



BESS Working Group                                           J. Tantsura
Internet-Draft                                            V. Venkatraman
Intended status: Standards Track                             K. Muppalla
Expires: 16 November 2026                                     P. Doijode
                                                                  Nvidia
                                                               M. Rzehak
                                                               CoreWeave
                                                             15 May 2026


                     EVPN Unreachability Signaling
               draft-tantsura-bess-evpn-unreachability-02

Abstract

   This document defines a new EVPN Route Type for signaling prefix
   unreachability information without affecting the forwarding plane.
   The route type reuses the Route Type 5 (IP Prefix Advertisement)
   field order defined for EVPN IP prefix routes, adds an Address Family
   octet for unambiguous IPv4/IPv6 parsing, and appends Reporter TLVs
   that allow aggregation of unreachability reports from multiple
   network vantage points.

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 16 November 2026.

Copyright Notice

   Copyright (c) 2026 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.



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   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 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  EVPN Unreachability Route Type  . . . . . . . . . . . . . . .   5
     2.1.  Route Type Definition . . . . . . . . . . . . . . . . . .   5
     2.2.  Route Distinguisher and Route Targets . . . . . . . . . .   6
   3.  NLRI Encoding . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Design Philosophy . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Approach to Multiple Reporters  . . . . . . . . . . . . .   6
     3.3.  IP Prefix Unreachability Route NLRI . . . . . . . . . . .   7
     3.4.  Field Usage for Information-Only Routes . . . . . . . . .   9
     3.5.  Reporter TLV Format . . . . . . . . . . . . . . . . . . .  10
     3.6.  Sub-TLV Types . . . . . . . . . . . . . . . . . . . . . .  11
       3.6.1.  Unreachability Reason Code Sub-TLV  . . . . . . . . .  11
       3.6.2.  Timestamp Sub-TLV . . . . . . . . . . . . . . . . . .  12
       3.6.3.  EVI Sub-TLV . . . . . . . . . . . . . . . . . . . . .  12
       3.6.4.  Sub-TLV Processing Rules  . . . . . . . . . . . . . .  13
   4.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     4.1.  Forwarding Plane Separation . . . . . . . . . . . . . . .  13
     4.2.  Generating Unreachability Routes  . . . . . . . . . . . .  14
     4.3.  Processing Unreachability Routes  . . . . . . . . . . . .  14
     4.4.  Aggregation Procedures  . . . . . . . . . . . . . . . . .  15
     4.5.  Withdrawal Procedures . . . . . . . . . . . . . . . . . .  16
       4.5.1.  Individual Reporter Withdrawal  . . . . . . . . . . .  16
       4.5.2.  Complete NLRI Withdrawal  . . . . . . . . . . . . . .  17
       4.5.3.  Stale Reporter Detection  . . . . . . . . . . . . . .  17
     4.6.  Interaction with Graceful Restart . . . . . . . . . . . .  17
       4.6.1.  Graceful Restart Capability . . . . . . . . . . . . .  18
       4.6.2.  Restarting Speaker Behavior . . . . . . . . . . . . .  18
       4.6.3.  Receiving Speaker Behavior  . . . . . . . . . . . . .  18
       4.6.4.  Route Reflector Considerations  . . . . . . . . . . .  19
       4.6.5.  Implementation Recommendations  . . . . . . . . . . .  19
     4.7.  Preventing State Explosion  . . . . . . . . . . . . . . .  19
     4.8.  Relationship to BGP Route Damping . . . . . . . . . . . .  20
     4.9.  Path Selection for Aggregation  . . . . . . . . . . . . .  20
     4.10. Communities and Attributes  . . . . . . . . . . . . . . .  21
     4.11. Error Handling  . . . . . . . . . . . . . . . . . . . . .  21
       4.11.1.  NLRI Structural Errors . . . . . . . . . . . . . . .  22
       4.11.2.  Non-Key Field Errors . . . . . . . . . . . . . . . .  22
       4.11.3.  Reporter TLV Errors  . . . . . . . . . . . . . . . .  22



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       4.11.4.  Sub-TLV Errors . . . . . . . . . . . . . . . . . . .  23
   5.  Interoperability Considerations . . . . . . . . . . . . . . .  23
     5.1.  Incremental Deployment  . . . . . . . . . . . . . . . . .  23
     5.2.  Interaction with Route Reflectors . . . . . . . . . . . .  23
     5.3.  Interaction with Other EVPN Route Types . . . . . . . . .  24
   6.  Deployment Considerations . . . . . . . . . . . . . . . . . .  24
     6.1.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . .  24
     6.2.  Operational Recommendations . . . . . . . . . . . . . . .  25
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  25
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
     8.1.  EVPN Route Type . . . . . . . . . . . . . . . . . . . . .  26
     8.2.  EVPN Unreachability Reporter TLV Types  . . . . . . . . .  26
     8.3.  EVPN Unreachability Sub-TLV Types . . . . . . . . . . . .  27
     8.4.  EVPN Unreachability Reason Codes  . . . . . . . . . . . .  27
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  28
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  28
     10.2.  Informative References . . . . . . . . . . . . . . . . .  29
   Appendix A: Encoding Examples . . . . . . . . . . . . . . . . . .  30
     Example 1: Minimal Unreachability Route . . . . . . . . . . . .  30
     Example 2: Aggregated Route with Multiple Reporters . . . . . .  31
     Example 3: IPv6 Unreachability Route  . . . . . . . . . . . . .  32
     Example 4: Complete BGP UPDATE Message  . . . . . . . . . . . .  33
     Example 5: Aggregation at a Receiving PE  . . . . . . . . . . .  35
     Example 6: Withdrawal Procedures  . . . . . . . . . . . . . . .  36
   Appendix B: Design Tradeoffs  . . . . . . . . . . . . . . . . . .  37
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  38

1.  Introduction

   EVPN (Ethernet VPN) [RFC7432] provides a flexible framework for Layer
   2 and Layer 3 VPN services.  While EVPN includes mechanisms for
   advertising reachable prefixes via Route Type 5 (IP Prefix
   Advertisement Route) [RFC9136], there is no standard way to signal
   unreachability information for monitoring and troubleshooting
   purposes without affecting the forwarding plane.

   Similar to the challenges in standard BGP, EVPN withdrawals are only
   propagated for prefixes that have been previously announced.  This
   behavior limits the ability of operators to share information about
   prefix unreachability for prefixes that were never announced or to
   correlate unreachability reports from multiple PE (Provider Edge)
   routers.

   Use cases for EVPN unreachability signaling include but not limited
   to:

   *  Multi-tenant network debugging and troubleshooting



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   *  Security event coordination across EVPN instances

   *  DDoS attack target information sharing without null-routing

   *  Monitoring tenant prefix health across multiple data centers

   *  Correlating unreachability from multiple PE vantage points

   The goal of this mechanism is to provide comprehensive information
   about unreachability events:

   *  Where the event has happened: Reporter Identifier, Reporter AS
      Number, and optionally EVPN Instance (EVI)

   *  Why the event has happened: Reason Code indicating the cause of
      unreachability

   *  When the event has happened: Timestamp of the unreachability
      detection

   This document defines a new EVPN Route Type that creates a parallel
   information channel for unreachability data, maintaining complete
   separation from the forwarding plane.  The encoding follows the
   architecture and terminology of [RFC9136], applying similar concepts
   to EVPN as defined for standard BGP in
   [I-D.tantsura-idr-unreachability-safi].

1.1.  Requirements Language

   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.

1.2.  Terminology

   EVPN:     Ethernet VPN

   NVE:      Network Virtualization Edge, as defined in [RFC7365] and
             [RFC9136].  An NVE is a network entity that provides
             virtualization functions.  In this document, NVE and PE are
             used interchangeably.

   PE:       Provider Edge router

   RT-5:     EVPN Route Type 5 (IP Prefix Advertisement Route), as
             defined in [RFC9136]



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   Address Family (unreachability NLRI):  1-octet field in the IP Prefix
             Unreachability Route NLRI, immediately after the Ethernet
             Tag ID, indicating IPv4 (value 1) or IPv6 (value 2).  The
             values are the existing BGP Address Family Identifier (AFI)
             numeric values assigned by IANA in the "Address Family
             Numbers" registry [RFC4760]; this document defines no new
             values and creates no new registry.  See Section 3.3.

