]> Tsinghua University

Beijing China xuke@tsinghua.edu.cn

Zhongguancun Laboratory

Beijing China jiangshl@zgclab.edu.cn

Zhongguancun Laboratory

Beijing China guoyangfei@zgclab.edu.cn

Tsinghua University

Beijing China wangxiaoliang0623@foxmail.com

SIDR Operations The Route Path Authorizations (RPA) is an RPKI object that attests to the complete routing paths description which an Autonomous System (AS) would obey in Border Gateway Protocol (BGP) route propagation. This document specifies an RPA-based AS Path Verification methodology to mitigate, even solve, AS Path forgery and route leaks. This document also explains the various BGP security threats that RPA can help address and provides operational considerations associated with RPA deployment. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the SIDR Operations mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction The Border Gateway Protocol (BGP) is vulnerable to route hijacks and route leaks . Some existing BGP extensions can partially solve or alleviate these problems. Resource Public Key Infrastructure (RPKI) based route origin validation (RPKI-ROV) and Signed Prefix List-based Route Origin Verification (SPL-ROV) can be used to detect and filter accidental mis-originations. BGPsec is designed to provide security for the AS-path attribute in the BGP UPDATE message . and Autonomous System Provider Authorization (ASPA) aim at detecting and mitigating accidental route leaks. However, there are still some issues that need to be addressed. ASPA is a genius mechanism to verify BGP AS-path attribute content, which only stores customer-to-provider information in RPKI. Though the validity of the ASPA objects is verified, the relationship between two BGP neighbors cannot be attested. When two ASes announce mutually exclusive relationships, for example, AS A says AS B is its Provider and AS B says AS A is its Provider, no other ASes can verify their real relationships. The Route Path Authorizations (RPA) is a Resource Public Key Infrastructure (RPKI) object that attests to the complete routing paths description an Autonomous System (AS) would obey in Border Gateway Protocol (BGP) route propagation. This document specifies an RPA-based AS Path Verification methodology to prevent AS path forgery in the BGP AS-path attribute of advertised routes. RPA-based AS_PATH verification also detects and mitigates route leaks.

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 when, and only when, they appear in all capitals, as shown here.

Definition of Commonly Used Terms The definitions and semantics of Route Path Authorizations (RPA) provided in are applied here.

• Route is ineligible: The term has the same meaning as in , i.e., "route is ineligible to be installed in Loc-RIB and will be excluded from the next phase of route selection."
• AS-path: This term defines a sequence of ASes listed in the BGP UPDATE AS_PATH or AS4_PATH attribute. This document uses the terms AS-path, AS_PATH, and AS4_PATH interchangeably.
• Weakly Valid: This is one of the verification results of using RPA objects to verify AS_PATH, indicating that at least one AS in the path is validated as VALID by RPA, while all other ASes yield an UNKNOWN verification result.
• VRPP: Validated RPA Payload (see ).

Route Path Authorizations (RPA) Route Path Authorizations (RPA) objects encapsulate the routing paths description of an Autonomous System (AS). Similar to most RPKI-signed objects, the verification results for RPA are classified into four distinct states: Valid, Weakly Valid, Invalid, and Unknown. It is RECOMMENDED that all routing paths be explicitly enumerated within a single RPA object. However, due to the inherent complexity of routing paths, providing a comprehensive list can be challenging. Consequently, it is RECOMMENDED to include routing paths with the origins/prefixes field designated as 'NONE' when the issuer is unable to specify which routes will be propagated from previousHops to nextHops. It may have a few of these routePathBlocks with the origins/prefixes field set as 'NONE'. In general, there exists a singular valid RPA object corresponding to a specific asID. However, in instances where multiple valid RPA objects containing the same asID are present, the union of the resulting routePathBlocks members constitutes the comprehensive set of members. This complete set, which may arise from either a single or multiple RPAs, is locally maintained by a Relying Party (RP) or a compliant router. Such an object is referred to as the Validated RPA Payload (VRPP) for the asID. Except for the empty origins, there would also be empty previousHops and nextHops in a routing path. It is NOT RECOMMENDED to describe routing path without nextHops as this does not help verify BGP AS_PATH. It is REQUIRED at least one routing path description in an RPA object. Otherwise, the empty RPA object means no routes can be transited or transformed from this asID.

AS_PATH Verification Using RPA RPAs describe the local routing paths of an AS. They can be used to verify the AS_PATH attribute in BGP UPDATE messages. Upon receiving a BGP UPDATE message, the AS_PATH verification procedure is initiated. This process involves querying the corresponding RPA for each AS along the path individually. If the prefixes field of an RPA object is non-empty, prefix matching is performed. Furthermore, if the origins field is present, additional validations are carried out using ROA-based Route Origin Validation (ROA-ROV) as defined in and SPL-ROV as defined in . An eBGP router that conforms to this specification MUST implement RPA-based AS_PATH verification procedures defined below. These procedures operates in a two-stage process:

1. Per-AS Verification: At the first stage, each AS in the AS_PATH is evaluated individually based on its corresponding RPA object, if available. This stage validates whether each AS's declared routing path is consistent with the received AS_PATH attributes.
2. Path-Level Verification: At the second stage, the system derives an overall path verification result by aggregating the outcomes of the per-AS verifications. The final status reflects the consistency and completeness of the entire path with respect to the available RPAs.

