| Internet-Draft | Destination-IP-Origin-AS Filter | October 2026 |
| Wang, et al. | Expires 3 May 2027 | [Page] |
This document defines an extension to the Border Gateway Protocol (BGP) Flow Specification Version 2 (FSv2) defined in [draft-ietf-idr-fsv2-ip-basic] 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 or optimizing traffic redirection where the target IP addresses are numerous or rapidly changing, but belong to a specific destination Origin AS.¶
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.¶
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BGP [RFC4271] Flow Specification, originally defined in [RFC8955] and [RFC8956], has evolved to Flow Specification Version 2 (FSv2) as specified in [I-D.ietf-idr-fsv2-ip-basic]. FSv2 introduces an extensible, TLV-based filter family architecture with explicit rule ordering and modular components.¶
In certain DDoS mitigation and traffic engineering scenarios, an operator may need to apply rate-limiting, redirection, or filtering to 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 and consumes significant Hardware Forwarding Information Base (FIB) / TCAM resources. This document introduces a new FSv2 component under the Routing Filter Family that allows operators to use the Destination Origin AS as a matching criterion.¶
This document proposes a new FSv2 component encoded within the Routing Filter Family (Type 1400). Unlike legacy FSv1 raw byte streams, FSv2 utilizes explicit TLV formatting.¶
Encoding format for the DIP-AS component:¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Type (100) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | <[numeric_op, Destination-IP-Origin-AS]+> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:¶
Flags (4 bits): Defined in FSv2 specifications.¶
Type (12 bits): Set to 100 for DIP-AS.¶
Length (16 bits): Length of the value field in octets.¶
<[numeric_op, Destination-IP-Origin-AS]+>: Contains a list of {numeric_op, Destination-IP-Origin-AS} pairs that are used to match the Destination-IP-Origin-AS.¶
numeric_op: This component uses the Numeric Operator (numeric_op) described in Section 4.1.1 of [I-D.ietf-idr-fsv2-ip-basic], Type 100 component values SHOULD be encoded as 4 octets (numeric_op len=10).¶
Destination-IP-Origin-AS (32 bits): A 4-octet Autonomous System Number encoded in network byte order.¶
As defined in [I-D.ietf-idr-fsv2-ip-basic], rules and components follow strict ordering principles. The DIP-AS component (Type 100) within the Routing Filter Family (1400) MUST be evaluated deterministically according to FSv2 component sequencing rules.¶
The implementation of Destination-IP-Origin-AS filtering relies on a cross-coupling mechanism between the Unicast BGP Forwarding Table (FIB) and the Flowspec Packet Inspection Engine. The detailed processing workflow is defined in the following three steps:¶
Control-Plane Origin AS Derivation and FIB Tagging: When a BGP speaker receives unicast BGP routes, and those routes are selected as best paths and installed into the Forwarding Information Base (FIB), the local system MUST derive and preserve the associated Origin AS attribute (or a local mapped metadata tag representing the Origin AS) within the corresponding FIB entries. The Origin AS for a route is evaluated as follows:¶
The Origin AS is defined as the rightmost AS number in the AS_SEQUENCE segment of the AS_PATH attribute.¶
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, or standard evaluation / local policy applies.¶
For example:¶
Flowspec Rule Installation: When a BGP Flowspec rule containing the DIP-AS component (Type 100) is received, the system programs a filtering rule into the forwarding hardware. The match parameters include both standard RFC 8955/8956 n-tuples (e.g., Destination IP, Source IP, Protocol, Port) and the target Origin AS value specified in the DIP-AS component (denoted as AS_Rule, e.g., 65001).¶
Datapath Two-Stage Packet Matching: Upon receiving a data packet:¶
The device evaluates the packet against installed Flowspec rules.¶
If a candidate rule contains a DIP-AS match condition, the forwarding engine performs a FIB lookup using the packet's Destination IP address to extract the associated FIB entry's Origin AS attribute (denoted as AS_FIB). Note: In multi-homing or multi-path scenarios where multiple valid active paths exist for the destination prefix, AS_FIB is determined based on the selected forwarding route(s) (e.g., the active best path or all installed ECMP paths in the FIB).¶
Evaluation:¶
If AS_FIB matches AS_Rule (e.g., both are 65001), the DIP-AS match condition is satisfied, and the configured Flowspec action (e.g., redirect, drop, rate-limit) is executed.¶
If AS_FIB does not match AS_Rule (e.g., AS_FIB is 65002 while AS_Rule is 65001), the match condition fails, and packet processing continues to subsequent rules or default forwarding.¶
This section describes a representative use case for traffic redirection and rate-limiting using the Destination-IP-Origin-AS filter under the FSv2 framework.¶
Consider the topology shown in Figure 2. ISP AS64597 receives traffic from AS64596 (Source IP Prefix 61) destined for AS64598.¶
+---------+
| 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+
* +---+ * +-------+
* *
*************************
Using traditional FlowSpec (RFC 8955), if AS64598 announces dozens or hundreds of individual prefixes (Prefix 81, 82, 83, 84...), AS64597 must inject separate FlowSpec rules for each destination prefix to redirect traffic coming from Source IP Prefix 61 towards Router R3:¶
+--------------+--------------+-------------------------+ | Destination | Source Prefix| Action / Next-hop | | Prefix | | | +--------------+--------------+-------------------------+ | IP Prefix 81 | IP Prefix 61 | Redirect to R3 | | IP Prefix 82 | IP Prefix 61 | Redirect to R3 | | IP Prefix 83 | IP Prefix 61 | Redirect to R3 | | IP Prefix 84 | IP Prefix 61 | Redirect to R3 | | ... | ... | ... | +--------------+--------------+-------------------------+
Using the extension defined in this draft, the BGP FlowSpec Server needs to generate only a single FlowSpec rule:¶
+--------------+--------------+--------------------+ | Destination | Source Prefix| Action / Next-hop | | IP Origin AS | | | +--------------+--------------+--------------------+ | 64598 | IP Prefix 61 | R3 | +--------------+--------------+--------------------+
This significantly reduces BGP NLRI messaging overhead, control plane churn, and hardware FIB/TCAM entry consumption on network elements.¶
This document extends BGP FlowSpec Version 2 (FSv2). Security considerations discussed in [I-D.ietf-idr-fsv2-ip-basic] apply directly.¶
In addition, operators MUST consider routing inconsistencies, RPKI-based Route Origin Validation (ROV) [RFC6811], and FSv2 route validation procedures.¶
IANA is requested to make the following allocations under the BGP Flow Specification Version 2 (FSv2) registries defined in [I-D.ietf-idr-fsv2-ip-basic]:¶
FSv2 Routing Filter Family Component Types Registry: +-------------+---------------------------+---------------+ | Type | Description | Reference | +-------------+---------------------------+---------------+ | 100 | DIP-AS (Destination-IP-AS)| This document | +-------------+---------------------------+---------------+¶
The following people made significant contributions to this document:¶
Tao Qin Huawei Email: qintao11@huawei.com¶
The authors would like to acknowledge the review and inputs from Susan Hares, Ke Ma, Xiaoying Huang, Gang Yan, Robert Raszuk, Jeffray Haas, Linda Dunbar, Zhenbin Li, Rainbow Wu, Jie Dong and Ziqing Cao.¶