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Versions: 00 01

Network Working Group                                              F. Xu
Internet-Draft                                                   Tencent
Intended status: Standards Track                                   Y. Gu
Expires: January 8, 2020                                       S. Zhuang
                                                                   Z. Li
                                                                  Huawei
                                                            July 7, 2019


             BGP Route Policy and Attribute Trace Using BMP
              draft-xu-grow-bmp-route-policy-attr-trace-01

Abstract

   The generation of BGP adj-rib-in, local-rib or adj-rib-out comes from
   BGP protocol communication, and route policy processing.  BGP
   Monitoring Protocol (BMP) provides the monitoring of BGP adj-rib-in
   [RFC7854], BGP local-rib [I-D.ietf-grow-bmp-local-rib] and BGP adj-
   rib-out [I-D.ietf-grow-bmp-adj-rib-out].  However, there lacks
   monitoring of how BGP routes are transformed from adj-rib-in into
   local-rib and then adj-rib-out (i.e., the BGP route policy processing
   procedures).  This document describes a method of using BMP to trace
   the change of BGP routes in correlation with responsible route
   policies.

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 RFC 2119 [RFC2119].

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/.

   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 January 8, 2020.




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Copyright Notice

   Copyright (c) 2019 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  BGP Route Policy and Attribute Trace Overview . . . . . .   3
     1.2.  Use cases . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Extension of BMP for Route Policy and Attribute Trace . . . .   4
     2.1.  Common Header . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Per Peer Header . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Route Policy and Attribute Trace Message  . . . . . . . .   4
       2.3.1.  VRF/Table Name TLV  . . . . . . . . . . . . . . . . .   8
       2.3.2.  Pre Policy Attribute TLV  . . . . . . . . . . . . . .   9
       2.3.3.  Post Policy Attribute TLV . . . . . . . . . . . . . .   9
       2.3.4.  Policy ID TLV . . . . . . . . . . . . . . . . . . . .  10
       2.3.5.  Optional TLV  . . . . . . . . . . . . . . . . . . . .  11
   3.  Implementation Considerations . . . . . . . . . . . . . . . .  12
   4.  Implementation Example  . . . . . . . . . . . . . . . . . . .  12
     4.1.  Route Distribution Tracking . . . . . . . . . . . . . . .  12
     4.2.  Route Leak Detection  . . . . . . . . . . . . . . . . . .  16
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  20
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   The typical processing procedure after receiving a BGP Update Message
   at a routing device is as follows: 1.  Adding the pre-policy routes
   into the pre-policy adj-rib-in (if any); 2.  Filtering the pre-policy
   routes through inbound route policies; 3.  Selecting the BGP best
   routes from the post-policy routes; 4.  Adding the selected routes
   into the BGP local-rib; 5-a.  Adding the BGP best routes from local-
   rib to the core routing table manager for selection; 5-b.  Filtering



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   the routes from BGP local-rib through outbound route policies w.r.t.
   per peer or peer groups; 6.  Sending the BGP adj-rib-out to the
   target peer or peer groups.  Details may vary by vendors.  The BGP
   Monitoring Protocol (BMP) can be utilized to monitor BGP routes in
   forms of adj-rib-in, local-rib and adj-rib-out.  However, the
   complete procedure from inbound to outbound policy processing,
   including other policies, e.g., route redistribution, route selection
   and so on, is currently unobserved.  For example, there are 10 policy
   items (or nodes) configured under one outbound route policy per a
   specific peer.  By collecting the local-rib and adj-rib-out through
   BMP, the operator finds that the outbound policy didn't work as
   expected.  However, it's hard to distinguish which one of the 10
   policy items/nodes is responsible for the failure.

1.1.  BGP Route Policy and Attribute Trace Overview

   This document describes a method that records and reports how each
   policy item/node processes the routes (e.g., changes the route
   attribute).  Each policy item/node processing is called an event
   thereafter in this document.  Compared with conventional BGP rib
   entry, which consists of prefix/mask, route attributes, e.g., next
   hop, MED, local preference, AS path, and so on, the event record
   discussed in this document includes extra information, such as event
   index, timestamp, policy information, and so on.  For example, if a
   route is processed by 5 policy items/nodes, there can be 5 event
   records for the same prefix/mask.  Each event is numbered in order of
   time (e.g., the time of policy execution).  The policy information
   includes the policy name and item/node ID/name so that the server/
   controller can map to the exact policy either directly from the
   device or from the configurations collected at the server side.

