Network Working Group                                              Z. Li
Internet-Draft                                                    Huawei
Intended status: Standards Track                                   L. Ou
Expires: 29 January 2022                                          Y. Luo
                                                  China Telcom Co., Ltd.
                                                                   S. Lu
                                                                 Tencent
                                                               G. Mishra
                                                            Verizon Inc.
                                                                 H. Chen
                                                               Futurewei
                                                               S. Zhuang
                                                                 H. Wang
                                                                  Huawei
                                                            28 July 2021


          BGP Extensions for Routing Policy Distribution (RPD)
                         draft-ietf-idr-rpd-12

Abstract

   It is hard to adjust traffic and optimize traffic paths in a
   traditional IP network from time to time through manual
   configurations.  It is desirable to have a mechanism for setting up
   routing policies, which adjusts traffic and optimizes traffic paths
   automatically.  This document describes BGP Extensions for Routing
   Policy Distribution (BGP RPD) to support this.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119] [RFC8174]
   when, and only when, they appear in all capitals, as shown here.

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 https://datatracker.ietf.org/drafts/current/.






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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 29 January 2022.

Copyright Notice

   Copyright (c) 2021 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 (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Inbound Traffic Control . . . . . . . . . . . . . . . . .   4
     3.2.  Outbound Traffic Control  . . . . . . . . . . . . . . . .   5
   4.  Protocol Extensions . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Using a New AFI and SAFI  . . . . . . . . . . . . . . . .   6
     4.2.  BGP Wide Community and Atoms  . . . . . . . . . . . . . .   8
       4.2.1.  RouteAttr Sub-TLV . . . . . . . . . . . . . . . . . .   8
       4.2.2.  Sub-TLVs of the Parameters TLV  . . . . . . . . . . .  12
     4.3.  Capability Negotiation  . . . . . . . . . . . . . . . . .  14
   5.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     5.1.  Application Scenario  . . . . . . . . . . . . . . . . . .  15
     5.2.  About Failure . . . . . . . . . . . . . . . . . . . . . .  16
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  17
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  17
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     9.1.  Existing Assignments  . . . . . . . . . . . . . . . . . .  17
     9.2.  RouteAttr Atom Type . . . . . . . . . . . . . . . . . . .  18
     9.3.  Route Attributes Sub-sub-TLV Registry . . . . . . . . . .  18
     9.4.  Attribute Change Sub-TLV Registry . . . . . . . . . . . .  18
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     10.2.  Informative References . . . . . . . . . . . . . . . . .  20



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   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   It is difficult to optimize traffic paths in a traditional IP network
   because of the following:

   *  Complex and error prone configuration.  Traffic can only be
      adjusted device by device.  The configurations on all the routers
      that the traffic traverses need to be changed or added.  There are
      already lots of policies configured on the routers in an
      operational network.  There are different types of policies, which
      include security, management and control policies.  These policies
      are relatively stable.  However, the policies for adjusting
      traffic are dynamic.  Whenever the traffic through a route is not
      expected, the policies to adjust the traffic for that route are
      configured on the related routers.  It is complex and error prone
      to dynamically add or change the policies to the existing policies
      on the special routers to adjust the traffic.

   *  Difficult maintenance.  The routing policies used to control
      network routes are dynamic, posing difficulties to subsequent
      maintenance.  High maintenance skills are required.

   It is desirable to have an automatic mechanism for setting up routing
   policies, which can simplify routing policy configuration.  This
   document describes extensions to BGP for Routing Policy Distribution
   to resolve these issues.

2.  Terminology

   The following terminology is used in this document.

   *  ACL: Access Control List

   *  BGP: Border Gateway Protocol [RFC4271]

   *  FS: Flow Specification

   *  NLRI: Network Layer Reachability Information [RFC4271]

   *  PBR: Policy-Based Routing

   *  RPD: Routing Policy Distribution

   *  VPN: Virtual Private Network





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3.  Problem Statement

   Providers have the requirement to adjust their business traffic
   routing policies from time to time because of the following:

   *  Business development or network failure introduces link congestion
      and overload.

   *  Business changes or network additions produce unused resources
      such as idle links.

   *  Network transmission quality is decreased as the result of delay,
      loss and they need to adjust traffic to other paths.

   *  To control OPEX and CPEX, they may prefer the transit provider
      with lower price.