   UI-RIB:   Unreachability Information RIB

   NLRI:     Network Layer Reachability Information

   TLV:      Type-Length-Value

   Reporter TLV:  A nested TLV structure containing information about
             one Reporting PE and its associated unreachability details

   Aggregation:  The process of combining multiple Reporter TLVs from
             different paths into a single NLRI

   Advertising PE:  The PE router that sends the BGP UPDATE message
             containing the unreachability information

   Reporting PE:  The PE router that originally generated the
             unreachability information (identified within a Reporter
             TLV)

   This document also assumes familiarity with the terminology of
   [RFC7365], [RFC7432], [RFC8365], and [RFC9136].

2.  EVPN Unreachability Route Type

2.1.  Route Type Definition

   This document defines a new EVPN Route Type:

   *  Route Type: TBD1 (to be assigned by IANA)

   *  Name: IP Prefix Unreachability Route Type

   *  Based on: Route Type 5 field order and definitions from [RFC9136],
      plus an Address Family octet after the Ethernet Tag ID (not
      present in reachability RT-5)

   This route type is carried in BGP UPDATE messages using the
   Multiprotocol Extensions for BGP-4 [RFC4760], with AFI = 25 (L2VPN)
   and SAFI = 70 (EVPN), following the same procedures as other EVPN
   route types defined in [RFC7432] and [RFC9136].



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   This route type creates a parallel information plane for
   unreachability signaling.  It MUST NOT affect the EVPN Loc-RIB or
   forwarding plane in any way.  PE routers receiving this route type
   MUST maintain it in a separate Unreachability Information RIB (UI-
   RIB) and MUST NOT install or remove routes in the Loc-RIB or
   forwarding table based on these advertisements.

2.2.  Route Distinguisher and Route Targets

   The Route Distinguisher (RD) field and Route Target (RT) extended
   communities operate as defined in [RFC7432] and [RFC9136].
   Unreachability routes for an EVPN instance SHOULD use the same RD and
   RTs as the corresponding reachability routes (Route Type 5), ensuring
   correlation with the same EVPN instance and following established
   EVPN patterns.

   Implementations MAY use distinct RTs for unreachability routes to
   limit distribution to specific PEs (e.g., monitoring systems) or to
   prevent distribution to legacy systems during incremental deployment.

3.  NLRI Encoding

3.1.  Design Philosophy

   The IP Prefix Unreachability Route encoding uses the Route Type 5
   field order and definitions from [RFC9136] to maximize consistency
   with existing EVPN implementations.  Implementations can reuse much
   of existing RT-5 parsing logic but MUST insert handling for the
   Address Family octet (immediately after the Ethernet Tag ID) before
   reading the IP Prefix field, because reachability RT-5 has no such
   field.

   This approach provides:

   *  Structural consistency with Route Type 5 (with the Address Family
      extension noted above)

   *  Simplified implementation by following familiar RT-5 field order
      and semantics aside from that extension

   *  Extensibility via TLV-based reporter information

   *  Future-proof design if any currently unused fields become relevant

3.2.  Approach to Multiple Reporters

   When multiple PE routers report unreachability for the same prefix,
   implementers have several options:



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   1.  Single Reporter: Do nothing and allow the Reporter Identifier of
       the best route to be used as the only Reporter.  This is the
       simplest approach but loses information from other reporters.
       This approach is fully compatible with all EVPN implementations.

   2.  Nested TLV Aggregation (Recommended): Implement the nested TLV
       aggregation approach described in this specification to preserve
       all reporter perspectives in a single NLRI.  This provides the
       most comprehensive view while maintaining a single EVPN route per
       prefix.  This approach is designed specifically for EVPN and does
       not require additional protocol extensions beyond this
       specification.

   3.  BGP ADD-PATH: Use BGP ADD-PATH [RFC7911] to maintain multiple
       paths, each carrying its own Reporter TLV.  ADD-PATH is defined
       for BGP-4 and can be applied to EVPN route types by prepending a
       Path Identifier to each NLRI.  However, ADD-PATH support for EVPN
       varies by implementation, and this approach would require both
       ADD-PATH capability negotiation and proper handling of Path
       Identifiers with EVPN Route Type structures.  This option
       preserves full BGP path attributes per reporter but has higher
       complexity and deployment requirements.

   This specification focuses on the nested TLV aggregation approach
   (option 2) as the preferred mechanism, providing detailed procedures
   and encodings for this method throughout the remainder of this
   document.  Option 2 is recommended because it provides comprehensive
   multi-reporter visibility while maintaining compatibility with
   standard EVPN processing and minimizing implementation complexity.

3.3.  IP Prefix Unreachability Route NLRI

   The IP Prefix Unreachability Route uses the Route Type 5 field order
   and definitions from [RFC9136], extended with Reporter TLVs and one
   additional field for address-family disambiguation (see below).

   The NLRI is uniquely identified by the combination of Route
   Distinguisher, Ethernet Tag ID, Address Family, IP Prefix Length, and
   IP Prefix.  Reporter TLVs are NOT part of the NLRI key but provide
   information about each Reporting PE.  The presence of an
   Unreachability Route for a prefix signifies that one or more PEs
   report the prefix as unreachable.  The withdrawal of such a route
   indicates that all reporters have cleared their unreachability
   reports for that prefix.

   For reachability RT-5 routes, [RFC9136] fixes the size of the route-
   type-specific NLRI (34 octets for IPv4 or 58 octets for IPv6), which
   allows a receiver to infer whether the IP Prefix field is 4 or 16



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   octets.  Because unreachability routes append a variable number of
   Reporter TLVs, the route-type-specific length is no longer sufficient
   to infer the address family: for example, an IPv4 prefix with a large
   set of Reporter TLVs can yield the same total size as a shorter IPv6
   encoding.  Furthermore, IP Prefix Length alone is ambiguous (e.g., a
   /24 can be valid for both IPv4 and IPv6).  Therefore, this route type
   includes an explicit Address Family field immediately after the
   Ethernet Tag ID.  Receivers MUST use this field to determine the
   width of the IP Prefix field before parsing Reporter TLVs.

   +---------------------------------------+
   |  Route Type (1 octet)                 |
   +---------------------------------------+
   |  Length (1 octet)                     |
   +---------------------------------------+
   |  Route Distinguisher (8 octets)       |
   +---------------------------------------+
   |  Ethernet Segment Identifier (10 octets)|
   +---------------------------------------+
   |  Ethernet Tag ID (4 octets)           |
   +---------------------------------------+
   |  Address Family (1 octet)             |
   +---------------------------------------+
   |  IP Prefix Length (1 octet)           |
   +---------------------------------------+
   |  IP Prefix (4 or 16 octets)           |
   +---------------------------------------+
   |  GW IP Address Length (1 octet) = 0   |
   +---------------------------------------+
   |  MPLS Label (3 octets) = 0            |
   +---------------------------------------+
   |  Reporter TLVs (variable)             |
   +---------------------------------------+

   Where:

   *  Route Type: TBD1 (IP Prefix Unreachability Route Type)

   *  Length: As defined in [RFC7432], the number of octets in the Route
      Type specific field (from Route Distinguisher through the end of
      the last Reporter TLV).  This differs from reachability RT-5 in
      [RFC9136], where Length is 34 (IPv4) or 58 (IPv6) and does not
      include Reporter TLVs.

   *  Route Distinguisher: As defined in [RFC7432] and [RFC9136], used
      to identify the EVPN instance.  The RD MUST be used as specified
      in those documents.




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   *  Ethernet Segment Identifier: As defined in [RFC7432].  MUST be set
      to 0 (all bytes zero) for unreachability routes.

   *  Ethernet Tag ID: As defined in [RFC7432] and [RFC9136], identifies
      the broadcast domain.  For unreachability routes, this SHOULD be
      set to 0 unless VLAN-aware bundle service is used, following the
      same conventions as reachability RT-5 routes.

