3.4, respectively.
 The two-way Delay Measurement message exchange is illustrated in
 Figure 5.
                            T1          T4
             Sender     -----------------------       ----> time
                             \          /\
                              \         /
                           DMM \       / DMR
                               \/     /
             Reflector  -----------------------
                               T2    T3
             Figure 5: Two-Way Delay Measurement
 The sender generates a DMM message incorporating its time of
 transmission, T1.  The reflector receives the DMM message and records
 its time of reception, T2.  The reflector then generates a DMR

Mizrahi, et al. Standards Track [Page 16] RFC 7456 Loss and Delay Measurement in TRILL March 2015

 message, incorporating T1, T2, and the DMR's transmission time, T3.
 The sender receives the DMR message at T4, and using the four
 timestamps, it calculates the two-way packet delay.

5.2.1. DMM Message Transmission

 DMM packets can be transmitted periodically or on-demand.
 A MEP that supports two-way Delay Measurement MUST support unicast
 transmission of DMM messages.
 A MEP that supports two-way Delay Measurement MAY support multicast
 transmission of DMM messages.
 A sender MAY include a Reflector Entropy TLV in a DMM message.  The
 Reflector Entropy TLV format is specified in [TRILL-FM].
 A DMM MAY be sent with a variable size Data TLV, allowing packet
 Delay Measurement for various packet sizes.
 The sender incorporates the DMM packet's time of transmission into
 the Timestamp T1 field.

5.2.2. DMM Message Reception

 Upon receiving a DMM packet, the reflector records its time of
 reception, T2.  The reflector MUST verify two conditions:
 o  The DMM packet is destined to the current MEP.
 o  The packet's MD level matches the MEP's MD level.
 If both conditions are satisfied, the reflector terminates the packet
 and generates a DMR packet.  The DMR is identical to the received
 DMM, except for the following modifications:
 o  The reflector incorporates T2 into the Timestamp T2 field of the
    DMR.
 o  The reflector incorporates the DMR's transmission time, T3, into
    the Timestamp T3 field of the DMR.
 o  The OpCode field in the OAM header is set to the DMR OpCode.
 o  If the received DMM includes a Reflector Entropy TLV [TRILL-FM],
    the reflector copies the value of the Flow Entropy from the TLV
    into the Flow Entropy field of the DMR message.  The outgoing DMR
    message does not include a Reflector Entropy TLV.

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 o  The TRILL Header and transport header are modified to reflect the
    source and destination of the DMR packet.  The DMR is always a
    unicast message.
 A MEP that supports two-way Delay Measurement MUST support reception
 of both unicast and multicast DMM messages.
 A reflector MUST support reception of DMM packets with a Data TLV.
 When receiving a DMM with a Data TLV, the reflector includes the
 unmodified TLV in the DMR.

5.2.3. DMR Message Reception

 Upon receiving the DMR message, the sender records its time of
 reception, T4.  The sender MUST verify:
 o  The DMR packet is destined to the current MEP.
 o  The packet's MD level matches the MEP's MD level.
 If both conditions above are met, the sender uses the four timestamps
 to compute the two-way delay:
          two-way delay = (T4-T1) - (T3-T2)       (5)
 Note that two-way delay can be computed even when the two peer MEPs
 are not time-synchronized.  One-way Delay Measurement, on the other
 hand, requires the two MEPs to be synchronized.
 Two MEPs running a two-way Delay Measurement protocol MAY be time-
 synchronized.  If two-way Delay Measurement is run between two time-
 synchronized MEPs, the sender MAY compute the one-way delays as
 follows:
          one-way delay {sender->reflector} = T2 - T1       (6)
          one-way delay {reflector->sender} = T4 - T3       (7)
 When two-way Delay Measurement is run periodically, the sender MAY
 also compute the delay variation based on multiple measurements.
 A sender MAY choose to monitor only the sender->reflector delay, that
 is, perform the computation in Equation (6) and ignore the
 computations in Equations (5) and (7).  Note that in this case, the
 sender can run flow-based PM of the path to the peer MEP without
 using the Reflector Entropy TLV.