3.1.  Inbound Traffic Control

   In Figure 1, for the reasons above, the provider P of AS100 may wish
   the inbound traffic from AS200 to enter AS100 through link L3 instead
   of the others.  Since P doesn't have any administrative control over
   AS200, there is no way for P to directly modify the route selection
   criteria inside AS200.



























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                  Traffic from PE1 to Prefix1
             ----------------------------------->

   +-----------------+            +-------------------------+
   |     +---------+ |        L1  | +----+      +----------+|
   |     |Speaker1 | +------------+ |IGW1|      |policy    ||
   |     +---------+ |**      L2**| +----+      |controller||
   |                 |  **    **  |             +----------+|
   | +---+           |    ****    |                         |
   | |PE1|           |    ****    |                         |
   | +---+           |  **    **  |                         |
   |     +---------+ |**      L3**| +----+                  |
   |     |Speaker2 | +------------+ |IGW2|      AS100       |
   |     +---------+ |        L4  | +----+                  |
   |                 |            |                         |
   |    AS200        |            |                         |
   |                 |            |  ...                    |
   |                 |            |                         |
   |     +---------+ |            | +----+      +-------+   |
   |     |Speakern | |            | |IGWn|      |Prefix1|   |
   |     +---------+ |            | +----+      +-------+   |
   +-----------------+            +-------------------------+

               Prefix1 advertised from AS100 to AS200
             <----------------------------------------

                   Figure 1: Inbound Traffic Control case

3.2.  Outbound Traffic Control

   In Figure 2, the provider P of AS100 prefers link L3 for the traffic
   to the destination Prefix2 among multiple exits and links to AS200.
   This preference can be dynamic and might change frequently because of
   the reasons above.  So, provider P expects an efficient and
   convenient solution.
















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                  Traffic from PE2 to Prefix2
             ----------------------------------->
   +-------------------------+            +-----------------+
   |+----------+      +----+ |L1          | +---------+     |
   ||policy    |      |IGW1| +------------+ |Speaker1 |     |
   ||controller|      +----+ |**        **| +---------+     |
   |+----------+             |L2**    **  |        +-------+|
   |                         |    ****    |        |Prefix2||
   |                         |    ****    |        +-------+|
   |                         |L3**    **  |                 |
   |      AS100       +----+ |**        **| +---------+     |
   |                  |IGW2| +------------+ |Speaker2 |     |
   |                  +----+ |L4          | +---------+     |
   |                         |            |                 |
   |+---+                    |            |    AS200        |
   ||PE2|              ...   |            |                 |
   |+---+                    |            |                 |
   |                  +----+ |            | +---------+     |
   |                  |IGWn| |            | |Speakern |     |
   |                  +----+ |            | +---------+     |
   +-------------------------+            +-----------------+

               Prefix2 advertised from AS200 to AS100
             <----------------------------------------

                  Figure 2: Outbound Traffic Control case

4.  Protocol Extensions

   This document specifies a solution using a new AFI and SAFI with the
   BGP Wide Community for encoding a routing policy.

4.1.  Using a New AFI and SAFI

   A new AFI and SAFI are defined: the Routing Policy AFI whose
   codepoint 16398 has been assigned by IANA, and SAFI whose codepoint
   75 has been assigned by IANA.

   The AFI and SAFI pair uses a new NLRI, which is defined as follows:












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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
   +-+-+-+-+-+-+-+-+
   |  NLRI Length  |
   +-+-+-+-+-+-+-+-+
   |  Policy Type  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Distinguisher (4 octets)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Peer IP (4/16 octets)                    ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

   NLRI Length:  1 octet represents the length of NLRI.  If the Length
      is anything other than 9 or 21, the NLRI is corrupt and the
      enclosing UPDATE message MUST be ignored.

   Policy Type:  1 octet indicates the type of a policy.  1 is for
      Export policy. 2 is for Import policy.  If the Policy Type is any
      other value, the NLRI is corrupt and the enclosing UPDATE message
      MUST be ignored.

   Distinguisher:  4 octet unsigned integer that uniquely identifies the
      content/policy.  It is used to sort/order the polices from the
      lower to higher distinguisher.  They are applied in order.  The
      policy with a lower/smaller distinguisher is applied before the
      policies with higher/larger distinguishers.

