



idr                                                              J. Haas
Internet-Draft                                                J. Scudder
Intended status: Standards Track                                     HPE
Expires: 21 February 2026                                 20 August 2025


               BGP-4 Path Attribute Filtering Capability
               draft-haas-idr-path-attribute-filtering-02

Abstract

   Path Attributes in the BGP-4 protocol (RFC 4271) carry data
   associated with BGP routes.  Many of the Path Attributes carried in
   BGP are intended for limited scope deployment.  However, the
   extension mechanism defined by BGP that carries these attributes
   often carries them farther than necessary, sometimes with unfortunate
   results.

   This document defines a mechanism using BGP Capabilities (RFC 5492)
   that permits eBGP speakers to determine what Path Attributes should
   be permitted to cross external BGP routing boundaries.

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 21 February 2026.

Copyright Notice

   Copyright (c) 2025 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



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   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Specification of Requirements . . . . . . . . . . . . . .   3
   2.  BGP Path Attribute Filtering Capability . . . . . . . . . . .   3
   3.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Selecting supported Path Attributes . . . . . . . . . . . . .   5
   5.  Error Handling  . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Operational Considerations  . . . . . . . . . . . . . . . . .   6
     6.1.  Impacts on Path Attribute Transitivity  . . . . . . . . .   6
     6.2.  Impacts on Incremental Deployment of New Features . . . .   6
     6.3.  Path Attribute Content Filtering Considerations . . . . .   6
     6.4.  Operational Visibility  . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  Recommendations for Future BGP Extensions . . . . . . . . . .   8
   10. Recommendations for Filtering Path Attributes . . . . . . . .   9
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  13
   References  . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     Normative References  . . . . . . . . . . . . . . . . . . . . .  13
     Informative References  . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   A BGP Route (Section 1.1 of [RFC4271]) is a tuple consisting of a set
   of Path Attributes (Section 5 of [RFC4271]) and sets of network
   reachability carried as Network Layer Reachability Information
   (NLRI).  Some of these Path Attributes are defined as part of the
   core BGP-4 protocol.  Path Attributes are the main extension
   mechanism defined by BGP, and may be scoped as "transitive" or "non-
   transitive."

   Non-Transitive Path Attributes require the BGP speaker to understand
   the attribute in order to determine if it will be locally used and
   perhaps later propagated to additional BGP speakers.  Unrecognized
   non-transitive Path Attributes are discarded by the receiving BGP
   speaker.

   Transitive Path Attributes, when not understood by the receiving BGP
   speaker, are required to be propagated to other BGP speakers.





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   Some Path Attributes defined by BGP extensions are intended to be
   used in limited scopes, such as a single BGP Autonomous System (AS).
   When such attributes are distributed beyond the expected scope, this
   is called an "Attribute Escape" [I-D.haas-idr-bgp-attribute-escape].

   Such attribute escapes may lead to improper BGP protocol behavior
   when received outside of their expected scope, and may lead to
   incorrect forwarding, or be a serious security consideration.

   This document defines a mechanism exchanged through BGP Capabilities
   [RFC5492] where BGP speakers can more appropriately scope both Path
   Attributes to prevent escape, and to limit the distribution of routes
   that carry escaped Path Attributes.

1.1.  Specification of Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "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.

2.  BGP Path Attribute Filtering Capability

   The BGP Path Attribute Filtering Capability is encoded as follows:

   *  Capability Code of (TBD).

   *  Capability Length of 0..32 octets.

   *  Capability Value contains a bit-string padded to an octet boundary
      where a bit is set if this BGP speaker considers the corresponding
      BGP Path Attribute from the remote BGP speaker to be unwanted.
      Bit number 0 is the most significant bit of the first octet, bit
      number 1 is the second most significant bit of the first octet,
      and so on.















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       0                   1                   2
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |1|0|0|0|0|1|0|0|0|1|1|1|1|1|0|0|1|0|0|1|1|1|1|1|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       In this example, bits are clear for Path Attributes:

         Origin (1),
         AS_PATH (2),
         NEXT_HOP (3),
         MULTI_EXIT_DISCR (4),
         ATOMIC_AGGREGATE (6),
         AGGREGATOR (7),
         COMMUNITIES (8),
         MP_REACH_NLRI (14),
         MP_UNREACH_NLRI (15),
         AS4_PATH (17),
         AS4_AGGREGATOR (18).