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6. Packet Formats

6.1. TRILL OAM Encapsulation

 The TRILL OAM packet format is generally discussed in [OAM-FRAMEWK]
 and specified in detail in [TRILL-FM].  It is quoted in this document
 for convenience.
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |
    .    Link  Header               . (variable)
    |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |
    +    TRILL Header               + 6 or more bytes
    |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |
    .   Flow Entropy                . 96 bytes
    .                               .
    |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   OAM Ethertype               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               |
    .   OAM Message Channel         . Variable
    .                               .
    |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Link Trailer              | Variable
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     Figure 6: TRILL OAM Encapsulation

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 The OAM Message Channel used in this document is defined in
 [TRILL-FM] and has the following structure:
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |MD-L | Version | OpCode        |     Flags     |FirstTLVOffset |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .         OpCode-specific fields                                .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .         TLVs                                                  .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      Figure 7: OAM Packet Format
 The first four octets of the OAM Message Channel are common to all
 OpCodes, whereas the rest is OpCode-specific.  Below is a brief
 summary of the fields in the first 4 octets:
 o  MD-L: Maintenance Domain Level.
 o  Version: indicates the version of this protocol.  Always zero in
    the context of this document.
 o  OpCode: Operation Code (8 bits).  Specifies the operation
    performed by the message.  Specific packet formats are presented
    in Sections 6.2 and 6.3 of this document.  A list of the PM
    message OpCodes is provided in Section 6.4.
 o  Flags: The definition of flags is OpCode-specific.  The value of
    this field is zero unless otherwise stated.
 o  FirstTLVOffset: defines the location of the first TLV, in octets,
    starting from the end of the FirstTLVOffset field.
 o  TLVs: one or more TLV fields.  The last TLV field is always an End
    TLV.
 For further details about the OAM packet format, including the format
 of TLVs, see [TRILL-FM].

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6.2. Loss Measurement Packet Formats

6.2.1. Counter Format

 Loss Measurement packets use a 32-bit packet counter field.  When a
 counter is incremented beyond its maximal value, 0xFFFFFFFF, it wraps
 around back to 0.

6.2.2. 1SL Packet 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |MD-L | Ver (0) | OpCode        |  Flags (0)    |FirstTLVOffset |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Sender MEP ID          |         Reserved (0)          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           Test ID                             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Counter TX                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Reserved (0)                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .         TLVs                                                  .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      Figure 8: 1SL Packet Format
 For fields not listed below, see Section 6.1.
 o  OpCode: see Section 6.4.
 o  FirstTLVOffset: defines the location of the first TLV, in octets,
    starting from the end of the FirstTLVOffset field.  The value of
    this field MUST be 16 in 1SL packets.
 o  Sender MEP ID: the MEP ID of the MEP that initiated the 1SL.
 o  Reserved (0): set to 0 by the sender and ignored by the receiver.
 o  Test ID: a 32-bit unique test identifier.
 o  Counter TX: the value of the sender's transmission counter,
    including this packet, at the time of transmission.

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6.2.3. SLM Packet 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |MD-L | Ver (0) | OpCode        |  Flags (0)    |FirstTLVOffset |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Sender MEP ID          | Reserved for Reflector MEP ID |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           Test ID                             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Counter TX                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                Reserved for SLR: Counter TRX (0)              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .         TLVs                                                  .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      Figure 9: SLM Packet Format
 For fields not listed below, see Section 6.1.
 o  OpCode: see Section 6.4.
 o  FirstTLVOffset: defines the location of the first TLV, in octets,
    starting from the end of the FirstTLVOffset field.  The value of
    this field MUST be 16 in SLM packets.
 o  Sender MEP ID: the MEP ID of the MEP that initiated this packet.
 o  Reserved for Reflector MEP ID: this field is reserved for the
    reflector's MEP ID, to be added in the SLR.
 o  Test ID: a 32-bit unique test identifier.
 o  Counter TX: the value of the sender's transmission counter,
    including this packet, at the time of transmission.
 o  Reserved for SLR: this field is reserved for the SLR corresponding
    to this packet.  The reflector uses this field in the SLR for
    carrying TRX, the value of its reception counter.