Per-AS Verification Algorithm The verification algorithm is applied to each individual AS in the AS_PATH of the received BGP UPDATE message. For each AS, its corresponding RPA object is examined to verify attributes such as prefix scope, authorized neighbors, and origin declaration. The verification result for each AS is one of: Valid, Invalid, or Unknown, depending on the presence and content of the RPA and its alignment with the BGP announcement.

1. Query the RPA associated with AS.
2. If RPA is not available, then set AS verification result is Unknown.
3. Perform authorized neighbors matching against the AS_PATH. If RPA.previousHops or RPA.nextHops do not match the AS_PATH context, set AS verification result is Invalid.
4. If RPA.prefixes is non-empty, perform prefix matching with the UPDATE message.
5. If RPA.origins is non-empty, perform ROA-ROV and SPL-ROV validation.
6. If both prefix and origin checks succeed, set AS verification result is Valid.
7. If either check fails, set AS verification result is Invalid.
8. Else, set AS verification result is Unknown.

Path-Level Verification Algorithm This process determines whether the sequence of ASes in the AS_PATH attribute conforms to the collectively declared routing paths published in RPAs. By aggregating the per-AS verification results, the algorithm computes a comprehensive path verification result for each received BGP route.

1. Let valid_count is set equal to number of ASes with Valid. Let invalid_count is set equal to number of ASes with Invalid. Let unknown_count is set equal to number of ASes with Unknown.
2. If valid_count == 0 AND invalid_count == 0, then the verification result is Unknown.
3. Else, if invalid_count == 0 AND unknown_count == 0, then the verification result is Valid.
4. Else, if valid_count >= 1 AND invalid_count == 0, then the verification result is Weakly Valid.
5. Else, if invalid_count >= 1, then the verification result is Invalid.
6. Else, the verification result is Unkown.

Mitigation Policy The specific configuration of a mitigation policy based on AS_PATH verification using RPA is at the discretion of the network operator. However, the following mitigation policy is highly recommended. Invalid: If the AS_PATH is determined to be Invalid, then the route SHOULD be considered ineligible for route selection and MUST be kept in the Adj-RIB-In for potential future re-evaluation (see ). Valid, Weakly Valid, or Unknown: When a route is evaluated as Unknown (using RPA-based AS_PATH verification), it SHOULD be treated at the same preference level as a route evaluated as Valid. But Valid has the highest priority in BGP route selection while Weakly Valid has a second priority.

Operational Considerations Multiple valid RPA objects that contain the same asID could exist. In such a case, the union of these objects forms the complete routing path set of this AS. For a given asID, it is RECOMMENDED that a CA maintains a single RPA. If an AS holder publishes an RPA, then relying parties SHOULD assume that this object is complete for that issuer AS. If one AS receives a BGP UPDATE message with the issuer AS in the AS-path attribute which cannot match any routing path of this issuer AS, it implies that there is an AS-path forgery in this message.

Security Considerations TODO Security

IANA Considerations This document has no IANA actions.