   Peer IP:  4/16 octet value indicates IPv4/IPv6 peers.  Its default
      value is 0, which indicates that when receiving a BGP UPDATE
      message with the NLRI, a BGP speaker will apply the policy in the
      message to all its IPv4/IPv6 peers.

   Under RPD AFI/SAFI, the RPD routes are stored and ordered according
   to their keys.  Under IPv4/IPv6 Unicast AFI/SAFI, there are IPv4/IPv6
   unicast routes learned and various static policies configured.  In
   addition, there are dynamic RPD policies from the RPD AFI/SAFI when
   RPD is enabled.

   Before advertising an IPv4/IPv6 Unicast AFI/SAFI route, the
   configured policies are applied to it first, and then the RPD Export
   policies are applied.

   The NLRI containing the Routing Policy is carried in MP_REACH_NLRI
   and MP_UNREACH_NLRI path attributes in a BGP UPDATE message, which
   MUST also contain the BGP mandatory attributes and MAY contain some
   BGP optional attributes.



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   When receiving a BGP UPDATE message with routing policy, a BGP
   speaker processes it as follows:

   *  If the peer IP in the NLRI is 0, then apply the routing policy to
      all the remote peers of this BGP speaker.

   *  If the peer IP in the NLRI is non-zero, then the IP address
      indicates a remote peer of this BGP speaker and the routing policy
      will be applied to it.

   The content of the Routing Policy is encoded in a BGP Wide Community.

4.2.  BGP Wide Community and Atoms

   The BGP wide community is defined in
   [I-D.ietf-idr-wide-bgp-communities].  It can be used to facilitate
   the delivery of new network services and be extended easily for
   distributing different kinds of routing policies.

   A wide community Atom is a TLV (or sub-TLV), which may be included in
   a BGP wide community container (or BGP wide community for short)
   containing some BGP Wide Community TLVs.  Three BGP Wide Community
   TLVs are defined in [I-D.ietf-idr-wide-bgp-communities], which are
   BGP Wide Community Target(s) TLV, Exclude Target(s) TLV, and
   Parameter(s) TLV.  The value of each of these TLVs comprises a series
   of Atoms, each of which is a TLV (or sub-TLV).  A new wide community
   Atom is defined for BGP Wide Community Target(s) TLV and a few new
   Atoms are defined for BGP Wide Community Parameter(s) TLV.  For your
   reference, the format of the TLV is illustrated below:

    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
   +-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |             Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Value (variable)                      ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Format of Wide Community Atom TLV

4.2.1.  RouteAttr Sub-TLV

   A RouteAttr Atom sub-TLV (or RouteAttr sub-TLV for short) is defined
   and may be included in a Target TLV.  It has the following format.







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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type (TBD1)  |        Length (variable)        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         sub-sub-TLVs                          ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Format of RouteAttr Atom sub-TLV

   The Type for RouteAttr is TBD1.  In RouteAttr sub-TLV, four sub-sub-
   TLVs are defined: IPv4 Prefix, IPv6 Prefix, AS-Path, and Community
   sub-sub-TLV.

   An IP prefix sub-sub-TLV gives matching criteria on IPv4 prefixes.
   Its format is illustrated below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type  1      |         Length (N x 8)        |M-Type | Flags |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          IPv4 Address                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Mask      |     GeMask    |     LeMask    |M-Type | Flags |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~       . . .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          IPv4 Address                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Mask      |     GeMask    |     LeMask    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Format of IPv4 Prefix sub-sub-TLV

   Type:  1 for IPv4 Prefix.

   Length:  N x 8, where N is the number of tuples <M-Type, Flags, IPv4
      Address, Mask, GeMask, LeMask>.  If Length is not a multiple of 8,
      the Atom is corrupt and the enclosing UPDATE message MUST be
      ignored.

   M-Type:  4-bit field specifying match type.  The following four
      values are defined:

      M-Type = 0:  Exact match with the Mask length IP address prefix.
         GeMask and LeMask MUST be sent as zero and ignored on receipt.




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      M-Type = 1:  Match prefix greater and equal to the given masks.

      M-Type = 2:  Match prefix less and equal to the given masks.

      M-Type = 3:  Match prefix within the range of the given masks.

   Flags:  4 bits.  No flags are currently defined.

   IPv4 Address:  4 octets for an IPv4 address.

   Mask:  1 octet for the IP address prefix length.

   GeMask:  1 octet for match range's lower bound, must not be less than
      Mask or be 0.