   This document defines a new BMP message type to carry the recorded
   policy and route data.  More detailed message format is defined in
   Section 2.  The message is called the BMP Route Policy and Attribute
   Trace Message thereafter in this document.

1.2.  Use cases

   There are cases that a new policy is configured incorrectly, e.g.,
   setting an incorrect community value, or policy placed in incorrect
   order among other policies.  These may result in incorrect route
   attribute modification, best route selection mistake, or route
   distribution mistake.  With the correlated record of policy and
   route, the server/controller is able to identify the unexpected route
   change and its responsible policy.  Considering the fact that the BGP
   route policy impacts not only the route processing within the
   individual device but also the route distribution to its peers, the




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   route trace data of a single device is always analyzed in correlation
   with such data collected from its peer devices.

   Apart from the policy validation application, the route trace data
   can also be analyzed to discover the route propagation path within
   the network.  With the route's inbound and outbound event records
   collect from each related device, the server is able to find the
   propagation path hop by hop.  The identified path is helpful for
   operators to better understand its network, and thus benefitting both
   network troubleshooting and network planning.

2.  Extension of BMP for Route Policy and Attribute Trace

2.1.  Common Header

   This document defines a new BMP message type to carry the Route
   Policy and Attribute Trace data.

   o  Type = TBD: Route Policy and Attribute Trace Message

   The new defined message type is indicated in the Message Type field
   of the BMP common header.

2.2.  Per Peer Header

   The Route Policy and Attribute Trace Message is not per peer based,
   thus it does not require the Per Peer Header.

2.3.  Route Policy and Attribute Trace Message

   The Route Policy and Attribute Trace Message format is defined as
   follows:



















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     +---------------------------------------------------------------+
     |                        Route Distinguisher                    |
     +---------------------------------------------------------------+
     |                          Prefix length                        |
     +---------------------------------------------------------------+
     |                              Prefix                           |
     +---------------------------------------------------------------+
     |                       Previous Hop Length                     |
     +---------------------------------------------------------------+
     |                           Previous Hop                        |
     +---------------------------------------------------------------+
     |                          Event count                          |
     +---------------------------------------------------------------+
     |                       Total event length                      |
     +---------------------------------------------------------------+
     |                            1st Event                          |
     +---------------------------------------------------------------+
     |                            2nd Event                          |
     +---------------------------------------------------------------+
     ~                                                               ~
     +                            ......                             +
     ~                                                               ~
     +---------------------------------------------------------------+
     |                           Last Event                          |
     +---------------------------------------------------------------+

       Figure 1: Route Policy and Attribute Trace Message format

   o  Route Distinguisher (8 Bytes): indicates the route distinguisher
      (RD) related to the route.

   o  Prefix Length (1 Byte): indicates the length of the prefix.

   o  Prefix (Variable): indicates the monitored prefix, with the length
      defined by Prefix Length field.

   o  Previous Hop Length (1 Byte): indicates the length of the
      following Previous Hop field.  If the BGP peer ID of previous hop
      is IPv4, it is set to 4, and if the BGP peer ID of the previous
      hop is an IPv6, it is set to 16.

   o  Previous Hop (Variable): indicates the BGP peer ID where this
      route is learnt from.  If the route is locally generated, then
      field is zero filled.

   o  Event Count (1 Byte): indicates the total number of policy
      processing event recorded in this message.




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   o  Total event length (2 Byte): indicates the total length of the
      following fields including all events, where the total number is
      indicated by the Event Count field.

   o  1 ~ Last event: indicates each event, stacked one by one in order
      of time.  The event format is further defined as follows.

