Network Working Group                                            S. Shah
Internet-Draft                                                  K. Patel
Intended status: Standards Track                           Cisco Systems
Expires: May 8, November 1, 2014                                       S. Bajaj
                                                        Juniper Networks
                                                             L. Tomotaki
                                                            M. Boucadair
                                                          France Telecom
                                                            Nov 04, 2013
                                                            Apr 30, 2014

                       Inter-domain SLA Exchange


   Network administrators typically enforce Quality of Service (QoS)
   policies according to Service Level Agreement (SLA) with their
   providers.  The enforcement of such policies often relies upon
   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 optional transitive attribute to signal SLA
   details in-band, across administrative boundaries (considered as
   Autonomous Systems (AS)), thus simplifying and facilitating some of
   the complex provisioning tasks.

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

Status of this Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on May 8, November 1, 2014.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  QoS Attribute Definition . . . . . . . . . . . . . . . . . . .  5
     3.1.  SLA, QoS attribute sub-type, Definition  . . . . . . . . .  6
   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  . . . . . . . . . . . . . . . . . . . . . 21
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 22
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 22
     11.2. Informative References . . . . . . . . . . . . . . . . . . 23
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23

1.  Introduction

   Typically there is a contractual Service Level Agreement (SLA)
   established between Customer and Provider or between providers,
   possibly using one or the other form of the template [CPP].  This
   contractual agreement usually 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 for the full line-rate
   or sub line-rate without granular traffic distinction or it could be
   for finer granular traffic classes, with services defined.  Finer
   granular classes can be based on some standard code-points (like
   DSCP) or for a specific set of prefixes or for a set of well-known
   application types.

   Once the SLA is established, SLA parameters are enforced in some or
   all participating devices by deriving SLA parameters into
   configuration information on respective devices.  SLA parameters may
   have to be exchanged through organizational boundaries, thru SLA
   documents or via some other off-band method to an administrator
   provisioning actual devices.  In a subsequent step, administrator
   requires to translate SLA to QoS policies using router (vendor)
   specific provisioning language.  In a multi-vendor network,
   translating SLAs into technology-specific and vendor-specific
   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 QoS
   parameters (like min/max rates) for such traffic based upon the 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, so that traffic exiting CE is marked
   properly, but will also have to know how to implement DSCP EF
   classification rule along with Low Latency Service, and possibly min/
   max rate enforcement for the optimal use of bandwidth, as per vendor
   specific provisioning language.

   An in-band signaling method of propagating SLA parameters from
   provider, PE in an example above, to contractual devices, CE in an
   example above, can help eliminate manual administrative process
   described above.  Provider may have SLA negotiated with the Customer
   via some defined off-band method (based on the specifics defined by
   the Provider or using protocols like [CPNP].  The Inter-domain SLA
   exchange proposal described in this document does not pre-requisite
   any specific method of establishing SLAs).  The Provider provisions
   established SLA on the Provider device.  This SLA instance then can
   be signaled to the Customer via in-band signaling protocol.  In
   reaction to this signal, receiver router may translate that to
   relevant QoS policy definition on the device.

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

        - The need to exchange SLA parameters between domains (Automated
          Systems (AS)), where in use-cases described in this document,
          BGP is a suitable protocol for inter-domain exchange [RFC4271]
        - There is no specifically defined protocol available today for
          SLA exchange
        - 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 destined ASes.  The advertised QoS
   information could be for the incoming traffic to the advertiser, 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.

   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 the QoS attribute open for extensions.
   For example, SLA Negotiation and Assurance is out of scope of this
   document but can be envisioned as another sub-type.

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   | Attr type QoS |                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
       ~                                                               ~
       |                     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

3.1.  SLA, QoS attribute sub-type, Definition

   The value field of the QoS Attribute contains TLVs, followed to 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                           |

    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 destination ASes this
            attribute is announced to, or MUST announce (if set to 0)
            further to BGP peers

            The purpose of this bit is discussed further in subsequent

        Remaining bits are currently unused and MUST be set to 0

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

    SLA sub-type specific value field details. These details contain
    information about 1) sender and receiver(s) and 2) SLA parameters.
    SLA Parameters include SLA event type (such as Advertise, Request)
    and contents 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                   |
       ~                                                               ~
       |                                                               |

    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

    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 = QoS attribute is relevant to every receiver of the message

    Destination AS list
        32-bit destination AS number
        .... [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
        source that is advertising SLA parameters. The SLA identifier
        is not globally unique but it MUST be unique within 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
        QoS attribute, that contains the SLA sub-type, 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 content 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       ~
       |                                                               |

        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 any

    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 that Traffic Class, that has 0 elements,
             is present last in the advertised list of Traffic Classes.
             If Advertised message has it positioned some-where else,
             then receiver MUST re-order it, for the forwarding purpose,
             to the last position in the advertised list of Traffic
             Classes from a given source AS. QoS attribute advertised
             from a specific source MUST NOT have more than one such
             Traffic Classes (Traffic Class with 0 element count). If
             there are more than one such Traffic Classes present then
             advertised SLA parameters MUST be ignored. It is okay
             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

        Given IPFIX [RFC5102] has well defined identifier set for a
        large number of packet attributes, IPFIX IANA registry is
        "" 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

    - 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]. Note that inheriting definition of TSpec
      here does not enable RFC2212 functionality. It purely is the
      Traffic Specification that is inherited here for the purpose of
      SLA exchange.

       |  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 other words this burst size can be considered as a buffer
      size. Value of 0 for parameter (b) means the 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 packets 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
      positive infinity. Value 0 is considered an error.

      Parameters (r), (b) and (p) are each set 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. For the
      receiver next hop, this overhead is the L2 overhead of the local
      link where advertised SLA is received. 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 packet size, sender may
      advertise this service with a value of 0.