   LeMask:  1 octet for match range's upper bound, must be greater than
      Mask or be 0.

   For example, tuple <M-Type=0, Flags=0, IPv4 Address = 1.1.0.0, Mask =
   22, GeMask = 0, LeMask = 0> represents an exact IP prefix match for
   1.1.0.0/22.

   <M-Type=1, Flags=0, IPv4 Address = 16.1.0.0, Mask = 24, GeMask = 24,
   LeMask = 0> represents match IP prefix 1.1.0.0/24 greater-equal 24
   (i.e., 1.1.0.0/24 or 1.1.0.0/25 or ... or 1.1.0.0/32).

   <M-Type=2, Flags=0, IPv4 Address = 17.1.0.0, Mask = 24, GeMask = 0,
   LeMask = 26> represents match IP prefix 17.1.0.0/24 less-equal 26
   (i.e., 17.1.0.0/24 or 17.1.0.0/25 or 17.1.0.0/26).

   <M-Type=3, Flags=0, IPv4 Address = 18.1.0.0, Mask = 24, GeMask = 24,
   LeMask = 32> represents match IP prefix 18.1.0.0/24 greater-equal 24
   and less-equal 32 (i.e., 18.1.0.0/24 or 18.1.0.0/25 or ... or
   18.1.0.0/32).

   Similarly, an IPv6 Prefix sub-sub-TLV represents match criteria on
   IPv6 prefixes.  Its format is illustrated below:














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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Type  4     |         Length (N x 20)       |M-Type | Flags |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     IPv6 Address (16 octets)                  ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Mask      |     GeMask    |     LeMask    |M-Type | Flags |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~       . . .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      IPv6 Address (16 octets                  ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Mask      |     GeMask    |     LeMask    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Format of IPv6 Prefix sub-sub-TLV

   An AS-Path sub-sub-TLV represents a match criteria in a regular
   expression string.  Its format is illustrated below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type  2      |      Length (Variable)        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    AS-Path Regex String                       |
   :                                                               :
   |                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Format of AS Path sub-sub-TLV

   Type:  2 for AS-Path.

   Length:  Variable, maximum is 1024.

   AS-Path Regex String:  AS-Path regular expression string.

   A community sub-sub-TLV represents a list of communities to be
   matched all.  Its format is illustrated below:










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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type  3      |        Length (N x 4 + 1)       |    Flags    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Community 1 Value                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                              . . .                            ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Community N Value                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Format of Community sub-sub-TLV

   Type:  3 for Community.

   Length:  N x 4 + 1, where N is the number of communities.  If Length
      is not a multiple of 4 plus 1, the Atom is corrupt and the
      enclosing UPDATE MUST be ignored.

   Flags:  1 octet.  No flags are currently defined.  These bits MUST be
      sent as zero and ignored on receipt.

4.2.2.  Sub-TLVs of the Parameters TLV

   This document introduces 2 community values:

   MATCH AND SET ATTR:  If the IPv4/IPv6 unicast routes to a remote peer
      match the specific conditions defined in the routing policy
      extracted from the RPD route, then the attributes of the IPv4/IPv6
      unicast routes will be modified when sending to the remote peer
      per the actions defined in the RPD route.

   MATCH AND NOT ADVERTISE:  If the IPv4/IPv6 unicast routes to a remote
      peer match the specific conditions defined in the routing policy
      extracted from the RPD route, then the IPv4/IPv6 unicast routes
      will not be advertised to the remote peer.

   For the Parameter(s) TLV, two action sub-TLVs are defined: MED change
   sub-TLV and AS-Path change sub-TLV.  When the community in the
   container is MATCH AND SET ATTR, the Parameter(s) TLV can include
   these sub-TLVs.  When the community is MATCH AND NOT ADVERTISE, the
   Parameter(s) TLV's value is empty.

   A MED change sub-TLV indicates an action to change the MED.  Its
   format is illustrated below:





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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type  1      |          Length (5)           |      OP       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Value                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Format of MED Change sub-TLV

   Type:  1 for MED Change.

   Length:  5.  If Length is any other value, the sub-TLV is corrupt and
      the enclosing UPDATE MUST be ignored.

   OP:  1 octet.  Three are defined:

      OP = 0:  assign the Value to the existing MED.

      OP = 1:  add the Value to the existing MED.  If the sum is greater
         than the maximum value for MED, assign the maximum value to
         MED.

