RFC 8671

Internet Engineering Task Force (IETF)                          T. Evens
Request for Comments: 8671                                  S. Bayraktar
Updates: 7854                                              Cisco Systems
Category: Standards Track                                     P. Lucente
ISSN: 2070-1721                                       NTT Communications
                                                                   P. Mi
                                                               S. Zhuang
                                                           November 2019

      Support for Adj-RIB-Out in the BGP Monitoring Protocol (BMP)


   The BGP Monitoring Protocol (BMP) only defines access to the Adj-RIB-
   In Routing Information Bases (RIBs).  This document updates BMP (RFC
   7854) by adding access to the Adj-RIB-Out RIBs.  It also adds a new
   flag to the peer header to distinguish between Adj-RIB-In and Adj-

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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.  Terminology
   3.  Definitions
   4.  Per-Peer Header
   5.  Adj-RIB-Out
     5.1.  Post-policy
     5.2.  Pre-policy
   6.  BMP Messages
     6.1.  Route Monitoring and Route Mirroring
     6.2.  Statistics Report
     6.3.  Peer Up and Down Notifications
       6.3.1.  Peer Up Information
   7.  Other Considerations
     7.1.  Peer and Update Groups
     7.2.  Changes to Existing BMP Session
   8.  Security Considerations
   9.  IANA Considerations
     9.1.  Addition to BMP Peer Flags Registry
     9.2.  Additions to BMP Statistics Types Registry
     9.3.  Addition to BMP Initiation Message TLVs Registry
   10. Normative References

   Authors' Addresses

1.  Introduction

   The BGP Monitoring Protocol (BMP) defines monitoring of the received
   (e.g., Adj-RIB-In) Routing Information Bases (RIBs) per peer.  The
   pre-policy Adj-RIB-In conveys to a BMP receiver all RIB data before
   any policy has been applied.  The post-policy Adj-RIB-In conveys to a
   BMP receiver all RIB data after policy filters and/or modifications
   have been applied.  An example of pre-policy versus post-policy is
   when an inbound policy applies attribute modification or filters.
   Pre-policy would contain information prior to the inbound policy
   changes or filters of data.  Post-policy would convey the changed
   data or would not contain the filtered data.

   Monitoring the received updates that the router received before any
   policy has been applied is the primary level of monitoring for most
   use cases.  Inbound policy validation and auditing are the primary
   use cases for enabling post-policy monitoring.

   In order for a BMP receiver to receive any BGP data, the BMP sender
   (e.g., router) needs to have an established BGP peering session and
   actively be receiving updates for an Adj-RIB-In.

   Being able to only monitor the Adj-RIB-In puts a restriction on what
   data is available to BMP receivers via BMP senders (e.g., routers).
   This is an issue when the receiving end of the BGP peer is not
   enabled for BMP or when it is not accessible for administrative
   reasons.  For example, a service provider advertises prefixes to a
   customer, but the service provider cannot see what it advertises via
   BMP.  Asking the customer to enable BMP and monitoring of the Adj-
   RIB-In are not feasible.

   BMP [RFC7854] only defines Adj-RIB-In being sent to BMP receivers.
   This document updates the per-peer header defined in Section 4.2 of
   [RFC7854] by adding a new flag to distinguish between Adj-RIB-In and
   Adj-RIB-Out. BMP senders use the new flag to send either Adj-RIB-In
   or Adj-RIB-Out.

   Adding Adj-RIB-Out provides the ability for a BMP sender to send to
   BMP receivers what it advertises to BGP peers, which can be used for
   outbound policy validation and to monitor routes that were

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Definitions

      As defined in [RFC4271], "The Adj-RIBs-Out contains the routes for
      advertisement to specific peers by means of the local speaker's
      UPDATE messages."

   Pre-policy Adj-RIB-Out
      The result before applying the outbound policy to an Adj-RIB-Out.
      This normally would match what is in the local RIB.

   Post-policy Adj-RIB-Out
      The result of applying outbound policy to an Adj-RIB-Out. This
      MUST convey to the BMP receiver what is actually transmitted to
      the peer.

4.  Per-Peer Header

   The per-peer header has the same structure and flags as defined in
   Section 4.2 of [RFC7854] with the addition of the O flag as shown

    0 1 2 3 4 5 6 7
   |V|L|A|O| Resv  |

   *  The O flag indicates Adj-RIB-In if set to 0 and Adj-RIB-Out if set
      to 1.

   The existing flags are defined in Section 4.2 of [RFC7854], and the
   remaining bits are reserved for future use.  They MUST be transmitted
   as 0, and their values MUST be ignored on receipt.