   *  Address Family: 1 octet.  The values are the existing BGP Address
      Family Identifier (AFI) numeric values assigned by IANA in the
      "Address Family Numbers" registry [RFC4760]; this document defines
      no new values and creates no new registry.  Value 1 (IPv4, BGP AFI
      1) requires an IP Prefix field of 4 octets and IP Prefix Length in
      the range 0-32 inclusive.  Value 2 (IPv6, BGP AFI 2) requires an
      IP Prefix field of 16 octets and IP Prefix Length in the range
      0-128 inclusive.  Handling of any other Address Family value is
      specified in Section 4.10.1.

   *  IP Prefix Length: Length of the IP prefix in bits.  Constraints
      depend on Address Family as described above.

   *  IP Prefix: IPv4 (4 octets) or IPv6 (16 octets) prefix being
      reported as unreachable, consistent with Address Family.

   *  GW IP Address Length: MUST be set to 0.  The GW IP Address field
      is not used for unreachability routes.

   *  GW IP Address: MUST be zero octets (GW IP Address Length = 0).
      Unreachability routes do not use overlay index resolution.

   *  MPLS Label: 3-octet field where the high-order 20 bits contain the
      MPLS label value, as specified in [RFC9136].  MUST be set to 0
      (reserved).  Since unreachability routes are information-only and
      do not establish forwarding state, and do not use overlay index
      resolution, the label field has no semantic meaning and MUST be
      zero.

   *  Reporter TLVs: One or more Reporter TLVs as defined in Section 3.5

3.4.  Field Usage for Information-Only Routes

   Since unreachability routes are information-only and do not use
   overlay indexes for recursive resolution, the following constraints
   apply to fields inherited from Route Type 5:

   *  ESI: MUST be 0 (all bytes zero).

   *  GW IP Address Length: MUST be 0; GW IP Address: zero octets.



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   *  MPLS Label: MUST be 0.

   *  Address Family: Used only to determine IP Prefix width for NLRI
      parsing.

   Receiving PEs MUST NOT use any of these fields for forwarding
   decisions or recursive resolution.  ESI, GW IP Address, and MPLS
   Label are maintained for structural consistency with [RFC9136];
   Address Family is an extension defined in this document.

   The [RFC9136] Section 3.1 rule that a route with a zero MPLS Label
   and no Overlay Index MUST be treated as withdrawn, and the
   Section 3.2 rule that a route with ESI, GW IP, Router's MAC, and MPLS
   Label all zero SHOULD be treated as withdrawn, apply only to Route
   Type 5.  The IP Prefix Unreachability Route Type defined here uses a
   distinct EVPN Route Type (Section 3.3) and is not subject to those
   rules.

   Unreachability Routes carry ESI=0 and encode no Ethernet-Segment
   membership.  They signal IP-prefix unreachability from the Reporting
   PE's local perspective.  DF election, Ethernet-Segment failure, and
   non-DF transitions do not in themselves trigger Unreachability
   Routes; the multi-homing procedures of [RFC7432] and [RFC9136] are
   unchanged.

3.5.  Reporter TLV Format

   The Reporter TLV encapsulates information about a single Reporting PE
   router.  Multiple Reporter TLVs may be included in a single NLRI to
   support aggregation of reports from different network vantage points.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |            Length             |               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |
   |                   Reporter Identifier (4 octets)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Reporter AS Number (4 octets)                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Sub-TLVs (variable)                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Reporter TLV Fields:

   Type:  1 octet.  Value: 1 (Reporter)

   Length:  2 octets.  Total length of Reporter Identifier, Reporter AS



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      Number, and Sub-TLVs fields in octets (minimum 8 octets when no
      Sub-TLVs are present)

   Reporter Identifier:  4 octets.  BGP Identifier (Router ID) of the
      Reporting PE in network byte order

   Reporter AS Number:  4 octets. 4-octet AS number of the Reporting PE
      in network byte order.  If the AS number is less than 65536, the
      upper 2 octets are set to 0.

   Sub-TLVs:  Variable length.  Contains zero or more Sub-TLVs providing
      additional context about the unreachability event.  A Reporter TLV
      carrying no Sub-TLVs is valid: the presence of the Reporter TLV
      itself conveys the fact of unreachability, with the Reporter
      Identifier and Reporter AS Number identifying the PE that observed
      it.  When the Unreachability Reason Code Sub-TLV (Section 3.6.1)
      is absent, the reason is treated as Unspecified (code 0).

   The combination of Reporter Identifier and Reporter AS Number
   uniquely identifies the Reporting PE.  Multiple Reporter TLVs with
   the same Reporter Identifier and AS Number MUST NOT appear in the
   same NLRI.  If such duplication occurs, only the first occurrence
   SHOULD be processed.

   Except that the first Reporter TLV in an NLRI corresponds to the best
   path (see Section 4.4), the order of subsequent Reporter TLVs is not
   significant; receivers MUST NOT derive meaning from their relative
   ordering.  Implementations MUST tolerate any ordering of Reporter
   TLVs past the first position.

3.6.  Sub-TLV Types

3.6.1.  Unreachability Reason Code Sub-TLV

   *  Sub-Type: 1

   *  Sub-Length: 2 octets

   *  Sub-Value: 2-octet reason code in network byte order

   Defined Reason Codes:

   *  0: Unspecified

   *  1: Policy Blocked

   *  2: Security Filtered




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   *  3: RPKI Invalid

   *  4: No Export Policy

   *  5: Martian Address

   *  6: Bogon Prefix

   *  7: Maintenance

   *  8: Local Administrative Action

   *  9: Local Link Down

   *  10: MAC Mobility Limit Exceeded (EVPN-specific)

   *  11: Tenant Isolation Violation (EVPN-specific)

   *  12: VTEP Unreachable (EVPN-specific)

   *  13-64535: Reserved for Future Use (IANA allocation required)

   *  64536-65535: Reserved for Private/Experimental Use

   Reason codes 0-9 align with the BGP Unreachability Information SAFI
   [I-D.tantsura-idr-unreachability-safi] for consistency across
   standard BGP and EVPN unreachability signaling.  Reason codes 10-12
   are EVPN-specific extensions.

3.6.2.  Timestamp Sub-TLV

   *  Sub-Type: 2

   *  Sub-Length: 8 octets

   *  Sub-Value: Unix timestamp (seconds since epoch) in network byte
      order, indicates when the unreachability event occurred or was
      detected by this reporter

3.6.3.  EVI Sub-TLV

   *  Sub-Type: 3

   *  Sub-Length: 4 octets

   *  Sub-Value: EVPN Instance (EVI) identifier where the unreachability
      was observed




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   Since the Route Distinguisher in the NLRI already identifies the EVPN
   instance in most deployments, this Sub-TLV SHOULD only be included
   when additional EVI-specific information is necessary that cannot be
   derived from the RD.

   Examples of when EVI Sub-TLV may be useful:

   *  Multiple EVIs share the same RD (non-recommended configuration)

   *  Correlation with locally-significant EVI identifiers

   *  Debugging scenarios requiring explicit EVI identification

   Omitting this Sub-TLV when not needed saves 7 octets (3 octets TLV
   overhead + 4 octets EVI value) per Reporter TLV.

3.6.4.  Sub-TLV Processing Rules

   Implementations MUST be prepared to receive Sub-TLVs in any order.
   Unknown Sub-TLV types MUST be silently ignored to allow for future
   extensibility.

   The Reason Code Sub-TLV SHOULD be included in all Reporter TLVs.  If
   absent, implementations SHOULD treat it as Reason Code 0
   (Unspecified).

4.  Operation

4.1.  Forwarding Plane Separation

   This route type creates a parallel information plane that operates
   independently of the EVPN forwarding plane.  Implementations MUST
   maintain strict separation between unreachability information and
   forwarding decisions.

