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TRILL OAM Framework
draft-salam-trill-oam-framework-00

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This is an older version of an Internet-Draft whose latest revision state is "Replaced".
Authors Samer Salam , Tissa Senevirathne , Sam Aldrin
Last updated 2012-07-02
Replaced by draft-ietf-trill-oam-framework, RFC 7174
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draft-salam-trill-oam-framework-00
TRILL Working Group                                          Samer Salam
INTERNET-DRAFT                                        Tissa Senevirathne
Intended Status: Informational                                     Cisco
                                                                        
                                                              Sam Aldrin
                                                                  Huawei
                                                                        
Expires: January 3, 2013                                    July 2, 2012

                          TRILL OAM Framework 
                   draft-salam-trill-oam-framework-00

Abstract

   This document specifies a reference framework for Operations,
   Administration and Management (OAM) in TRILL networks. The focus of
   the document is on the fault and performance management aspects of
   TRILL OAM. 

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

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   http://www.ietf.org/1id-abstracts.html

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   http://www.ietf.org/shadow.html

Copyright and License Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors. All rights reserved.
 

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   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 . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.2 Relationship to Other OAM Work . . . . . . . . . . . . . . .  4
   2. TRILL OAM Model . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1 OAM Layering . . . . . . . . . . . . . . . . . . . . . . . .  5
       2.1.1 Relationship to CFM  . . . . . . . . . . . . . . . . . .  6
       2.1.2 Relationship to BFD and Link OAM . . . . . . . . . . . .  7
     2.2 TRILL OAM in RBridge Port Model  . . . . . . . . . . . . . .  7
     2.3 Network, Service and Flow OAM  . . . . . . . . . . . . . . .  8
     2.4 Maintenance Domains  . . . . . . . . . . . . . . . . . . . .  9
     2.5 Maintenance Entity and Maintenance Entity Group  . . . . . . 10
     2.6 MEPs and MIPs  . . . . . . . . . . . . . . . . . . . . . . . 10
     2.7 Maintenance Point Addressing . . . . . . . . . . . . . . . . 11
   3. OAM Frame Format  . . . . . . . . . . . . . . . . . . . . . . . 12
     3.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 12
     3.2 Determination of Flow Entropy  . . . . . . . . . . . . . . . 13
     3.2 OAM Message Channel  . . . . . . . . . . . . . . . . . . . . 14
     3.3 Identification of OAM Messages . . . . . . . . . . . . . . . 14
   4. Fault Management  . . . . . . . . . . . . . . . . . . . . . . . 14
     4.1 Proactive Fault Management Functions . . . . . . . . . . . . 14
       4.1.1 Fault Detection (Continuity Check) . . . . . . . . . . . 14
       4.1.2 Defect Indication  . . . . . . . . . . . . . . . . . . . 15
         4.1.2.1 Forward Defect Indication  . . . . . . . . . . . . . 15
         4.1.2.2 Reverse Defect Indication (RDI)  . . . . . . . . . . 15
     4.2 On-Demand Fault Management Functions . . . . . . . . . . . . 16
       4.2.1 Connectivity Verification  . . . . . . . . . . . . . . . 16
         4.2.1.1 Unicast  . . . . . . . . . . . . . . . . . . . . . . 16
         4.2.1.2 Multicast  . . . . . . . . . . . . . . . . . . . . . 17
       4.2.2 Fault Isolation  . . . . . . . . . . . . . . . . . . . . 17
   5. Performance Management  . . . . . . . . . . . . . . . . . . . . 17
     5.1 Packet Loss  . . . . . . . . . . . . . . . . . . . . . . . . 18
     5.2 Packet Delay . . . . . . . . . . . . . . . . . . . . . . . . 18
   6. Security Considerations . . . . . . . . . . . . . . . . . . . . 19
   7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 19
 

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   8. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 19
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     9.1  Normative References  . . . . . . . . . . . . . . . . . . . 19
     9.2  Informative References  . . . . . . . . . . . . . . . . . . 20
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20

 

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1.  Introduction

   This document specifies a reference framework for Operations,
   Administration and Management (OAM) in TRILL networks. 