       Other path attributes through attribute 23 are unwanted.
       Path attributes 24 and beyond are accepted.

              Figure 1: Example encoding for Capability Value

   Bits 1, 2, 3, 6, 7, 14, 15, 17, 18 MUST be clear (value 0), because
   support for [RFC4271], [RFC4760], and [RFC6793] procedures are
   required when this specification is in use.

   Any bit not explicitly represented (e.g., bits 24 and beyond in the
   above example) is deemed to be clear (value 0).  That is, the default
   is to accept any path attribute not explicitly unwanted.

3.  Operation

   A clear (value 0) bit in the Path Attribute Filtering capability
   indicates that the BGP speaker advertising it is willing to accept
   the corresponding Path Attribute and will process it according to the
   normal rules of the BGP protocol and the attribute in question.

   A set (value 1) bit in the Path Attribute Filtering capability
   indicates that the BGP speaker advertising it is not willing to
   accept the corresponding Path Attribute.  We refer to such Path
   Attributes as "unwanted Path Attributes".







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   A BGP speaker MUST NOT send an unwanted Path Attribute to its peer.
   (Of course, this expectation will be met only by BGP speakers that
   support this specification; therefore a BGP speaker that implements
   this specification SHOULD be prepared for the possibility it will
   receive unwanted Path Attributes; this is discussed below.)

   One strategy to accomplish the above requirement is for the BGP
   speaker to not advertise BGP routes containing the unwanted Path
   Attribute in question.  This might require a withdraw to be sent
   instead.  This is similar to treat-as-withdraw as defined in
   [RFC7606].

   Another strategy that could be used, when appropriate for the
   procedure covering a given BGP Path Attribute, is for the BGP speaker
   to remove the unwanted Path Attributes when it distributes the route
   to the remote BGP speaker.  This is similar to the Attribute Discard
   behavior defined in [RFC7606].

   Receiving BGP speakers SHOULD filter routes or discard unwanted Path
   Attributes if they are incorrectly sent by the remote BGP speaker.
   Minimally, a receiving BGP speaker receiving an unwanted Path
   Attribute SHOULD use treat-as-withdraw procedures.  Receiving BGP
   speakers MAY accept the route and discard the unwanted Path Attribute
   if permitted to by local configuration.

4.  Selecting supported Path Attributes

   Implementations MUST, as described in Figure 1, clear the bits
   covering required core eBGP Path Attributes.

   Common BGP features that are defined for Internet use SHOULD be clear
   by default between two BGP speakers.  These include:

   *  Communities (8)

   *  Extended Communities (16)

   *  Large BGP Communities (32)

   *  BGPsec_Path (33)

   *  Only To Customer (OTC) (35)

   BGP features required to support a given AFI/SAFI MUST also be clear
   when that address family is configured.  An example of this is the
   BGP-LS attribute (29) when the BGP-LS feature is in use.





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5.  Error Handling

   If the received Capability Length for the Path Attributes Filtering
   Capability is greater than 32, the filtering capability MUST be
   ignored and treated as if not received by the BGP speaker.

   To support core BGP features, Section 2 requires that bits 1, 2, 3,
   6, 7, 14, 15, 17, 18 be clear (value 0).  A BGP speaker receiving a
   Path Attribute Filtering Capability with these bits set (value 1) MAY
   reject the BGP session.  If it does so, it uses a NOTIFICATION
   message with an error subcode of "Unsupported Capability".

6.  Operational Considerations

6.1.  Impacts on Path Attribute Transitivity

   The feature described in this document does not change the semantics
   of when a Path Attribute is intended to be transitive per RFC-4271
   definition.  However, it does act as a policy to limit the
   distribution of routes containing a transitive Path Attribute, or may
   cause that attribute to be filtered.

6.2.  Impacts on Incremental Deployment of New Features

   eBGP speakers using this features must be cognizant of the impact
   their filtering policies will have on the incremental deployment of
   new BGP features.

6.3.  Path Attribute Content Filtering Considerations

   Path Attributes originally defined for use solely for one AFI/SAFI
   may later be updated to be applicable for other AFI/SAFIs, including
   those used by the Internet.  Similarly, some Path Attribute features
   may be internally extensible in a way where filtering choices may be
   difficult to characterize using the coarse filtering feature defined
   by this document.

