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Versions: (draft-svshah-interdomain-sla-exchange) 00 01 02 03 04 05 06 07 08 09 10 11 12 13

Network Working Group                                            S. Shah
Internet-Draft                                                  K. Patel
Intended status: Standards Track                           Cisco Systems
Expires: December 29, 2013                                      S. Bajaj
                                                        Juniper Networks
                                                             L. Tomotaki
                                                            M. Boucadair
                                                          France Telecom
                                                            Jun 27, 2013

                       Inter-domain SLA Exchange


   Network administrators typically provision QoS (Quality of Service)
   policies for their application traffic (such as voice, video) based
   on SLAs (Service Level Agreements) negotiated with their providers,
   and translate those SLAs to vendor specific configuration language.
   Both learning of SLA, either thru SLA documents or via some other
   out-of-band method, and translating them to vendor specific
   configuration language is a complex, many times manual, process and
   prone to errors.  This document proposes an in-band method of SLA
   signaling which can help to simplify some of the complexities.

   This document defines an operational transitive attribute to signal
   SLA details in-band, across administrative boundaries (considered as
   Autonomous Systems (AS)), thus simplify and speed-up some of the
   complex provisioning tasks.

   Though the use case with the proposed attribute is explicitly defined
   in this document, purpose of this attribute is not limited to this
   use case only.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any

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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 29, 2013.

Copyright Notice

   Copyright (c) 2013 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.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  QoS Attribute Definition . . . . . . . . . . . . . . . . . . .  6
     3.1.  SLA, QoS attribute sub-type, Definition  . . . . . . . . .  7
   4.  Originating SLA Notification . . . . . . . . . . . . . . . . . 16
     4.1.  SLA Contexts . . . . . . . . . . . . . . . . . . . . . . . 16
       4.1.1.  SLA Advertisement for Point-to-Point Connection  . . . 16
       4.1.2.  SLA Advertisement for Destination AS Multiple Hops
               Away . . . . . . . . . . . . . . . . . . . . . . . . . 17
   5.  SLA Attribute Handling at Forwarding Nodes . . . . . . . . . . 17
     5.1.  BGP Node Capable of Processing QoS Attribute . . . . . . . 17
     5.2.  BGP Node not Capable of Processing QoS Attribute . . . . . 18
     5.3.  Aggregator . . . . . . . . . . . . . . . . . . . . . . . . 18
   6.  SLA Attribute Handling at Receiver . . . . . . . . . . . . . . 18
     6.1.  Traffic Class Mapping  . . . . . . . . . . . . . . . . . . 19
   7.  Deployment Considerations  . . . . . . . . . . . . . . . . . . 20
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 22
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 22
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 22
     11.2. Informative References . . . . . . . . . . . . . . . . . . 23
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23

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1.  Introduction

   Typically there is a contractual Service Level Agreement (SLA)
   negotiated between Customer and Provider or between one Provider to
   another Provider [CPP].  This contractual agreement defines the
   nature of the various traffic classes (i.e., traffic match
   conditions) and services needed for each traffic class.  The contract
   may exist at different levels of traffic granularity.  The contract
   could be full line-rate or sub rate for aggregate traffic or it could
   be even finer granular traffic distinction with services defined for
   standard code-points or for specific set of prefix or for set of
   well-known application types.

   Once the SLA is negotiated, it needs to be translated into enforcing
   configuration data and policies on the Provider's Edge (PE) as well
   as on the Customer's Edge (CE).  At the Customer side, a person
   administering the CE device may be a different person, or even a
   different department, from the ones negotiating SLA contracts with
   the Provider and thus an administrator at the CE first requires to
   manually learn negotiated SLA, thru SLA documents or via some other
   off-band method.  In a subsequent step an administrator requires to
   translate SLA to QoS policies using router (vendor) specific
   provisioning language.  In a multi-vendor environment, translating
   the SLA into technology-specific configuration and then enforcing
   that configuration requires to consider specificities of each vendor.
   There does not exist any standard protocol to translate SLA
   agreements into technical clauses and configurations and thus both
   the steps of out of band learning of negotiated SLA and provisioning
   them in a vendor specific language can be complex and error-prone.
   As an example for voice service, the Provider may negotiate service
   for such traffic thru use of EF code-point in Diffserv-enabled
   [RFC2475] networks.  Administrator at the CE side not only will have
   to know that Provider's service for voice traffic is EF-based but
   will also have to implement DSCP EF classification rule along with
   Low Latency Service rule as per vendor's provisioning language.