   +---------------------------------------------------------------+
   |                       Single event length                     |
   +---------------------------------------------------------------+
   |                           Event index                         |
   +---------------------------------------------------------------+
   |                       Timestamp(seconds)                      |
   +---------------------------------------------------------------+
   |                       Timestamp(microseconds)                 |
   +---------------------------------------------------------------+
   |                       Policy Classification                   |
   +---------------------------------------------------------------+
   |                           Peer ID                             |
   +---------------------------------------------------------------+
   |                           Peer AS                             |
   +---------------------------------------------------------------+
   |                        Path Identifier                        |
   +---------------------------------------------------------------+
   |                           Peer AFI                            |
   +---------------------------------------------------------------+
   |                           Peer SAFI                           |
   +---------------------------------------------------------------+
   |                        VRF/Table Name TLV                     |
   +---------------------------------------------------------------+
   |                     Pre Policy Attribute TLV                  |
   +---------------------------------------------------------------+
   |                     Post Policy Attribute TLV                 |
   +---------------------------------------------------------------+
   |                          Policy ID TLV                        |
   +---------------------------------------------------------------+
   |                           Optional TLV                        |
   +---------------------------------------------------------------+

                       Figure 2: Event format

   o  Single event length (2 Byte): indicates the total length of a
      single policy process event, including the following fields that
      belong to this event.

   o  Event index (1 Byte): indicates the sequence number of this event,
      staring from 1 and increases by 1 for each event recorded in
      order.



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   o  Timestamp (8 Bytes): indicates the time when the policy of this
      event starts execution, expressed in seconds and microseconds
      since midnight (zero hour), January 1, 1970 (UTC).

   o  Peer ID (4 Bytes): indicates the BGP Peer ID where this policy is
      configured under.  This field is used in combination with the
      Policy Direction field.  If the Policy Direction field is set to
      "0000", meaning Inbound policy, then this field is set to the BGP
      Peer ID where the route is received from; if the Policy Direction
      field is set to "0001", meaning Outbound policy, then this field
      is set to the BGP Peer ID where the route is distributed to; If
      the Policy Direction field is set to "0010", "0010","0100" meaning
      Redistribution/Network/Aggregation policy, then this field is set
      to all zeros.

   o  Peer AS (4 Bytes): indicates the AS number of the BGP Peer that
      defined the Peer ID field.

   o  Policy Classification (1 Byte): indicates the category of the
      policy.  Currently 5 policy categories are defined: "0000"
      indicating the Inbound policy, "0001" indicating the Outbound
      policy, "0010" indicating the Redistribution policy (e.g., route
      import from other sources, like ISIS/OSPF), "0011" indicates the
      Route Leak policy (route leaking from the global routing table to
      a VRF or from a VRF to the global routing table, or between VRFs),
      "0100" indicates the Network policy (BGP network installment and
      advertisement), "0101" indicating the Aggregation policy.  More
      categories can be defined.

   o

   +--------------------------------+
   |   Value  |Policy Classification|
   +--------------------------------+
   | 00000000 | Inbound policy      |
   | 00000001 | Outbound policy     |
   | 00000010 | Redistribution      |
   | 00000011 | Route Leak          |
   | 00000100 | Network             |
   | 00000101 | Aggregation         |
   +----------+---------------------+

     Table 1: Policy Classification

   o  Path Identifier (4 Bytes): used to distinguish multiple BGP paths
      for the same prefix.  If there's no path ID, this field is zero
      filled.




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   o  Peer AFI (2 Bytes)/Peer SAFI (1 Byte): indicates the AFI/SAFI of
      the route.  The AFI/SAFI information varies for the same route
      under different policy processing event.  For example, an IPv4
      Unicast route is received from a CE router at the PE router
      through eBGP, an RD is attached to this IPv4 Unicast route and
      making it a VPNv4 route, and then this VPNv4 route is distributed
      to the RR.  During this process, the AFI/SAFI information changes
      from IPv4 Unicast (1/1) to VPNv4 (1/128) at the inbound policy and
      outbound policy.

   o  VRF/Table Name TLV (Variable): indicates the VRF name or table
      name of the route.  The format of the VRF/Table Name TLV is
      further defined in Figure 3.  The VRF/Table Name TLV is non-
      optional.

   o  Pre-policy Attribute TLV (Variable): include the BGP route
      atttributes before the policy is executed.  The format of the Pre-
      policy Attribute TLV is further defined in Figure 4.  The Pre-
      policy Attribute TLV is optional.

   o  Post-policy Attribute TLV (Variable): include the BGP route
      atttributes after the policy is executed.  The format of the Post-
      policy Attribute TLV is further defined in Figure 5.  The Post-
      policy Attribute TLV is optional.

   o  Policy ID TLV (Variable): indicates the ID of the route policy of
      this event, which is user specific or vendor specific, which can
      be used for mapping to the actual policy content.  The policy
      content data retrieval is out of the scope of this document.  The
      format of the Policy ID TLV is further defined in Figure 6.  The
      Policy ID TLV is optional.

   o  Optional TLV (Variable): leaves for future extension.  The
      Optioanl TLV is optional.