   Documents defining new BGP Path Attributes MUST discuss their
   filtering, transitivity, and attribute escape considerations, and
   adopt strategies to limit unintentional escape of Path Attributes, or
   scoped sub-features of a Path Attribute.  At a minimum, the new
   attribute's registration must provide values for the "Should Filter
   By Default" and "Filtering Profile" columns (see Section 7).  This
   is, however, a minimum.  If the attribute has needs more nuanced
   propagation control than the all-or-nothing (per attribute type code)
   behavior offered by the present specification, it must be specified
   and handled on a case-by-case basis.




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6.4.  Operational Visibility

   eBGP speakers that do not propagate a route on transmit or do not
   accept a route on reception due to unwanted Path Attributes SHOULD
   provide operationally visible feedback for this filtering behavior.
   Using terminology consistent with BMP ([RFC7854], et seq.) or the BGP
   YANG model ([I-D.ietf-idr-bgp-model]), routes that are not sent may
   have visibility in the Pre-Policy Adj-Ribs-Out view, but not be
   available in the Post-Policy Adj-Ribs-Out view.  Updates to BMP or
   BGP YANG may provide operational visibility to this filtering.  eBGP
   speakers that do not discard received routes with unwanted Path
   Attributes may be able to provide similar visibility in the Pre- and
   Post-Policy Adj-Ribs-In views.

   Since utilizing treat-as-withdraw for routes received with unwanted
   Path Attributes is a likely implementation choice, implementations
   SHOULD provide operational visibility when treat-as-withdraw is done,
   via logging or aggregate statistics, on a per-BGP neighbor basis.
   Such logging or aggregate statistics should include the unwanted Path
   Attribute codes that cause routes to be discarded.

   For some unwanted Path Attributes, an implementation may choose to
   use attribute discard for the unwanted Path Attributes rather than
   using treat-as-withdraw for the entire route.  Implementations SHOULD
   provide operational visibility when attribute discard is done, via
   logging or aggregate statistics, on a per-BGP neighbor basis.  Such
   logging or aggregate statistics should include the Path Attribute
   codes that are discarded.

   Future extensions to BMP or BGP YANG may be proposed to support these
   operational considerations.

7.  IANA Considerations

   This document requests a new BGP Capability Code to be allocated from
   the First Come First Served range of the Capability Codes registry.
   The description should be "Path Attribute Filtering", and the
   reference should be this document.

   This document requests that the "BGP Path Attributes" registry be
   updated to add two new columns, called "Should Filter By Default" and
   "Filtering Profile".  These columns are to be seeded with the values
   shown in Table 1.  This document should be added as a reference for
   the registry.  Authors seeking guidance for how to populate these
   columns should refer to Section 6.3 and Section 10.






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8.  Security Considerations

   The motivation for this feature is to attempt to address the numerous
   BGP security implications where BGP Path Attributes propagate beyond
   their intended scope.

   The definition of a feature that limits the distribution of BGP Path
   Attributes unfortunately moves BGP's default behavior away from
   "distribute unknown things easily" and thus hampers incremental
   deployment of new features.  However, operators have already begun
   indiscriminate filtering of Path Attributes they do not themselves
   require.  This feature attempts to provide a more flexible negotiated
   mode to permit such filtering while at the same time not completely
   precluding incremental deployment of new features.

9.  Recommendations for Future BGP Extensions

   When a new BGP extension defines a new BGP Path Attribute, the
   specifying document MUST define its expected filtering profile for
   routes containing the new Path Attribute.  The following are
   suggested propagation policies for new features:

   *  Default deny: Without explicit configuration from the sending BGP
      speaker and the receiving BGP speaker, routes containing the new
      Path Attribute are considered unwanted.  Implementations
      supporting the Path Attribute Filtering Capability SHOULD set the
      bit for this Path Attribute to 1 (unwanted) by default.  The
      sending BGP speaker MUST NOT advertise routes containing such a
      Path Attribute to the remote BGP speaker.  BGP speakers receiving
      routes containing the unwanted Path Attribute SHOULD NOT accept
      the route into its Adj-Rib-In for that peer (treat-as-withdraw).

   *  Default discard: Without explicit configuration from the sending
      BGP speaker and the receiving BGP speaker, routes containing the
      new Path Attribute are considered unwanted.  Implementations
      supporting the Path Attribute Filtering Capability SHOULD set the
      bit of this Path Attribute to 1 (unwanted) by default.