   Given the Provider also maintains established contracts, which very
   well may even be enforced at the PE, an in-band method of signaling
   it from the PE to the CE can help eliminate manual administrative
   process, at the CE, described above.  Provider may have SLA
   negotiated with the Customer via some defined off-band method (could
   be specifics defined by Provider or could be based on some protocols
   like [CPNP]), orthogonal to actual SLA exchange proposal described in
   this document.  Once negotiated, the Provider may translate that SLA
   in networking language on the PE (this process remains same as is
   done today).  This SLA instance then can be signaled to the CE via
   some in-band protocol exchange.  In reaction to that message,
   receiver CE router may automatically translate that to relevant QoS

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   policy definition on the box.  This in-band signaling method helps
   eliminate manual complex process required by administrator at the CE.
   Taking same voice service as an example, a given Provider might
   already provision definition of EF code-point for such traffic.
   Signaling EF code-point for this traffic class along with signaling
   low latency service definition, would avoid manual administration at
   the CE.

   For in-band signaling, we propose to use BGP as a transport.  The
   details of SLAs are independent of BGP and are specific to the
   granularity of traffic classes and their subsequent treatment.
   Though we find BGP as a suitable transport for inter-domain SLA
   exchange for the following reasons:

        - The most common use case of SLA exchange is across Autonomous
          Systems. And BGP is the most suitable protocol for any inter-
          domain exchange [RFC4271][RFC4364]
        - There is no other suitable protocol available today for SLA
        - BGP updates already advertise specific set of prefixes (flow
          or flow-group). Other QoS-related attributes, apart from the
          the use of SLA advertisement, can be added to these updates
          in the future

   The proposal is to define a new BGP attribute to advertise/learn SLA
   details in-band.  The proposed attribute is intended to advertise SLA
   from one AS to a list of interested ASes.  QoS services advertised
   could be for the incoming traffic to the AS community, that is
   advertising SLA or could be for the outgoing traffic from the
   advertiser or could be for both directions.  Reception of and
   reaction to advertised SLAs are optional for the receiver.

   The aim with the signaling of this attribute, across administrative
   boundaries, is to help network administrators speed up and simplify
   QoS provisioning with automatic learning of SLAs and thus avoiding
   complexities and possible errors with manual learning.

   We propose QoS as an optional transitive attribute, keeping SLA
   advertisement and discovery (request) as one of the sub-types of QoS
   attribute.  This is to keep QoS attribute open for extensions, in
   future, for other SLA specific requirements or even beyond SLA
   specific needs.  For example, SLA Negotiation and Assurance is out of
   scope of this document which can be envisioned as another sub-type.

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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  QoS Attribute Definition

   The QoS Attribute proposed here is an optional transitive attribute
   (attribute type code to be assigned by IANA).  SLA is defined as one
   of the sub-types in the QoS attribute.

       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
       |   Attr flag   | QoS Attr type |                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
       ~                                                               ~
       |                     QoS Attr length/Value                     |

    Attribute flags
        highest order bit (bit 0) -
            MUST be set to 1, since this is an optional attribute

        2nd higher order bit (bit 1) -
            MUST be set to 1, since this is a transitive attribute

    The first octet in the Value field of the QoS attribute is QoS
    attribute specific flags

        highest order bit (bit 0) -
            It defines if update message MUST be dropped (if set to 1)
            without updating routing information base, when this is the
            last BGP receiver from the list of AS this attribute is
            announced to, or MUST announce (if set to 0) further to BGP

            The purpose of this bit is discussed further in subsequent

        Remaining bits are currently unused and MUST be set to 0

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3.1.  SLA, QoS attribute sub-type, Definition

   The value field of the QoS Attribute contains further TLVs, following
   QoS Attribute flags described in the previous section.  One of the
   TLVs that we define is a tuple of (SLA sub-type, Length, Value)

       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
       | QoS Attr flags|      subType  |         sub type Length       |
       ~                                                               ~
       |                               Value                           |

    subType - 8 bits
        0x00        = reserved
        0x01        = SLA
        0x02 - 0x0f = for future use

    SLA sub-type specific value field details 1) sender and receiver(s)
    and 2) SLA parameters. SLA Parameters include SLA event type (such
    as Advertise, Request) and content associated to that event type.