2.3.1.  VRF/Table Name TLV

     +-------------------------------+-------------------------------+
     |           Type = TBD1         |      VRF/Table name length    |
     +-------------------------------+-------------------------------+
     |                          VRF/Table name                       |
     +---------------------------------------------------------------+

                        Figure 3: VRF/Table name TLV

   o  Type = TBD1 (2 Byte): indicates the type of VRF/Table name TLV.





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   o  VRF/Table name length (2 Byte): indicates the length of the VRF/
      Table name field.

   o  VRF/Table name (Variable): indicates the VRF or table name of this
      route in the format of ASCII string.  The string size MUST be
      within the range of 1 to 255 bytes.  The VRF/Table name varies for
      the same route under different events.  For example, an IPv4
      Unicast route is received from a CE router at the PE router
      through iBGP, an RD is attached to this IPv4 route (under VRF A)
      and making it a VPNv4 route, and then this VPNv4 route (under the
      Global routing table) is distributed to the RR.  During the whole
      process, the VRF/Table name changes from VRF A to the Global
      routing Table name at the inbound event and outbound event.

2.3.2.  Pre Policy Attribute TLV

   +-------------------------------+-------------------------------+
   |           Type = TBD2         |     Pre Policy Attr. length   |
   +-------------------------------+-------------------------------+
   |                Pre Policy Attribute sub TLVs                  |
   +---------------------------------------------------------------+

                   Figure 4: Pre Policy Attribute TLV

   o  Type = TBD2 (2 Byte): indicates the type of Pre Policy Attribute
      TLV.

   o  Pre Policy Attribute length (2 Byte): indicates the total length
      of the following Pre Policy Attribute sub TLVs.

   o  Pre Policy Attribute sub TLVs (Variable): include the BGP route
      attributes before the policy is executed.

2.3.3.  Post Policy Attribute TLV

   +-------------------------------+-------------------------------+
   |           Type = TBD3         |    Post Policy Attr. length   |
   +-------------------------------+-------------------------------+
   |                Post Policy Attribute sub TLVs                 |
   +---------------------------------------------------------------+

                   Figure 5: Post Policy Attribute TLV

   o  Type = TBD3 (2 Byte): indicates the type of Pre Policy Attribute
      TLV.

   o  Pre Policy Attribute length (2 Byte): indicates the total length
      of the following Pre Policy Attribute sub TLVs.



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   o  Pre Policy Attribute sub TLVs (Variable): include the BGP route
      attributes before the policy is executed.

2.3.4.  Policy ID TLV

   The Route Policy and Attribute Trace Message is not per peer based,
   thus it does not require the Per Peer Header.

          +------------------------+---------------------------+
          |      Type = TBD4       |     Policy ID length      |
          +----------------------------------------------------+
          |M|          Res.        |       Policy Count        |
          +----------------------------------------------------+
          |     1st  Policy        |C|R|         Res.          |
          +----------------------------------------------------+
          ~                        |                           ~
          +        ...             |             ...           +
          ~                        |                           ~
          +----------------------------------------------------+
          |     Last Policy        |C|R|         Res.          |
          +----------------------------------------------------+

                      Figure 6: Policy ID TLV

   Considering the chaining and recursion of polices and policy items,
   the Policy ID TLV is defined as follows.

   o  Type = TBD4 (2 Byte): indicates the type of Policy ID TLV.

   o  Policy ID length (2 Byte): indicates the length of the Policy ID
      value field that follows it.  The Policy ID value field includes
      the Reserved bits, the Flag bits, Policy Count field, and Policy
      field.

   o  Flag bit M (1 bit): indicates if the route in this event is
      matched (once or multiple times) or not by any policies. "0" means
      no match and "1" means elsewise.  The remaining 7 bits are
      reserved for future extension.

   o  Policy Count (1 Byte): indicates the number of policies (in the
      format of Policy name + Item ID) carried in this event.

   o  1st ~ Last Policy (Variable): indicates the Policy name and the
      Item ID of each policy match.

   o  Flag bit C (1 bit): indicates if the next subsequent policy has
      chaining relationship to the current policy. "1" means it's




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      chaining relationship and "0" means elsewise.  For the flag byte
      following the Last Policy field, the C bit SHALL be set to "0".

   o  Flag bit R (1 bit): indicates if the next subsequent policy has
      recursioning relationship to the current policy. "1" means it's
      recursioning relationship and "0" means elsewise.  For the flag
      byte following the Last Policy field, the R bit SHALL be set to
      "0".