   Specifically, implementations MUST:

   *  NOT install or remove any routes in the Loc-RIB or forwarding
      table based on unreachability information

   *  Maintain unreachability routes in a separate Unreachability
      Information RIB (UI-RIB) that is not consulted for forwarding
      decisions

   *  NOT modify forwarding table entries (including next-hop, label, or
      other attributes) based on unreachability information





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   *  Process unreachability routes with lower priority than forwarding
      routes to prevent resource contention

   *  Implement separate rate limiting for unreachability routes

   Violation of these separation requirements could lead to incorrect
   forwarding behavior, traffic blackholing, or routing instability.
   Implementers MUST ensure proper separation through careful software
   architecture and testing.

4.2.  Generating Unreachability Routes

   A PE MAY generate an IP Prefix Unreachability Route when local
   processing determines, for any reason, that a prefix is to be
   reported as unreachable.  The triggering condition is conveyed by the
   Reason Code Sub-TLV (Section 3.6.1).  This document does not mandate
   the set of local conditions that cause generation; that set is
   implementation- and deployment-specific, constrained only by the
   Reason Codes defined in this document or subsequently registered.

   The Reporting PE MUST set Address Family to 1 (IPv4) or 2 (IPv6)
   consistent with the IP Prefix field.  The Reporting PE MUST populate
   the Reporter TLV with its own BGP Identifier and AS Number.  The PE
   SHOULD include a Reason Code Sub-TLV and SHOULD include a Timestamp
   Sub-TLV to facilitate temporal correlation.

   Implementations SHOULD provide configuration options to control:

   *  Which events trigger unreachability route generation

   *  Rate limiting on route generation per prefix and globally

   *  Filtering criteria for which prefixes can be reported

   *  Default Reason Codes for different trigger conditions

4.3.  Processing Unreachability Routes

   When a PE router receives an IP Prefix Unreachability Route:

   1.  It MUST validate that the route type is recognized

   2.  It MUST parse the NLRI using the Address Family field to
       determine whether the IP Prefix is 4 or 16 octets, then parse
       Reporter TLVs according to Section 3.  Error handling for invalid
       Address Family or IP Prefix Length values is specified in
       Section 4.10.1.




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   3.  It MUST NOT install or remove any routes in the Loc-RIB or
       forwarding table based on this route

   4.  It MUST maintain a separate UI-RIB for unreachability routes

   5.  It SHOULD apply standard BGP path selection to UI-RIB entries for
       consistency

   6.  It MAY propagate the route according to standard EVPN rules and
       local policy

   7.  It MAY aggregate Reporter TLVs as described in Section 4.4

   8.  It SHOULD make unreachability information available to management
       systems and monitoring tools

   Unknown Sub-TLV types within Reporter TLVs MUST be silently ignored
   to allow for future extensibility.

4.4.  Aggregation Procedures

   When multiple routes arrive for the same prefix (identified by RD,
   Ethernet Tag ID, Address Family, IP Prefix Length, and IP Prefix), a
   PE supporting aggregation SHOULD combine Reporter TLVs from multiple
   paths into a single advertisement.

   Aggregation procedure:

   1.  Perform standard BGP path selection based on BGP attributes (NOT
       Reporter TLV content) to select the best path

   2.  Extract Reporter TLVs from the best path

   3.  For each non-selected feasible path, extract Reporter TLVs and
       add unique reporters (by Reporter Identifier and Reporter AS) to
       the aggregated set.  If a reporter already exists, keep the entry
       with the most recent timestamp (if present).

   4.  Create a new NLRI with all unique Reporter TLVs

   5.  Advertise the aggregated NLRI using BGP attributes from the best
       path









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   A speaker performing Reporter TLV aggregation MUST place the Reporter
   TLV corresponding to the best path in the first position of the
   resulting NLRI.  Reporter TLVs drawn from non-selected feasible paths
   MAY follow in any order.  Pinning the first position provides a
   deterministic fallback for speakers that do not perform aggregation
   (see below).

   A receiver MUST parse all Reporter TLVs present in a received NLRI,
   up to the implementation limit defined in this section (RECOMMENDED
   50).  How the received Reporter TLVs are consumed locally -- stored
   in the UI-RIB, exported via BMP, displayed to operators -- is an
   implementation matter and does not affect wire behavior.

   A speaker that does not perform Reporter TLV aggregation, when re-
   advertising an IP Prefix Unreachability Route to its peers, MUST
   include only the first Reporter TLV from the received NLRI and MUST
   NOT append Reporter TLVs drawn from other paths.  Because EVPN does
   not negotiate per-Route-Type capabilities, this rule -- together with
   the sender ordering rule above -- constitutes the interoperability
   contract between aggregating and non-aggregating speakers: at the
   first non-aggregating hop, the propagated view degrades to the best-
   path Reporter TLV only, with no loss of correctness.

   The maximum number of Reporter TLVs per route SHOULD be limited to
   prevent excessive route sizes.  RECOMMENDED maximum: 50 Reporter TLVs
   per route.

   If the maximum is reached and a new reporter must be added,
   implementations SHOULD remove the oldest Reporter TLV based on
   Timestamp Sub-TLV (if present).  The reporter from the best path MUST
   NOT be removed; if it is the oldest, remove the second-oldest
   instead.

4.5.  Withdrawal Procedures

   Withdrawal of unreachability information operates at two levels:

4.5.1.  Individual Reporter Withdrawal

   When a PE determines that a specific reporter no longer considers a
   prefix unreachable (e.g., receives an UPDATE from that reporter's PE
   that does not include the unreachability NLRI, or local policy
   determines the report is stale), it SHOULD:

   1.  Remove the corresponding Reporter TLV from the NLRI

   2.  If other Reporter TLVs remain, re-advertise the NLRI with the
       remaining Reporter TLVs



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   3.  If no Reporter TLVs remain, withdraw the entire NLRI as described
       below

   To facilitate individual reporter withdrawal, implementations MUST
   track the source of each Reporter TLV (which BGP neighbor or local
   process it came from).

4.5.2.  Complete NLRI Withdrawal

   A PE MUST withdraw an Unreachability Route (send the NLRI key fields
   in MP_UNREACH_NLRI) when:

   *  All Reporter TLVs have been removed

   *  The prefix is explicitly withdrawn by all upstream sources

   *  Local policy dictates the information should no longer be
      propagated

   The MP_UNREACH_NLRI contains the NLRI fields (Route Distinguisher,
   Ethernet Segment Identifier, Ethernet Tag ID, Address Family, IP
   Prefix Length, IP Prefix, GW IP Address Length, and MPLS Label)
   without any Reporter TLVs.

4.5.3.  Stale Reporter Detection

   Implementations MAY implement aging mechanisms to remove stale
   Reporter TLVs:

   *  If a Timestamp Sub-TLV is present and indicates the report is
      older than a configurable threshold (RECOMMENDED default: 24
      hours), the Reporter TLV MAY be removed

   *  If the BGP session to the neighbor that provided a Reporter TLV
      goes down, implementations MAY mark associated Reporter TLVs as
      potentially stale and MAY remove them after a grace period

4.6.  Interaction with Graceful Restart

   BGP Graceful Restart [RFC4724] applies to the EVPN SAFI (AFI=25,
   SAFI=70) and thus to Unreachability Routes.  GR procedures for other
   EVPN route types ([RFC7432], [RFC9136]) are unchanged.

   Unreachability Routes follow the same GR procedures as RT-5
   [RFC9136]: one GR Capability for SAFI=70, one End-of-RIB (EoR)
   marker, one Restart Time.  They are marked stale, retained,
   refreshed, and removed identically.  The sole departure is the
   "Forwarding State" (F) bit.  Unreachability Routes install no



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   forwarding state (Section 4.1); the F bit has no meaning for this
   Route Type.  Its interpretation for forwarding-state-bearing route
   types is unchanged.

4.6.1.  Graceful Restart Capability

   No new capability is defined.  GR is negotiated using the EVPN AFI/
   SAFI (25/70).

   Implementations MUST NOT treat any F bit value as indicating
   forwarding-state preservation for Unreachability Routes.  The F bit
   advertised for SAFI=70 is determined by the preservation properties
   of the other route types carried in the SAFI.