    The format of SLA message is,
       |                    32-bit source AS (Advertiser)              |
       |Optional advertiserid total len|      Advertiser id TLVs       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               ~
       |                                                               |
       ~                                                               ~
       |                                                               |
       |                  32-bit destination AS count                  |
       |                variable list of destination AS                |
       ~                            ....                               ~
       |                            ....                               |
       | Event |             SLA id            |      SLA length       |
       |                    Content as per SLA Event                   |
       ~                                                               ~
       |                                                               |

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    Source AS
        32-bit source AS number. This is the AS that is advertising SLA
        0 = ignore Source and Destination AS list from this Value field.
            Instead refer to Source and Destination AS as defined by BGP
            message. SLA sub-type specifics, from the QoS attribute,
            MUST be removed by the receiver in such case.

    Optional advertiser id total len
        16-bit Source address identifier (optional).
        0 = No optional identifier

        In general any additional qualifier for an advertiser is not
        required. The SLA definition is in the context of prefix
        advertised in the NLRI definition. The exception is where a BGP
        speaker, in the middle of an update path to the destination AS,
        aggregates prefixes. We will refer this middle BGP speaker,that
        aggregates routes, as an Aggregator. Aggregator is then required
        to insert original NLRI details in the optional advertiser field

    Optional Advertiser id TLV
        4-bit type
        0x0  = reserved
        0x1  = ORIGIN_NLRI, variable length
        0x2 to 0xf = for future use,

    Destination AS count
        32-bit destination AS count to take variable length AS list.
        This count has no functional value when Source AS is 0

        0 = broadcast

    Destination AS list
        32-bit destination AS number, this field is omitted if broadcast
        .... [as many as AS count]

    SLA Event Type
        0x0 = reserved
        0x1 = ADVERTISE
        0x2 = REQUEST
        0x3 to 0xf, for future use

    SLA Id
        16-bit identifier unique within the scope of source AS

        The significance of an SLA identifier is in the context of the

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        source that is advertising SLA. SLA identifier is not globally
        unique but it MUST be unique in the context of the source
        AS (advertiser).

        The SLA content is optional for an advertised SLA id. If SLA
        content does not exist in BGP update messages with advertised
        SLA attribute then receiver MUST inherit prior advertised SLA
        content for the same SLA id from the same Source AS.

        If advertised SLA id is different from earlier advertised one,
        for the same prefix, previous SLA MUST be replaced with the new
        advertised one.

        SLA is aggregate for all the traffic to prefixes that share
        same source AS and SLA id.

    SLA Length

    The format of SLA ADVERTISE event message is,

       |dir|       Traffic Class count     | Class Desc Len|           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+           ~
       |                                                               |
       ~                  Traffic Class Description                    ~
       |                                                               |
       |                                                               |
       ~              Traffic Class Elements count/values              ~
       |                                                               |
       | Service  Count|      service type/value pair                  |
       +-+-+-+-+-+-+-+-+                                               ~
       |                                                               |
       ~                                                               ~
       |                                                               |
       |                                                               |
       ~  Repeat from Traffic Class Description for next Traffic Class ~
       |                                                               |
       |                                                               |
       ~    Repeat from direction for SLA in the other direction       ~
       |                                                               |

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        02-bit for incoming or outgoing traffic,
        0x0 = reserved
        0x1 = incoming, from destination AS towards source AS
        0x2 = outgoing, from source AS towards destination AS
        0x3 = for future use

    Traffic Class count (Classifier Groups count)
        16-bit, count of number of classifier groups
        00 = Advertisement to invalidate previous advertised SLA if was

    Traffic Class Descr Length
        08-bit, size of the length

        0 = No description

    Traffic Class Description
        Ascii Description of the Traffic Class

    Traffic Class Elements Count in a Traffic Class,

        08-bit count of classifier elements in a specific Traffic Class

        00 = this has relative definition. It means classify rest all
             traffic that is not classified via earlier described
             Traffic Classes.
             It is RECOMMENDED to have 0 elements Traffic Class
             definition last in the ordered list.If Advertised SLA does
             not have this Traffic Class last in the advertised list,
             receivers MUST re-order it, for the forwarding purpose, as
             the last Traffic Class, in the ordered list, from the
             source AS. It is MUST that advertisement from a specific
             source does not have more than one Traffic classes with
             element count 0. If there are more than one such Traffic
             Classes then advertised SLA MUST be ignored. It is okay
             for SLA message though to have none Traffic Class with
             element count 0.