                +----------------------------------------+
                |           Policy Name length           |
                +----------------------------------------+
                |           Policy Name                  |
                +----------------------------------------+
                |           Item ID length               |
                +----------------------------------------+
                |           Item ID                      |
                +----------------------------------------+

                      Figure 7: Policy field format

   The Policy ID field consists of the Route Policy Name and the Route
   Policy Item ID.  The Policy name and Item ID are in the format of
   ASCII string, the length of both fields are indicated by the Policy
   Name length (2 Bytes) and Item length (1 Byte) fields, respectively.

2.3.5.  Optional TLV

   +-------------------------------+-------------------------------+
   |           Type = TBD5         |             Length            |
   +-------------------------------+-------------------------------+
   |                             Value                             |
   +---------------------------------------------------------------+

                     Figure 8: Optional TLV

   The Optional TLV remains to be defined.  One or more Optional TLV
   types can be defined.  One or more Optional TLVs can be used.

   One possible way of utilizing the Optional TLV is to define a string
   Type TLV.  The String Type TLV allows flexible textual expression of
   user-specific information without requiring structural format.  Some
   examples:

   o  The Policy ID TLV is defined as optional, considering that users
      may don't want detailed information about the policy but only the
      result and/or the reasons.  Using a string type TLV, one may
      express "Route rejected due to inbound filtering".  However, such



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      expression still requires the tracking of policy processing in
      realtime, it's just another form of tracking representation to the
      BMP server and the user.

   o  Another possible application is for route leak detection.  One may
      express the business relations as "P2C", "P2P" and so on, with the
      inbound filtering event or the outbound filtering event.  Detailed
      usage is discussed in Section 4.2.

3.  Implementation Considerations

   Considering the data amount of monitoring the route and policy trace
   of all routes from all BMP clients, users MAY trigger the monitoring
   at any user-specific time.  Users MAY configure locally at the BMP
   client to monitor only user-specific routes or all the routes.  In
   addition, users MAY configure locally at the BMP client whether to
   report the TLVs that are optional according to their own
   requirements, i.e., the Pre Policy Attribute TLV, Post Policy
   Attribute TLV, Policy ID TLV, and Optional TLV.

   Successive recored events from one device MAY be encapsulated in one
   Route Policy and Attribute Trace Message or multiple Route Policy and
   Attribute Trace Messages per the user configuration.

4.  Implementation Example

4.1.  Route Distribution Tracking
























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                           +----------+
                   +------>+BMP server+<-------+
                   |       +--+-------+        |
                   +          ^    ^           |
           Event 1,2,3  +-----+    |           +
                   +    +          +       Event 9,10,11
                   | Event 4,5  Event 6,7,8    +
                   |    +          +           |
                   |    |          |           |
10.1.1.1/32    ****|****|**********|***********|*****
+--------->    *   |    |          |           | AS0*
+-----+        *   |    |       +--+--+        |    *
| CE1 ++eBGP+  *   | +--------->+ RR  +------+ |    *
+-----+     |  *   | |  |       ++----+      | |    *
  AS1       |  *   | |  |        ^    iBGP   | |    *
            |  *   | | ++----+   | 65000:10  | |    *     10.1.1.1/32
10.1.1.1/32 +----------> PE2 +---+10.1.1.1/32| |    *    +----------->
+--------->    *   | | +-----+               | |    *         +-----+
+-----+        *   | |                 iBGP  | |    *  +eBGP+>+ CE4 |
| CE2 ++eBGP+  *   | |  iBGP        65000:10 + |    *  |      +-----+
+-----+     |  *   | +65000:10     10.1.1.1/32 |    *  |        AS4
  AS2       |  *   | 10.1.1.1/32             + |    *  |
            |  *  ++----+                 +--v-++   *  |
+-----+     +-----> PE1 |                 | PE3 +------+      +-----+
| CE3 ++eBGP+----->     |                 |     +------+eBGP+>+ CE5 |
+-----+        *  +-----+                 +-----+   *         +-----+
10.1.1.1/32    *                                    *     10.1.1.1/32
+-------->     **************************************    +----------->
  AS3                                                         AS5

