A Profile for Traffic Origin Authorizations (TOAs)

Source Address Validation (SAV) aims to detect and discard data packets that use a spoofed source IP address. The fundamental concept of the current practice is directionality: for data packets using a given source IP address, only those coming from a specific direction are considered legitimate. BCP84 introduces a more structured direction-based logic, i.e., identifying the incoming directions for traffic of a given source AS and determining the source prefix space that the AS is authorized to use. To support such validation, a mechanism is needed to allow entities to verify that an AS has been authorized to originate traffic using one or more prefixes as the source IP address. One of the main challenges is that the current infrastructure for validating the right to originate traffic with a given source address has so far been built almost entirely on top of mechanisms designed to validate the right to originate routing information for destination-based routing. In most cases, where the two use cases overlap, this approach works reasonably well. However, when the traffic origin diverges from the route origin, ambiguity and misalignment arise between the intended use case and the mechanisms being applied. The purpose of a Traffic Origin Authorization (TOA) is to explicitly authorize an AS to originate traffic using a given prefix as a source address, even when that AS is not authorized to originate any BGP routes to that prefix. A TOA provides a clear separation between the authorization to originate routing information and the authorization to originate data traffic. This distinction is particularly important in scenarios where traffic is unidirectional and there is no need to attract return traffic via route announcements, or where the return traffic is intentionally directed to another location. Examples include: Content Delivery Networks (CDNs) using Direct Server Return (DSR): Users send requests to an anycast service address that is advertised by one AS. The response traffic is generated by a content server located in a different AS, but uses the same anycast service address as the source IP address. The AS hosting the content server does not advertise a route for the anycast prefix because it does not attract request traffic from users (see ). IP multicast: Sources send multicast traffic to receivers via multicast mechanisms and do not need to advertise routes to attract return traffic from receivers. Traffic using non-routed source prefixes: Control or operational traffic may use IP addresses that are never advertised in BGP. These non-routed prefixes are used solely for protocol operation or internal purposes, and the traffic origin does not announce routes for these prefixes. The TOA makes use of the template for RPKI digitally signed object , which defines a Cryptographic Message Syntax (CMS) wrapper for a generic validation procedure for RPKI signed objects. Therefore, to complete the specification of the TOA (see Section 4 of ), this document defines: The OID that identifies the signed object as being a TOA. (This OID appears within the eContentType in the encapContentInfo object as well as the content-type signed attribute in the signerInfo object.) The ASN.1 syntax for the TOA eContent. (This is the payload that specifies the ASes being authorized to originate traffic as well as the prefixes that the ASes may use as the source IP address.) The TOA eContent is ASN.1 encoded using the Distinguished Encoding Rules (DER) . Additional steps required to validate TOAs (in addition to the validation steps specified in ). The content of a TOA identifies a list of one or more ASes that have been authorized by the IP address block holder to originate traffic and a list of one or more IP address prefixes within the address block that will be used as the source IP address. The IP address block holder can register one or more TOAs to authorize which ASes can originate traffic using specific prefixes within the block as the source IP address. By registering TOAs, IP address block holders can prevent their source IP addresses from being forged by unauthorized ASes, while allowing legitimate but non-announcing ASes to originate traffic. AS operators can leverage TOAs to improve the accuracy and robustness of SAV, thereby enhancing protection against source address spoofing attacks.

The content-type for a TOA is defined as id-ct-trafficOriginAuthz and has the numerical value of 1.2.840.113549.1.9.16.1.TBD. This OID MUST appear within both the eContentType in the encapContentInfo object and the content-type signed attribute in the signerInfo object (see ).

The content of a TOA identifies a list of one or more ASes that have been authorized by the address block holder to originate traffic and a list of one or more IP address prefixes within the address block that will be used as the source IP address. A TOA is formally defined as:

The version number of the TrafficOriginAttestation entry MUST be 0.

The asSet element contains a set of AS numbers that are authorized to originate traffic using source IP addresses within the given IP address prefixes.

The ipAddrBlocks element encodes the set of IP address prefixes that the specified set of ASes is authorized to use as source addresses when originating traffic.

Within the TOAIPAddressFamily structure, the addressFamily element contains the Address Family Identifier (AFI) of an IP address family. Each addressFamily MUST be either 0001 or 0002. There MUST be only one instance of TOAIPAddressFamily per unique AFI in the TOA. The addresses field contains IP prefixes as a sequence of type TOAIPAddress.

This element is of type BIT STRING and represents a single IP address prefix .

To validate a TOA, the Relying Party (RP) MUST perform all the validation checks specified in as well as the following additional specific validation steps: The IP address delegation extension is present in the end-entity (EE) certificate (contained within the TOA), and every IP address prefix in the TOA payload is contained within the set of IP addresses specified by the EE certificate's IP address delegation extension. The EE certificate's IP address delegation extension MUST NOT contain "inherit" elements as described in . The Autonomous System identifier delegation extension described in is not used in TOAs and MUST NOT be present in the EE certificate. The TOA content fully conforms with all requirements specified in Sections 2 and 3. If any of the above checks fail, the TOA MUST be considered invalid and an error SHOULD be logged.

The security considerations of , , , and also apply to the TOA object.

