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Versions: 00 01 02 03 draft-ietf-trill-oam-framework

TRILL Working Group                                          Samer Salam
INTERNET-DRAFT                                        Tissa Senevirathne
Intended Status: Informational                                     Cisco

                                                              Sam Aldrin
                                                         Donald Eastlake

Expires: April 22, 2013                                 October 19, 2012

                          TRILL OAM Framework


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

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
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   and may be updated, replaced, or obsoleted by other documents at any
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   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

Copyright and License Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the

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   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 . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.2 Relationship to Other OAM Work . . . . . . . . . . . . . . .  5
   2. TRILL OAM Model . . . . . . . . . . . . . . . . . . . . . . . .  6
     2.1 OAM Layering . . . . . . . . . . . . . . . . . . . . . . . .  6
       2.1.1 Relationship to CFM  . . . . . . . . . . . . . . . . . .  7
       2.1.2 Relationship to BFD  . . . . . . . . . . . . . . . . . .  8
       2.1.3 Relationship to Link OAM . . . . . . . . . . . . . . . .  8
     2.2 TRILL OAM in the RBridge Port Model  . . . . . . . . . . . .  9
     2.3 Network, Service and Flow OAM  . . . . . . . . . . . . . . . 10
     2.4 Maintenance Domains  . . . . . . . . . . . . . . . . . . . . 11
     2.5 Maintenance Entity and Maintenance Entity Group  . . . . . . 12
     2.6 MEPs and MIPs  . . . . . . . . . . . . . . . . . . . . . . . 12
     2.7 Maintenance Point Addressing . . . . . . . . . . . . . . . . 14
   3. OAM Frame Format  . . . . . . . . . . . . . . . . . . . . . . . 14
     3.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 14
     3.2 Determination of Flow Entropy  . . . . . . . . . . . . . . . 16
       3.2.1 Address Learning and Flow Entropy  . . . . . . . . . . . 16
     3.3 OAM Message Channel  . . . . . . . . . . . . . . . . . . . . 16
     3.4 Identification of OAM Messages . . . . . . . . . . . . . . . 17
   4. Fault Management  . . . . . . . . . . . . . . . . . . . . . . . 17
     4.1 Proactive Fault Management Functions . . . . . . . . . . . . 17
       4.1.1 Fault Detection (Continuity Check) . . . . . . . . . . . 17
       4.1.2 Defect Indication  . . . . . . . . . . . . . . . . . . . 18 Forward Defect Indication  . . . . . . . . . . . . . 18 Reverse Defect Indication (RDI)  . . . . . . . . . . 18
     4.2 On-Demand Fault Management Functions . . . . . . . . . . . . 19
       4.2.1 Connectivity Verification  . . . . . . . . . . . . . . . 19 Unicast  . . . . . . . . . . . . . . . . . . . . . . 19 Multicast  . . . . . . . . . . . . . . . . . . . . . 20
       4.2.2 Fault Isolation  . . . . . . . . . . . . . . . . . . . . 20
   5. Performance Management  . . . . . . . . . . . . . . . . . . . . 21

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     5.1 Packet Loss  . . . . . . . . . . . . . . . . . . . . . . . . 21
     5.2 Packet Delay . . . . . . . . . . . . . . . . . . . . . . . . 21
   6. Security Considerations . . . . . . . . . . . . . . . . . . . . 22
   7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 22
   8. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 22
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     9.1  Normative References  . . . . . . . . . . . . . . . . . . . 22
     9.2  Informative References  . . . . . . . . . . . . . . . . . . 23
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23

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1.  Introduction

   This document specifies a reference framework for Operations,
   Administration and Maintenance (OAM, [RFC6291]) in TRILL (Transparent
   Interconnection of Lots of Links) networks.

   TRILL [RFC6325] specifies a protocol for shortest-path frame routing
   in multi-hop networks with arbitrary topologies and link
   technologies, using the IS-IS routing protocol. TRILL capable devices
   are referred to as TRILL Switches or RBridges (Routing Bridges).
   RBridges provide an optimized and transparent Layer 2 delivery
   service for Ethernet unicast and multicast traffic. Some
   characteristics of a TRILL network that are different from Ethernet
   bridging are the following:

   -    TRILL networks support arbitrary link technology between TRILL
   switches. Hence, a TRILL switch port may not have a 48-bit MAC
   Address [802] but might, for example, have an IP address as an
   identifier [TRILL-IP] or no unique identifier (PPP [RFC6361]).

