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Versions: (draft-svshah-bgp-qos-sla-attribute) 00 01 02 03 draft-ietf-idr-sla-exchange

Network Working Group                                            S. Shah
Internet-Draft                                                  K. Patel
Intended status: Standards Track                           Cisco Systems
Expires: April 22, 2013                                         S. Bajaj
                                                        Juniper Networks
                                                             L. Tomotaki
                                                                 Verizon
                                                            M. Boucadair
                                                          France Telecom
                                                            Oct 19, 2012


                       Inter-domain SLA Exchange
                draft-svshah-interdomain-sla-exchange-03

Abstract

   Network administrators typically provision QoS policies for their
   application traffic (such as voice, video) based on SLAs 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)), and thus simplify/speed-up some of the
   complex 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 April 22, 2013.

Copyright Notice

   Copyright (c) 2012 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
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   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.




















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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  QoS Attribute Definition . . . . . . . . . . . . . . . . . . .  6
     3.1.  SLA, QoS attribute sub-type, Definition  . . . . . . . . .  6
   4.  Originating SLA Notification . . . . . . . . . . . . . . . . . 14
     4.1.  SLA Contexts . . . . . . . . . . . . . . . . . . . . . . . 15
       4.1.1.  SLA advertisement for point to point connection  . . . 15
       4.1.2.  SLA advertisement for destination AS multiple hops
               away . . . . . . . . . . . . . . . . . . . . . . . . . 15
   5.  SLA Attribute handling at forwarding nodes . . . . . . . . . . 16
     5.1.  BGP node capable of processing QoS attribute . . . . . . . 16
     5.2.  BGP node not capable of processing QoS attribute . . . . . 17
     5.3.  Aggregator . . . . . . . . . . . . . . . . . . . . . . . . 17
   6.  SLA attribute handling at Receiver . . . . . . . . . . . . . . 17
     6.1.  Traffic class mapping  . . . . . . . . . . . . . . . . . . 18
   7.  Deployment Consideration . . . . . . . . . . . . . . . . . . . 18
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 21
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 22
     11.2. Informative References . . . . . . . . . . . . . . . . . . 22
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22


























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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, 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.
   For an example for voice service, the Provider may negotiate service
   for such traffic thru EF code-point in Diffserv networks.
   Administrator at the CE 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 described above.  Provider may have SLA negotiated with the
   Customer via some defined off-band method.  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 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



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   example, given Provider already may provision definition of EF code-
   point for such, signaling this code-point traffic class from PE to CE
   along with low latency service definition, omits administrator at the
   CE to worry about such translation.

   For in-band signaling, we propose use of BGP 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
        - There is no other suitable 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 a definition of a new BGP attribute to advertise/
   learn SLA details in-band.  The BGP attribute proposed, in this
   document, is intended to advertise SLA from one AS to a list of
   interested AS.  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.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this



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   document are to be interpreted as described in RFC2119.


3.  QoS Attribute Definition

   The QoS Attribute proposed, in BGP, 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 data-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 peers

               The purpose of this bit is discussed further in
               subsequent sections.

           Remaining bits are currently unused and MUST be set to 0


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)



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       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                   |
       ~                                                               ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Source AS



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        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
        4-bits
        0x0 = reserved
        0x1 = ADVERTISE
        0x2 = REQUEST
        0x3 to 0xf, for future use




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   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. 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
        12-bits


   The format of SLA ADVERTISE event 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 ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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       |                                                               |
       ~    Repeat from direction for SLA in the other direction       ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   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 was
             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 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.




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   Classifier Element values in a Traffic Class (optional),

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

        Element Types (08-bit)
        0x00 = Invalid
        0x01 = Reserved
        0x02 = IP_DSCP,   (length = 06-bits, value = 0..63)
        0x03 = MPLS_TC,   (length = 03-bits, value = 0..7)
        0x04 = 802_1Q_COS,(length = 03-bits, value = 0..7)
        0x05 = 802_1Q_DEI,(length = 01-bit, value = 0..1)
        0x06 = PHB_ID,    (length = 12-bits, value = 0..4095)
        0x07 to 0xff = for future use




   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


    - 0x01 = MINRATE
      04-bit, unit type
          0x00 = reserved
          0x04 = PERCENT
          0x05 = KBPS
          0x06 to 0x0f = for future use
      32-bit, value in unit kbps


    - 0x02 = MINRATE_BURST
      32-bit, value in bytes




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    - 0x03 = MINRATE_IN_PROFILE_MARKING
      04-bit, re-mark type
              0x00 = Invalid
              0x01 = Reserved
              0x02 = IP_DSCP
              0x03 = MPLS_TC
              0x04 = 802_1Q_COS
              0x05 = 802_1Q_DEI
              0x06 to 0x0f = for future use
      08-bit, value


    - 0x04 = MINRATE_OUT_PROFILE_MARKING
      04-bit, re-mark type
              0x00 = Invalid
              0x01 = Reserved
              0x02 = IP_DSCP
              0x03 = MPLS_TC
              0x04 = 802_1Q_COS
              0x05 = 802_1Q_DEI
              0x06 to 0x0f = for future use
      08-bit, value


    - 0x05 = MAXRATE
      04-bit, unit type
          0x00 = reserved
          0x04 = PERCENT
          0x05 = KBPS
          0x06 to 0x0f = for future use
      32-bit, value


    - 0x06 = MAXRATE_BURST
      32-bit, value in bytes


    - 0x07 = MAXRATE_IN_PROFILE_MARKING
      04-bit, re-mark type
              0x00 = Invalid
              0x01 = Reserved
              0x02 = IP_DSCP
              0x03 = MPLS_TC
              0x04 = 802_1Q_COS
              0x05 = 802_1Q_DEI
              0x06 to 0x0f = for future use
      08-bit, value