   TRILL [RFC6325] defines a solution for shortest-path frame routing in
   multi-hop Ethernet networks with arbitrary topologies, using the IS-
   IS routing protocol. TRILL capable devices are referred to as Routing
   Bridges or RBridges. RBridges provide an optimized and transparent
   Layer 2 delivery service for Ethernet unicast and multicast traffic.
   The characteristics of a TRILL network are such that it differs from
   Ethernet in the following aspects:

   - TRILL networks do not enforce congruency of unicast and multicast
   paths between a given pair of RBridges.

   - TRILL networks do not impose symmetry of the forward and reverse
   paths between a given pair of RBridges.

   - TRILL supports multipathing of unicast as well as multicast
   traffic.

   OAM, in general, covers multiple areas, including:
   - Fault Management
   - Performance Management
   - Configuration
   - Accounting
   - Security

   The focus of this document is on the first two aspects of OAM,
   namely: Fault Management and Performance Management in the context of
   TRILL networks. The draft provides a generic framework for a
   comprehensive solution that meets the requirements outlined in
   [TRILL-OAM-REQ]. However, specific mechanisms to address these
   requirements are considered to be outside the scope of this document.

1.1  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

1.2 Relationship to Other OAM Work

   OAM is a technology area where a wealth of prior art exists. This
   document leverages concepts and draws upon elements defined and/or
   used in the following documents:

 

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   [TRILL-OAM-REQ] defines the requirements for TRILL OAM which serve as
   the basis for this framework.

   [802.1ag] specifies the Connectivity Fault Management protocol, which
   defines the concepts of Maintenance Domains, Maintenance End Points,
   and Maintenance Intermediate Points.

   [Y.1731] extends IEEE 802.1ag in the following areas: it defines
   fault notification and alarm suppression functions for Ethernet.  It
   also specifies mechanisms for Ethernet performance management,
   including loss, delay, jitter, and throughput measurement.

   [RFC6136] specifies a reference model for OAM as it relates to L2VPN
   services, pseudowires and associated Public Switched Network (PSN)
   tunnels. The document also specifies OAM requirements for L2VPN
   services.

   [RFC6371] describes a framework to support a comprehensive set of OAM
   procedures that fulfill the MPLS-TP OAM requirements for fault,
   performance, and protection-switching management and that do not rely
   on the presence of a control plane.

   [TRILL-BFD] defines a TRILL encapsulation for BFD that enables the
   use of the latter for network fast convergence.

2. TRILL OAM Model

2.1 OAM Layering

   In the RBridge architecture, the TRILL layer is independent of the
   underlying Link Layer technology. Therefore, it is possible to run
   TRILL over any transport layer capable of carrying Layer 2 frames
   such as Ethernet, PPP, or MPLS. Furthermore, TRILL provides a virtual
   Ethernet connectivity service that is transparent to higher layer
   entities (e.g. Layer 3 and above). This strict layering is observed
   by TRILL OAM. 

   Of particular interest is the layering of TRILL OAM with respect to:
   - BFD, which is typically used for fast convergence
   - Ethernet CFM [802.1ag], especially that TRILL switches are likely
   to be deployed alongside existing 802.1 bridges in a network. 

   - Link OAM, which is media specific.

   Consider the example network depicted in Figure 1 below, where a
   TRILL network is interconnected via Ethernet links:

 

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                           LAN                LAN
           +---+   +---+  ======  +---+  =============  +---+
    +--+   |   |   |   | | +--+ | |   | | +--+   +--+ | |   |   +--+ 
    |B1|---|RB1|---|RB2|---|B2|---|RB3|---|B3|---|B4|---|RB4|---|B5|
    +--+   |   |   |   | | +--+ | |   | | +--+   +--+ | |   |   +--+
           +---+   +---+  ======  +---+  =============  +---+

    a. Ethernet CFM (Client Layer)
       >---o------------------------------------------------o---<

    b. TRILL OAM (Network Layer)
               >------o-----------o---------------------< 

    c. Ethernet CFM (Transport Layer) 
                      >---o--o---<    >---o--o---o--o---<

    d. BFD (Media Independent Link Layer)
               #---#   #----------#   #-----------------#

    e. Link OAM (Media Dependent Link Layer)
       *---*   *---*   *---*  *---*   *---*  *---*  *---*   *---*

    Legend:  > MEP    o MIP    # BFD Endpoint    * Link OAM Endpoint 

   Figure 1: OAM Layering in TRILL

   Where Bn and RBn (n= 1,2,3,4) denote IEEE 802.1 bridges and TRILL
   RBridges, respectively.