 Figure 9: Route Policy and Attribute Trace record implementation example

   We take the network shown in Figure 9 as an example to show how to
   use Route Policy and Attribute Trace Messages to recover the
   footprint of the route propagation.  Notice that only basic events
   required for footprint recovery are illustrated here.  Also notice
   that the event index shown in Figure 9, 10, 11 are for illustration
   purpose, and may not reflect the actual indexing.

   Suppose a prefix 10.1.1.1/32 is sent from both CE2 and CE3 to PE1
   through eBGP peering, PE1 processes the two Update messages through
   inbound policies.  Such procedure is recorded as two events, namely
   Event 1 and Event 2.  Then PE1 selects the route from CE2 as the best
   route, add it to VRF 1, and then distribute the VPNv4 route to RR.
   The distribution procedure is recorded by PE1 as Event 3.  As an
   example, the Route Policy and Attribute Trace Message of Event 1, 2,
   3 is listed as follows.  Only fields related to footprint recovery
   are listed in the message shown below.  Specifically, the Previous



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   Hop information is carried in Event 3 when outbounding the route,
   indicating that the outbounded route is learnt from CE2.  The same
   prefix is sent from CE1 to PE2, added to VRF 1 and then distributed
   to RR in the form of VPNv4 route.  Two events, Event 4 (inbound) and
   Event 5 (outbound) are recorded by PE2.  Now for RR, prefix
   10.1.1.1/32 is received from both PE1 and PE2 in the form of VPNv4
   route.  RR selects the route from PE1 as the best route, and
   distribute it to PE3.  Three events, Event 6 (PE2 inbound), Event 7
   (PE1 inbound), Event 8 (PE3 outbound) are recorded in this case.  PE3
   receives the VPNv4 route from RR, adds it to VRF 1 and then
   distribute the IPv4 route to CE4 and CE5, respectively.  Here, three
   events are recorded, Event 9 (RR inbound), Event 10 (CE4 outbound)
   and Event 11 (CE5 outbound).

     +---------------------------------------------------------------+
     |                         RD: 65000:10                          |
     +---------------------------------------------------------------+
     |                      Prefix:  10.1.1.1/32                     |
     +---------------------------------------------------------------+
     |                        Previous hop: CE2                      |
     +---------------------------------------------------------------+
     |                          Event count: 2                       |
     +---------------------------------------------------------------+
     |                             Event 1                           |
     +---------------------------------------------------------------+
     |                            Timestamp 1                        |
     +---------------------------------------------------------------+
     |                          Inbound policy                       |
     +---------------------------------------------------------------+
     |                           Peer ID: CE2                        |
     +---------------------------------------------------------------+
     |                           Peer AS: AS2                        |
     +---------------------------------------------------------------+
     |                            Path ID: 0                         |
     +---------------------------------------------------------------+
     |                       AFI/SAFI: IPv4 Unicast                  |
     +---------------------------------------------------------------+
     |                       VRF/Table name: VRF 1                   |
     +---------------------------------------------------------------+
     |                       Pre Policy Attributes                   |
     +---------------------------------------------------------------+
     |                      Post Policy Attributes                   |
     +---------------------------------------------------------------+
     |                     Policy ID: WC1, node 101                  |
     +---------------------------------------------------------------+
     |                             Event 3                           |
     +---------------------------------------------------------------+
     |                            Timestamp 3                        |



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     +---------------------------------------------------------------+
     |                         Outbound policy                       |
     +---------------------------------------------------------------+
     |                           Peer ID: RR                         |
     +---------------------------------------------------------------+
     |                           Peer AS: AS0                        |
     +---------------------------------------------------------------+
     |                            Path ID: 0                         |
     +---------------------------------------------------------------+
     |                       AFI/SAFI: VPNv4                         |
     +---------------------------------------------------------------+
     |                  VRF/Table name: Global/Default               |
     +---------------------------------------------------------------+
     |                       Pre Policy Attributes                   |
     +---------------------------------------------------------------+
     |                      Post Policy Attributes                   |
     +---------------------------------------------------------------+
     |                     Policy ID: RR1, node 200                  |
     +---------------------------------------------------------------+