4.6.2.  Restarting Speaker Behavior

   A PE that has negotiated GR for SAFI=70:

   1.  SHOULD re-advertise its preserved Unreachability Information RIB
       (UI-RIB) as soon as practicable; gradual re-advertisement is
       permitted to limit burstiness.

   2.  If the UI-RIB was not preserved, SHOULD rebuild it from local
       sources (link-down state, policy decisions) before re-
       advertising.

   3.  MUST send the SAFI=70 EoR marker [RFC4724] after re-advertisement
       completes.  This marker covers all EVPN route types in the SAFI;
       no Route-Type-specific EoR is defined.

4.6.3.  Receiving Speaker Behavior

   On detection of peer restart:

   1.  All Unreachability Routes from the restarting peer MUST be marked
       stale, irrespective of the F bit.

   2.  Stale routes MUST NOT be withdrawn.  They MUST be retained until
       the SAFI=70 EoR is received or the peer's Restart Time expires,
       whichever occurs first.

   3.  While stale, the routes MAY be used for monitoring and
       correlation, MAY be distinguished in display and APIs, and SHOULD
       NOT be propagated to other peers absent explicit configuration.

   4.  On receipt of the EoR:

       *  unrefreshed stale routes MUST be removed;



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       *  Reporter TLVs from the restarted peer within aggregated NLRIs
          MUST be removed if not refreshed;

       *  if Reporter TLVs from other sources remain for the same NLRI
          key, the route SHOULD be re-advertised with those remaining
          TLVs (Section 4.4).

   5.  If the Restart Time expires before the EoR arrives, all stale
       routes MUST be removed.

4.6.4.  Route Reflector Considerations

   A Route Reflector participating in GR for SAFI=70:

   *  MUST stale-mark Unreachability Routes from restarting clients
      identically to other EVPN route types;

   *  SHOULD NOT reflect stale Unreachability Routes absent an explicit
      reflection policy;

   *  MUST preserve ORIGINATOR_ID and CLUSTER_LIST across stale-to-
      refreshed transitions;

   *  SHOULD send the SAFI=70 EoR to clients after completing its own
      restart processing.

4.6.5.  Implementation Recommendations

   Restart Time is shared with the rest of SAFI=70.  Operators SHOULD
   account for the additional UI-RIB re-advertisement volume when tuning
   it.

   Implementations SHOULD expose:

   *  UI-RIB preservation, toggled independently of other EVPN route
      types;

   *  propagation of stale Unreachability Routes during GR;

   *  action on EoR timeout.

   Implementations SHOULD log, per GR cycle: peer-restart detection
   affecting the UI-RIB, stale marking, EoR receipt, and stale removal.

4.7.  Preventing State Explosion

   To prevent unbounded growth of the UI-RIB, implementations SHOULD
   enforce the following limits:



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   *  Maximum Reporter TLVs per route (RECOMMENDED: 50)

   *  Maximum total UI-RIB routes (SHOULD be configurable; RECOMMENDED
      default: 100,000)

   *  Rate limiting on accepting new unreachability routes

   *  Per-peer rate limiting

   When limits are reached, implementations SHOULD log the event, apply
   aging policies to remove oldest entries, and continue accepting
   withdrawals to allow state to decrease.

4.8.  Relationship to BGP Route Damping

   Unreachability routes SHOULD NOT be subject to standard BGP route
   damping mechanisms since they do not affect forwarding and represent
   information that operators explicitly want to propagate.

   However, implementations MAY implement rate limiting specific to
   unreachability routes to prevent:

   *  UI-RIB resource exhaustion

   *  Excessive BGP UPDATE message generation

   *  Processing overhead on Receiving PEs

   *  Malicious or misconfigured PEs flooding the network

   Rate limiting should be applied at:

   *  Route generation (at Reporting PE)

   *  Route acceptance (at Receiving PE)

   *  Per-peer basis

   *  Global aggregate level

4.9.  Path Selection for Aggregation

   Path selection for Unreachability Routes follows standard BGP best
   path selection ([RFC7432] Section 15, incorporating [RFC9136]) with
   the following clarifications:

   *  Weight/Local Preference: Apply normally based on local policy.




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   *  AS_PATH Length: Shorter AS_PATH is preferred.  This represents the
      path the UPDATE message took.

   *  ORIGIN: IGP preferred over EGP over INCOMPLETE.

   *  MED: Apply if comparing paths from the same neighboring AS.

   *  BGP Identifier: Use for tie-breaking.

   The content of Reporter TLVs (number of reporters, reason codes,
   timestamps, etc.)  MUST NOT influence path selection.  Path selection
   determines which UPDATE's BGP attributes are used for propagation,
   while aggregation combines Reporter TLVs from multiple paths.

4.10.  Communities and Attributes

   Standard BGP communities and attributes apply to the UPDATE message
   carrying Unreachability Routes:

   *  NO_EXPORT, NO_ADVERTISE, and NO_EXPORT_SUBCONFED work as defined
      in their respective specifications

   *  Large Communities [RFC8092] MAY be used for policy control of
      aggregation behavior

   *  AS_PATH is constructed normally for the UPDATE message path

   *  ORIGIN SHOULD be set to INCOMPLETE for locally generated
      unreachability information, reflecting that the information does
      not originate from routing protocol state

   *  The Router's MAC Extended Community has no effect on
      Unreachability Routes; overlay index semantics do not apply
      (Section 3.4).  Senders SHOULD NOT attach it; receivers MUST
      ignore it if present.

   These attributes represent the path taken by the UPDATE message
   itself, not the paths of individual reporters (which are preserved in
   Reporter TLVs).

4.11.  Error Handling

   Error handling for IP Prefix Unreachability Routes follows [RFC7606]
   and [I-D.ietf-bess-rfc7432bis] Section 7.14.1.  Per-class actions are
   specified in Sections 4.10.1 through 4.10.4.  Per
   [I-D.ietf-bess-rfc7432bis] Section 7.14, "session reset" MAY be
   replaced with "AFI/SAFI disable" behavior where supported.  Checks in
   Section 4.10.1 are performed before those in Section 4.10.2; on first



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   error the corresponding action MUST be taken and further NLRI parsing
   MUST cease.  All error conditions MUST be logged.

4.11.1.  NLRI Structural Errors

   A receiver MUST apply "session reset" per [I-D.ietf-bess-rfc7432bis]
   Section 7.14.1 on:

   *  Length below the minimum for this route type.

   *  Length inconsistent with the enclosing MP_REACH_NLRI or
      MP_UNREACH_NLRI attribute.

   *  Address Family other than 1 or 2: the IP Prefix field boundary
      cannot be determined, and subsequent Key fields cannot be parsed.

   *  IP Prefix Length outside the range permitted for the indicated
      Address Family: the prefix cannot be unambiguously constructed and
      is not suitable as a lookup key.

4.11.2.  Non-Key Field Errors

   A receiver MUST apply "treat-as-withdraw" per
   [I-D.ietf-bess-rfc7432bis] Section 7.14.1 on:

   *  Non-zero Ethernet Segment Identifier, GW IP Address Length, GW IP
      Address, or MPLS Label (Section 3.4 requires each to be zero).

   *  No Reporter TLVs present (Section 3.3 requires one or more).

4.11.3.  Reporter TLV Errors

   Per [RFC9552] Section 5.1, unknown or malformed Reporter TLVs MUST
   NOT cause the NLRI to be considered malformed.

   *  Unrecognized TLV Type: the TLV is ignored; parsing resumes at the
      next TLV boundary.

   *  Malformed TLV (Length inconsistent with remaining NLRI data or
      below the 8-octet minimum): the TLV MUST be discarded.  If well-
      formed Reporter TLVs remain, they are processed; otherwise "treat-
      as-withdraw" MUST be applied.

   *  Duplicate Reporter TLVs (same Identifier and AS Number): only the
      first is processed (Section 3.5).

   *  Reporter TLV count exceeding the implementation limit
      (Section 4.6): excess TLVs MUST be discarded.



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4.11.4.  Sub-TLV Errors

   An unrecognized Sub-TLV Type within a Reporter TLV is silently
   ignored (Section 3.6.4).  A Sub-TLV whose Length is inconsistent with
   available data MUST be discarded; processing of the enclosing
   Reporter TLV and remaining Sub-TLVs continues.