2.1.1 Relationship to CFM

   In the context of a TRILL network, CFM can be used as either a client
   layer OAM or a transport layer OAM mechanism. 

   When acting as a client layer OAM (see Figure 1a), CFM provides fault
   management capabilities for the user VLAN (or fine-grain label), on
   an end-to-end basis over the TRILL network. Edge ports of the TRILL
   network may be visible to CFM operations through the presence of a
   CFM Maintenance Intermediate Point (MIP).

   When acting as a transport layer OAM (see Figure 1c), CFM provides
   fault management functions for the IEEE 802.1 Ethernet bridged
   networks that may interconnect RBridges. RBridges directly connected
 

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   to the intervening 802.1 bridges may host CFM Down Maintenance End
   Points (MEPs).

2.1.2 Relationship to BFD and Link OAM

   One-hop BFD (see Figure 1d) runs between adjacent RBridges and
   provides fast link as well as node failure detection capability. Note
   that BFD sits a layer above Link OAM, which is media specific. BFD
   provides fast convergence characteristics to TRILL networks.

   Link OAM (see Figure 1e) depends on the nature of the physical medium
   used in the links interconnecting RBridges. For e.g., for Ethernet
   links, [802.3] Clause 57 OAM may be used.

2.2 TRILL OAM in RBridge Port Model

   TRILL OAM processing can be modeled as shim situated between the
   Extended Internal Sublayer Service (EISS) in [802.1Q] and the RBridge
   Forwarding Engine function, on a virtual port with no physical layer
   (Null PHY). TRILL OAM requires services of the RBridge forwarding
   engine and utilizes information from the IS-IS control plane. Figure
   2 below depicts TRILL OAM processing in the context of the RBridge
   port model defined in [RFC6325]. In this figure, double lines
   represent flow of both frames and information whereas single lines
   represent flow of information only.

   While this figure shows a conceptual model, it is to be understood
   that implementations need not mirror this exact model as long as the
   intended OAM requirements and functionality are preserved.

 

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              +-----------------------------------------------+----
              |          RBridge                 (Flow of OAM Messages)
              |                                +-------------+ 
              |   Forwarding Engine,           |             |
              |   IS-IS, Etc.                  |             |
              |   Processing of native         |             |
              |    and TRILL frames            V             V
              +--------------------------------|-------------+-----
                                              ||         other ports...
                                        +------------+  
                                        | TRILL OAM  |  
                                        | Processing |  
                                        |            |  
                                        +------------+    <- EISS
                                        |            |  
                                        |   802.1Q   |  
                                        | Port VLAN  |  
                                        | Processing |  
                                        |            |  
         +------------------------------+------------+--+ <-- ISS
         |                                              |
         |    802.1/802.3 Low Level Control Frame       |
         |    Processing, Port/Link Control Logic       |
         |                                              |
         +-----------++---------------------------------+
                     ||
                     ||        +------------+
                     ||        | NULL PHY   |
                     |+--------+ (Virtual   | 
                     +---------+ Interface) | 
                               |            |
                               +------------+

   Figure 2: TRILL OAM in RBridge Port Model

   Note that there is a single virtual interface which hosts the TRILL
   OAM shim per RBridge. The rationale for this model is discussed in
   section 2.6 "MEPs and MIPs". 

2.3 Network, Service and Flow OAM 

   OAM functions in a TRILL network can be conducted at different levels
   of granularity. This gives rise to 'Network', 'Service' and 'Flow'
   OAM, listed in order of increasing granularity.

   Network OAM mechanisms provide fault and performance management
   functions in the context of a representative 'test' VLAN (or fine
   grain label). The test VLAN can be thought of as a management or
 

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   diagnostics VLAN which extends to all RBridges in a TRILL network. In
   order to account for multipathing, Network OAM functions also make
   use of test flows (both unicast and multicast) to provide coverage of
   the various paths in the network. 

   Service OAM mechanisms provide fault and performance management
   functions in the context of the actual VLAN (or fine grain label) set
   for which end station service is enabled. Test flows are used here,
   as well, to provide coverage in the case of multipathing.