    Classifier Element values in a Traffic Class (optional),

        08-bit          = IPFIX Element Identifier
        variable-length = based on type of the Element

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        Given IPFIX [RFC5102] has well defined identifier set for a
        large number of packet attributes, IPFIX IANA registry is
        "https://www.ietf.org/assignments/ipfix" chosen to specify
        packet classification attributes. However, since not all
        identifiers from IPFIX would be applicable to this proposal,
        only a limited set identified here can be supported by BGP
        SLA exchange. Any new element identifier, in future, added
        to the IPFIX IANA registry does not automatically mean
        supported for this proposal.

       | ID | Name                       |
       |195 | ipDiffServCodePoint        |
       |203 | mplsTopLabelExp            |
       |244 | dot1qPriority              |
       |  8 | sourceIPv4Address          |
       | 27 | sourceIPv6Address          |
       |  9 | sourceIPv4PrefixLength     |
       | 29 | sourceIPv6PrefixLength     |
       | 44 | sourceIPv4Prefix           |
       |170 | sourceIPv6Prefix           |
       | 12 | destinationIPv4Address     |
       | 28 | destinationIPv6Address     |
       | 13 | destinationIPv4PrefixLength|
       | 30 | destinationIPv6PrefixLength|
       | 45 | destinationIPv4Prefix      |
       |169 | destinationIPv6Prefix      |
       |  4 | protocolIdentifier         |
       |  7 | sourceTransportPort        |
       | 11 | destinationTransportPort   |

    Traffic Class Service count (for a Traffic Class under definition)
        08-bit count of service attributes fields to follow with
               type/value pair
        List of service types and relevant values are discussed below

        00 = no bounded service (also means Best Effort)

    Traffic Class Service (optional),
        16-bit          = type of the field
        variable-length = based on type of the service

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    - 0x00 = reserved

      160-bits TSpec Parameter

      The TRAFFIC_CLASS_TSPEC parameter consists of the (r), (b), (p),
      (m) and (M) parameters as described in Invocation Information
      section of [RFC2212].

       |  Minimum Rate (r) (32-bit IEEE floating point number)         |
       |  Burst Size (b) (32-bit IEEE floating point number)           |
       |  Maximum Rate (p) (32-bit IEEE floating point number)         |
       |  Minimum Policed Unit (m) (32-bit integer)                    |
       |  Maximum Packet Size (M)  (32-bit integer)                    |

      Parameter (r) indicates min-rate of the traffic class. This rate
      indicates the minimum rate, measured in bytes of Layer 2 (L2)
      datagrams per second, service advertiser is providing for a given
      class of traffic on advertiser's hop. Note that it does not
      necessarily translate to a minimum rate service to receiver of an
      SLA unless the traffic class definition clearly represents a sole
      receiver of an SLA. If there is no SLA for min-rate, the value of
      (r) MUST be set to 0.

      Parameter (b) indicates maximum burst size, measured in bytes of
      L2 datagram size. Since queuing delay can be considered a
      function of burst size (b) and min-rate (r), in presence of non-
      zero parameter (r), parameter (b) represents bounded delay for
      the Traffic Class. This delay is a single hop queuing delay when
      SLA is to be implemented at the resource constrained bottleneck.
      In another words this burst size can be considered buffer size.
      Value of 0 for parameter (b) means advertiser does not mandate
      specific bounded delay.

      Parameter (p) indicates max-rate of the traffic class. Just like
      min-rate, max-rate, measured in bytes of L2 datagrams per second,
      field here also indicates service provided by advertiser. If
      advertiser does not have any specific value to set for a given
      class of traffic, it MAY be set to physical interface line rate
      or any other indirect limit that may affect this class' maximum
      rate. In absence of any such known value, it MUST be set to

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      positive infinity. Value 0 is considered an error.

      Parameters (r), (b) and (p) are set each as 32-bit IEEE floating
      point numbers. Positive infinity is represented as an IEEE single
      precision floating-point number with an exponent of all ones and
      a sign mantissa of all zeros.  The format of IEEE floating-point
      numbers is further summarized in [RFC4506].

      The minimum policed unit (m) and maximum packet size (M)
      parameters have no relevance for the purpose of SLA exchange.
      Thus they MUST be ignored.

    - 0x02, L2_OVERHEAD
      08-bit, value

      By default specification of rate and other packet size related
      parameters, advertised in an SLA, includes L2 overhead. This
      overhead by default is L2 overhead of the local link to which SLA
      is advertised to. However, in cases where advertised SLA is for a
      receiver multiple hops away, L2 overhead consideration from the
      source perspective may be different from the local L2 overhead at
      the receiver. Explicit notification of size of L2 overhead from a
      sender, in such cases, is useful for a receiver to distinguish
      local L2 overhead from the sender advertised one. When receiver
      choose to react to an advertised SLA and if this service type is
      present in advertised SLA, receiver MUST use advertised L2
      overhead over local L2 overhead.