   When the O flag is set to 1, the following fields in the per-peer
   header are redefined:

   *  Peer Address: The remote IP address associated with the TCP
      session over which the encapsulated Protocol Data Unit (PDU) is

   *  Peer AS: The Autonomous System number of the peer to which the
      encapsulated PDU is sent.

   *  Peer BGP ID: The BGP Identifier of the peer to which the
      encapsulated PDU is sent.

   *  Timestamp: The time when the encapsulated routes were advertised
      (one may also think of this as the time when they were installed
      in the Adj-RIB-Out), expressed in seconds and microseconds since
      midnight (zero hour), January 1, 1970 (UTC).  If zero, the time is
      unavailable.  Precision of the timestamp is implementation-

5.  Adj-RIB-Out

5.1.  Post-policy

   The primary use case in monitoring Adj-RIB-Out is to monitor the
   updates transmitted to a BGP peer after outbound policy has been
   applied.  These updates reflect the result after modifications and
   filters have been applied (e.g., post-policy Adj-RIB-Out).  Some
   attributes are set when the BGP message is transmitted, such as next
   hop.  Post-policy Adj-RIB-Out MUST convey to the BMP receiver what is
   actually transmitted to the peer.

   The L flag MUST be set to 1 to indicate post-policy.

5.2.  Pre-policy

   Similar to Adj-RIB-In policy validation, pre-policy Adj-RIB-Out can
   be used to validate and audit outbound policies.  For example, a
   comparison between pre-policy and post-policy can be used to validate
   the outbound policy.

   Depending on the BGP peering session type -- Internal BGP (IBGP),
   IBGP route reflector client, External BGP (EBGP), BGP confederations,
   route server client -- the candidate routes that make up the pre-
   policy Adj-RIB-Out do not contain all local RIB routes.  Pre-policy
   Adj-RIB-Out conveys only routes that are available based on the
   peering type.  Post-policy represents the filtered/changed routes
   from the available routes.

   Some attributes are set only during transmission of the BGP message,
   i.e., post-policy.  It is common that the next hop may be null,
   loopback, or similar during the pre-policy phase.  All mandatory
   attributes, such as next hop, MUST be either zero or have an empty
   length if they are unknown at the pre-policy phase completion.  The
   BMP receiver will treat zero or empty mandatory attributes as self-

   The L flag MUST be set to 0 to indicate pre-policy.

6.  BMP Messages

   Many BMP messages have a per-peer header, but some are not applicable
   to Adj-RIB-In or Adj-RIB-Out monitoring, such as Peer Up and Down
   Notifications.  Unless otherwise defined, the O flag should be set to
   0 in the per-peer header in BMP messages.

6.1.  Route Monitoring and Route Mirroring

   The O flag MUST be set accordingly to indicate if the route monitor
   or route mirroring message conveys Adj-RIB-In or Adj-RIB-Out.

6.2.  Statistics Report

   The Statistics Report message has a Stat Type field to indicate the
   statistic carried in the Stat Data field.  Statistics report messages
   are not specific to Adj-RIB-In or Adj-RIB-Out and MUST have the O
   flag set to zero.  The O flag SHOULD be ignored by the BMP receiver.

   This document defines the following new statistics types:

   *  Stat Type = 14: Number of routes in pre-policy Adj-RIB-Out. This
      statistics type is 64-bit Gauge.

   *  Stat Type = 15: Number of routes in post-policy Adj-RIB-Out. This
      statistics type is 64-bit Gauge.

   *  Stat Type = 16: Number of routes in per-AFI/SAFI pre-policy Adj-
      RIB-Out.  The value is structured as: 2-byte Address Family
      Identifier (AFI), 1-byte Subsequent Address Family Identifier
      (SAFI), followed by a 64-bit Gauge.

   *  Stat Type = 17: Number of routes in per-AFI/SAFI post-policy Adj-
      RIB-Out.  The value is structured as: 2-byte Address Family
      Identifier (AFI), 1-byte Subsequent Address Family Identifier
      (SAFI), followed by a 64-bit Gauge.

6.3.  Peer Up and Down Notifications

   Peer Up and Down Notifications convey BGP peering session state to
   BMP receivers.  The state is independent of whether or not route
   monitoring or route mirroring messages will be sent for Adj-RIB-In,
   Adj-RIB-Out, or both.  BMP receiver implementations SHOULD ignore the
   O flag in Peer Up and Down Notifications.

6.3.1.  Peer Up Information

   This document defines the following Peer Up Information TLV type:

   *  Type = 4: Admin Label.  The Information field contains a free-form
      UTF-8 string whose byte length is given by the Information Length
      field.  The value is administratively assigned.  There is no
      requirement to terminate the string with null or any other

      Multiple Admin Labels can be included in the Peer Up Notification.
      When multiple Admin Labels are included, the BMP receiver MUST
      preserve their order.