   Flow OAM mechanisms provide the most granular fault and performance
   management capabilities, where OAM functions are performed in the
   context of end station service VLANs (or fine grain labels) and user
   flows. While Flow OAM provides the most granular control, it clearly
   poses scalability challenges if attempted on large numbers of flows.
   

2.4 Maintenance Domains 

   The concept of Maintenance Domains, or OAM Domains, is well known in
   the industry. IEEE 802.1ag, RFC6136, RFC5654, etc... all define the
   notion of a Maintenance Domain as a collection of devices (e.g.
   network elements) that are grouped for administrative and/or
   management purposes. Maintenance domains usually delineate trust   
   relationships, varying addressing schemes, network infrastructure
   capabilities, etc... 

   When mapped to TRILL, a Maintenance Domain is defined as a collection
   of RBridges in a network for which faults in connectivity or
   performance are to be managed by a single operator. All RBridges in a
   given Maintenance Domain are, by definition, owned and operated by a
   single entity (e.g. an enterprise or a data center operator, etc...).
   RFC6325 defines the operation of TRILL in a single IS-IS area, with
   the assumption that the network is managed by a single operator. In
   this context, a single (default) Maintenance Domain is sufficient for
   TRILL OAM.

   However, when considering scenarios where different TRILL networks
   need to be interconnected, for e.g. as discussed in [TRILLML], then
   the introduction of multiple Maintenance Domains and Maintenance
   Domain hierarchies becomes useful to map and contain administrative
   boundaries. When considering multi-domain scenarios, the following
   rules must be followed: TRILL OAM domains MUST NOT overlap, but MUST
   either be disjoint or nest to form a hierarchy (i.e. a higher
   Maintenance Domain MAY completely engulf a lower Domain). A
   Maintenance Domain is typically identified by a Domain Name and a
   Maintenance Level (a numeric identifier). The larger the Domain, the
   higher the Level.
 

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        +-------------------+  +---------------+   +-------------------+
        |                   |  |     TRILL     |   |                   |
        |       Site 1      |  | Interconnect  |   |     Site 2        |
        |       TRILL       |--|   Network     |---|     TRILL         |
        |      (Level 1)    |  |   (Level 2)   |   |    (Level 1)      |
        |                   |  |               |   |                   |
        +-------------------+  +---------------+   +-------------------+

        <------------------------End-to-End Domain--------------------->

        <----Site Domain---->   <----Inter/---->   <----Site Domain---->
                                 connect Domain

                         Figure 3: TRILL OAM Maintenance Domains

2.5 Maintenance Entity and Maintenance Entity Group

   TRILL OAM functions are performed in the context of logical endpoint
   pairs referred to as Maintenance Entities (ME). A Maintenance Entity
   defines a relationship between two points in a TRILL network where
   OAM functions (e.g. monitoring operations) are applied. The two
   points which define a Maintenance Entity are known as Maintenance End
   Points (MEPs) - see section 2.6 below. The set of Maintenance
   Entities that belong to the same Maintenance Domain are referred to
   as a Maintenance Entity Group (MEG). On the network path in between
   MEPs, there can be zero or more intermediate points, called
   Maintenance Intermediate Points (MIPs).  MEPs and MIPs are associated
   with the MEG and can be part of more than one ME in a given MEG.

2.6 MEPs and MIPs

   OAM capabilities on RBridges can be defined in terms of logical
   groupings of functions that can be categorized into two functional
   objects: Maintenance End Points (MEPs) and Maintenance Intermediate
   Points (MIPs). The two are collectively referred to as Maintenance
   Points (MPs).

   MEPs are the active components of TRILL OAM: MEPs source TRILL OAM
   messages proactively or on-demand based on operator invocation.
   Furthermore, MEPs ensure that TRILL OAM messages do not leak outside
   a given Maintenance Domain, e.g. out of the TRILL network and into
   end stations. MIPs, on the other hand, are internal to a Maintenance
   Domain. They are the passive components of TRILL OAM, primarily
   responsible for forwarding TRILL OAM messages and selectively
   responding to a subset of these messages.

   The following figure shows the MEP and MIP placement for the
   Maintenance Domains depicted in Figure 3 above.
 