      If SLA is required to consider only IP datagram size, sender can
      advertise this service with a value of 0.

      08-bit          = IPFIX Element Identifier
      variable-length = based on type of the Element

       | ID | Name                       |
       |195 | ipDiffServCodePoint        |
       |203 | mplsTopLabelExp            |
       |244 | dot1qPriority              |

      08-bit          = IPFIX Element Identifier

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      variable-length = based on type of the Element

       | ID | Name                       |
       |195 | ipDiffServCodePoint        |
       |203 | mplsTopLabelExp            |
       |244 | dot1qPriority              |

      08-bit          = IPFIX Element Identifier
      variable-length = based on type of the Element

       | ID | Name                       |
       |195 | ipDiffServCodePoint        |
       |203 | mplsTopLabelExp            |
       |244 | dot1qPriority              |

      08-bit          = IPFIX Element Identifier
      variable-length = based on type of the Element

       | ID | Name                       |
       |195 | ipDiffServCodePoint        |
       |203 | mplsTopLabelExp            |
       |244 | dot1qPriority              |

      In the case when MINRATE_IN_PROFILE_MARKING,
      MAXRATE_OUT_PROFILE_MARKING all of them are advertised,
          - MINRATE_IN_PROFILE_MARKING takes highest precedence
            (that is over MAXRATE_IN_PROFILE_MARKING)

          - MAXRATE_IN_PROFILE_MARKING takes precedence over

          - and MAXRATE_OUT_PROFILE_MARKING takes precedence over

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    - 0x07  = DROP_THRESHOLD
      03-bit count of drop-priority fields to follow with
               (type, type-value, burst size) tuple

      04-bit, drop priority type
        08-bit          = IPFIX Element Identifier
        variable-length = based on type of the Element
        32-bit, Burst Size (32-bit IEEE floating point number)

       | ID | Name                       |
       |195 | ipDiffServCodePoint        |
       |203 | mplsTopLabelExp            |
       |244 | dot1qPriority              |

      This finer granular drop threshold does not require separate
      buffer space from the aggregate buffer space. It is just an
      indicator that beyond what size from the aggregate space, this
      code-point specific traffic should all be dropped.

      04-bit, priority value
              lower the value, higher the priority

      Relative priority indicates scheduling priority. For example
      voice traffic, that requires lowest latency compare to any
      other traffic, will have lowest value advertised in relative
      priority. For two different traffic classification groups
      where one application group may be considered more important
      than the other but from scheduling perspective do not require
      to be distinguish with different priority, relative priority
      for those classification groups may be advertised with the
      same value.

      variable-length, repeats all content described above from Traffic
                       Class count onwards.

      For SLAs where a specific Traffic Class may further have
      different sub-services for sub-group of Classifier Elements,
      this service type SHOULD be used to further divide Traffic Class
      in multiple sub-classes. Each sub-class then defined with their
      own classifier elements and service types.

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4.  Originating SLA Notification

   QoS attribute to advertise SLA MUST be added by the originator of a
   BGP UPDATE message.  Any BGP speaker in the forwarding path of a
   message MUST NOT insert QoS attribute for the same prefix.

   SLA messages SHOULD NOT be sent periodically just for the purpose of
   keep alive.  Since SLA changes are in-frequent, some sort of SLA
   policy change can be considered as a trigger for the advertisement.

   For any SLA modification, originator MUST re-advertise entire SLA.
   There is no provision to advertise partial SLA.  To invalidate
   previously advertised SLA, a message MUST be sent with new SLA
   advertisement with Traffic Class count as 0.

4.1.  SLA Contexts

   In certain cases, the advertisement may be to establish SLA for
   aggregate traffic on a point to point connection between a specific
   destination and a specific source.  A point to point connection may
   be a physical link, connecting BGP peers, or may be a virtual link
   (like tunnel).  A BGP update message, in such cases, with source AS
   number and NLRI prefix of source end-point can uniquely identify
   physical/virtual link and so establishes advertised SLA's context for
   aggregate traffic for that point to point link.