      The sending BGP speaker MUST use one of the following two options
      to avoid sending the unwanted Path Attribute: it can either send
      the route to the remote speaker after discarding the offending
      Path Attribute (attribute discard) or it can avoid sending the
      route to such a peer.








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      The receiving BGP speaker SHOULD NOT accept routes with the
      offending Path Attribute into its Adj-Rib-In for that peer (treat-
      as-withdraw) or MAY discard the offending Path Attribute
      (attribute-discard).  The choice of the desired behavior to
      discard or to not propagate will depend on the operational
      expectations for the feature.

   *  AFI/SAFI conditional: When the specified AFI/SAFI is configured
      for the BGP session and the Path Attribute Filtering Capability is
      supported, the filtering capability bit SHOULD be set to 0
      (wanted) by default.  When that AFI/SAFI is not configured, the
      defining specification should detail whether the default filtering
      policy is wanted and the filtering capability bit for that Path
      Attribute MUST be set accordingly.

   *  Default permit: Without explicit configuration from the sending
      BGP speaker and the receiving BGP speaker, routes containing the
      new Path Attribute are considered wanted.  Implementations
      supporting the Path Attribute Filtering Capability SHOULD set the
      bit of this Path Attribute to 0 (wanted) by default.

10.  Recommendations for Filtering Path Attributes

   The table below provides suggested default filtering behaviors for
   many BGP Path Attributes.  In addition to "yes" and "no", which
   indicate that an implementation SHOULD either filter, or not filter,
   the given attribute by default, "never" indicates that an
   implementation MUST NOT filter the given attribute under any
   circumstances, and "-" indicates that no recommendation is made.

   The table also recommends filtering profiles, as defined in
   Section 9.  Where no filtering recommendation is made, no profile is
   suggested either.

   It is not recommended that BGP Path Attributes that are deprecated
   should be filtered by default.  This permits their long term
   reassignment and re-use.  Operators with a strong filtering policy
   may consider filtering these to block routes from older
   implementations of these features that may still be deployed.

   Upon publication of this document as an RFC, this table will become
   historic and the authoritative source of recommendations will be the
   relevant IANA registry (Section 7).








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   +=======+==================================+=========+=============+
   | Code  | Name                             | Should  | Filtering   |
   | Point |                                  | Filter  | Profile     |
   |       |                                  | By      |             |
   |       |                                  | Default |             |
   +=======+==================================+=========+=============+
   | 0     | Reserved                         | Yes     | Default     |
   |       |                                  |         | deny        |
   +-------+----------------------------------+---------+-------------+
   | 1     | ORIGIN [RFC4271]                 | Never   | Default     |
   |       |                                  |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 2     | AS_PATH [RFC4271]                | Never   | Default     |
   |       |                                  |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 3     | NEXT_HOP [RFC4271]               | Never   | Default     |
   |       |                                  |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 4     | MULTI_EXIT_DISC [RFC4271]        | No      | Default     |
   |       |                                  |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 5     | LOCAL_PREF [RFC4271]             | Yes     | Default     |
   |       |                                  |         | discard     |
   +-------+----------------------------------+---------+-------------+
   | 6     | ATOMIC_AGGREGATE [RFC4271]       | No      | Default     |
   |       |                                  |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 7     | AGGREGATOR [RFC4271]             | No      | Default     |
   |       |                                  |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 8     | COMMUNITIES [RFC1997]            | No      | Default     |
   |       |                                  |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 9     | ORIGINATOR_ID [RFC4456]          | Yes     | Default     |
   |       |                                  |         | discard     |
   +-------+----------------------------------+---------+-------------+
   | 10    | CLUSTER_LIST [RFC4456]           | Yes     | Default     |
   |       |                                  |         | discard     |
   +-------+----------------------------------+---------+-------------+
   | 11    | DPA (deprecated) [RFC6938]       | -       |             |
   +-------+----------------------------------+---------+-------------+
   | 12    | ADVERTISER (historic)            | -       |             |
   |       | (deprecated)                     |         |             |
   |       | [RFC1863][RFC4223][RFC6938]      |         |             |
   +-------+----------------------------------+---------+-------------+
   | 13    | RCID_PATH / CLUSTER_ID           | -       |             |
   |       | (Historic) (deprecated)          |         |             |
   |       | [RFC1863][RFC4223][RFC6938]      |         |             |