5.  Interoperability Considerations

5.1.  Incremental Deployment

   The IP Prefix Unreachability Route Type can be deployed incrementally
   without requiring network-wide upgrades:

   *  PEs that don't support this route type will ignore it per standard
      BGP behavior (unknown route type handling)

   *  Mixed environments with supporting and non-supporting PEs work
      correctly

   *  The feature can be enabled on specific EVPN instances for testing
      before broader deployment

   *  Aggregation support is OPTIONAL; PEs that do not implement
      aggregation can still propagate single-reporter routes

   *  Distinct Route Targets allow control over which PEs receive
      unreachability information

5.2.  Interaction with Route Reflectors

   Route Reflectors process Unreachability Routes like any other EVPN
   route type:

   *  Apply standard route reflection rules

   *  ORIGINATOR_ID and CLUSTER_LIST attributes apply normally to the
      UPDATE message, not to individual reporters

   *  Route Reflectors SHOULD support aggregation to combine reports
      from multiple clients

   *  When reflecting to clients, include all aggregated Reporter TLVs

   The distinction between the ORIGINATOR_ID BGP attribute and the
   Reporter Identifier field in Reporter TLVs is important:





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   *  ORIGINATOR_ID identifies the originator of the BGP UPDATE message
      for loop prevention

   *  Reporter Identifier identifies the PE that observed and reported
      the unreachability condition

   *  These MAY be different in aggregated scenarios

   Route Reflectors that do not support aggregation will still properly
   reflect unreachability routes using standard route reflection
   procedures.  In this case, only the best path's Reporter TLV(s) will
   be visible to clients.

   Operators deploying this feature SHOULD enable aggregation on Route
   Reflectors to maximize the utility of multi-vantage-point reporting.

5.3.  Interaction with Other EVPN Route Types

   IP Prefix Unreachability Routes are completely independent from other
   EVPN route types.  Specifically:

   *  A Route Type 5 (IP Prefix Advertisement) and an IP Prefix
      Unreachability Route for the same logical prefix (same Route
      Distinguisher, Ethernet Tag ID, IP Prefix Length, and IP Prefix
      value, with the unreachability Address Family value matching the
      IPv4 or IPv6 encoding of that RT-5 per [RFC9136]) are independent
      and may coexist

   *  Presence of an unreachability route does NOT imply absence of a
      reachability route

   *  Withdrawal of a reachability route does NOT automatically generate
      an unreachability route

   *  BGP path selection is performed independently for each route type

   This independence is crucial for maintaining forwarding plane
   separation and allowing unreachability signaling for prefixes that
   were never advertised as reachable.

6.  Deployment Considerations

6.1.  Use Cases

   Multi-Tenant Data Centers:  Share unreachability information across
      tenant networks for coordinated security response without
      affecting tenant traffic forwarding




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   DCI (Data Center Interconnect):  Correlate unreachability reports
      from multiple data centers to distinguish between local issues and
      global prefix problems

   Security Monitoring:  Track suspicious prefix patterns across EVPN
      instances, coordinate DDoS response, and share threat intelligence

   Troubleshooting:  Debug prefix reachability issues without impacting
      production forwarding, identify asymmetric reachability, and
      correlate with overlay network health

   Compliance and Auditing:  Maintain records of unreachability events
      for compliance purposes and SLA verification

   Policy-Driven Actions:  Trigger an action, as defined by a local
      policy, in response to received unreachability information (e.g.,
      traffic engineering adjustments, alerting, or logging)

6.2.  Operational Recommendations

   *  Enable aggregation on Route Reflectors to maximize visibility
      while minimizing route count

   *  Include Timestamp Sub-TLVs for temporal correlation

   *  Monitor UI-RIB size for capacity planning

   *  Test the feature on non-production EVPN instances before
      production deployment

   Implementations SHOULD provide management interfaces to query the UI-
   RIB, display reporters per prefix, and export unreachability data to
   external monitoring systems.

7.  Security Considerations

   This route type SHOULD only be enabled between trusted BGP peers.
   The trust model is similar to that required for standard EVPN route
   types.

   The following threats are specific to unreachability signaling:

   1.  Information Leakage: Unreachability information may reveal
       network topology or operational issues.  Operators SHOULD use
       Route Target filtering to restrict distribution.






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   2.  State Exhaustion: Malicious peers could exhaust UI-RIB memory.
       Implementations SHOULD enforce the limits described in
       Section 4.4 and the Preventing State Explosion section.

   3.  False Information: Peers could advertise false unreachability
       data.  Since this SAFI does not affect forwarding, the impact is
       limited to monitoring systems.

   4.  Reporter Impersonation: A peer could include Reporter TLVs
       claiming to represent other PEs.  Implementations SHOULD validate
       that Reporter AS Numbers are consistent with the AS_PATH of the
       UPDATE that introduced them.

   5.  Aggregation Amplification: A peer could send many UPDATEs with
       different Reporter TLVs for the same prefix.  Reporter TLV limits
       and rate limiting mitigate this.

   6.  Tenant Isolation: Improper RT configuration could leak
       unreachability information between tenants.  Use separate RDs and
       tenant-specific RTs.

   Operators SHOULD use BGP session security (TCP-AO per [RFC5925]),
   validate Reporter Identifiers against known PE lists, configure per-
   peer rate limits, and maintain audit logs of unreachability route
   updates.

8.  IANA Considerations

8.1.  EVPN Route Type

   IANA is requested to assign a new EVPN Route Type value from the
   "EVPN Route Types" registry within the "Border Gateway Protocol (BGP)
   Parameters" registry group:

   *  Value: TBD1

   *  Description: IP Prefix Unreachability Route Type

   *  Reference: This document

8.2.  EVPN Unreachability Reporter TLV Types

   IANA is requested to create a new registry called "EVPN
   Unreachability Reporter TLV Types" under the "Border Gateway Protocol
   (BGP) Parameters" registry page.

   Registration Procedure: Standards Action




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   Initial registrations:

   Value   Description                          Reference
   -----   ------------------------------------  -----------
   0       Reserved                             This document
   1       Reporter TLV                         This document
   2-254   Unassigned
   255     Reserved                             This document

8.3.  EVPN Unreachability Sub-TLV Types

   IANA is requested to create a new registry called "EVPN
   Unreachability Sub-TLV Types" under the "Border Gateway Protocol
   (BGP) Parameters" registry page.

   Registration Procedure: RFC Required

   Initial registrations:

   Value   Description                          Reference
   -----   ------------------------------------  -----------
   0       Reserved                             This document
   1       Unreachability Reason Code           This document
   2       Timestamp                            This document
   3       EVI                                  This document
   4-254   Unassigned
   255     Reserved                             This document

8.4.  EVPN Unreachability Reason Codes

   IANA is requested to create a new registry called "EVPN
   Unreachability Reason Codes" under the "Border Gateway Protocol (BGP)
   Parameters" registry page.

   Registration Procedure: RFC Required for values 0-64535, Reserved for
   Private Use for values 64536-65535

   Initial registrations:













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   Value   Description                          Reference
   -----   ------------------------------------  -----------
   0       Unspecified                          This document
   1       Policy Blocked                       This document
   2       Security Filtered                    This document
   3       RPKI Invalid                         This document
   4       No Export Policy                     This document
   5       Martian Address                      This document
   6       Bogon Prefix                         This document
   7       Maintenance                         This document
   8       Local Administrative Action          This document
   9       Local Link Down                      This document
   10      MAC Mobility Limit Exceeded          This document
   11      Tenant Isolation Violation           This document
   12      VTEP Unreachable                     This document
   13-64535    Unassigned
   64536-65535 Reserved for Private Use         This document

9.  Acknowledgements

   The authors would like to thank the BESS working group for their
   valuable feedback and suggestions on this proposal.  Special thanks
   to the EVPN protocol designers whose work on RFC 7432, RFC 9136, and
   related specifications provided the foundation for this extension.