                  Figure 10: Event 1,3 data view






























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   +---------------------------------------------------------------+
   |                         RD: 65000:10                          |
   +---------------------------------------------------------------+
   |                      Prefix:  10.1.1.1/32                     |
   +---------------------------------------------------------------+
   |                        Previous hop: CE3                      |
   +---------------------------------------------------------------+
   |                          Event count: 1                       |
   +---------------------------------------------------------------+
   |                             Event 2                           |
   +---------------------------------------------------------------+
   |                            Timestamp 2                        |
   +---------------------------------------------------------------+
   |                          Inbound policy                       |
   +---------------------------------------------------------------+
   |                           Peer ID: CE3                        |
   +---------------------------------------------------------------+
   |                           Peer AS: AS3                        |
   +---------------------------------------------------------------+
   |                            Path ID: 0                         |
   +---------------------------------------------------------------+
   |                       AFI/SAFI: IPv4 Unicast                  |
   +---------------------------------------------------------------+
   |                       VRF/Table name: VRF 1                   |
   +---------------------------------------------------------------+
   |                       Pre Policy Attributes                   |
   +---------------------------------------------------------------+
   |                      Post Policy Attributes                   |
   +---------------------------------------------------------------+
   |                     Policy ID: WC1, node 102                  |
   +---------------------------------------------------------------+

                   Figure 11: Event 2 data view

   The BMP server can use the collected events to recover the route
   footprint.  The key information required from recovery is the
   Timestamp of each event, and the Previous Hop of the route.  The
   Timestamp allows the server to identify the order of each event,
   while the Previous Hop information, combined with the outbound peer
   information, allows the server to recover the route propagation hop
   by hop.

4.2.  Route Leak Detection

   Reusing Figure 9, the Optional TLV of the RoFT Message can be
   utilized to carry user-specific strings.  We present a route leak
   detection example here.




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   Suppose, a route leak happens (10.1.1.1/32: AS2 --> AS0 --> AS4).
   The Bussiness relationships between ASes are shown in Table 2.

                     +----------------+--------------+
                     |  Neighbor ASes |   Bussiness  |
                     |                | Relationship |
                     +-------------------------------+
                     |   AS 1 : AS 0  |     P2C      |
                     +-------------------------------+
                     |   AS 2 : AS 0  |     P2C      |
                     +-------------------------------+
                     |   AS 3 : AS 0  |     P2C      |
                     +-------------------------------+
                     |   AS 0 : AS 4  |     C2P      |
                     +-------------------------------+
                     |   AS 0 : AS 5  |     P2C      |
                     +----------------+--------------+

                     Table 2: Bussiness Relationship

   To detect the route leak, the BMP server analyzes the events with
   bussiness relationship information reported from the ingress device
   and egress device of AS0 (regarding a specific route)).  In this
   example, regarding 10.1.1.1/32, data from PC1 and PE3 are analized.
   The bussiness relationship can be expressed in strings, such as "P2C"
   or "P2P".  At PE1, when 10.1.1.1/32 is received from CE2 and going
   through the inbound policy, PE1 uses the Optional TLV (more
   specifically the String Type TLV) to carry the text "Bussiness
   Relationship: P2C" in the Inound Policy event.  On the other hand, at
   PE3, when 10.1.1.1/32 goes through the outbound policy and then sent
   to CE4, PE3 adds the "Bussiness Relationship: P2C", using the
   Optional TLV, in the Outbound Policy event.  More specifically, the
   format of the above mentioned two events are listed in Figure 12
   (Event 1) and Figure 13 (Event 10), respecitvely.

