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   +-------+----------------------------------+---------+-------------+
   | 14    | MP_REACH_NLRI [RFC4760]          | Never   | Default     |
   |       |                                  |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 15    | MP_UNREACH_NLRI [RFC4760]        | Never   | Default     |
   |       |                                  |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 16    | EXTENDED COMMUNITIES             | No      | Default     |
   |       | [Eric_Rosen][draft-ramachandra-  |         | permit      |
   |       | bgp-ext-communities-00][RFC4360] |         |             |
   +-------+----------------------------------+---------+-------------+
   | 17    | AS4_PATH [RFC6793]               | Never   | Default     |
   |       |                                  |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 18    | AS4_AGGREGATOR [RFC6793]         | Never   | Default     |
   |       |                                  |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 19    | SAFI Specific Attribute (SSA)    | -       |             |
   |       | (deprecated)                     |         |             |
   |       | [Gargi_Nalawade][draft-kapoor-   |         |             |
   |       | nalawade-idr-bgp-ssa-00][draft-  |         |             |
   |       | nalawade-idr-mdt-safi-00][draft- |         |             |
   |       | wijnands-mt-discovery-00]        |         |             |
   +-------+----------------------------------+---------+-------------+
   | 20    | Connector Attribute (deprecated) | -       |             |
   |       | [RFC6037]                        |         |             |
   +-------+----------------------------------+---------+-------------+
   | 21    | AS_PATHLIMIT (deprecated)        | -       |             |
   |       | [draft-ietf-idr-as-pathlimit-02] |         |             |
   +-------+----------------------------------+---------+-------------+
   | 22    | PMSI_TUNNEL [RFC6514]            | Yes     | Default     |
   |       |                                  |         | deny        |
   +-------+----------------------------------+---------+-------------+
   | 23    | Tunnel Encapsulation [RFC9012]   | Yes     | Default     |
   |       |                                  |         | deny        |
   +-------+----------------------------------+---------+-------------+
   | 24    | Traffic Engineering [RFC5543]    | Yes     | Default     |
   |       |                                  |         | discard     |
   +-------+----------------------------------+---------+-------------+
   | 25    | IPv6 Address Specific Extended   | No      | Default     |
   |       | Community [RFC5701]              |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 26    | AIGP [RFC7311]                   | Yes     | Default     |
   |       |                                  |         | discard     |
   +-------+----------------------------------+---------+-------------+
   | 27    | PE Distinguisher Labels          | Yes     | Default     |
   |       | [RFC6514]                        |         | deny        |
   +-------+----------------------------------+---------+-------------+



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   | 28    | BGP Entropy Label Capability     | -       |             |
   |       | Attribute (deprecated)           |         |             |
   |       | [RFC6790][RFC7447]               |         |             |
   +-------+----------------------------------+---------+-------------+
   | 29    | BGP-LS Attribute [RFC9552]       | Yes     | AFI/SAFI    |
   |       |                                  |         | Conditional |
   +-------+----------------------------------+---------+-------------+
   | 30    | Deprecated [RFC8093]             | -       |             |
   +-------+----------------------------------+---------+-------------+
   | 31    | Deprecated [RFC8093]             | -       |             |
   +-------+----------------------------------+---------+-------------+
   | 32    | LARGE_COMMUNITY [RFC8092]        | No      | Default     |
   |       |                                  |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 33    | BGPsec_Path [RFC8205]            | Never   | Default     |
   |       |                                  |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 34    | BGP Community Container          | No      | Default     |
   |       | Attribute (TEMPORARY -           |         | permit      |
   |       | registered 2017-07-28, extension |         |             |
   |       | registered 2024-08-22, expires   |         |             |
   |       | 2025-07-28) [draft-ietf-idr-     |         |             |
   |       | wide-bgp-communities-11]         |         |             |
   +-------+----------------------------------+---------+-------------+
   | 35    | Only to Customer (OTC) [RFC9234] | Never   | Default     |
   |       |                                  |         | permit      |
   +-------+----------------------------------+---------+-------------+
   | 36    | BGP Domain Path (D-PATH)         | Yes     | Default     |
   |       | (TEMPORARY - registered          |         | deny        |
   |       | 2019-07-08, extension registered |         |             |
   |       | 2025-06-06, expires 2026-07-08)  |         |             |
   |       | [draft-ietf-bess-evpn-ipvpn-     |         |             |
   |       | interworking-10]                 |         |             |
   +-------+----------------------------------+---------+-------------+
   | 37    | SFP attribute [RFC9015]          | Yes     | Default     |
   |       |                                  |         | deny        |
   +-------+----------------------------------+---------+-------------+
   | 38    | BFD Discriminator [RFC9026]      | Yes     | Default     |
   |       |                                  |         | discard     |
   +-------+----------------------------------+---------+-------------+
   | 39    | BGP Next Hop Dependent           | Yes     | Default     |
   |       | Capabilities (NHC) (TEMPORARY -  |         | discard     |
   |       | registered 2022-12-20, extension |         |             |
   |       | registered 2024-12-10, expires   |         |             |
   |       | 2025-12-20) [draft-ietf-idr-     |         |             |
   |       | entropy-label-13]                |         |             |
   +-------+----------------------------------+---------+-------------+
   | 40    | BGP Prefix-SID [RFC8669]         | Yes     | Default     |