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           TRILL Site 1          Interconnect            TRILL Site 2
        +-------------------+  +---------------+   +-------------------+
        |                   |  |               |   |                   |
        | +---+       +---+ |  | +---+   +---+ |   | +---+       +---+ |
        | |RB1|-------|RB2| |--| |RB3|   |RB4| |---| |RB5|-------|RB6| |
        | +---+       +---+ |  | +---+   +---+ |   | +---+       +---+ |
        |                   |  |               |   |                   |
        +-------------------+  +---------------+   +-------------------+

            <E--------I-------------I-----I--------------I--------E>

            <E--------E>           <E-----E>            <E--------E>

         Legend E: MEP      I: MIP

                              Figure 4: MEPs and MIPs

   It is worth noting that a single RBridge port may host multiple MEPs
   of different technologies, e.g. TRILL OAM MEP(s) and [802.1ag]
   MEP(s). This does not mean that the protocol operation is necessarily
   consolidated into a single functional entity on those ports. The
   protocol functions for each MEP remain independent and reside in
   different shims in the RBridge Port model of figure 2: the TRILL OAM
   MEP resides in the "TRILL OAM Processing" block whereas a CFM MEP
   resides in the "802.1Q Port VLAN Processing" block.

   The model of section 2.2 implies that a single MEP and/or MIP per MEG
   can be instantiated per RBridge. This simplifies implementations and
   enables TRILL OAM to perform management functions on sections, as
   specified in [TRILL-OAM-REQ], while maintaining the simplicity of a
   single TRILL OAM Maintenance Domain. Furthermore, [RFC6325] defines
   identification of TRILL frames received from the wire only. It does
   not define methods to identify frames egress to the wire. Due to this
   reason, we do not distinguish between Up MPs and Down MPs (as defined
   in [802.1ag]) in this framework. Given that the MPs always reside on
   a special virtual port with no PHY layer, MP directionality is
   irrelevant.

2.7 Maintenance Point Addressing

   TRILL OAM functions must provide the capability to address a specific
   Maintenance Point or a set of one or more Maintenance Points in a
   MEG. To that end, RBridges need to recognize two sets of addresses:

   - Individual MP addresses
 

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   - Group MP Addresses 

   TRILL OAM must support the Shared MP address model, where all MPs on
   an RBridge share the same Individual MP address. In other words,
   TRILL OAM messages can be addressed to a specific RBridge but not to
   a specific port on an RBridge.

   One cannot discern, from observing the external behavior of an
   RBridge, whether TRILL OAM messages are actually delivered to a
   certain MP or another entity within the RBridge. The Shared MP
   address model takes advantage of this fact by allowing MPs in
   different RBridge ports to share the same Individual MP address. The
   MPs may still reside on different RBridge ports and for the most
   part, they have distinct identities.

   The Group MP addresses enable the OAM mechanism to reach all the MPs
   in a given MEG. Certain OAM functions, e.g. pruned tree verification,
   require addressing a subset of the MPs in a MEG. Group MP addresses
   are not defined for such subsets. Rather, the OAM function in
   question must use the Group MP addresses combined with an indication
   of the scope of the MP subset encoded in the OAM Message Channel.
   This prevents the unwieldy proliferation of Group MP addresses. 

3. OAM Frame Format

3.1 Motivation

   In order for TRILL OAM messages to accurately test the data-path, the
   OAM message must be indiscernible from a data message to the
   transient RBridges. Only the target RBridge, which needs to process
   the message, must be able to identify the packet as a control
   message. For this reason, the Outer Header and the TRILL Header must
   carry no indication that distinguishes an OAM message from user data.

   The TRILL OAM frame format proposed in [TRILL-OAM-REQ] provides the
   necessary flexibility to exercise the data path as close as possible
   to actual data packets. This frame format is captured below for quick
   reference:

 

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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   .    Outer Header               . Variable                 
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   +    TRILL Header               + 8 bytes
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   .   Flow Entropy                . 128 bytes
   .                               .
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   .   OAM Message Channel         . Variable
   .                               .
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Figure 5 Frame format of OAM Messages

   The Outer Header and TRILL Header are as specified in [RFC6325] and
   need to be as close as possible to the Outer Header and TRILL Header
   of the normal data frame corresponding to the traffic that OAM is
   testing.