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   +---------------------------------------------------------------+
   |                         RD: 65000:10                          |
   +---------------------------------------------------------------+
   |                      Prefix:  10.1.1.1/32                     |
   +---------------------------------------------------------------+
   |                        Previous hop: CE2                      |
   +---------------------------------------------------------------+
   |                          Event count: 1                       |
   +---------------------------------------------------------------+
   |                             Event 1                           |
   +---------------------------------------------------------------+
   |                            Timestamp 1                        |
   +---------------------------------------------------------------+
   |                          Inbound policy                       |
   +---------------------------------------------------------------+
   |                           Peer ID: CE2                        |
   +---------------------------------------------------------------+
   |                           Peer AS: AS2                        |
   +---------------------------------------------------------------+
   |                            Path ID: 0                         |
   +---------------------------------------------------------------+
   |                       AFI/SAFI: IPv4 Unicast                  |
   +---------------------------------------------------------------+
   |                       VRF/Table name: VRF 1                   |
   +---------------------------------------------------------------+
   |                       Pre Policy Attributes                   |
   +---------------------------------------------------------------+
   |                      Post Policy Attributes                   |
   +---------------------------------------------------------------+
   |                     Policy ID: WC1, node 101                  |
   +---------------------------------------------------------------+
   |          Optional TLV: "Bussiness Relationship: P2C"          |
   +---------------------------------------------------------------+

                  Figure 12: Event 1 data view
















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   +---------------------------------------------------------------+
   |                         RD: 65000:10                          |
   +---------------------------------------------------------------+
   |                      Prefix:  10.1.1.1/32                     |
   +---------------------------------------------------------------+
   |                        Previous hop: RR                       |
   +---------------------------------------------------------------+
   |                          Event count: 1                       |
   +---------------------------------------------------------------+
   |                             Event 10                          |
   +---------------------------------------------------------------+
   |                            Timestamp 10                       |
   +---------------------------------------------------------------+
   |                         Outbound policy                       |
   +---------------------------------------------------------------+
   |                           Peer ID: CE4                        |
   +---------------------------------------------------------------+
   |                           Peer AS: AS4                        |
   +---------------------------------------------------------------+
   |                            Path ID: 0                         |
   +---------------------------------------------------------------+
   |                       AFI/SAFI: IPv4 Unicast                  |
   +---------------------------------------------------------------+
   |                       VRF/Table name: VRF 3                   |
   +---------------------------------------------------------------+
   |                       Pre Policy Attributes                   |
   +---------------------------------------------------------------+
   |                      Post Policy Attributes                   |
   +---------------------------------------------------------------+
   |                     Policy ID: OB1, node 300                  |
   +---------------------------------------------------------------+
   |          Optional TLV: "Bussiness Relationship: C2P"          |
   +---------------------------------------------------------------+

                  Figure 13: Event 10 data view

   The BMP server can use the two Optional TLVs from Event 1 and Event
   10 to detect the route leak.  What's more, the repsonsible
   configurations are directly shown in the two events, i.e., the
   Inbound policy at PE1: "Policy ID: WC1, node 101", the Outbound
   policy at PE3: "Policy ID: OB1, node 300".  No need to correlate with
   other data sources, the user can detect the leak and figure out the
   root cause.








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5.  Acknowledgements

   TBD.

6.  IANA Considerations

   TBD.

7.  Security Considerations

   TBD.

8.  Normative References

   [I-D.ietf-grow-bmp-adj-rib-out]
              Evens, T., Bayraktar, S., Lucente, P., Mi, K., and S.
              Zhuang, "Support for Adj-RIB-Out in BGP Monitoring
              Protocol (BMP)", draft-ietf-grow-bmp-adj-rib-out-06 (work
              in progress), June 2019.

   [I-D.ietf-grow-bmp-local-rib]
              Evens, T., Bayraktar, S., Bhardwaj, M., and P. Lucente,
              "Support for Local RIB in BGP Monitoring Protocol (BMP)",
              draft-ietf-grow-bmp-local-rib-04 (work in progress), June
              2019.

   [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>.

   [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>.

   [RFC7854]  Scudder, J., Ed., Fernando, R., and S. Stuart, "BGP
              Monitoring Protocol (BMP)", RFC 7854,
              DOI 10.17487/RFC7854, June 2016,
              <https://www.rfc-editor.org/info/rfc7854>.







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Authors' Addresses

   Feng Xu
   Tencent
   Guangzhou
   China

   Email: oliverxu@tencent.com


   Yunan Gu
   Huawei
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: guyunan@huawei.com


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

   Email: zhuangshunwan@huawei.com


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

   Email: lizhenbin@huawei.com
















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