IDR Working Group H. Wang Internet-Draft Huawei Intended status: Standards Track A. Wang Expires: 25 March 2027 China Telecom S. Zhuang J. Dong Y. Huang T. Qin Huawei 21 September 2026 Source-IP-Origin-AS Filter for BGP Flow Specification draft-wang-idr-flowspec-sip-origin-as-filter-02 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 source IP address. This extension is particularly useful in mitigating Distributed Denial of Service (DDoS) attacks where the source IP addresses are dynamic or numerous but belong to a specific source AS. 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. 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 25 March 2027. Wang, et al. Expires 25 March 2027 [Page 1] Internet-Draft Source-IP-Origin-AS Filter September 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. Flow Specification Encoding for Source-IP-Origin-AS Filter . 3 3.1. Ordering of Components . . . . . . . . . . . . . . . . . 4 3.2. Operational Procedures and Packet Matching Logic . . . . 4 4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 9.2. Informative References . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction BGP [RFC4271] 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, redirection, or filtering to traffic sourced from a particular network (Autonomous System), even when the specific source IP prefixes within that AS are numerous or rapidly changing. Manually updating hundreds of prefix-based FlowSpec rules is inefficient and consumes excessive Hardware Forwarding Information Base (FIB) / TCAM resources. This document introduces a new FlowSpec component that allows operators to use the Source Origin AS as a matching criterion. Wang, et al. Expires 25 March 2027 [Page 2] Internet-Draft Source-IP-Origin-AS Filter September 2026 2. Definitions and Acronyms * FS: Flow Specification * Source-IP-Origin-AS: The origin AS number associated with the source IP address of a transit packet, determined from the rightmost AS in the AS_PATH attribute of the active BGP route matching that source IP. 3. Flow Specification Encoding for Source-IP-Origin-AS Filter This document proposes a new Flow Specification component type that is encoded in the BGP FlowSpec NLRI [RFC8955] [RFC8956]. * Type TBD1 - Source-IP-Origin-AS Encoding: It contains a set of {operator, value} pairs used to match the Source-IP-Origin-AS. The operator byte (numeric_op) is encoded as specified in Section 4.2 of [RFC8955]: 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 (0) in the Source-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. For 4-byte AS numbers, len MUST be set to 10 (4 octets). * lt, gt, eq - Less than, Greater than, and Equal comparison bits. Wang, et al. Expires 25 March 2027 [Page 3] Internet-Draft Source-IP-Origin-AS Filter September 2026 The value field contains a 4-octet Autonomous System Number encoded in network byte order: 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 +---------------------------------------------------------------+ ~ Source-IP-Origin-AS (4 octets) ~ +---------------------------------------------------------------+ Figure 2: Source-IP-Origin-AS Value 3.1. Ordering of Components As defined in [RFC8955], a strict ordering of components MUST be followed to ensure a deterministic comparison of FlowSpec NLRIs. The Source-IP-Origin-AS component (Type TBD1) MUST be ordered after Type 2 (Source Prefix) and before Type 3 (IP Protocol). [Note to IANA: The exact numeric order will depend on the assigned Type value.] 3.2. Operational Procedures and Packet Matching Logic When a BGP speaker receives and installs a FlowSpec route containing the Source-IP-Origin-AS component, the matching process for a transit data packet MUST proceed as follows: 1. The router extracts the packet's Source IP address. 2. The router performs a longest-prefix match (LPM) lookup for the Source IP in its local BGP Loc-RIB / FIB to retrieve the associated active BGP route. 3. The router evaluates the AS_PATH attribute of the retrieved BGP route: * The Origin AS is defined as the rightmost AS number in the AS_SEQUENCE segment of the AS_PATH. * If the AS_PATH ends with an AS_SET or AS_CONFED_SEQUENCE, the match fails unless all ASes in the set match, or the implementation supports evaluating each AS in the AS_SET against the filter. 