   In the simplest case where PE and CE are directly connected via a
   physical link and have only single link between them, CE can uniquely
   identify forwarding link to PE with AS number of the PE and NLRI
   prefix being an address of PE, to CE (that is next hop address from
   CE to PE).  SLA advertised thru BGP update message from PE to CE,
   with PE's AS number and IP address, establishes SLA context for the
   aggregate traffic through link CE to PE.  SLA advertised thru BGP
   update message from PE to CE, with PE's AS number and any other
   prefix establishes SLA for that specific prefix, subset of traffic
   under CE to PE link.

   Even though this example is in the context of IP prefix, SLA exchange
   does not have to be limited to IPv4 family only.  SLA advertisement
   is generic to all forms of NLRI types that are supported by the BGP
   protocol specification (like IPV4, IPV6, VPN-IPV4, VPN-IPV6).

4.1.1.  SLA Advertisement for Point-to-Point Connection

   When SLA messages are intended to be advertised for the point to
   point connection (physical or logical), the message is destined for
   the next hop and advertised message is in the context of the prefix
   of the source end-point of the point to point connection.

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   The destination AS number set to, within QoS SLA attribute, typically
   is of the neighbor BGP speaker's.  Alternatively, originator MAY not
   encode source/destination AS numbers (that is source AS set to 0 and
   destination AS count set to 0), in the QoS attribute.  The most
   significant bit of the QoS attribute flag MAY be set to 1,
   specifically it MUST be set to 1 when intention is to not install
   route update, at the receiver, for the advertised message.

4.1.2.  SLA Advertisement for Destination AS Multiple Hops Away

   When SLA messages are to be advertised beyond next hop, value of
   source AS, in the QoS attribute, MUST be set by the originator of the
   update message.  If such update is meant to be for a specific list of
   AS(es) as receiver then list of destination AS MUST be populated in
   the QoS attribute message to avoid flooding of the QoS attribute data
   in the network beyond those destinations.

   When a new prefix is added in the AS, AS for which SLA has already
   been advertised before for other existing prefixes, then to advertise
   that new prefix to be part of earlier advertised SLA, a trigger of
   new BGP update message with QoS attribute containing SLA id is
   sufficient.  Update message does not require to have whole SLA

   When BGP update messages are triggered as a result of SLA policy
   change and thus only for the purpose of SLA exchange, forwarding BGP
   update messages beyond intended receivers are not necessary.  Highest
   order bit in the QoS Attribute flag MUST be set to suggest receiver
   to drop entire BGP update message [Note that it is an indication to
   drop entire update message, not only QoS attribute], after all
   intended receivers have processed it.  If update message contains
   list of destination AS then message MUST be dropped only after all
   intended receivers (destinations) have received it.

5.  SLA Attribute Handling at Forwarding Nodes

5.1.  BGP Node Capable of Processing QoS Attribute

   If a BGP node is capable of processing QoS attribute, it optionally
   MAY process the message.  If advertised SLA has list of destination
   AS, it MAY trim list and so count of destination AS to exclude ones
   that are not required in further announcement of BGP updates.

   BGP node MUST drop SLA related sub type from the QoS attribute, if
   none of the AS from the destination list is in the forwarding path.

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   Rest of the QoS attributes message MAY be forwarded if there exist
   other sub-types of QoS attribute and forwarding rules meets other
   sub-types requirements.  If there is no other sub-types existing in
   the QoS attribute message then node MUST drop QoS attribute all
   together.  Rest other attributes and NLRI may be announced further if
   it meets rules defined by other attributes and BGP protocol.

   If most significant bit in the QoS attribute flag is set to 1 then
   entire BGP update message MUST be dropped if there are no destination
   left in the list to advertise to.  However, If SLA message is meant
   to be broadcast then message MUST NOT be dropped/trimmed.

   Except extracting entire SLA sub-type of the QoS attribute and
   trimming the list of destination AS list and inserting NLRI at the
   Aggregator node, rest all other content MUST NOT be modified by any
   intermediate receivers of the message.

5.2.  BGP Node not Capable of Processing QoS Attribute

   If BGP node is not capable of processing QoS attribute, it MUST
   forward attribute message as it is received.

5.3.  Aggregator

   It is RECOMMENDED to not aggregate prefixes from BGP update messages
   that contain QoS SLA attribute.  If Aggregator MUST aggregate
   prefixes then it MUST copy QoS SLA attribute in new aggregated BGP
   update message.  At the same time, it MUST also insert NLRI, from the
   original update message, as an optional advertiser id to go along
   with source AS inside the QoS attribute.

   To support SLA exchange multiple hops away in the path that has one
   of the forwarding node in the path acting as Aggregator, it is
   required Aggregator node to be capable of processing QoS attribute.

