GROW C. Lin Internet-Draft New H3C Technologies Intended status: Standards Track P. Narasimha Expires: 23 April 2026 Cisco M. Srivastava Juniper Networks J. Li China Mobile 20 October 2025 Peer Capability Update Notification in BGP Monitoring Protocol (BMP) draft-lin-grow-bmp-cap-notification-00 Abstract When BGP Dynamic Capability is supported, dynamic updates of capabilities are allowed over an established BGP session. At present, after the BGP session is established, the monitored router sends a BMP Peer Up Notification message first, containing the initial capabilities. If BGP Dynamic Capability is supported, using BMP Peer Up Notification messages to report subsequent capability changes for a BGP session becomes inappropriate. This document defines a new Peer Capability Update Notification message type in BMP to report peer capability changes. 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 23 April 2026. Copyright Notice Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved. Lin, et al. Expires 23 April 2026 [Page 1] Internet-Draft BMP Peer Capability Update Notification October 2025 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include 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 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Peer Capability Update Notification Message . . . . . . . . . 3 3.1. Message Format . . . . . . . . . . . . . . . . . . . . . 3 4. Example and Use Case . . . . . . . . . . . . . . . . . . . . 4 5. Operational Considerations . . . . . . . . . . . . . . . . . 4 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 8.1. Normative References . . . . . . . . . . . . . . . . . . 5 Appendix A. Option 1 . . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction [I-D.ietf-idr-dynamic-cap] introduces BGP Dynamic Capability, which enables dynamic updates of capabilities over an established BGP session. This feature allows BGP speakers to negotiate capabilities without disrupting the existing session. When a BGP session is established, a BMP Peer UP Notification message containing the initial capabilities is first sent to monitor this session [RFC7854]. If BGP Dynamic Capability is implemented, subsequent capability changes can be reported to the monitoring station by resending a Peer UP Notification message that includes all current capabilities. The capabilities in the latter message must override those in the former. Normally, a BMP Peer Up Notification message should only be sent once when a BGP session is established. If the BMP Peer Up Notification message is sent multiple times, the monitoring station may mistakenly interpret the event as a peer session re-established, potentially causing the clearing of previously received route monitoring messages for the affected peers in that session. In this case, all routing monitoring messages for those peers must be resent, significantly increasing the network load. Lin, et al. Expires 23 April 2026 [Page 2] Internet-Draft BMP Peer Capability Update Notification October 2025 Therefore, when BGP Dynamic Capability is implemented, using BMP Peer Up Notification messages to report subsequent capability changes becomes unsuitable. To avoid potential problems caused by the above solution, this document defines a new BMP message type, Peer Capability Update Notification, for reporting BGP dynamic capability changes. 2. Terminology 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. 3. Peer Capability Update Notification Message This section defines a new BMP message type for monitoring BGP dynamic capabilities. The assigned value for this message type is placed in the Message Type field of the common header. Message Type = TBD: Peer Capability Update Notification 3.1. Message Format This section defines the Peer Capability Update Notification BMP message format, as illustrated in Figure 1. The message consists of four components: a Common Header, a Per-Peer Header, a CAP Flags, and a BGP Dynamic Capability PDU. The Common Header and Per-Peer Header follow the same format as defined in Sections 4.1 and 4.2 of [RFC7854] respectively. The BGP Dynamic Capability PDU uses the format specified in Section 3 of [I-D.ietf-idr-dynamic-cap]. The Peer CAP Flags field is defined as follows: +---------------------------------------+ | Common Header | +---------------------------------------+ | Per-Peer Header | +---------------------------------------+ | Peer CAP Flags | +---------------------------------------+ | BGP Dynamic Capability PDU | +---------------------------------------+ Figure 1: Peer Capability Update Notification Message Format Lin, et al. Expires 23 April 2026 [Page 3] Internet-Draft BMP Peer Capability Update Notification October 2025 Peer CAP Flags (1 byte): This field provides status information about the Capability Update, including the direction of the BGP Dynamic Capability PDU. The direction flag fields are defined as follows: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |T| Reserved | +-+-+-+-+-+-+-+-+ The T flag (1 bit) signals the direction of the BGP Dynamic Capability PDU: * 1: Received from a peer. * 0: Sent to a peer. The remaining bits are reserved for future