4. If the evaluated Origin AS matches the criterion in the FlowSpec rule, the packet matches this component. Wang, et al. Expires 25 March 2027 [Page 4] Internet-Draft Source-IP-Origin-AS Filter September 2026 5. In multi-homing or multipath scenarios where a source prefix is reachable via paths with different Origin ASes, the match MUST succeed if ANY valid active path for the source prefix matches the Origin AS defined in the FlowSpec rule. If a receiving BGP speaker cannot support this new component type, it MUST follow the error handling and component skipping procedures defined in Section 10 of [RFC8955] and [RFC8956]. 4. Use Cases This section describes how to use this function in a simple scenario. Consider the topology shown in Figure 3. Router R2 in AS64597 receives traffic originating from AS64598 destined for IP Prefix 61. The operator wants to redirect all traffic originating from AS64598 towards Router R3 before forwarding it to IP Prefix 61. +---------+ | 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: Traffic Redirection Using FlowSpec Using the traditional method, ISP AS64597 must inject multiple "Destination Prefix + Source Prefix" FlowSpec rules into Router R2: Wang, et al. Expires 25 March 2027 [Page 5] Internet-Draft Source-IP-Origin-AS Filter September 2026 +--------------+--------------+-------------------------+ | Destination | Source Prefix| Action / Next-hop | | Prefix | | | +--------------+--------------+-------------------------+ | IP Prefix 61 | IP Prefix 81 | Redirect to R3 | | IP Prefix 61 | IP Prefix 82 | Redirect to R3 | | IP Prefix 61 | IP Prefix 83 | Redirect to R3 | | IP Prefix 61 | IP Prefix 84 | Redirect to R3 | | ... | ... | ... | +--------------+--------------+-------------------------+ Figure 4: Traditional FlowSpec Matching Using the method defined in this draft, ISP AS64597 needs to inject only a single "Destination Prefix + Source IP Origin AS" FlowSpec rule: +--------------+--------------+-------------------------+ | Destination | Source IP | Action / Next-hop | | Prefix | Origin AS | | +--------------+--------------+-------------------------+ | IP Prefix 61 | AS64598 | Redirect to R3 | +--------------+--------------+-------------------------+ Figure 5: Source-IP-Origin-AS FlowSpec Matching This method saves significant TCAM space on network elements, reduces BGP UPDATE messaging load on the control plane, and simplifies operational management when a source AS advertises numerous dynamic prefixes. 5. Security Considerations In addition to the security considerations in [RFC8955] and [RFC8956], operators MUST be aware of the following: * Routing Inconsistency: Packet classification relies on the local BGP RIB state of the forwarding router. If different ingress routers have different active BGP routes (and thus different Origin AS views) for a given source IP, filtering or redirection actions may be applied inconsistently. * BGP Origin Validation: Malicious or misconfigured networks may spoof AS_PATH attributes. Operators SHOULD deploy RPKI-based Route Origin Validation (ROV) [RFC6811] in their networks to ensure that the Source Origin AS matching is performed against validated BGP routes. Wang, et al. Expires 25 March 2027 [Page 6] Internet-Draft Source-IP-Origin-AS Filter September 2026 * Validation of FlowSpec Routes: BGP FlowSpec routes MUST be validated against originating BGP peers according to the FlowSpec validation rules (Section 6 of [RFC8955]) to prevent cross- administrative-domain traffic hijacking. 6. IANA Considerations IANA is requested to allocate a new component type in the "Flow Spec Component Types" registry defined in [RFC8955]: +-------+-------------------------------+---------------+ | Type | Description | Reference | +-------+-------------------------------+---------------+ | TBD1 | Source-IP-Origin-AS | This-Draft | +-------+-------------------------------+---------------+ 7. Contributors TBD 8. Acknowledgments TBD 9. References 9.1. 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, . [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, . Wang, et al. Expires 25 March 2027 [Page 7] Internet-Draft Source-IP-Origin-AS Filter September 2026 [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, . 9.2. Informative References [RFC6811] Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R. Austein, "BGP Prefix Origin Validation", RFC 6811, DOI 10.17487/RFC6811, January 2013, . Authors' Addresses 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 Jie Dong Huawei 156 Beiqing Road Beijing 100095 P.R. China Email: jie.dong@huawei.com Wang, et al. Expires 25 March 2027 [Page 8] Internet-Draft Source-IP-Origin-AS Filter September 2026 Yang Huang Huawei 156 Beiqing Road Beijing 100095 P.R. China Email: yang.huang@huawei.com Tao Qin Huawei 156 Beiqing Road Beijing 100095 P.R. China Email: qintao11@huawei.com Wang, et al. Expires 25 March 2027 [Page 9]