      OP = 2:  subtract the Value from the existing MED.  If the
         existing MED minus the Value is less than 0, assign 0 to MED.

      If OP is any other value, the sub-TLV is ignored.

   Value:  4 octets.

   An AS-Path change sub-TLV indicates an action to change the AS-Path.
   Its format is illustrated below:



















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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type  2      |        Length (n x 5)         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             AS1                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Count1     |
   +-+-+-+-+-+-+-+-+
   ~       . . .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             ASn                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Countn     |
   +-+-+-+-+-+-+-+-+

                         Format of AS-Path Change sub-TLV

   Type:  2 for AS-Path Change.

   Length:  n x 5.  If Length is not a multiple of 5, the sub-TLV is
      corrupt and the enclosing UPDATE MUST be ignored.

   ASi:  4 octet.  An AS number.

   Counti:  1 octet.  ASi repeats Counti times.

   The sequence of AS numbers are added to the existing AS Path.

4.3.  Capability Negotiation

   It is necessary to negotiate the capability to support BGP Extensions
   for Routing Policy Distribution (RPD).  The BGP RPD Capability is a
   new BGP capability [RFC5492].  The Capability Code for this
   capability is 72 assigned by the IANA.  The Capability Length field
   of this capability is variable.  The Capability Value field consists
   of one or more of the following tuples:

           +--------------------------------------------------+
           |  Address Family Identifier (2 octets)            |
           +--------------------------------------------------+
           |  Subsequent Address Family Identifier (1 octet)  |
           +--------------------------------------------------+
           |  Send/Receive (1 octet)                          |
           +--------------------------------------------------+

                          BGP RPD Capability




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   The meaning and use of the fields are as follows:

   Address Family Identifier (AFI): This field is the same as the one
   used in [RFC4760].

   Subsequent Address Family Identifier (SAFI): This field is the same
   as the one used in [RFC4760].

   Send/Receive: This field indicates whether the sender is (a) willing
   to receive Routing Policies from its peer (value 1), (b) would like
   to send Routing Policies to its peer (value 2), or (c) both (value 3)
   for the <AFI, SAFI>.  If Send/Receive is any other value, that tuple
   is ignored but any other tuples present are still used.

5.  Operations

   This section presents a typical application scenario and some details
   about handling a related failure.

5.1.  Application Scenario

   Figure 3 illustrates a typical scenario, where RPD is used by a
   controller with a Route Reflector (RR) to adjust traffic dynamically.

            +--------------+
            |  Controller  |
            +-------+------+
                     \
                      \ RPD
                    .--\._.+--+                       ___...__
                __(     \       '.---...             (         )
               /      RR o -------- A o) ---------- (o X   AS2  )
              (o E       |\             )     _____//(___   ___)
               (         | \_______ B o) ____/     /     '''
                (o F      \           )       ____/
                 (         \_____ C o) ______/         ___...__
                  '    AS1        _)  \_____          (         )
                   '---._.-.     )          \_______ (o Y   AS3  )
                            '---'                     (___   ___)
                                                          '''

                Figure 3: Controller with RR Adjusts Traffic

   The controller connects the RR through a BGP session.  There is a BGP
   session between the RR and each of routers A, B and C in AS1, which
   is shown in the figure.  Other sessions in AS1 are not shown in the
   figure.




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   There is router X in AS2.  There is a BGP session between X and each
   of routers A, B and C in AS1.

   There is router Y in AS3.  There is a BGP session between Y and
   router C in AS1.

   The controller sends a RPD route to the RR.  After receiving the RPD
   route from the controller, the RR reflects the RPD route to routers
   A, B and C.  After receiving the RPD route from the RR, routers A, B
   and C extract the routing policy from the RPD route.  If the peer IP
   in the NLRI of the RPD route is 0, then apply the routing policy to
   all the remote peers of routers A, B and C.  If the peer IP in the
   NLRI of the RPD route is non-zero, then the IP address indicates a
   remote peer of routers A, B and C and such routing policy is applied
   to the specific remote peer.  The IPv4/IPv6 unicast routes towards
   router X in AS2 and router Y in AS3 will be adjusted based on the
   routing policy sent by the controller via a RPD route.

   The controller uses the RT extend community to notify a router
   whether to receive a RPD policy.  For example, if there is not any
   adjustment on router B, the controller sends RPD routes with the RTs
   for A and C.  B will not receive the routes.