6.  SLA Attribute Handling at Receiver

   Reception of and reaction to advertised messages are optional for the

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    As described in earlier section, while reacting to SLA advertisement
    - receiver SHOULD invalidate previous advertised SLA and then if one
      exists for advertised NLRI. If new advertised SLA update is with
      non-zero Traffic Class count, new advertised SLA SHOULD be
      installed.  If new advertised SLA update is with Traffic Class
      count 0, no action is required.

    - If advertised QoS Attribute, inside an update message, is with a
      flag set indicating to drop that message, a receiver MUST drop
      message if it is the last receiver, in update path, that message
      is advertised to.

   If advertised SLA is from the next hop, in reverse path, the receiver
   can establish advertised SLA for the whole link, the link could be
   physical or virtual link, associated with the next hop.  If NLRI
   advertised in update message is not of the next hop, receiver may
   establish advertised SLA for that specific prefix list under the
   relevant link.  It is completely up to the receiver to decide for
   which prefixes to accept advertised SLA and for which ones to not.

   For cases where if earlier message has not yet reached to the
   intended receiver, a re-signaling is required.  A signaling event
   REQUEST is required, for this purpose, to be triggered by intended
   receiver.  Since BGP messages are considered reliable, it is assumed
   that advertised messages always reach intended receivers.  Thus
   discussion of REQUEST message, for this purpose or any other purpose,
   is considered out of the scope of this document.

   To handle error conditions, the approach of "attribute-discard" as
   mentioned in [IDR-ERR] MAY be used in an event if a QOS attribute
   parsing results in any attribute errors.  Alternatively, an approach
   of "treat-as-withdraw" MAY be used as mentioned in [IDR-ERR] if an
   implementation also wishes to withdraw the associated prefix.

6.1.  Traffic Class Mapping

   It is common that switching/routing methods used in 2 different AS
   could be different.  For example, Provider may tunnel Customer's IP
   traffic thru MPLS cloud.  In such cases traffic class definition for
   QoS services may differ in both ASes.  For the meaningful use of
   advertised SLA in such cases, receiver is required to map traffic
   class from one type to another.

   In the example given, traffic classification in Customer AS could be
   IP Diffserv based whereas traffic classification in Provider AS could
   be MPLS TC based.  Thus for advertised MPLS TC based SLA from PE, CE
   would require to map traffic class from IP Diffserv based to MPLS TC

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   There are well-defined recommendations that exist for traffic class
   mapping between two technologies.  Receiver MAY use those defined
   recommendations for traffic class mapping or MAY define its own as
   per its network Traffic Class service definition to map to advertised
   Traffic Classes.  It is completely up to the receiver how to define
   such traffic class mapping.

7.  Deployment Considerations

   Typical use case aimed with this proposal is for Provider to
   advertise contracted SLA to Customer Edge.  SLA established between
   customer and Provider is provisioned by the provider on the PE device
   (facing Customer Edge).  This provisioning, in a form supported by
   Provider, is advertised thru proposed BGP QoS attribute to the
   Customer Edge.  Customer may read thru advertised SLA to provision
   one on the Customer Edge link facing towards PE.

   Contracted SLA from PE to CE may be full line-rate or sub-rate of a
   link or finer granular controlled services.  SLA is not required to
   be advertised if the SLA contract is simply a physical link.  SLA
   advertise can be useful when contracted service is sub-rate of a link
   and/or if for finer granular traffic classes that are controlled.
   Like voice, video services may be capped to certain rate.

                __________         /               \
               /          \       /                 \
              /            \     /                   \
              |CustomerSite|-----|      Provider     |
              \           C/E   P\E                  /
               \__________/       \                 /
                   AS 3                   AS 2

                                  SLA_ADVERTISE: AS2 to AS3
                                                 NLRI = PE ip address

   Another use case can be to advertise SLA among different network
   sites within one Enterprise network.  In Hub and Spoke deployments,
   Administrator, being aware of each Spoke's SLA, may define SLAs for
   each of them at the Hub and advertise them thru BGP updates, where at
   each Spoke advertised SLA may translate to a forwarding policy.
   Today administrator has to manually define SLA based forwarding
   policy separately on the Hub as well as on each Spoke.  In a scale

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   network, managing large number of Spokes can be complex.  The
   proposal in such cases would be to define SLAs, to be implemented
   both at the Hub and each Spoke side, on the Hub only and distribute
   them to each Spoke with SLA exchange.