   The aggregation mechanism in this specification draws inspiration
   from similar multi-reporter approaches in other monitoring and
   troubleshooting protocols.

10.  References

10.1.  Normative References

   [I-D.ietf-bess-rfc7432bis]
              Sajassi, A., Ed., Burdet, L., Ed., Drake, J., and J.
              Rabadan, "BGP MPLS-Based Ethernet VPN", Work in Progress,
              Internet-Draft, draft-ietf-bess-rfc7432bis-14, March 2026,
              <https://datatracker.ietf.org/doc/draft-ietf-bess-
              rfc7432bis/>.

   [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>.







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

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

   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
              2015, <https://www.rfc-editor.org/info/rfc7432>.

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

   [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>.

   [RFC9136]  Rabadan, J., Ed., Henderickx, W., Drake, J., Lin, W., and
              A. Sajassi, "IP Prefix Advertisement in Ethernet VPN
              (EVPN)", RFC 9136, DOI 10.17487/RFC9136, October 2021,
              <https://www.rfc-editor.org/info/rfc9136>.

   [RFC9552]  Talaulikar, K., Ed., "Distribution of Link-State and
              Traffic Engineering Information Using BGP", RFC 9552,
              DOI 10.17487/RFC9552, January 2024,
              <https://www.rfc-editor.org/info/rfc9552>.

10.2.  Informative References

   [I-D.tantsura-idr-unreachability-safi]
              Tantsura, J., Sharp, D., Venkatraman, V., Muppalla, K.,
              and M. Rzehak, "BGP Unreachability Information SAFI", Work
              in Progress, Internet-Draft, draft-tantsura-idr-
              unreachability-safi-03, April 2026,
              <https://datatracker.ietf.org/doc/html/draft-tantsura-idr-
              unreachability-safi-03>.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.




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   [RFC7365]  Lasserre, M., Balus, F., Morin, T., Bitar, N., and Y.
              Rekhter, "Framework for Data Center (DC) Network
              Virtualization", RFC 7365, DOI 10.17487/RFC7365, October
              2014, <https://www.rfc-editor.org/info/rfc7365>.

   [RFC7911]  Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", RFC 7911,
              DOI 10.17487/RFC7911, July 2016,
              <https://www.rfc-editor.org/info/rfc7911>.

   [RFC8092]  Heitz, J., Ed., Snijders, J., Ed., Patel, K., Bagdonas,
              I., and N. Hilliard, "BGP Large Communities Attribute",
              RFC 8092, DOI 10.17487/RFC8092, February 2017,
              <https://www.rfc-editor.org/info/rfc8092>.

   [RFC8365]  Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Isaac, A.,
              Henderickx, W., and R. Shekhar, "A Network Virtualization
              Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
              DOI 10.17487/RFC8365, March 2018,
              <https://www.rfc-editor.org/info/rfc8365>.

Appendix A: Encoding Examples

Example 1: Minimal Unreachability Route

   IPv4 tenant prefix 192.0.2.0/24 reported unreachable by a single leaf
   PE because egress export policy suppresses the prefix (Reason Code 4,
   "No Export Policy"):























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   Route Type: TBD1
   Length: 48 octets (route-type-specific)
   Route Distinguisher: 198.51.100.1:100 (RD Type 1, 8 octets)
   Ethernet Segment Identifier: 0 (10 octets)
   Ethernet Tag ID: 0 (4 octets)
   Address Family: 1 (IPv4)
   IP Prefix Length: 24 (1 octet)
   IP Prefix: 192.0.2.0 (4 octets)
   GW IP Address Length: 0 (1 octet)
   MPLS Label: 0 (3 octets)

   Reporter TLV (on-wire: 16 octets = 1 Type + 2 Length + 13 payload):
     Type: 1
     Length: 13 (payload octets)
     Reporter Identifier: 198.51.100.1 (4 octets)
     Reporter AS: 65001 (4 octets)
     Sub-TLV Reason Code:
       Sub-Type: 1
       Sub-Length: 2
       Value: 4 (No Export Policy)

   Route-type-specific = 8 + 10 + 4 + 1 + 1 + 4 + 1 + 3 + 16 = 48 octets
   NLRI (with Route Type + Length) = 2 + 48 = 50 octets

   Hexadecimal encoding (TT = TBD1 Route Type):
   TT 30 00 01 C6 33 64 01 00 64 00 00 00 00 00 00
   00 00 00 00 00 00 00 00 01 18 C0 00 02 00 00 00
   00 00 01 00 0D C6 33 64 01 00 00 FD E9 01 00 02
   00 04

   See Example 3 for the equivalent IPv6 encoding.

Example 2: Aggregated Route with Multiple Reporters

   IPv4 tenant prefix 198.51.100.0/24 reported by three leaf PEs in the
   same DC fabric following a coordinated administrative action (Reason
   Code 8, "Local Administrative Action").  Timestamps are spaced by a
   few seconds, consistent with propagation of the administrative event
   across the fabric:

   Route Type: TBD1
   Length: 113 octets (route-type-specific)
   Route Distinguisher: 198.51.100.1:100
   Ethernet Segment Identifier: 0
   Ethernet Tag ID: 0
   Address Family: 1 (IPv4)
   IP Prefix Length: 24
   IP Prefix: 198.51.100.0



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   GW IP Address Length: 0
   MPLS Label: 0

   Reporter TLV #1 (on-wire: 27 octets):
     Type: 1, Length: 24 (payload)
     Reporter Identifier: 198.51.100.1
     Reporter AS: 65001
     Sub-TLVs:
       Reason Code (Type 1, Length 2): 8 (Local Administrative Action)
       Timestamp (Type 2, Length 8): 1704672000

   Reporter TLV #2 (on-wire: 27 octets):
     Type: 1, Length: 24
     Reporter Identifier: 198.51.100.2
     Reporter AS: 65001
     Sub-TLVs:
       Reason Code (Type 1, Length 2): 8
       Timestamp (Type 2, Length 8): 1704672005

   Reporter TLV #3 (on-wire: 27 octets):
     Type: 1, Length: 24
     Reporter Identifier: 198.51.100.3
     Reporter AS: 65001
     Sub-TLVs:
       Reason Code (Type 1, Length 2): 8
       Timestamp (Type 2, Length 8): 1704672008

   Fields through MPLS Label: 32 octets
   Reporter TLVs on wire: 3 x 27 = 81 octets
   Route-type-specific total: 32 + 81 = 113 octets
   NLRI (with Route Type + Length) = 2 + 113 = 115 octets

   Hexadecimal encoding (TT = TBD1 Route Type):
   TT 71 00 01 C6 33 64 01 00 64 00 00 00 00 00 00
   00 00 00 00 00 00 00 00 01 18 C6 33 64 00 00 00
   00 00 01 00 18 C6 33 64 01 00 00 FD E9 01 00 02
   00 08 02 00 08 00 00 00 00 65 9B 3B 00 01 00 18
   C6 33 64 02 00 00 FD E9 01 00 02 00 08 02 00 08
   00 00 00 00 65 9B 3B 05 01 00 18 C6 33 64 03 00
   00 FD E9 01 00 02 00 08 02 00 08 00 00 00 00 65
   9B 3B 08

Example 3: IPv6 Unreachability Route

   IPv6 tenant prefix 2001:db8::/32 reported unreachable by a leaf PE
   following a local CE-facing link-down event (Reason Code 9, "Local
   Link Down"):




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  Route Type: TBD1
  Length: 60 octets (route-type-specific)
  Route Distinguisher: 198.51.100.1:100 (RD Type 1, 8 octets)
  Ethernet Segment Identifier: 0 (10 octets)
  Ethernet Tag ID: 0 (4 octets)
  Address Family: 2 (IPv6)
  IP Prefix Length: 32 (1 octet)
  IP Prefix: 2001:db8:: (16 octets)
  GW IP Address Length: 0 (1 octet)
  MPLS Label: 0 (3 octets)

  Reporter TLV (on-wire: 16 octets = 1 Type + 2 Length + 13 payload):
    Type: 1
    Length: 13 (payload octets)
    Reporter Identifier: 198.51.100.1 (4 octets)
    Reporter AS: 65001 (4 octets)
    Sub-TLV Reason Code:
      Sub-Type: 1
      Sub-Length: 2
      Value: 9 (Local Link Down)