Operators should exercise care when deciding to register a Traffic Origin Authorization (TOA). A TOA is primarily useful in scenarios where the traffic origin AS and the route origin AS differ. In such cases, registering a TOA provides the necessary authorization for traffic origination while avoiding ambiguity between routing and traffic authorization. Conversely, when the same AS is both authorized to originate routes (via an existing Route Origin Authorization (ROA) ) and to originate traffic from a given prefix, creating an duplicated TOA would add unnecessary storage and transmission overhead in the RPKI system. Therefore, operators are RECOMMENDED to follow these practices: Operators SHOULD NOT register a TOA that is identical to or covered by an existing ROA, unless there are valid operational reasons. TOA registrations SHOULD be periodically reviewed and updated to reflect current operational practices. Another operational consideration concerns situations where a prefix holder has already signed a ROA for an AS and intends to register a TOA that covers multiple ASNs and prefixes. For example, suppose a prefix holder has an existing ROA {AS1, Prefix1} and wishes to create a TOA {(AS1, AS2, AS3), (Prefix1, Prefix2, Prefix3)}. In this case, the portion {AS1, Prefix1} is already covered by the ROA and is therefore redundant within the TOA. A straightforward way to avoid redundancy would be to split the TOA into smaller objects, such as {(AS1), (Prefix2, Prefix3)} and {(AS2, AS3), (Prefix1, Prefix2, Prefix3)}. However, doing so may unnecessarily increase operational complexity and management overhead. Therefore, it is RECOMMENDED to register a single consolidated TOA covering all relevant ASNs and prefixes. The existence of an overlapping ROA does not invalidate the TOA but should be understood in its respective scope: the ROA authorizes route origin, while the TOA authorizes traffic origin. This approach maintains clear semantics between routing and traffic authorization while minimizing operational burden. Following these recommendations minimizes overhead on the RPKI system while ensuring that TOAs are deployed effectively to enhance Source Address Validation (SAV).

Without TOAs, current SAV mechanisms (e.g., BAR-SAV ) typically use BGP data, ROAs, or IRR route objects to determine the legitimate source IP address space of a given AS. However, due to the asymmetry between prefixes used as the source IP address and prefixes advertised into the routing system (as mentioned in Section 1), using BGP data, ROAs, and IRR route objects to perform SAV will cause improper blocks (i.e., blocking legitimate data packets). By registering TOAs, IP address block holders can prevent their source IP addresses from being forged by unauthorized ASes, while allowing legitimate but non-announcing ASes to originate traffic. AS operators can leverage TOAs to improve the accuracy and robustness of SAV, thereby enhancing protection against source address spoofing attacks. Note: If different ASes are authorized for overlapping prefixes (e.g., there are two TOAs {AS1, 203.0.113.0/24} and {AS2, 203.0.113.0/28}), both AS1 and AS2 MUST be interpreted as authorized for the more specific prefix. If the intent is to restrict AS1 from the more specific prefix, the first TOA must be modified to explicitly exclude the more specific prefix.

This section is to be removed before publishing as an RFC. Recent discussions on the SAVNET mailing list have considered whether it would be feasible to create a special ROA for an AS that is not authorized to originate a route to a given prefix, as an alternative to implementing TOA. Doing so would require extending ROAs or overloading their semantics to cover this use case, and may require modifications to existing Route Origin Validation (ROV) processing to prevent these special ROAs from being used. The TOA authors consulted ASN.1 experts on this approach, who strongly advised against it. Other participants also recommended against overloading ROA semantics. Accordingly, the current consensus among the TOA authors and many SAVNET participants is that defining a dedicated TOA object represents a more appropriate and robust solution. Some discussions have also proposed creating a conventional ROA for such scenarios, even though the AS is not authorized to originate routes to the given prefix. However, our analysis indicates that registering such a ROA introduces additional risks of forged-origin hijacking: an attacker could impersonate the AS listed in the ROA and announce a BGP route that would be considered RPKI-valid. Fundamentally, the choice of how to authorize the traffic origin rests with the prefix holder . If the prefix holder wishes ROAs to include only ASes authorized to originate routes to its prefix, there is a clear need to register a TOA to authorize other ASes to source traffic from the prefix. Conversely, if the prefix holder is unconcerned about forged-origin hijacking or other potential risks, they may instead choose to register a conventional ROA.

IANA is requested to allocate the following in the "SMI Security for S/MIME CMS Content Type (1.2.840.113549.1.9.16.1)" registry: Decimal Description Reference TBD id-ct-trafficOriginAuthz draft-qin-savnet-toa

Please add an item for the TOA file extension to the RPKI Signed Object registry (https://www.iana.org/assignments/rpki/rpki.xhtml#signed-objects) as follows: Name OID Reference Traffic Origin Authorization 1.2.840.113549.1.9.16.1.TBD draft-qin-savnet-toa

Please add an item for the TOA file extension to the "RPKI Repository Name Scheme" registry created by as follows: Filename Extension RPKI Object Reference .toa Traffic Origin Authorization draft-qin-savnet-toa

IANA is requested to allocate the following in the "SMI Security for S/MIME Module Identifier (1.2.840.113549.1.9.16.0)" registry: Decimal Description Reference TBD id--rpkiTOA-2026 draft-qin-savnet-toa

The IANA is requested to register the media type application/rpki-toa in the "Media Type" registry as follows:

Intended usage: COMMON Restrictions on usage: None Change controller: IETF]]>

The authors would like to thank Jeffrey Haas for his valuable contributions in enriching the use cases and clarifying the challenges described in Section 1. Special thanks also go to Job Snijders, who provided expert feedback on the ASN.1 considerations discussed in Section 8.