   Alternatively, in a fully automated SLA exchange network, manual
   administration can be avoided or minimized even at the Hub. As shown
   in the figure below, AS2 may first learn its SLA with the Provider
   from the Provider Edge it is connected to.  AS2 then can advertise
   the same or subset of that SLA to AS3 in the context of tunnel's ip

                                                       AS 2
                              _______________        ________
                             /               \      /        \
           __________       /                 \-----| Spoke2 |
          /          \     /                   \    \________/
          |    Hub   |-----|      Provider     |     ________
          \__________/     \                   /    /        \
                            \                 /-----| Spoke1 |
              AS 3           \_______________/      \________/

                                                       AS 1

                                SLA_ADVERTISE: AS2 to AS3
                                               NLRI = AS2 tunnel address

                                SLA_ADVERTISE: AS1 to AS3
                                               NLRI = AS1 tunnel address

   Deployment options are not limited to involving CEs, PE-to-CE or CE-
   to-CE, only.  For any contract between Provider to Provider, SLA may
   be advertised from one PE to another PE also.

8.  Acknowledgements

   Thanks to Fred Baker, David Black, Sue Hares and Benoit Claise for
   their suggestions and to Ken Briley, Rahul Patel, Fred Yip, Lou
   Berger, Brian Carpenter, Bertrand Duvivier for the review.

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9.  IANA Considerations

   The proposal in this document defines a new BGP attribute.  IANA
   maintains the list of existing BGP attribute types.  A new type to be
   added in the list for the QoS attribute.

   The proposal also defines a list for Service types associated to
   Traffic Class.  IANA will be required to maintain this list for
   Traffic Class Service type as a new registry.  Where-as Traffic Class
   Element types, defined in the proposal, refer to existing IPFIX IANA

         Proposed definition of Traffic Class Service Types
             0x00 = reserved
             0x01 = TRAFFIC_CLASS_TSPEC
             0x02 = L2_OVERHEAD
             0x03 = MINRATE_IN_PROFILE_MARKING
             0x05 = MAXRATE_IN_PROFILE_MARKING
             0x07 = DROP_THRESHOLD
             0x08 = RELATIVE_PRIORITY
             0x09 = SUB_TRAFFIC_CLASSES

10.  Security Considerations

   There is a potential for mis-behaved AS to advertise wrong SLA,
   stealing identity of another AS.  This resembles to problems already
   identified and resolved, in the routing world, thru reverse path
   forwarding check.  One proposal, inline to RPF, to resolve such
   threats is to have each BGP speaker node, in the forwarding path,
   perform reverse path check on source AS.  Since we expect these
   messages to originate and distributed in the managed network, there
   should not be any risks for identity theft.  Thus reverse path check
   is not considered in this proposal nor have we considered any
   alternates.  Such solutions can be explored later if any such need.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2212]  Shenker, S., Partridge, C., and R. Guerin, "Specification
              of Guaranteed Quality of Service", RFC 2212,

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              September 1997.

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, February 2006.

   [RFC4506]  Eisler, M., "XDR: External Data Representation Standard",
              STD 67, RFC 4506, May 2006.

   [RFC5102]  Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
              Meyer, "Information Model for IP Flow Information Export",
              RFC 5102, January 2008.

11.2.  Informative References

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, December 1998.

   [IDR-ERR]  Scudder, J., Chen, E., Mohapatra, P., and K. Patel,
              "Revised Error Handling for BGP UPDATE Message,
              I-D.draft-ietf-idr-error-handling", June 2012.

   [CPP]      Boucadair, M., Jacquenet, C., and N. Wang, "IP/MPLS
              Connectivity Provisioning Profile, I-D.boucadair-
              connectivity-provisioning-profile", Sep 2012.

   [CPNP]     Boucadair, M. and C. Jacquenet, "Connectivity Provisioning
              Negotiation Protocol (CPNP), I-D.boucadair-connectivity-
              provisioning-protocol", May 2013.

Authors' Addresses

   Shitanshu Shah
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134

   Email: svshah@cisco.com

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   Keyur Patel
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134

   Email: keyupate@cisco.com

   Sandeep Bajaj
   Juniper Networks
   1194 N. Mathilda Avenue
   Sunnyvale, CA  94089

   Email: sbajaj@juniper.net

   Luis Tomotaki
   400 International
   Richardson, TX  75081

   Email: luis.tomotaki@verizon.com

   Mohamed Boucadair
   France Telecom
   Rennes 35000

   Email: mohamed.boucadair@orange.com

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