   The process of adjusting traffic in a network is a close loop.  The
   loop starts from the controller with some traffic expectations on a
   set of routes.  The controller obtains the information about traffic
   flows for the related routes.  It analyzes the traffic and checks
   whether the current traffic flows meet the expectations.  If the
   expectations are not met, the controller adjusts the traffic.  And
   then the loop goes to the starter of the loop (The controller obtains
   the information about traffic ...).

5.2.  About Failure

   A RPD route is not a configuration.  When it is sent to a router, no
   ack is needed from the router.  The existing BGP mechanisms are re-
   used for delivering a RPD route.  After the route is delivered to a
   router, it will be successful.  This is guaranteed by the BGP
   protocols.

   If there is a failure for the router to install the route locally,
   this failure is a bug of the router.  The bug needs to be fixed.

   For the errors mentioned in [RFC7606], they are handled according to
   [RFC7606].  These errors are bugs, which need to be resolved.






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   Regarding to the failure of the controller, some existing mechanisms
   such BGP GR [RFC4724] and BGP Long-lived Graceful Restart (LLGR) can
   be used to let the router keep the routes from the controller for
   some time.

   With support of "Long-lived Graceful Restart Capability"
   [I-D.ietf-idr-long-lived-gr], the routes can be retained for a longer
   time after the controller fails.

   In the worst case, the controller fails and the RPD routes for
   adjusting the traffic are withdrawn.  The traffic adjusted/redirected
   may take its old path.  This should be acceptable.

6.  Contributors

   The following people have substantially contributed to the definition
   of the BGP-FS RPD and to the editing of this document:

   Peng Zhou
   Huawei
   Email: Jewpon.zhou@huawei.com

7.  Security Considerations

   Protocol extensions defined in this document do not affect BGP
   security other than as discussed in the Security Considerations
   section of [RFC5575].

8.  Acknowledgements

   The authors would like to thank Acee Lindem, Jeff Haas, Jie Dong,
   Lucy Yong, Qiandeng Liang, Zhenqiang Li, Robert Raszuk, Donald
   Eastlake, Ketan Talaulikar, and Jakob Heitz for their comments to
   this work.

9.  IANA Considerations

9.1.  Existing Assignments

   IANA has assigned an AFI of value 16398 from the registry "Address
   Family Numbers" for Routing Policy.

   IANA has assigned a SAFI of value 75 from the registry "Subsequent
   Address Family Identifiers (SAFI) Parameters" for Routing Policy.

   IANA has assigned a Code Point of value 72 from the registry
   "Capability Codes" for Routing Policy Distribution.




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9.2.  RouteAttr Atom Type

   IANA is requested to assign a code-point from the registry "BGP
   Community Container Atom Types" as follows:

    +---------------------+------------------------------+-------------+
    | Atom Code Point     | Description                  | Reference   |
    +---------------------+------------------------------+-------------+
    | TBD1 (48 suggested) | RouteAttr Atom               |This document|
    +---------------------+------------------------------+-------------+

9.3.  Route Attributes Sub-sub-TLV Registry

   IANA is requested to create a registry called "Route Attributes Sub-
   sub-TLV" under RouteAttr Atom Sub-TLV.  The allocation policy of this
   registry is "First Come First Served (FCFS)".

   The initial code points are as follows:

      +-------------+-----------------------------------+-------------+
      | Code Point  | Description                       | Reference   |
      +-------------+-----------------------------------+-------------+
      |      0      |  Reserved                         |             |
      +-------------+-----------------------------------+-------------+
      |      1      |  IPv4 Prefix Sub-sub-TLV          |This document|
      +-------------+-----------------------------------+-------------+
      |      2      |  AS-Path Sub-sub-TLV              |This document|
      +-------------+-----------------------------------+-------------+
      |      3      |  Community Sub-sub-TLV            |This document|
      +-------------+-----------------------------------+-------------+
      |      4      |  IPv6 Prefix Sub-sub-TLV          |This document|
      +-------------+-----------------------------------+-------------+
      |   5 - 255   |  Available                        |             |
      +-------------+-----------------------------------+-------------+

9.4.  Attribute Change Sub-TLV Registry

   IANA is requested to create a registry called "Attribute Change Sub-
   TLV" under Parameter(s) TLV.  The allocation policy of this registry
   is "First Come First Served (FCFS)".