3.2 Determination of Flow Entropy

   The Flow Entropy is a fixed 128 byte field that is populated with
   either real packet data or synthetic data that mimics the intended
   flow.

   For a Layer 2 flow (i.e. non-IP) the Flow Entropy must specify the
   Ethernet header, including the MAC destination and source addresses
   as well as an optional VLAN tag. 

   For a Layer 3 flow, the Flow Entropy must specify the Ethernet
   header, the IP header and UDP or TCP header fields. 

   Not all fields in the Flow Entropy field need to be identical to the
   data flow that the OAM message is mimicking. The only requirement is
   for the selected flow entropy to follow the same path as the data
   flow that it is mimicking. In other words, the selected flow entropy
   must result in the same ECMP selection or multicast pruning behavior
   or other applicable forwarding paradigm.  

 

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   When performing diagnostics on user flows, the OAM mechanisms must
   allow the network operator to configure the flow entropy parameters
   (L2, L3 and L4) on the RBridge from which the diagnostic operations
   are to be triggered.

   When running OAM functions over Test Flows, the TRILL OAM should
   provide a mechanism for discovering the flow entropy parameters by
   querying the RBridges dynamically.

3.2 OAM Message Channel

   OAM Message Channel provides methods to communicate OAM specific
   details between RBridges. [802.1ag] and [RFC4379] have implemented
   OAM message channels. It is important to select the appropriate
   technology and re-use it, instead of redesigning yet another OAM
   channel. TRILL is a transport layer that carries Ethernet frames, as
   such there are close links between TRILL and other 802.1
   technologies. The TRILL OAM model specified earlier is based on
   the[802.1ag] model. The use of [802.1ag] encoding format for the OAM
   Message channel is one possible choice. [TRILL-OAM] presents a
   proposal on the use of 802.1ag messaging as the OAM message channel.

3.3 Identification of OAM Messages

   RBridges must be able to identify OAM messages that are destined to
   them, either individually or as a group, so as to properly process
   them. To that end, those target RBridges must discern OAM messages
   from normal data traffic and from data traffic experiencing errors
   (e.g. Hop Count expiry). 

   Given that the Outer Header and TRILL Header carry no indication that
   distinguishes an OAM message from data messages, the identification
   of OAM messages needs to be done based on fields in the OAM Message
   Channel, and potentially selective subset of the fields in the Flow
   Entropy which do not polarize the hop-by-hop behavior. The latter
   will vary depending on the type of flows (L2 vs. L3). 

4. Fault Management 

4.1 Proactive Fault Management Functions

   Proactive fault management functions are configured by the network
   operator to run periodically without a time bound, or are configured
   to trigger certain actions upon the occurrence of specific events. 

4.1.1 Fault Detection (Continuity Check)

   Proactive fault detection is performed by periodically monitoring the
 

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   reachability between service endpoints, i.e. MEPs in a given MEG,
   through the exchange of Continuity Check messages. The reachability
   between any two arbitrary MEP may be monitored for a specified path,
   all paths or any representative path. The fact that TRILL networks do
   not enforce congruency between unicast and multicast paths means that
   the proactive fault detection mechanism must provide procedures to
   monitor the unicast paths independently of the multicast paths.
   Furthermore, where the network has ECMP, the proactive fault
   detection mechanism must be capable of exercising the equal-cost
   paths individually. 

   The set of MEPs exchanging Continuity Check messages in a given
   domain and for a specific monitored entity (flow, network or service)
   must use the same transmission period. As long as the fault detection
   mechanism involves MEPs transmitting periodic heartbeat messages
   independently, then this OAM procedure is not affected by the lack of
   forward/reverse path symmetry in TRILL.

   The proactive fault detection function must detect the following
   types of defects:

   - Loss of continuity (LoC) to one or more remote MEPs- Unexpected
   connectivity between isolated VLANs (mismerge)- Unexpected
   connectivity to one or more remote MEPs- Period mis-configuration

4.1.2 Defect Indication

   TRILL OAM MUST support event-driven defect indication upon the
   detection of a connectivity defect. Defect indications can be
   categorized into two types:

4.1.2.1 Forward Defect Indication

   This is used to signal a failure that is detected by a lower layer
   OAM mechanism. Forward Defect indication is transmitted away from the
   direction of the failure.