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    - 0x08 = MAXRATE_OUT_PROFILE_MARKING
      04-bit, re-mark type
              0x00 = Invalid
              0x01 = DROP
              0x02 = IP_DSCP
              0x03 = MPLS_TC
              0x04 = 802_1Q_COS
              0x05 = 802_1Q_DEI
              0x06 to 0x0f = for future use
      08-bit, value

      In the case when MINRATE_IN_PROFILE_MARKING,
      MINRATE_OUT_PROFILE_MARKING, MAXRATE_IN_PROFILE_MARKING and
      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
            MINRATE_OUT_PROFILE_MARKING

          - and MAXRATE_OUT_PROFILE_MARKING takes precedence over
            MINRATE_OUT_PROFILE_MARKING



    - 0x09  = DROP_THRESHOLD
      03-bit count of drop-priority fields to follow with
               (type,value, unit,value) tuple

      04-bit, drop priority type
              0x00 = Invalid
              0x01 = None
              0x02 = IP_DSCP
              0x03 = MPLS_EXP
              0x04 = 802_1Q_COS
              0x05 = 802_1Q_DEI
              0x06 to 0x0f = for future use
      08-bit, drop priority type value

      04-bit, unit type
          0x00 = reserved
          0x01 = TIME_US
          0x02 = PERCENT
          0x03 to 0x0f = for future use
      08-bit, drop threshold value as per unit type





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    - 0x0A = RELATIVE_PRIORITY
      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.




    - 0x0B = SUB_TRAFFIC_CLASSES
      variable-length, repeats all content described above from Traffic
                       Class count onwards.

      For SLAs where a specific Traffic Class may further have
      differentiated 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

   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.







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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 that is 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.

   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 specific list of
   AS(es) as receiver then list of destination AS MUST be populated in



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   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
   content.



   When BGP update messages are triggered as a result of SLA policy
   change and so for the purpose of SLA exchange only, 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 of 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.
   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, trimming
   the list of destination AS list and inserting NLRI at Aggregator



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   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 in 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
   receiver.

    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 is with flag set to indicate to drop
      this message, receiver MUST drop message if it is the last
      receiver, in the update path, this 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



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   REQUEST is required, for this purpose, to be triggered by intended
   receiver.  Since BGP messages are considered reliable, discussion of
   REQUEST, 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 technologies 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 is also different in both AS.  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
   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 Consideration

   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



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   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,
   Hub may define SLA for individual spokes and advertise this SLA thru
   BGP updates.



                                                       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 = AS2 tunnel address


   It very well could be possible that AS2 may first learn its SLA with
   Provider from Provider Edge it is connected to and then advertises



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   same or subset of the SLA to AS3 with AS2 to AS3 tunnel's ip address
   as NLRI.

   Deployment options are not limited to involving CEs 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 for his suggestions and to Ken Briley, Rahul
   Patel, Fred Yip, Lou Berger and Brian Carpenter for the review.
   Thanks to Bertrand Duvivier for his valuable contributions to help
   make subsequent revision better.


9.  IANA Considerations

   This document defines a new BGP attribute.  IANA maintains the list
   of existing BGP attribute types.  Proposal is to define a new
   attribute type code for the QoS attribute.

   With the proposal, there is a list defined for Traffic Class Elements
   type and associated Service types.  IANA will be required to maintain
   list of both new types.


























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         Proposed definition of Traffic Class Element Types
              0x00 = Invalid
              0x01 = Reserved
              0x02 = IP_DSCP,   (length = 06-bits, value = 0..63)
              0x03 = MPLS_TC,   (length = 03-bits, value = 0..7)
              0x04 = 802_1Q_COS,(length = 03-bits, value = 0..7)
              0x05 = 802_1Q_DEI,(length = 01-bit, value = 0..1)
              0x06 = PHB_ID,    (length = 12-bits, value = 0..4095)

         Proposed definition of Traffic Class Service Types
             0x00 = reserved
             0x01 = MINRATE
             0x02 = MINRATE_BURST
             0x03 = MINRATE_IN_PROFILE_MARKING
             0x04 = MINRATE_OUT_PROFILE_MARKING
             0x05 = MAXRATE
             0x06 = MAXRATE_BURST
             0x07 = MAXRATE_IN_PROFILE_MARKING
             0x08 = MAXRATE_OUT_PROFILE_MARKING
             0x09 = DROP_THRESHOLD
             0x0A = RELATIVE_PRIORITY
             0x0B = SUB_TRAFFIC_CLASSES


         Proposed definition of Unit Types
             0x00 = reserved
             0x01 = TIME_US
             0x02 = PERCENT
             0x03 = KBPS


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



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11.1.  Normative References

   [RFC1771]  Rekhter, Y. and T. Li, "A Border Gateway Protocol 4
              (BGP-4)", RFC 1771, March 1995.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              December 1998.

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

   [RFC3140]  Black, D., Brim, S., Carpenter, B., and F. Le Faucheur,
              "Per Hop Behavior Identification Codes", RFC 3140,
              June 2001.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              July 2003.

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

   [RFC4360]  Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
              Communities Attribute", RFC 4360, February 2006.

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

   [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.

11.2.  Informative References

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











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Authors' Addresses

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

   Email: svshah@cisco.com


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

   Email: keyupate@cisco.com


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

   Email: sbajaj@juniper.net


   Luis Tomotaki
   Verizon
   400 International
   Richardson, TX  75081
   US

   Email: luis.tomotaki@verizon.com


   Mohamed Boucadair
   France Telecom
   Rennes 35000
   France

   Email: mohamed.boucadair@orange.com







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