IDR Working Group H. Wang Internet-Draft Huawei Intended status: Standards Track A. Wang Expires: 1 September 2026 China Telecom S. Zhuang T. Qin Huawei 28 February 2026 Destination-IP-Origin-AS Filter for BGP Flow Specification draft-wang-idr-flowspec-dip-origin-as-filter-12 Abstract This document defines an extension to the Border Gateway Protocol (BGP) Flow Specification (FlowSpec) to enable filtering based on the Origin Autonomous System (AS) of the destination IP address. This extension is particularly useful in mitigating Distributed Denial of Service (DDoS) attacks where the target IP addresses are dynamic but belong to a specific destination AS. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 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 1 September 2026. Wang, et al. Expires 1 September 2026 [Page 1] Internet-Draft Destination-IP-Origin-AS Filter February 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. 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. Definitions and Acronyms . . . . . . . . . . . . . . . . . . 3 3. The Flow Specification Encoding for Destination-IP-Origin-AS Filter . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Operational Procedures . . . . . . . . . . . . . . . . . 4 4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. IANA . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction BGP Flow Specification (FlowSpec), defined in [RFC8955] and [RFC8956], allows for the dissemination of traffic filtering rules. Current FlowSpec components support filtering by destination prefix, source prefix, and various Layer 4 parameters. In certain DDoS mitigation scenarios, an operator may need to apply rate-limiting or filtering to all traffic destined for a particular network (Autonomous System), even when the specific target IP prefixes within that AS are numerous or rapidly changing. Manually updating hundreds of prefix-based FlowSpec rules is inefficient. This document introduces a new FlowSpec component that allows operators to use the Destination Origin AS as a matching criterion. Wang, et al. Expires 1 September 2026 [Page 2] Internet-Draft Destination-IP-Origin-AS Filter February 2026 2. Definitions and Acronyms * FS: Flow Specification * Destination-IP-Origin-AS: The origin AS number of the destination IP address 3. The Flow Specification Encoding for Destination-IP-Origin-AS Filter This document proposes a new flow specification component type that is encoded in the BGP Flowspec NLRI. The following new component type is defined. * Destination-IP-Origin-AS Type TBD1 - Destination-IP-Origin-AS Encoding: Contains a set of {operator, value} pairs that are used to match the Destination-IP-Origin-AS (i.e. the origin AS number of the destination IP address). The operator byte is encoded as: 0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ | e | a | len | 0 |lt |gt |eq | +---+---+---+---+---+---+---+---+ Figure 1: Numeric Operator (numeric_op) Where: e - end-of-list bit. Set in the last {op, value} pair in the list. a - AND bit. If unset, the previous term is logically ORed with the current one. If set, the operation is a logical AND. It MUST be unset in the Destination-IP-Origin-AS filter. len - The length of the value field for this operator given as (1 << len). This encodes 1 (len=00), 2 (len=01), 4 (len=10), and 8 (len=11) octets. lt - less than comparison between data and value. gt - greater than comparison between data and value. Wang, et al. Expires 1 September 2026 [Page 3] Internet-Draft Destination-IP-Origin-AS Filter February 2026 eq - equality between data and value. The bits lt, gt, and eq can be combined to produce match the Destination-IP-Origin-AS filter or a range of Destination-IP-Origin- AS filter(e.g. less than AS1 and greater than AS2). The value field is encoded as: 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 +---------------------------------------------------------------+ ~ Destination-IP-Origin-AS (4 octets) ~ +---------------------------------------------------------------+ Figure 2: Destination-IP-Origin-AS Per section 10 of [RFC8955] , If a receiving BGP speaker cannot support this new Flow Specification component type, it MUST discard the NLRI value field that contains such unknown components. Since the NLRI field encoding (Section 4 of [RFC8955]) is defined in the form of a 2-tuple , message decoding can skip over the unknown NLRI value and continue with subsequent remaining NLRI. In cases of multi-homed prefixes with multiple Origin ASes, the match succeeds if any of the valid Origin ASes match the filter. 3.1. Operational Procedures When a BGP speaker receives a FlowSpec update containing the Destination Origin AS component: It MUST determine the Origin AS of the destination IP of the transit packet by performing a lookup in its local BGP RIB. If the packet's destination IP matches a prefix whose BGP path has an AS_PATH where the rightmost AS (the origin) matches the value in the FlowSpec rule, the action (e.g., rate-limit, discard) MUST be applied. 