   Forward defect indication may be used for alarm suppression and/or
   for purpose of inter-working with other layer OAM protocols. Alarm
   suppression is useful when a transport/network level fault translates
   to multiple service or flow level faults. In such a scenario, it is
   enough to alert a network management station (NMS) of the single
   transport/network level fault in lieu of flooding that NMS with a
   multitude of Service or Flow granularity alarms.

4.1.2.2 Reverse Defect Indication (RDI) 

   RDI is used to signal that the advertising MEP has detected a loss of
 

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   continuity (LoC) defect. RDI is transmitted in the direction of the
   failure.

   RDI allows single-sided management, where the network operator can
   examine the state of a single MEP and deduce the overall health of a
   monitored entity (network, flow or service).

4.2 On-Demand Fault Management Functions

   On-demand fault management functions are initiated manually by the
   network operator and continue for a time bound period. These
   functions enable the operator to run diagnostics to investigate a
   defect condition.

4.2.1 Connectivity Verification

   As specified in [TRILL-OAM-REQ], TRILL OAM must support on-demand
   connectivity verification for unicast and multicast. The connectivity
   verification mechanism must provide a means for specifying and
   carrying in the messages:
   - variable length payload/padding to test MTU related connectivity
   problems.
   - test traffic patterns as defined in [RFC2544].

4.2.1.1 Unicast

   Unicast connectivity verification operation must be initiated from a
   MEP and may target either a MIP or another MEP. For unicast,
   connectivity verification can be performed at either Network or Flow
   granularity.

   Connectivity verification at the Network granularity tests
   connectivity between a MEP on a source RBridge and a MIP or MEP on a
   target RBridge over a representative test VLAN and for a test flow.
   The user must supply the source and target RBridges for the
   operation, and the test VLAN/flow information uses pre-set values or
   defaults.

   Connectivity verification at the Network granularity tests
   connectivity between a MEP on a source RBridge and a MIP or MEP on a
   target RBridge over a user specified VLAN and flow parameters.

   The above functions must be supported on sections, as defined in
   [TRILL-OAM-REQ]. When connectivity verification is triggered over a
   section, and the initiating MEP does not coincide with the edge
   (ingress) RBridge, the MEP must use the edge RBridge nickname instead
   of the local RBridge nickname on the associated connectivity
   verification messages. The user must supply the edge RBridge nickname
 

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   as part of the operation parameters.

4.2.1.2 Multicast

   For multicast, the connectivity verification function tests all
   branches and leaf nodes of a multicast distribution tree for
   reachability. This function should include mechanisms to prevent
   reply storms from overwhelming the initiating RBridge. This may be
   done, for e.g., by staggering the replies. To further prevent reply
   storms, connectivity verification operation is initiated from a MEP
   and must target MEPs only. MIPs are transparent to multicast
   connectivity verification.

   Per [TRILL-OAM-REQ], multicast connectivity verification must provide
   the following granularity of operation:

   A. Un-pruned Tree
   - Connectivity verification for un-pruned multicast distribution
   tree. The user in this case supplies the tree identifier (egress
   RBridge nickname). 

   B. Pruned Tree
   - Connectivity verification for a VLAN (or fine-grain label) in a
   given multicast distribution tree. The user in this case supplies the
   tree identifier and VLAN (or fine-grain label).
   - Connectivity verification for an IP multicast group in a given
   multicast distribution tree. The user in this case supplies: the tree
   identifier, VLAN and IP (S,G) or (*,G).

4.2.2 Fault Isolation

   TRILL OAM MUST support an on-demand connectivity fault localization
   function. This is the capability to trace the path of a Flow on a
   hop-by-hop (i.e. RBridge by RBridge) basis to isolate failures. This
   involves the capability to narrow down the locality of a fault to a
   particular port, link or node. The characteristic of forward/reverse
   path asymmetry, in TRILL, renders fault isolation into a direction-
   sensitive operation. That is, given two RBridges A and B,
   localization of connectivity faults between them requires running
   fault isolation procedures from RBridge A to RBridge B as well as
   from RBridge B to RBridge A. Generally speaking, single-sided fault
   isolation is not possible in TRILL OAM. 

