Source-IP-Origin-AS Filter for BGP Flow Specification
draft-wang-idr-flowspec-sip-origin-as-filter-01
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Haibo Wang , Aijun Wang , Shunwan Zhuang , Jie Dong , Yang Huang , Tao Qin | ||
| Last updated | 2026-03-19 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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draft-wang-idr-flowspec-sip-origin-as-filter-01
IDR Working Group H. Wang
Internet-Draft Huawei
Intended status: Standards Track A. Wang
Expires: 21 September 2026 China Telecom
S. Zhuang
J. Dong
Y. Huang
T. Qin
Huawei
20 March 2026
Source-IP-Origin-AS Filter for BGP Flow Specification
draft-wang-idr-flowspec-sip-origin-as-filter-01
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 but
belong to a specific source 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."
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This Internet-Draft will expire on 21 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
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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 sourced from a particular
network (Autonomous System), even when the specific souce 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 Source Origin AS as a matching criterion.
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2. Definitions and Acronyms
* FS: Flow Specification
* Source-IP-Origin-AS: The origin AS number of the source 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.
* Source-IP-Origin-AS
Type TBD1 - Source-IP-Origin-AS
Encoding: <type (1 octet), [op, value]+>
Contains a set of {operator, value} pairs that are used to match the
Source-IP-Origin-AS (i.e. the origin AS number of the source 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 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.
lt - less than comparison between data and value.
gt - greater than comparison between data and value.
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eq - equality between data and value.
The bits lt, gt, and eq can be combined to produce match the Source-
IP-Origin-AS filter or a range of Source-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
+---------------------------------------------------------------+
~ Source-IP-Origin-AS (4 octets) ~
+---------------------------------------------------------------+
Figure 2: Source-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 <length, NLRI value>, 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 Source-
IP-Origin-AS component:
It MUST determine the Origin AS of the souce IP of the transit packet
by performing a lookup in its local BGP RIB.
If the packet's source 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 R2, if the
ISP AS64597 wants to redirect all packets originating from AS64598 to
IP Prefix 61:
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"first go to R3, then forward them to IP Prefix 61", 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
"Source Prefix + Destination Prefix" rules in Router R2 as following:
+--------------+--------------+-------------------------+
| Destination | Source Prefix| Redirect to IP Nexthop |
| Prefix | | |
+--------------+--------------+-------------------------+
| IP Prefix 61 | IP Prefix 81 | R3 |
+--------------+--------------+-------------------------+
| IP Prefix 61 | IP Prefix 82 | R3 |
+--------------+--------------+-------------------------+
| IP Prefix 61 | IP Prefix 83 | R3 |
+--------------+--------------+-------------------------+
| IP Prefix 61 | IP Prefix 84 | R3 |
+--------------+--------------+-------------------------+
| More ... |
+--------------+--------------+-------------------------+
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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 "Source IP Origin AS + Destination Prefix" rule in
Router R2 as following:
+--------------+--------------+-------------------------+
| Soure IP | Destination | Redirect to IP Nexthop |
| Origin AS | Prefix | |
+--------------+--------------+-------------------------+
| 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
source 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 | Source-IP-Origin-AS |
+---------+--------------+---------------------------------+
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7. Contributors
TBD
8. Acknowledgments
TBD
9. References
[I-D.ietf-idr-flowspec-l2vpn]
Hao, W., 3rd, D. E. E., Litkowski, S., and S. Zhuang, "BGP
Dissemination of L2 Flow Specification Rules", Work in
Progress, Internet-Draft, draft-ietf-idr-flowspec-l2vpn-
27, 16 March 2026, <https://datatracker.ietf.org/doc/html/
draft-ietf-idr-flowspec-l2vpn-27>.
[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>.
[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,
<https://www.rfc-editor.org/info/rfc4271>.
[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>.
[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,
<https://www.rfc-editor.org/info/rfc8955>.
[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,
<https://www.rfc-editor.org/info/rfc8956>.
Authors' Addresses
Haibo Wang
Huawei
156 Beiqing Road
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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
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
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Email: qintao11@huawei.com
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