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   |       |                                  |         | discard     |
   +-------+----------------------------------+---------+-------------+
   | 41    | BIER [RFC9793]                   | Yes     | Default     |
   |       |                                  |         | deny        |
   +-------+----------------------------------+---------+-------------+
   | 42    | Edge Metadata Path Attribute     | Yes     |             |
   |       | (TEMPORARY - registered          |         |             |
   |       | 2025-04-23, expires 2026-04-23)  |         |             |
   |       | [draft-ietf-idr-5g-edge-service- |         |             |
   |       | metadata-27]                     |         |             |
   +-------+----------------------------------+---------+-------------+
   | 128   | ATTR_SET [RFC6368]               | Yes     | Default     |
   |       |                                  |         | deny        |
   +-------+----------------------------------+---------+-------------+
   | 129   | Deprecated [RFC8093]             | -       |             |
   +-------+----------------------------------+---------+-------------+
   | 241   | Deprecated [RFC8093]             | -       |             |
   +-------+----------------------------------+---------+-------------+
   | 242   | Deprecated [RFC8093]             | -       |             |
   +-------+----------------------------------+---------+-------------+
   | 243   | Deprecated [RFC8093]             | -       |             |
   +-------+----------------------------------+---------+-------------+
   | 255   | Reserved for development         | Yes     | Default     |
   |       | [RFC2042]                        |         | discard     |
   +-------+----------------------------------+---------+-------------+

                                 Table 1

Acknowledgements

   The authors would like to thank the following individuals whose
   comments contributed to the refinement of this document: Donatas
   Abraitis, Ignas Bagdonas, Bruno Decraene, David Lamparter, Robert
   Raszuk.

References

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,
              <https://www.rfc-editor.org/rfc/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/rfc/rfc4271>.



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

   [RFC6793]  Vohra, Q. and E. Chen, "BGP Support for Four-Octet
              Autonomous System (AS) Number Space", RFC 6793,
              DOI 10.17487/RFC6793, December 2012,
              <https://www.rfc-editor.org/rfc/rfc6793>.

   [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/rfc/rfc7606>.

   [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/rfc/rfc8174>.

Informative References

   [I-D.haas-idr-bgp-attribute-escape]
              Haas, J., "BGP Attribute Escape", Work in Progress,
              Internet-Draft, draft-haas-idr-bgp-attribute-escape-03, 9
              April 2025, <https://datatracker.ietf.org/doc/html/draft-
              haas-idr-bgp-attribute-escape-03>.

   [I-D.ietf-idr-bgp-model]
              Jethanandani, M., Patel, K., Hares, S., and J. Haas, "YANG
              Model for Border Gateway Protocol (BGP-4)", Work in
              Progress, Internet-Draft, draft-ietf-idr-bgp-model-18, 21
              October 2024, <https://datatracker.ietf.org/doc/html/
              draft-ietf-idr-bgp-model-18>.

   [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/rfc/rfc4760>.

   [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/rfc/rfc7854>.

Authors' Addresses







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   Jeffrey Haas
   HPE
   1133 Innovation Way
   Sunnyvale, CA 94089
   United States of America
   Email: jhaas@juniper.net


   John Scudder
   HPE
   1133 Innovation Way
   Sunnyvale, CA 94089
   United States of America
   Email: jgs@juniper.net





































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