References Normative References This document discusses the Border Gateway Protocol (BGP), which is an inter-Autonomous System routing protocol. The primary function of a BGP speaking system is to exchange network reachability information with other BGP systems. This network reachability information includes information on the list of Autonomous Systems (ASes) that reachability information traverses. This information is sufficient for constructing a graph of AS connectivity for this reachability from which routing loops may be pruned, and, at the AS level, some policy decisions may be enforced. BGP-4 provides a set of mechanisms for supporting Classless Inter-Domain Routing (CIDR). These mechanisms include support for advertising a set of destinations as an IP prefix, and eliminating the concept of network "class" within BGP. BGP-4 also introduces mechanisms that allow aggregation of routes, including aggregation of AS paths. This document obsoletes RFC 1771. [STANDARDS-TRACK] This document describes an architecture for an infrastructure to support improved security of Internet routing. The foundation of this architecture is a Resource Public Key Infrastructure (RPKI) that represents the allocation hierarchy of IP address space and Autonomous System (AS) numbers; and a distributed repository system for storing and disseminating the data objects that comprise the RPKI, as well as other signed objects necessary for improved routing security. As an initial application of this architecture, the document describes how a legitimate holder of IP address space can explicitly and verifiably authorize one or more ASes to originate routes to that address space. Such verifiable authorizations could be used, for example, to more securely construct BGP route filters. This document is not an Internet Standards Track specification; it is published for informational purposes. To help reduce well-known threats against BGP including prefix mis- announcing and monkey-in-the-middle attacks, one of the security requirements is the ability to validate the origination Autonomous System (AS) of BGP routes. More specifically, one needs to validate that the AS number claiming to originate an address prefix (as derived from the AS_PATH attribute of the BGP route) is in fact authorized by the prefix holder to do so. This document describes a simple validation mechanism to partially satisfy this requirement. [STANDARDS-TRACK] This document describes BGPsec, an extension to the Border Gateway Protocol (BGP) that provides security for the path of Autonomous Systems (ASes) through which a BGP UPDATE message passes. BGPsec is implemented via an optional non-transitive BGP path attribute that carries digital signatures produced by each AS that propagates the UPDATE message. The digital signatures provide confidence that every AS on the path of ASes listed in the UPDATE message has explicitly authorized the advertisement of the route. This document defines a standard profile for Route Origin Authorizations (ROAs). A ROA is a digitally signed object that provides a means of verifying that an IP address block holder has authorized an Autonomous System (AS) to originate routes to one or more prefixes within the address block. This document obsoletes RFC 6482. Route leaks are the propagation of BGP prefixes that violate assumptions of BGP topology relationships, e.g., announcing a route learned from one transit provider to another transit provider or a lateral (i.e., non-transit) peer or announcing a route learned from one lateral peer to another lateral peer or a transit provider. These are usually the result of misconfigured or absent BGP route filtering or lack of coordination between autonomous systems (ASes). Existing approaches to leak prevention rely on marking routes by operator configuration, with no check that the configuration corresponds to that of the External BGP (eBGP) neighbor, or enforcement of the two eBGP speakers agreeing on the peering relationship. This document enhances the BGP OPEN message to establish an agreement of the peering relationship on each eBGP session between autonomous systems in order to enforce appropriate configuration on both sides. Propagated routes are then marked according to the agreed relationship, allowing both prevention and detection of route leaks. Zhongguancun Laboratory Tsinghua University Tsinghua University Tsinghua University Tsinghua University This document defines a Cryptographic Message Syntax (CMS) protected content type for Forwarding Commitments (FCs) objects used in Resource Public Key Infrastructure (RPKI). An FC is a digitally signed object that provides a means of verifying whether an IP address block is received from AS a to AS b and announced from AS b to AS c. When validated, an FC's eContent can be used for the detection and mitigation of route hijacking, especially providing protection for the AS_PATH attribute in BGP-UPDATE. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References A systemic vulnerability of the Border Gateway Protocol routing system, known as "route leaks", has received significant attention in recent years. Frequent incidents that result in significant disruptions to Internet routing are labeled route leaks, but to date a common definition of the term has been lacking. This document provides a working definition of route leaks while keeping in mind the real occurrences that have received significant attention. Further, this document attempts to enumerate (though not exhaustively) different types of route leaks based on observed events on the Internet. The aim is to provide a taxonomy that covers several forms of route leaks that have been observed and are of concern to the Internet user community as well as the network operator community. This document recommends ways to reduce the forged-origin hijack attack surface by prudently limiting the set of IP prefixes that are included in a Route Origin Authorization (ROA). One recommendation is to avoid using the maxLength attribute in ROAs except in some specific cases. The recommendations complement and extend those in RFC 7115. This document also discusses the creation of ROAs for facilitating the use of Distributed Denial of Service (DDoS) mitigation services. Considerations related to ROAs and RPKI-based Route Origin Validation (RPKI-ROV) in the context of destination-based Remotely Triggered Discard Route (RTDR) (elsewhere referred to as "Remotely Triggered Black Hole") filtering are also highlighted. A BGP speaker performing policy based on the Resource Public Key Infrastructure (RPKI) should not issue route refresh to its neighbors because it has received new RPKI data. This document updates RFC 8481 by describing how to avoid doing so by either keeping a full Adj-RIB-In or saving paths dropped due to ROV (Route Origin Validation) so they may be reevaluated with respect to new RPKI data. Yandex JetLend Internet Initiative Japan Vigil Security, LLC Workonline This document defines a Cryptographic Message Syntax (CMS) protected content type for Autonomous System Provider Authorization (ASPA) objects for use with the Resource Public Key Infrastructure (RPKI). An ASPA is a digitally signed object through which the issuer (the holder of an Autonomous System identifier), can authorize one or more other Autonomous Systems (ASes) as its upstream providers. When validated, an ASPA's eContent can be used for detection and mitigation of route leaks. Fastly APNIC This document defines a "Signed Prefix List", a Cryptographic Message Syntax (CMS) protected content type for use with the Resource Public Key Infrastructure (RPKI) to carry the complete list of prefixes which an Autonomous System (the subject AS) may originate to all or any of its routing peers. The validation of a Signed Prefix List confirms that the holder of the subject AS produced the object, and that this list is a current, accurate and complete description of address prefixes that may be announced into the routing system originated by the subject AS. USA National Institute of Standards and Technology Fastly USA National Institute of Standards and Technology The Signed Prefix List (SPL) is an RPKI object that attests to the complete list of prefixes which an Autonomous System (AS) may originate in the Border Gateway Protocol (BGP). This document specifies an SPL-based Route Origin Verification (SPL-ROV) methodology and combines it with the ROA-based ROV (ROA-ROV) to facilitate an integrated mitigation strategy for prefix hijacks and AS forgery. The document also explains the various BGP security threats that SPL can help address and provides operational considerations associated with SPL-ROV deployment.

Acknowledgments TODO acknowledge.