      The Admin Label is optional.

7.  Other Considerations

7.1.  Peer and Update Groups

   Peer and update groups are used to group updates shared by many
   peers.  This is a level of efficiency in implementations, not a true
   representation of what is conveyed to a peer in either pre-policy or

   One of the use cases to monitor post-policy Adj-RIB-Out is to
   validate and continually ensure the egress updates match what is
   expected.  For example, wholesale peers should never have routes with
   community X:Y sent to them.  In this use case, there may be hundreds
   of wholesale peers, but a single peer could have represented the

   From a BMP perspective, it should be simple to include a group name
   in the Peer Up, but it is more complex than that.  BGP
   implementations have evolved to provide comprehensive and structured
   policy grouping, such as session, AFI/SAFI, and template-based group
   policy inheritances.

   This level of structure and inheritance of polices does not provide a
   simple peer group name or ID, such as wholesale peer.

   This document defines a new Admin Label type for Peer Up Information
   TLVs (Section 6.3.1) that can be used instead of requiring a group
   name.  These labels have administrative scope relevance.  For
   example, labels "type=wholesale" and "region=west" could be used to
   monitor expected policies.

   Configuration and assignment of labels to peers are BGP

7.2.  Changes to Existing BMP Session

   In case of any change that results in the alteration of behavior of
   an existing BMP session (i.e., changes to filtering and table names),
   the session MUST be bounced with a Peer Down/Peer Up sequence.

8.  Security Considerations

   The considerations in Section 11 of [RFC7854] apply to this document.
   Implementations of this protocol SHOULD require establishing sessions
   with authorized and trusted monitoring devices.  It is also believed
   that this document does not add any additional security

9.  IANA Considerations

   IANA has assigned the following new parameters to the "BGP Monitoring
   Protocol (BMP) Parameters" registry

9.1.  Addition to BMP Peer Flags Registry

   IANA has made the following assignment for the per-peer header flag
   defined in Section 4 of this document:

   | Flag | Description | Reference |
   | 3    | O flag      | RFC 8671  |

     Table 1: Addition to the "BMP
          Peer Flags" Registry

9.2.  Additions to BMP Statistics Types Registry

   IANA has made the following assignment for the four statistics types
   defined in Section 6.2 of this document:

   | Stat Type | Description                  | Reference |
   | 14        | Number of routes in pre-     | RFC 8671  |
   |           | policy Adj-RIB-Out           |           |
   | 15        | Number of routes in post-    | RFC 8671  |
   |           | policy Adj-RIB-Out           |           |
   | 16        | Number of routes in per-AFI/ | RFC 8671  |
   |           | SAFI pre-policy Adj-RIB-Out  |           |
   | 17        | Number of routes in per-AFI/ | RFC 8671  |
   |           | SAFI post-policy Adj-RIB-Out |           |

       Table 2: Additions to the "BMP Statistics Types"

9.3.  Addition to BMP Initiation Message TLVs Registry

   IANA has made the following assignment per Section 6.3.1 of this

   | Type | Description | Reference |
   | 4    | Admin Label | RFC 8671  |

     Table 3: Addition to the "BMP
        Initiation Message TLVs"

10.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [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,

   [RFC7854]  Scudder, J., Ed., Fernando, R., and S. Stuart, "BGP
              Monitoring Protocol (BMP)", RFC 7854,
              DOI 10.17487/RFC7854, June 2016,

   [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>.


   The authors would like to thank John Scudder and Mukul Srivastava for
   their valuable input.


   The following individuals contributed to this document:

   *  Manish Bhardwaj, Cisco Systems

   *  Xianyu Zheng, Tencent

   *  Wei Guo, Tencent

   *  Shugang Cheng, H3C

Authors' Addresses

   Tim Evens
   Cisco Systems
   2901 Third Avenue, Suite 600
   Seattle, WA 98121
   United States of America

   Email: tievens@cisco.com

   Serpil Bayraktar
   Cisco Systems
   3700 Cisco Way
   San Jose, CA 95134
   United States of America

   Email: serpil@cisco.com

   Paolo Lucente
   NTT Communications
   Siriusdreef 70-72
   2132 Hoofddorp

   Email: paolo@ntt.net

   Penghui Mi
   Tengyun Building, Tower A, No. 397 Tianlin Road

   Email: Penghui.Mi@gmail.com

   Shunwan Zhuang
   Huawei Building, No.156 Beiqing Rd.

   Email: zhuangshunwan@huawei.com