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6.2.4. SLR Packet 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |MD-L | Ver (0) | OpCode        |  Flags (0)    |FirstTLVOffset |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Sender MEP ID          |       Reflector MEP ID        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           Test ID                             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Counter TX                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Counter TRX                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .         TLVs                                                  .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      Figure 10: SLR Packet Format
 For fields not listed below, see Section 6.1.
 o  OpCode: see Section 6.4.
 o  FirstTLVOffset: defines the location of the first TLV, in octets,
    starting from the end of the FirstTLVOffset field.  The value of
    this field MUST be 16 in SLR packets.
 o  Sender MEP ID: the MEP ID of the MEP that initiated the SLM that
    this SLR replies to.
 o  Reflector MEP ID: the MEP ID of the MEP that transmits this SLR
    message.
 o  Test ID: a 32-bit unique test identifier, copied from the
    corresponding SLM message.
 o  Counter TX: the value of the sender's transmission counter at the
    time of the SLM transmission.
 o  Counter TRX: the value of the reflector's reception counter,
    including this packet, at the time of reception of the
    corresponding SLM packet.

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6.3. Delay Measurement Packet Formats

6.3.1. Timestamp Format

 The timestamps used in Delay Measurement packets are 64 bits long.
 These timestamps use the 64 least significant bits of the IEEE
 1588-2008 (1588v2) Precision Time Protocol timestamp format
 [IEEE1588v2].
 This truncated format consists of a 32-bit seconds field followed by
 a 32-bit nanoseconds field.  This truncated format is also used in
 IEEE 1588v1 [IEEE1588v1], in [Y.1731-2013], and in [MPLS-LM-DM].

6.3.2. 1DM Packet 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |MD-L | Ver (1) | OpCode        | Reserved (0)|T|FirstTLVOffset |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Timestamp T1                          |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           Reserved for 1DM receiving equipment (0)            |
    |                      (for Timestamp T2)                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .         TLVs                                                  .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      Figure 11: 1DM Packet Format
 For fields not listed below, see Section 6.1.
 o  OpCode: see Section 6.4.
 o  Reserved (0): Upper part of Flags field.  Set to 0 by the sender
    and ignored by the receiver.
 o  T: Type flag.  When this flag is set, it indicates proactive
    operation; when cleared, it indicates on-demand mode.
 o  FirstTLVOffset: defines the location of the first TLV, in octets,
    starting from the end of the FirstTLVOffset field.  The value of
    this field MUST be 16 in 1DM packets.
 o  Timestamp T1: specifies the time of transmission of this packet.

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 o  Reserved for 1DM: this field is reserved for internal usage of the
    1DM receiver.  The receiver can use this field for carrying T2,
    the time of reception of this packet.

6.3.3. DMM Packet 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |MD-L | Ver (1) | OpCode        | Reserved (0)|T|FirstTLVOffset |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Timestamp T1                          |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           Reserved for DMM receiving equipment (0)            |
    |                      (for Timestamp T2)                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Reserved for DMR (0)                      |
    |                      (for Timestamp T3)                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            Reserved for DMR receiving equipment               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .         TLVs                                                  .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      Figure 12: DMM Packet Format
 For fields not listed below, see Section 6.1.
 o  OpCode: see Section 6.4.
 o  Reserved (0): Upper part of Flags field.  Set to 0 by the sender
    and ignored by the receiver.
 o  T: Type flag.  When this flag is set, it indicates proactive
    operation; when cleared, it indicates on-demand mode.
 o  FirstTLVOffset: defines the location of the first TLV, in octets,
    starting from the end of the FirstTLVOffset field.  The value of
    this field MUST be 32 in DMM packets.
 o  Timestamp T1: specifies the time of transmission of this packet.

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 o  Reserved for DMM: this field is reserved for internal usage of the
    MEP that receives the DMM (the reflector).  The reflector can use
    this field for carrying T2, the time of reception of this packet.
 o  Reserved for DMR: two timestamp fields are reserved for the DMR
    message.  One timestamp field is reserved for T3, the DMR
    transmission time, and the other field is reserved for internal
    usage of the MEP that receives the DMR.

6.3.4. DMR Packet 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |MD-L | Ver (1) | OpCode        | Reserved (0)|T|FirstTLVOffset |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Timestamp T1                          |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Timestamp T2                          |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Timestamp T3                          |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            Reserved for DMR receiving equipment               |
    |                      (for Timestamp T4)                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    .         TLVs                                                  .
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      Figure 13: DMR Packet Format
 For fields not listed below, see Section 6.1.
 o  OpCode: see Section 6.4.
 o  Reserved (0): Upper part of Flags field.  Set to 0 by the sender
    and ignored by the receiver.
 o  T: Type flag.  When this flag is set, it indicates proactive
    operation; when cleared, it indicates on-demand mode.
 o  FirstTLVOffset: defines the location of the first TLV, in octets,
    starting from the end of the FirstTLVOffset field.  The value of
    this field MUST be 32 in DMR packets.