   - 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

   In this document, we refer to the term OAM as defined in [RFC6291].
   The Operations aspect involves finding problems that prevent proper
   functioning of the network.  It also includes monitoring of the
   network to identify potential problems before they occur.
   Administration involves keeping track of network resources.
   Maintenance activities are focused on facilitating repairs and
   upgrades as well as corrective and preventive measures. [ISO/IEC
   7498-4] defines 5 functional areas in the OSI model for network
   management, commonly referred to as FCAPS:

   -Fault Management
   -Configuration Management
   -Accounting Management
   -Performance Management
   -Security Management

   The focus of this document is on the first and fourth functional
   aspects, namely Fault Management and Performance Management, in TRILL
   networks. These primarily map to the "Operations" and "Maintenance"

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   part of OAM.

   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",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   In addition, the following acronyms are used:
      BFD - Bidirectional Forwarding Detection [RFC5880]
      CFM - Connectivity Fault Management [802.1Q]
      FGL - Fine Grained Label(ing) [TRILL-FGL]
      IEEE - Institute for Electrical and Electronic Engineers
      IP - Internet Protocol, includes both IPv4 and IPv6
      L2VPN - Layer 2 Virtual Private Network
      LAN - Local Area Network
      MEG - Maintenance Entity Group
      MEP - Maintenance End Point
      MIP - Maintenance Intermediate Point
      MP - Maintenance Point (MEP or MIP)
      OAM - Operations, Administration, and Maintenance [RFC6291]
      RBridge - Routing Bridge, a device implementing TRILL [RFC6325]
      TRILL - Transparent Interconnection of Lots of Links [RFC6325]
      TRILL Switch - an alternate name for an RBridge
      VLAN - Virtual LAN

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:

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

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

   [Y.1731] extends Connectivity Fault Management 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

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   [RFC6136] specifies a reference model for OAM as it relates to L2VPN
   services, pseudowires and associated Public Switched Network 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 TRILL 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 TRILL frames such
   as Ethernet [RFC6325], PPP [RFC6361], 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 [802.1Q] on paths from an external device, over a
   TRILL campus, to another external device, especially since TRILL
   switches are likely to be deployed where existing 802.1 bridges can
   be such external devices.

   - Link OAM, on links interior to a TRILL campus, which is link
   technology 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
           +---+   +---+  ======  +---+  =============  +---+
    +--+   |   |   |   | | +--+ | |   | | +--+   +--+ | |   |   +--+
    +--+   |   |   |   | | +--+ | |   | | +--+   +--+ | |   |   +--+
           +---+   +---+  ======  +---+  =============  +---+

    a. Ethernet CFM (Client Layer) on path over the TRILL campus

    b. TRILL OAM (Network Layer)

    c. Ethernet CFM (Transport Layer) on interior Ethernet LANs
                      >---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, ...) denote IEEE 802.1Q 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, on an end-to-end basis over the
   TRILL network. Edge ports of the TRILL network may be visible to CFM
   operations through the optional presence of a CFM Maintenance
   Intermediate Point (MIP) in the TRILL switches edge Ethernet ports.

   When acting as a transport layer OAM (see Figure 1c), CFM provides
   fault management functions for the IEEE 802.1Q bridged LANs that may
   interconnect RBridges. Such bridged LANs can be used as TRILL level

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   links between RBridges. RBridges directly connected to the
   intervening 802.1Q bridges may host CFM Down Maintenance End Points

2.1.2 Relationship to BFD

   One-hop BFD (see Figure 1d) runs between adjacent RBridges and
   provides fast link as well as node failure detection capability
   [TRILL-BFD]. Note that BFD sits a layer above Link OAM, which is
   media specific. BFD provides fast convergence characteristics to
   TRILL networks. It is worth noting that the requirements for BFD are
   different from those of the TRILL OAM mechanisms that are the prime
   focus of this document. Furthermore, BFD does not use the frame
   format described in section 3.1.

   TRILL BFD differs from TRILL OAM in two significant ways:

   1.   A TRILL BFD transmitter is bound to a specific TRILL output port
   as explained below.

   2.   TRILL BFD messages can be transmitted by the originator out a port
   to a neighbor RBridge when the adjacency is in the Detect or Two-Way
   states as well as when the adjacency is in the Up state [RFC6327].