  Route-type-specific = 8 + 10 + 4 + 1 + 1 + 16 + 1 + 3 + 16 = 60 octets
  NLRI (with Route Type + Length) = 2 + 60 = 62 octets

  Hexadecimal encoding (TT = TBD1 Route Type):
  TT 3C 00 01 C6 33 64 01 00 64 00 00 00 00 00 00
  00 00 00 00 00 00 00 00 02 20 20 01 0D B8 00 00
  00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 00
  0D C6 33 64 01 00 00 FD E9 01 00 02 00 09

Example 4: Complete BGP UPDATE Message

   A PE (198.51.100.1, AS 65001) advertises that 192.0.2.0/24 is
   unreachable, with Reason RPKI Invalid and a detection timestamp:

















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   BGP UPDATE Message:
     Withdrawn Routes Length: 0
     Total Path Attribute Length: (calculated)

     Path Attributes:
       ORIGIN (Type 1):
         Value: INCOMPLETE (2)

       AS_PATH (Type 2):
         Segment Type: AS_SEQUENCE
         Segment Length: 1
         AS: 65001

       MP_REACH_NLRI (Type 14, Flags 0x90):
         AFI: 25 (L2VPN)
         SAFI: 70 (EVPN)
         Next Hop Length: 4
         Next Hop: 198.51.100.1
         Reserved: 0
         NLRI:
           Route Type: TBD1 (IP Prefix Unreachability)
           Length: 59
           Route Distinguisher: 198.51.100.1:100
           Ethernet Segment Identifier: 0
           Ethernet Tag ID: 0
           Address Family: 1 (IPv4)
           IP Prefix Length: 24
           IP Prefix: 192.0.2.0
           GW IP Address Length: 0
           MPLS Label: 0
           Reporter TLV:
             Type: 1
             Length: 24
             Reporter Identifier: 198.51.100.1
             Reporter AS: 65001
             Sub-TLV (Reason):
               Sub-Type: 1
               Sub-Length: 2
               Value: 3 (RPKI Invalid)
             Sub-TLV (Timestamp):
               Sub-Type: 2
               Sub-Length: 8
               Value: 1733789400

       EXTENDED_COMMUNITIES (Type 16):
         Route Target: 65001:100





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Example 5: Aggregation at a Receiving PE

   Router R1 receives two UPDATEs for the same Unreachability NLRI key
   (RD 198.51.100.1:100, Ethernet Tag 0, IPv4, 192.0.2.0/24) from
   different upstream neighbors.  R1 selects a best path by standard BGP
   procedure, extracts Reporter TLVs from the best path plus feasible
   paths, de-duplicates by (Reporter Identifier, Reporter AS), and re-
   advertises a single aggregated NLRI.











































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   UPDATE 1 (from Neighbor N1, AS 65100):
     AFI: 25, SAFI: 70
     AS_PATH: 65100
     NLRI (192.0.2.0/24 Unreachability):
       Reporter TLV:
         Reporter ID: 198.51.100.1, AS: 65001
         Reason: RPKI Invalid (3)
         Timestamp: 1733789400

   UPDATE 2 (from Neighbor N2, AS 65200):
     AFI: 25, SAFI: 70
     AS_PATH: 65200
     NLRI (192.0.2.0/24 Unreachability):
       Reporter TLV:
         Reporter ID: 198.51.100.2, AS: 65002
         Reason: Policy Blocked (1)
         Timestamp: 1733789410

   R1 Path Selection:
     - Compare AS_PATH length: both length 1
     - Compare by BGP Identifier: UPDATE 1 wins

   R1 Aggregation:
     - Extract Reporter TLV from UPDATE 1 (best path)
     - Extract Reporter TLV from UPDATE 2 (feasible path)
     - No duplicate (distinct Reporter ID + AS)
     - Build NLRI with both Reporter TLVs

   R1 Advertisement to downstream:
     AFI: 25, SAFI: 70
     AS_PATH: 65100 (from best path)
     NLRI (192.0.2.0/24 Unreachability):
       Reporter TLV #1:
         Reporter ID: 198.51.100.1, AS: 65001
         Reason: 3 (RPKI Invalid)
         Timestamp: 1733789400
       Reporter TLV #2:
         Reporter ID: 198.51.100.2, AS: 65002
         Reason: 1 (Policy Blocked)
         Timestamp: 1733789410

Example 6: Withdrawal Procedures

   Continuing from Example 5, Reporter 198.51.100.1 clears its report
   first (partial withdrawal), then Reporter 198.51.100.2 also clears
   (complete withdrawal).





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   Initial State on R1:
     UI-RIB Entry for NLRI key
     (RD 198.51.100.1:100, ETag 0, IPv4, 192.0.2.0/24):
       Reporter TLV #1: 198.51.100.1 / AS 65001 (from N1)
       Reporter TLV #2: 198.51.100.2 / AS 65002 (from N2)

   Event: N1 sends MP_UNREACH_NLRI for the NLRI key.

   R1 Processing:
     1. Identify withdrawal source: N1
     2. Remove Reporter TLVs sourced from N1
        (Reporter 198.51.100.1 / AS 65001)
     3. Reporter TLV #2 remains
     4. Re-advertise with the remaining Reporter TLV

   R1 Advertisement to downstream:
     MP_REACH_NLRI (AFI 25, SAFI 70):
       NLRI (192.0.2.0/24 Unreachability):
         Reporter TLV:
           Reporter ID: 198.51.100.2, AS: 65002
           Reason: 1 (Policy Blocked)
           Timestamp: 1733789410

   Later Event: N2 also sends MP_UNREACH_NLRI for the NLRI key.

   R1 Processing:
     1. Remove Reporter TLVs sourced from N2
     2. No Reporter TLVs remain
     3. Withdraw the entire NLRI

   R1 Advertisement to downstream:
     MP_UNREACH_NLRI (AFI 25, SAFI 70):
       Withdrawn NLRI:
         Route Type: TBD1
         Length: 32
         Route Distinguisher: 198.51.100.1:100
         Ethernet Segment Identifier: 0
         Ethernet Tag ID: 0
         Address Family: 1 (IPv4)
         IP Prefix Length: 24
         IP Prefix: 192.0.2.0
         GW IP Address Length: 0
         MPLS Label: 0

Appendix B: Design Tradeoffs

   This appendix summarizes encoding choices and their rationale.




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   Explicit Address Family vs inferring IPv4/IPv6:  Reachability RT-5
      uses a fixed route-type-specific size (34 or 58 octets), so
      receivers can infer prefix width.  Unreachability NLRIs append
      variable-length Reporter TLVs, so total length no longer implies
      address family, and IP Prefix Length alone is ambiguous (e.g., /24
      is valid for both).  A 1-octet Address Family field resolves this.

   One route type vs two (per address family):  Separate route type
      values would remove the Address Family octet but duplicate
      specifications and IANA registrations.  This document uses one
      type with an explicit family indicator.

   RT-5-shaped NLRI vs minimal custom encoding:  Reusing the RT-5 field
      order maximizes familiarity and parser reuse, at the cost of
      carrying unused fields (ESI, GW IP, MPLS Label) plus one new octet
      for Address Family.  Reporter detail is concentrated in TLVs.

   Route-type-specific Length limit:  The Length field is one octet
      ([RFC7432]), so the route-type-specific portion cannot exceed 255
      octets.  Implementations MUST stay within that limit by bounding
      the number of Reporter TLVs per NLRI.

Authors' Addresses

   Jeff Tantsura
   Nvidia
   Email: jefftant.ietf@gmail.com


   Vivek Venkatraman
   Nvidia
   Email: vivek@nvidia.com


   Karthikeya Venkat Muppalla
   Nvidia
   Email: kmuppalla@nvidia.com


   Pooja Jagadeesh Doijode
   Nvidia
   Email: pdoijode@nvidia.com


   Maciej Rzehak
   CoreWeave
   Email: mrzehak@coreweave.com




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