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 o  Timestamp T1: specifies the time of transmission of the DMM packet
    that this DMR replies to.
 o  Timestamp T2: specifies the time of reception of the DMM packet
    that this DMR replies to.
 o  Timestamp T3: specifies the time of transmission of this DMR
    packet.
 o  Reserved for DMR: this field is reserved for internal usage of the
    MEP that receives the DMR (the sender).  The sender can use this
    field for carrying T4, the time of reception of this packet.

6.4. OpCode Values

 As the OAM packets specified herein conform to [Y.1731-2013], the
 same OpCodes are used:
    OpCode   OAM packet
    value    type
    ------   ----------
    45       1DM
    46       DMR
    47       DMM
    53       1SL
    54       SLR
    55       SLM
 These OpCodes are from the range of values that has been allocated by
 IEEE 802.1 [802.1Q] for control by ITU-T.

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7. Performance Monitoring Process

 The Performance Monitoring process is made up of a number of
 Performance Monitoring instances, known as PM Sessions.  A PM session
 can be initiated between two MEPs on a specific flow and be defined
 as either a Loss Measurement session or Delay Measurement session.
 The Loss Measurement session can be used to determine the performance
 metrics Frame Loss Ratio, availability, and resiliency.  The Delay
 Measurement session can be used to determine the performance metrics
 Frame Delay, Inter-Frame Delay Variation, Frame Delay Range, and Mean
 Frame Delay.
 The PM session is defined by the specific PM function (PM tool) being
 run and also by the Start Time, Stop Time, Message Period,
 Measurement Interval, and Repetition Time.  These terms are defined
 as follows:
 o  Start Time - the time that the PM session begins.
 o  Stop Time - the time that the measurement ends.
 o  Message Period - the message transmission frequency (the time
    between message transmissions).
 o  Measurement Interval - the time period over which measurements are
    gathered and then summarized.  The Measurement Interval can align
    with the PM Session duration, but it doesn't need to.  PM messages
    are only transmitted during a PM Session.
 o  Repetition Time - the time between start times of the Measurement
    Intervals.
        Measurement Interval     Measurement Interval
        (Completed, Historic)    (In Process, Current)
    |                         |
    |                         |
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ^                 ^ ^                                         ^
    |                 | |                                         |
  Start Time          Message                               Stop Time
 (service enabled)    Period                        (Service disabled)
       Figure 14: Relationship between Different Timing Parameters

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8. Security Considerations

 The security considerations of TRILL OAM are discussed in [OAM-REQ],
 [OAM-FRAMEWK], and [TRILL-FM].  General TRILL security considerations
 are discussed in [TRILL].
 As discussed in [OAM-Over], an attack on a PM protocol can falsely
 indicate nonexistent performance issues or prevent the detection of
 actual ones, consequently resulting in DoS (Denial of Service).
 Furthermore, synthetic PM messages can be used maliciously as a means
 to implement DoS attacks on RBridges.  Another security aspect is
 network reconnaissance; by passively eavesdropping on PM messages, an
 attacker can gather information that can be used maliciously to
 attack the network.
 As in [TRILL-FM], TRILL PM OAM messages MAY include the OAM
 Authentication TLV.  It should be noted that an Authentication TLV
 requires a cryptographic algorithm, which may have performance
 implications on the RBridges that take part in the protocol; thus,
 they may, in some cases, affect the measurement results.  Based on a
 system-specific threat assessment, the benefits of the security TLV
 must be weighed against the potential measurement inaccuracy it may
 inflict, and based on this trade-off, operators should make a
 decision on whether or not to use authentication.

9. References

9.1. Normative References

 [KEYWORDS]    Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997,
               <http://www.rfc-editor.org/info/rfc2119>.
 [TRILL]       Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and
               A. Ghanwani, "Routing Bridges (RBridges): Base Protocol
               Specification", RFC 6325, July 2011,
               <http://www.rfc-editor.org/info/rfc6325>.
 [FGL]         Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R.,
               and D. Dutt, "Transparent Interconnection of Lots of
               Links (TRILL): Fine-Grained Labeling", RFC 7172, May
               2014, <http://www.rfc-editor.org/info/rfc7172>.
 [TRILL-FM]    Senevirathne, T., Finn, N., Salam, S., Kumar, D.,
               Eastlake 3rd, D., Aldrin, S., and Y. Li, "Transparent
               Interconnection of Lots of Links (TRILL): Fault
               Management", RFC 7455, March 2015,
               <http://www.rfc-editor.org/info/rfc7455>.