   In contrast, TRILL OAM messages are initially transmitted by
   appearing to have been received on a virtual TRILL input port (refer
   to Section 2.2 for details). The output ports on which TRILL OAM
   message are sent are determined by the TRILL routing function, which
   will only send on links that are in the Up state and have been
   incorporated into the local view of the campus topology.

   For example, assume there are five parallel equal cost links between
   RB1 and RB2 that have not been aggregated. (Links that are aggregated
   with [802.1AX] appear to TRILL to be a single link accessible through
   a single TRILL port.) However, RB1 is only capable of doing up to 4-
   way ECMP. TRILL OAM messages, as dispatched by the TRILL Routing
   function, will use 4 of the 5 links. But it is desirable to be able
   to monitor the fifth link to be sure it is available for failover.
   TRILL BFD messages sent by RB1 will use the output port to which
   their session is bound. RB1 can easily monitor all 5 links to RB2 by
   using a TRILL BFD session bound to each of the 5 output ports.

2.1.3 Relationship to Link OAM

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

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2.2 TRILL OAM in the RBridge Port Model

   TRILL OAM processing can be modeled as a 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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           |              (Flow of OAM Messages)       RBridge
           |             +----------------------+
           |             |+-------------------+||  Forwarding Engine,
           |             ||                    ||  IS-IS, Etc.
           |             ||                    ||  Processing of native
           |             V                      V  and TRILL frames
            ||          ||                     ||  ...other trunk ports
            ||    +------------+             +------------+
            ||    | TRILL OAM  |             |            |
            ||    | Processing |             | Port VLAN  |
            ||    +------------+             | Processing |
            ||                               |            |
            |+-------------------------+     |            |
            +-------------------------+|     +------------+ <-- ISS
                                      ||     |802.1/802.3 |
   +-------------------------------+  ||     |Low Level   |
   |             MAC Relay         |  ||     |Control     |
   +----||------------------||-----+  ||     |Frame       |
   +----||------+ ... +-----||-----+  ||     |Processing, |
   |            |     |            |  ||     |Port/Link   |
   | Port VLAN  |     | Port VLAN  |  ||     |Control     |
   | Processing |     | Processing |  ||     |Logic       |
   +------------+     +------------+  ||     +------------+
   |802.1/802.3 |     |802.1/802.3 |  ||     | 802.3PHY   |
   |Low Level   |     |Low Level   |  ||     +------------+
   |Control     |     |Control     |  ||
   |Frame       |     |Frame       |  ||
   |Processing, |     |Processing, |  ||
   |Port/Link   |     |Port/Link   |  ||
   |Control     |     |Control     |  ||
   |Logic       |     |Logic       |  ||
   +------------+     +------------+  ||
   | 802.3PHY   | ... | 802.3PHY   |  ||
   +------------+     +------------+  ||
     Access/Shared          ||        ||
       Ports                |+--------+|

   Figure 2: TRILL OAM in RBridge Port Model

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

2.3 Network, Service and Flow OAM

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   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
   grained label [TRILL-FGL]. The test VLAN can be thought of as a
   management or 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 grained 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 grained 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 [802.1Q], [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, managed 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

   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

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   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 number.

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

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

        <----Site Domain----> <--Interconnect --> <----Site 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

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   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 more 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.

           TRILL Site 1          Interconnect       TRILL Site 2
        +-----------------+ +------------------+ +-----------------+
        |                 | |                  | |                 |
        |  +---+  +---+  +---+  +---+  +---+  +---+  +---+  +---+  |
        |  |RB1|--|RB2|--|RB3|--|RB4|--|RB5|--|RB6|--|RB7|--|RB8|  |
        |  +---+  +---+  +---+  +---+  +---+  +---+  +---+  +---+  |
        |                 | |                  | |                 |
        +-----------------+ +------------------+ +-----------------+



         Legend E: MEP      I: MIP

                              Figure 4: MEPs and MIPs

   It is worth noting that a single RBridge may host multiple MEPs of
   different technologies, e.g. TRILL OAM MEP(s) and [802.1Q] 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. We do not distinguish between Up
   MPs and Down MPs (as defined in [802.1Q]) in this framework. Given
   that the MPs always reside on a special virtual port with no PHY
   layer, MP directionality is irrelevant.