4. Use Cases This section describes how to use this function in a simple scenario. Considering the topology shown in Figure 3. In AS64597's R1, if the ISP AS64597 wants to redirect all packets originating from IP Prefix 61 to AS64598: Wang, et al. Expires 1 September 2026 [Page 4] Internet-Draft Destination-IP-Origin-AS Filter February 2026 "first go to R3, then forward them to AS64598", the ISP AS64597 can use the traditional method or the method defining in this draft. +---------+ | BGP FS | | Server | +----|----+ | | / / ************/************ IP Prefix 81 * / * IP Prefix 82 IP Prefix 61 * / AS64597 * IP Prefix 83 * / * IP Prefix 84 +-------+ * +---+/ +---+ * +-------+ +AS64596+-------+ R1+---------+ R2|------+AS64598+ +-------+ * +-+-+\ +---+ */ +-------+ * \ |\ / * \ | \ /* IP Prefix 91 * \ | /\* IP Prefix 92 * \ | / \ IP Prefix 93 * \ |/ *\ IP Prefix 94 * \ +-+-+ * \ +-------+ * \-+ R3+------+AS64599+ * +---+ * +-------+ * * ************************* Figure 3: Redirect the traffic using Flowspec Using the traditional method, the ISP AS64597 needs to setup multiple "Destination Prefix + Source Prefix" rules in Router R1 as following: +--------------+--------------+-------------------------+ | Destination | Source Prefix| Redirect to IP Nexthop | | Prefix | | | +--------------+--------------+-------------------------+ | IP Prefix 81 | IP Prefix 61 | R3 | +--------------+--------------+-------------------------+ | IP Prefix 82 | IP Prefix 61 | R3 | +--------------+--------------+-------------------------+ | IP Prefix 83 | IP Prefix 61 | R3 | +--------------+--------------+-------------------------+ | IP Prefix 84 | IP Prefix 61 | R3 | +--------------+--------------+-------------------------+ | More ... | +--------------+--------------+-------------------------+ Wang, et al. Expires 1 September 2026 [Page 5] Internet-Draft Destination-IP-Origin-AS Filter February 2026 Figure 4: Using the traditional method to redirect the traffic Using the method defining in this draft, the ISP AS64597 needs to setup only one "Destination Origin AS + Source Prefix" rule in Router R1 as following: +--------------+--------------+-------------------------+ | Destination | Source Prefix| Redirect to IP Nexthop | | IP Origin AS | | | +--------------+--------------+-------------------------+ | 64598 | IP Prefix 61 | R3 | +--------------+--------------+-------------------------+ Figure 5: Using the AS-level filtering method to redirect the traffic Obviously, the new method defining in this draft saves a lot of entry spaces on the control plane and forwarding plane, and it would greatly simplify the operation of the control plane, and the more destination prefixes an AS has, the more obvious the benefit. 5. Security Considerations In addition to the security considerations in [RFC8955], operators must be aware of: * Routing Inconsistency: If different routers in the network have different views of the BGP table, the "Origin AS" for a given IP may differ, leading to inconsistent filter application. * AS_PATH Manipulation: An attacker could potentially spoof or prepend ASes to bypass filters if the local BGP table is compromised. * Validation: Implementations SHOULD ensure that FlowSpec rules are validated against the originating peer to prevent unauthorized AS- based filtering across administrative boundaries. 6. IANA IANA is requested to a new entry in "Flow Spec component types registry" with the following values: +---------+--------------+---------------------------------+ | Type | RFC or Draft | Description | +---------+--------------+---------------------------------+ | TBD1 | This Draft | Destination-IP-Origin-AS | +---------+--------------+---------------------------------+ Wang, et al. Expires 1 September 2026 [Page 6] Internet-Draft Destination-IP-Origin-AS Filter February 2026 7. Contributors TBD 8. Acknowledgments The authors would like to acknowledge the review and inputs from Gang Yan, Robert Raszuk, Jeffray Haas, Linda Dunbar, Zhenbin Li, Rainbow Wu, Jie Dong and Ziqing Cao. 9. References [I-D.ietf-idr-flowspec-l2vpn] Weiguo, H., Eastlake, D. E., Litkowski, S., and S. Zhuang, "BGP Dissemination of L2 Flow Specification Rules", Work in Progress, Internet-Draft, draft-ietf-idr-flowspec- l2vpn-26, 23 September 2025, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8955] Loibl, C., Hares, S., Raszuk, R., McPherson, D., and M. Bacher, "Dissemination of Flow Specification Rules", RFC 8955, DOI 10.17487/RFC8955, December 2020, . [RFC8956] Loibl, C., Ed., Raszuk, R., Ed., and S. Hares, Ed., "Dissemination of Flow Specification Rules for IPv6", RFC 8956, DOI 10.17487/RFC8956, December 2020, . Authors' Addresses Wang, et al. Expires 1 September 2026 [Page 7] Internet-Draft Destination-IP-Origin-AS Filter February 2026 Haibo Wang Huawei 156 Beiqing Road Beijing 100095 P.R. China Email: rainsword.wang@huawei.com Aijun Wang China Telecom Beiqijia Town, Changping District Beijing 102209 P.R. China Email: wangaj3@chinatelecom.cn Shunwan Zhuang Huawei 156 Beiqing Road Beijing 100095 P.R. China Email: zhuangshunwan@huawei.com Tao Qin Huawei 156 Beiqing Road Beijing 100095 P.R. China Email: qintao11@huawei.com Wang, et al. Expires 1 September 2026 [Page 8]