5. Performance Management 

   Performance Management functions can be performed both proactively
   and on-demand. Proactive management involves a scheduling function,
   where the performance management probes can be triggered on a
 

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   recurring basis. Since the basic performance management functions
   involved are the same, we make no distinction between proactive and
   on-demand functions in this section.

5.1 Packet Loss

   Given that TRILL provides inherent support for multipoint-to-
   multipoint connectivity, then packet loss cannot be accurately
   measured by means of counting user data packets. This is because user
   packets can be delivered to more RBridges or more ports than are
   necessary (e.g. due to broadcast, un-pruned multicast or unknown
   unicast flooding). As such, a statistical means of approximating
   packet loss rate is required. This can be achieved by sending
   "synthetic" (i.e. TRILL OAM) packets that are counted only by those
   ports (MEPs) that are required to receive them. This provides a
   statistical approximation of the number of data frames lost, even
   with multipoint-to-multipoint connectivity.

   Packet loss probes must be initiated from a MEP and must target a
   MEP. This function must be supported on sections, as defined in
   [TRILL-OAM-REQ]. When packet loss is measured over a section, and the
   initiating MEP does not coincide with the edge (ingress) RBridge, the
   MEP must use the edge RBridge nickname instead of the local RBridge
   nickname on the associated loss measurement messages. The user must
   supply the edge RBridge nickname as part of the operation parameters.

5.2 Packet Delay

   Packet delay is measured by inserting time-stamps in TRILL OAM
   packets. In order to ensure high accuracy of measurement, TRILL OAM
   must specify the time-stamp location at fixed offsets within the OAM
   packet in order to facilitate hardware-based time-stamping. Hardware
   implementation must implement the time-stamping function as close to
   the wire as possible in order to maintain high accuracy. 

 

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6. Security Considerations

   TRILL OAM must provide mechanisms for:

   - Preventing denial of service attacks caused by exploitation of the
   OAM message channel.- Optionally authenticate communicating endpoints
   (MEPs and MIPs)- Preventing TRILL OAM packets from leaking outside of
   the TRILL network or outside their corresponding Maintenance Domain.
   This can be done by having MEPs implement a filtering function based
   on the Maintenance Level associated with received OAM packets.

7. IANA Considerations

   None.

8. Acknowledgements

   We invite feedback and contributors.

9.  References

9.1  Normative References

   [TRILL-OAM-REQ] Senevirathne, "Requirements for Operations,
              Administration and Maintenance (OAM) in TRILL", draft-
              tissa-trill-oam-req-01.txt, work in progress, May 2012.

   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6136]  Sajassi, A., Ed., and D. Mohan, Ed., "Layer 2 Virtual
              Private Network (L2VPN) Operations, Administration, and
              Maintenance (OAM) Requirements and Framework", RFC 6136,
              March 2011.

   [RFC2544]  Bradner, S. and J. McQuaid, "Benchmarking Methodology for
              Network Interconnect Devices", RFC 2544, March 1999.

   [802.1ag]  "IEEE Standard for Local and metropolitan area networks -
              Virtual Bridged Local Area Networks, Amendment 5:
              Connectivity Fault Management", 2007.

   [Y.1731]  "ITU-T Recommendation Y.1731 (02/08) - OAM functions and
              mechanisms for Ethernet based networks", February 2008.

   [RFC6371]  Busi & Allan, "Operations, Administration, and Maintenance
 

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              Framework for MPLS-Based Transport Networks", RFC 6371,
              September 2011.

9.2  Informative References

   [RFC6325]  Perlman, et al., "Routing Bridges (RBridges): Base
              Protocol Specification", RFC 6325, July 2011.

   [TRILL-BFD] V. Manral, et al., "TRILL (Transparent Interconnetion of
              Lots of Links): Bidirectional Forwarding Detection (BFD)
              Support", draft-ietf-trill-rbridge-bfd-06.txt, work in
              progress, June 2012.

Authors' Addresses

   Samer Salam
   Cisco
   595 Burrard Street, Suite 2123
   Vancouver, BC V7X 1J1, Canada
   Email: ssalam@cisco.com

   Tissa Senevirathne
   Cisco
   375 East Tasman Drive
   San Jose, CA 95134, USA
   Email: tsenevir@cisco.com

   Sam Aldrin
   Huawei Technologies
   Email: sam.aldrin@gmail.com

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