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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

   - Group MP Addresses

   TRILL OAM will 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 be implemented as residing 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 response to Group MP addresses.

3. OAM Frame Format

3.1 Motivation

   In order for TRILL OAM messages to accurately test the data-path,
   these messages must be transparent to transit RBridges. That is, a
   TRILL OAM message must be indistinguishable from a TRILL data frame
   through normal transit RBridge processing. Only the target RBridge,
   which needs to process the message, should identify and trap the
   packet as a control message through normal processing. Additionally
   methods must be provided to prevent OAM packets from being
   transmitted out as native frames.

   The TRILL OAM frame format proposed below provides the necessary
   flexibility to exercise the data path as closely as possible to
   actual data packets.

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   |                               |
   .      Link Header              . Variable
   |                               |
   |                               |
   +      TRILL Header             + 8 bytes
   |                               |
   |                               |
   .   Flow Entropy                . Fixed Size
   .                               .
   |                               |
   |       OAM EtherType           | 2 bytes
   |                               |
   .   OAM Message Channel         . Variable
   .                               .
   |                               |
   |                               |
   .    Link Trailer               . Variable
   |                               |

   Figure 5: OAM Frame Format

   The TRILL Header is as specified in [RFC6325] and the Link Header and
   Trailer are as specified for the link technology. (Link types
   standardized so far are [RFC6325] for Ethernet and [RFC6361] for
   PPP). These fields need to be as similar as practical to the Link
   Header/Trailer and TRILL Header of the normal TRILL data frame
   corresponding to the traffic that OAM is testing.

   The OAM EtherType demarcates the boundary between the Flow Entropy
   and the OAM Message Channel. The OAM EtherType is expected at a
   deterministic offset from the TRILL Header, thereby allowing
   applications to clearly identify the beginning of the OAM Message
   Channel. Additionally, it facilitates the use of the same OAM frame
   structure by different Ethernet technologies.

   The Link Trailer is usually a checksum, such as the Ethernet Frame
   Check Sequence, which is examined at a low level very early in the
   frame input process and automatically generated as part of the low
   level frame output process. If the checksum fails, the frame is

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   normally discarded with no higher level processing.

3.2 Determination of Flow Entropy

   The Flow Entropy is a fixed length field that is populated with
   either real packet data or synthetic data that mimics the intended

   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 a VLAN tag or fine grain label.

   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.

   When performing diagnostics on user flows, the OAM mechanisms must
   allow the network operator to configure the flow entropy parameters
   (e.g. Layer 2 and/or 3) 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.

3.2.1 Address Learning and Flow Entropy

   Edge TRILL switches, like traditional 802.1 bridges, are required to
   learn MAC address associations. Learning is accomplished either by
   snooping data packets or through other methods. The flow entropy
   field of TRILL OAM messages mimics real packets and may impact the
   address learning process of the TRILL data plane. TRILL OAM is
   required to provide methods to prevent any learning of addresses from
   the flow entropy field of OAM messages that would interfere with
   normal TRILL operation. This can be done, for e.g., by
   suppressing/preventing MAC address learning from OAM messages.

3.3 OAM Message Channel

   The OAM Message Channel provides methods to communicate OAM specific
   details between RBridges. [802.1Q] CFM and [RFC4379] have implemented
   OAM message channels. It is desirable to select an appropriate

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   technology and re-use it, instead of redesigning yet another OAM
   channel. TRILL is a transport layer that carries Ethernet frames, so
   the TRILL OAM model specified earlier is based on the [802.1Q] CFM
   model. The use of [802.1Q] CFM encoding format for the OAM Message
   channel is one possible choice. [TRILL-OAM] presents a proposal on
   the use of [802.1Q] CFM payload as the OAM message channel.

3.4 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
   those messages.

   It may be possible to use a combination of one of the unused fields
   or bits in the TRILL Header and the OAM EtherType to identify TRILL
   OAM messages.

   [RFC6325] does not specify any method of identifying OAM messages.
   Hence, for backwards compatibility reasons, TRILL OAM solutions must
   provide methods to identify OAM messages through the use of well-
   known patterns in the Flow Entropy field; for e.g., by using a
   reserved MAC address as the inner MAC SA.

4. Fault Management

   Section 4.1 below discusses proactive fault management and Section
   4.2 discusses on-demand 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
   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.