   Initial code points are as follows:









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      +-------------+-----------------------------------+-------------+
      | Code Point  | Description                       | Reference   |
      +-------------+-----------------------------------+-------------+
      |      0      |  Reserved                         |             |
      +-------------+-----------------------------------+-------------+
      |      1      |  MED Change Sub-TLV               |This document|
      +-------------+-----------------------------------+-------------+
      |      2      |  AS-Path Change Sub-TLV           |This document|
      +-------------+-----------------------------------+-------------+
      |   3 - 255   |  Available                        |             |
      +-------------+-----------------------------------+-------------+

10.  References

10.1.  Normative References

   [I-D.ietf-idr-wide-bgp-communities]
              Raszuk, R., Haas, J., Lange, A., Decraene, B., Amante, S.,
              and P. Jakma, "BGP Community Container Attribute", Work in
              Progress, Internet-Draft, draft-ietf-idr-wide-bgp-
              communities-05, 2 July 2018,
              <https://www.ietf.org/archive/id/draft-ietf-idr-wide-bgp-
              communities-05.txt>.

   [RFC1997]  Chandra, R., Traina, P., and T. Li, "BGP Communities
              Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
              <https://www.rfc-editor.org/info/rfc1997>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <https://www.rfc-editor.org/info/rfc4760>.

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <https://www.rfc-editor.org/info/rfc5492>.





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   [RFC5575]  Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
              and D. McPherson, "Dissemination of Flow Specification
              Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
              <https://www.rfc-editor.org/info/rfc5575>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

10.2.  Informative References

   [I-D.ietf-idr-long-lived-gr]
              Uttaro, J., Chen, E., Decraene, B., and J. G. Scudder,
              "Support for Long-lived BGP Graceful Restart", Work in
              Progress, Internet-Draft, draft-ietf-idr-long-lived-gr-00,
              5 September 2019, <https://www.ietf.org/archive/id/draft-
              ietf-idr-long-lived-gr-00.txt>.

   [I-D.ietf-idr-registered-wide-bgp-communities]
              Raszuk, R. and J. Haas, "Registered Wide BGP Community
              Values", Work in Progress, Internet-Draft, draft-ietf-idr-
              registered-wide-bgp-communities-02, 31 May 2016,
              <https://www.ietf.org/archive/id/draft-ietf-idr-
              registered-wide-bgp-communities-02.txt>.

   [RFC4724]  Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y.
              Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724,
              DOI 10.17487/RFC4724, January 2007,
              <https://www.rfc-editor.org/info/rfc4724>.

   [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
              Patel, "Revised Error Handling for BGP UPDATE Messages",
              RFC 7606, DOI 10.17487/RFC7606, August 2015,
              <https://www.rfc-editor.org/info/rfc7606>.

Authors' Addresses










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   Zhenbin Li
   Huawei
   Huawei Bld., No.156 Beiqing Rd.
   Beijing
   100095
   China

   Email: lizhenbin@huawei.com


   Liang Ou
   China Telcom Co., Ltd.
   109 West Zhongshan Ave,Tianhe District
   Guangzhou
   510630
   China

   Email: ouliang@chinatelecom.cn


   Yujia Luo
   China Telcom Co., Ltd.
   109 West Zhongshan Ave,Tianhe District
   Guangzhou
   510630
   China

   Email: luoyuj@sdu.edu.cn


   Sujian Lu
   Tencent
   Tengyun Building,Tower A ,No. 397 Tianlin Road
   Shanghai
   Xuhui District, 200233
   China

   Email: jasonlu@tencent.com


   Gyan S. Mishra
   Verizon Inc.
   13101 Columbia Pike
   Silver Spring,  MD 20904
   United States of America

   Phone: 301 502-1347
   Email: gyan.s.mishra@verizon.com



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   Huaimo Chen
   Futurewei
   Boston, MA,
   United States of America

   Email: Huaimo.chen@futurewei.com


   Shunwan Zhuang
   Huawei
   Huawei Bld., No.156 Beiqing Rd.
   Beijing
   100095
   China

   Email: zhuangshunwan@huawei.com


   Haibo Wang
   Huawei
   Huawei Bld., No.156 Beiqing Rd.
   Beijing
   100095
   China

   Email: rainsword.wang@huawei.com

























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