Mizrahi, et al. Standards Track [Page 29] RFC 7456 Loss and Delay Measurement in TRILL March 2015

9.2. Informative References

 [OAM-REQ]     Senevirathne, T., Bond, D., Aldrin, S., Li, Y., and R.
               Watve, "Requirements for Operations, Administration,
               and Maintenance (OAM) in Transparent Interconnection of
               Lots of Links (TRILL)", RFC 6905, March 2013,
               <http://www.rfc-editor.org/info/rfc6905>.
 [OAM-FRAMEWK] Salam, S., Senevirathne, T., Aldrin, S., and D.
               Eastlake 3rd, "Transparent Interconnection of Lots of
               Links (TRILL) Operations, Administration, and
               Maintenance (OAM) Framework", RFC 7174, May 2014,
               <http://www.rfc-editor.org/info/rfc7174>.
 [Y.1731-2013] ITU-T, "OAM functions and mechanisms for Ethernet based
               Networks", ITU-T Recommendation G.8013/Y.1731, November
               2013.
 [802.1Q]      IEEE, "IEEE Standard for Local and metropolitan area
               networks -- Bridges and Bridged Networks", IEEE Std
               802.1Q, December 2014.
 [IEEE1588v1]  IEEE, "IEEE Standard for a Precision Clock
               Synchronization Protocol for Networked Measurement and
               Control Systems Version 1", IEEE Standard 1588, 2002.
 [IEEE1588v2]  IEEE, "IEEE Standard for a Precision Clock
               Synchronization Protocol for Networked Measurement and
               Control Systems Version 2", IEEE Standard 1588, 2008.
 [MPLS-LM-DM]  Frost, D. and S. Bryant, "Packet Loss and Delay
               Measurement for MPLS Networks", RFC 6374, September
               2011, <http://www.rfc-editor.org/info/rfc6374>.
 [OAM]         Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
               D., and S. Mansfield, "Guidelines for the Use of the
               "OAM" Acronym in the IETF", BCP 161, RFC 6291, June
               2011, <http://www.rfc-editor.org/info/rfc6291>.
 [IPPM-1DM]    Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
               Delay Metric for IPPM", RFC 2679, September 1999,
               <http://www.rfc-editor.org/info/rfc2679>.
 [IPPM-2DM]    Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-
               trip Delay Metric for IPPM", RFC 2681, September 1999,
               <http://www.rfc-editor.org/info/rfc2681>.

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 [IPPM-Loss]   Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
               Packet Loss Metric for IPPM", RFC 2680, September 1999,
               <http://www.rfc-editor.org/info/rfc2680>.
 [OAM-Over]    Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
               Weingarten, "An Overview of Operations, Administration,
               and Maintenance (OAM) Tools", RFC 7276, June 2014,
               <http://www.rfc-editor.org/info/rfc7276>.

Acknowledgments

 The authors gratefully acknowledge Adrian Farrel, Alexey Melnikov,
 Jan Novak, Carlos Pignataro, Gagan Mohan Goel, Pete Resnick, and
 Prabhu Raj for their helpful comments.

Mizrahi, et al. Standards Track [Page 31] RFC 7456 Loss and Delay Measurement in TRILL March 2015

Authors' Addresses

 Tal Mizrahi
 Marvell
 6 Hamada St.
 Yokneam, 20692
 Israel
 EMail: talmi@marvell.com
 Tissa Senevirathne
 Cisco
 375 East Tasman Drive
 San Jose, CA 95134
 United States
 EMail: tsenevir@cisco.com
 Samer Salam
 Cisco
 595 Burrard Street, Suite 2123
 Vancouver, BC V7X 1J1
 Canada
 EMail: ssalam@cisco.com
 Deepak Kumar
 Cisco
 510 McCarthy Blvd,
 Milpitas, CA 95035
 United States
 Phone : +1 408-853-9760
 EMail: dekumar@cisco.com
 Donald Eastlake 3rd
 Huawei Technologies
 155 Beaver Street
 Milford, MA 01757
 United States
 Phone: +1-508-333-2270
 EMail: d3e3e3@gmail.com

Mizrahi, et al. Standards Track [Page 32]

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