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   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: 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. For e.g., consider a simple network
   comprising of four RBridges connected in tandem: RB1, RB2, RB3 and
   RB4. Both RB1 and RB4 are hosting TRILL OAM MEPs, whereas RB2 and RB3
   have MIPs. If the link between RB2 and RB3 fails, then RB2 can send a
   forward defect indication towards RB1 while RB3 sends a forward
   defect indication towards RB4.

   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. Reverse Defect Indication (RDI)

   RDI is used to signal that the advertising MEP has detected a loss of
   continuity (LoC) defect. RDI is transmitted in the direction of the
   failure. For e.g., consider the same tandem network of the previous
   section. If RB1 detects that is has lost connectivity to RB4 because
   it is no longer receiving Continuity Check messages from the MEP on
   RB4, then RB1 can transmit an RDI towards RB4 to inform the latter of

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   the failure. If the failure is unidirectional (i.e. it is affecting
   the direction from RB4 to RB1), then the RDI enables RB4 to become
   aware of the unidirectional connectivity anomaly.

   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

   - test traffic patterns as defined in [RFC2544]. 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

   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 operator must supply the source and target RBridges for the
   operation, and the test VLAN/flow information uses pre-set values or

   Connectivity verification at the Flow granularity tests connectivity
   between a MEP on a source RBridge and a MIP or MEP on a target
   RBridge over an operator specified VLAN or fine grain label with
   operator specified flow parameters.

   The above functions must be supported on sections, as defined in
   [TRILL-OAM-REQ]. When connectivity verification is triggered over a

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   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 operator must supply the edge RBridge
   nickname as part of the operation parameters. Multicast

   For multicast, the connectivity verification function tests all
   branches and leaf nodes of a multidestination 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 multidestination
   distribution tree. The operator in this case supplies the tree
   identifier (root RBridge nickname) and campus wide diagnostic VLAN.

   B. Pruned Tree

   - Connectivity verification for a VLAN or fine-grain label in a given
   multidestination distribution tree. The operator in this case
   supplies the tree identifier and VLAN or fine grain label.

   - Connectivity verification for an IP multicast group in a given
   multidestination distribution tree. The operator in this case
   supplies: the tree identifier, VLAN or fine grain label 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

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   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
   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
   implementations must implement the time-stamping function as close to
   the wire as practical 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.

   For general TRILL Security Considerations, see [RFC6325].

7. IANA Considerations

   This document requires no IANA Actions. RFC Editor: Please delete
   this section before publication.

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, work in progress.

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

   [RFC2119]  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.

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   [RFC6291]  Andersson et al., BCP 161 "Guidelines for the Use of the
              "OAM" Acronym in the IETF", June 2011.

   [RFC6327]  Eastlake 3rd, D., Perlman, R., Ghanwani, A., Dutt, D., and
              V. Manral, "Routing Bridges (RBridges): Adjacency", RFC
              6327, July 2011.

   [TRILL-FGL] D. Eastlake et al., "TRILL Fine-Grained Labeling", draft-
              ietf-trill-fine-labeling, work in progress.

   [802.1Q]   "IEEE Standard for Local and metropolitan area networks -
              Media Access Control (MAC) Bridges and Virtual Bridge
              Local Area Networks", IEEE Std 802.1Q-2011, 31 August

   [RFC6371]  Busi & Allan, "Operations, Administration, and Maintenance
              Framework for MPLS-Based Transport Networks", RFC 6371,
              September 2011.

   [802]      "IEEE Standard for Local and Metropolitan Area Networks -
              Overview and Architecture", IEEE Std 802-2001, 8 Match

9.2  Informative References

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

   [ISO/IEC 7498-4] "Information processing systems -- Open Systems
              Interconnection -- Basic Reference Model -- Part 4:
              Management framework", ISO/IEC, 1989.

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

   [TRILL-OAM] T. Senevirathne, et al., "Use of 802.1ag for TRILL OAM
              Messages", draft-tissa-trill-8021ag, work in progress,
              June 2012.

Authors' Addresses

   Samer Salam

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

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

   Sam Aldrin
   Huawei Technologies
   2330 Central Expressway
   Santa Clara, CA 95050, USA
   Email: sam.aldrin@gmail.com

   Donald Eastlake
   Huawei Technologies
   155 Beaver Street
   Milford, MA 01757, USA
   Tel: 1-508-333-2270
   Email: d3e3e3@gmail.com

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