use. They MUST be transmitted as 0 and their values MUST be ignored on receipt. The BMP Peer Capability Update Notification MUST be sent before sending any Route Monitoring message corresponding to the updated capability for the Peer. 4. Example and Use Case The Peer Capability Update Notification message of BMP provides real- time notifications of BGP dynamic capability changes. Consider a BGP speaker with a peer that supports both BGP Dynamic Capability and VPNv4 Address Family Identifier/Subsequent Address Family Identifier (AFI/SAFI) [RFC4364], where the corresponding BGP session is already established. When this peer subsequently enables the EVPN address family [RFC7432], the BGP speaker will send a BGP Dynamic Capability message containing Multiprotocol Extensions Capability for BGP-4 (including EVPN AFI/SAFI information) [RFC4760]. If the peer is being monitored via BMP, the BGP speaker must generate a BMP Peer Capability Update Notification message (with the T flag set to 0) to report this capability change, before sending any Route Monitoring Messages for EVPN address family. 5. Operational Considerations When a BGP speaker sends a BGP Dynamic Capability message to its peer, the generation of a corresponding BMP Peer Capability Update Notification message (with the T flag set to 0) should be generated immediately and not need to await successful receipt of the BGP Dynamic Capability acknowledgment (ACK), per the procedures in [I-D.ietf-idr-dynamic-cap]. Lin, et al. Expires 23 April 2026 [Page 4] Internet-Draft BMP Peer Capability Update Notification October 2025 When a BGP speaker receives a BGP Dynamic Capability message from its peer, a corresponding BMP Peer Capability Update Notification message (with the T flag set to 1) should be generated immediately. If a new BGP capability is added, after both the corresponding BMP Peer Capability Update Notification message with the T flag set to 0 and that with the T flag set to 1 are sent to monitoring station, the route information and End-of-RIB (EOR) of corresponding peer will be sent via BMP. If an existing BGP capability is removed, only the corresponding BMP Peer Capability Update Notification messages will be sent, but the route withdrawal information of corresponding peer will not be sent via BMP. 6. Security Considerations The security considerations in Section 11 of [RFC7854] apply to this document. It is also believed that this document does not add any additional security considerations. 7. IANA Considerations This document requests IANA to assign the following new parameter in the BMP Parameters registry (maintained at https://www.iana.org/assignments/bmp-parameters/bmp- parameters.xhtml). New BMP Message Type: Value: TBD (to be assigned by IANA) Name: Peer Capability Update Notification Reference: This document 8. References 8.1. 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, . [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 2006, . Lin, et al. Expires 23 April 2026 [Page 5] Internet-Draft BMP Peer Capability Update Notification October 2025 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, "Multiprotocol Extensions for BGP-4", RFC 4760, DOI 10.17487/RFC4760, January 2007, . [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, . [RFC7854] Scudder, J., Ed., Fernando, R., and S. Stuart, "BGP Monitoring Protocol (BMP)", RFC 7854, DOI 10.17487/RFC7854, June 2016, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [I-D.ietf-idr-dynamic-cap] Chen, E. and S. R. Sangli, "Dynamic Capability for BGP-4", Work in Progress, Internet-Draft, draft-ietf-idr-dynamic- cap-17, 6 July 2025, . Appendix A. Option 1 In addition to the aforementioned solutions (Using New BMP Type or Peer Up Notification) to report the BGP Capability changes, This document can also define a New TLV as part of Peer Up Notification or other available BMP Message types defined in existing documents. The New TLV format is defined below: +---------------------------------------+ | Type (2 byte) | +---------------------------------------+ | Length (2 byte) | +---------------------------------------+ | Peer CAP Flags (1 byte) | +---------------------------------------+ | BGP Dynamic Capability PDU | +---------------------------------------+ Type = TBD: Peer Capability Update Notification; Lin, et al. Expires 23 April 2026 [Page 6] Internet-Draft BMP Peer Capability Update Notification October 2025 Length: indicates the length of value in this TLV, including Peer CAP Flags and BGP Dynamic Capability PDU; Peer CAP Flags and BGP Dynamic Capability PDU is same with the definition of Section 3.1 in this document. Authors' Addresses Changwang Lin New H3C Technologies 8 Yongjia North Road Beijing Haidian District, 100094 China Email: linchangwang.04414@h3c.com Prasad S. Narasimha Cisco Cessna Business Park SEZ, Kadubeesanahalli Bangalore India Email: snprasad@cisco.com Mukul Srivastava Juniper Networks 10 Technology Park Dr Westford, MA 01886 United States of America Email: msri@juniper.net Jinming Li China Mobile 32 Xuanwumen West Street Beijing Xicheng District, 100053 China Email: lijinming@chinamobile.com Lin, et al. Expires 23 April 2026 [Page 7]