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

      00 Identifier = drop, variable-length for this id is 0.

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

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

      00 Identifier = drop, variable-length for this id is 0.

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

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

      00 Identifier = drop, variable-length for this id is 0.

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

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

      00 Identifier = drop, variable-length for this id is 0.

       | 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

    - 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 beyond which code-point specific traffic to be
      discarded when occupancy of aggregate buffers reached to that

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

      Relative priority indicates scheduling priority. For example
      voice traffic, which requires lowest latency compare to any
      other traffic, may 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 a scheduling perspective does not
      require to be distinguished with a 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.

4.  Originating SLA Notification

   The QoS attribute to advertise SLA sub-type MUST be added by the
   originator of a BGP UPDATE message.

   SLA messages SHOULD NOT be sent periodically just for the purpose of
   keep alive.  Some sort of SLA policy change may be considered as a
   trigger for the advertisement.

   For any modified SLA parameters, the originator MUST re-advertise the
   entire set of SLA parameters.  There is no provision to advertise
   partial set of parameters.  To invalidate previously advertised SLA
   parameters, a message MUST be sent with the same SLA id for the same
   source with the Traffic Class count set to 0.

4.1.  SLA Contexts

   In certain cases, the advertisement may relate to an SLA for
   aggregate traffic over a point-to-point connection between a specific
   destination and a specific source.  A point-to-point connection may
   be the physical link, that connects two BGP peers, or may be a
   virtual link (e.g. a 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 that point to point link.

   In the simplest case where Provider (e.g.  PE) and Customer (e.g.
   CE) devices are directly connected via a physical link and have only
   single link between them, CE can uniquely identify the forwarding
   link to PE with AS number of the PE and NLRI prefix being an IP
   address of PE, to CE (that is the 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 prefixes, SLA
   exchange does not have to be limited to the IP address 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.

   The destination AS number set to, within QoS SLA attribute, typically
   is of the neighbor BGP speaker's.  Alternatively, the originator MAY
   not encode source/destination AS numbers (that is the source AS is
   set to 0 and destination AS count is 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 receivers, then the list of destination AS MUST be
   explicitly described 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 parameters
   have already been advertised before for other existing prefixes, and
   if traffic to this new prefix is subject to the same SLA advertised
   earlier then BGP update for this new prefix may include QoS attribute
   containing just an SLA id, an id that was advertised earlier.  The
   corresponding Update message does not require to have the whole SLA
   content.  SLA id is sufficient to relate SLA parameters to new
   advertised prefix.

   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 a
   list of destination ASes, then the 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 a list of destination
   ASes, 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.
   The rest of the QoS attribute contents 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 in the
   QoS attribute content then the node MUST drop the QoS attribute all
   together.  The other attributes and NLRI information may be announced
   further if they meet rules defined by other attributes and BGP

   If the most significant bit in the QoS attribute flag is set to 1
   then the entire BGP update message MUST be dropped if there are no
   destinations left in the list to advertise to.

   Except extracting the entire SLA sub-type of the QoS attribute and
   trimming the list of destination AS list and inserting NLRI at the
   Aggregator node, 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 the BGP node is not capable of processing QoS attribute, it MUST
   forward the QoS attribute message unaltered.

5.3.  Aggregator

   It is RECOMMENDED to not aggregate prefixes from 2 or more BGP update
   messages into one BGP update, when original messages contain the QoS
   attribute with SLA sub-type contents.  If Aggregator MUST aggregate
   them then it MUST copy entire parameter set of an SLA sub-type from
   the QoS attribute in the new aggregated BGP update message.  At the
   same time, it MUST also insert NLRI information, 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 acting as an Aggregator, it is required that
   the Aggregator node is capable of processing the QoS attribute.

6.  SLA Attribute Handling at Receiver

   Reception of and processing of advertised QoS SLA content are
   optional for the receiver.

      While reacting to SLA advertisement
      - receiver SHOULD invalidate previous advertised SLA parameters if
        one exists for the same SLA id and source AS. 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 the advertised SLA is from the next hop, in the reverse path, the
   receiver may implement 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 it should accept advertised SLA and for which ones it

   For cases where if earlier messages have not reached the intended
   receiver yet, a re-signaling is required.  A receiver may intend to
   request an SLA message from the originator in such case.  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 the event 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 possible that switching/routing methods used in 2 different
   ASes 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 the other.

   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 would
   require to map traffic class from IP Diffserv-based to MPLS TC type.

   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

   One of the use cases is for a Provider to advertise contracted SLA
   parameters to Customer Edge (CE).  The SLA parameters are provisioned
   by the provider on the PE device (facing CE).  This provisioned SLA
   parameters are then advertised thru proposed BGP QoS attribute to the
   CE device.  CE device may read the attribute and SLA sub-type content
   to implement the QoS policy on the device.

   Contracted SLA from PE to CE may be full line-rate or sub line-rate
   or finer granular controlled services.  SLA advertise can be useful
   when contracted service is sub-rate of a link and/or when for finer
   granular traffic classes that are controlled (e.g. 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 SLAs 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.  In
   a scale network, managing a large number of Spokes can be complex.
   The proposal in such cases would be to provision SLA parameters at
   the Hub only and distribute them to each Spoke with SLA exchange
   protocol described here.

   Alternatively, in a network that supports SLA parameters signaling
   capabilities with the Provider, 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 can advertise the same or a subset of that SLA to
   AS3 in the context of tunnel's ip address.

                                                       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 two providers, SLA parameters
   may be advertised from one to the other.

8.  Acknowledgements

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

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,
              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


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

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


   Luis Tomotaki
   400 International
   Richardson, TX  75081


   Mohamed Boucadair
   France Telecom
   Rennes 35000