A Profile of Signed SAVNET-Peering Information (SiSPI) Object for Deploying Inter-domain SAVNET

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Table of Contents

1. Introduction

Attacks based on source IP address spoofing, such as reflective DDoS and flooding attacks, continue to present significant challenges to Internet security. Mitigating these attacks in inter-domain networks requires effective source address validation (SAV). While BCP84 [RFC3704] [RFC8704] offers some SAV solutions, such as ACL-based ingress filtering and uRPF-based mechanisms, existing inter-domain SAV mechanisms have limitations in terms of validation accuracy and operational overhead in different scenarios [I-D.ietf-savnet-inter-domain-problem-statement].¶

Inter-domain SAVNET [I-D.ietf-savnet-inter-domain-architecture] proposes to exchange SAV-specific information among ASes to solve the problems of existing inter-domain SAV mechanisms. Two SAV-specific information exchanging protocols (or SAVNET protocols for short) are shown to achieve higher validation accuracy and lower operational overhead in large-scale emulations [emu-9-savs]. However, operators face significant difficulties in deploying SAVNET protocols. To benefit Internet routing, supporting incremental deployment is an essential requirement of SAVNET protocols [I-D.ietf-savnet-inter-domain-problem-statement]. As illustrated in the Section 9.2 of [I-D.ietf-savnet-inter-domain-architecture], during the partial or incremental deployment of SAVNET protocols, protocol-speaking agents (or SAVNET agents) within the SAVNET-adopting ASes need to find and establish connections with other SAVNET agents. Currently, there is no mechanism to achieve this automatically, and operators of SAVNET-adopting ASes must configure peering SAVNET relationship by hand, which is slow and error-prone.¶

The neighbor discovery and connection setup process of SAV protocols can be done in an automatic and correct manner, with the introduction of a public registry that contains all ASes which both deploy SAVNET and are willing to setup SAVNET peering relationships. A newly adopting AS can use this registry as a reference, and pick appropriate ASes to setup SAVNET peering relationship.¶

The Resource Public Key Infrastructure (RPKI) is the most suitable to host this public registry, because the primary purpose of RPKI is to improve routing security [RFC6480], and defending against address spoofing is a main aspect of routing security. To this end, a mechanism is needed to facilitate holders of Automous System (AS) identifiers to declare their deployment of SAVNET [I-D.ietf-savnet-inter-domain-architecture]. The digitally Signed SAVNET-Peering Information (SiSPI) object described in this document serves the function.¶

A SiSPI object is a cryptographically verifiable attestation signed by the holder of an AS identifier. It contains the identification information of one AS, which means the listed AS has deployed SAVNET and can perform SAV on its data plane.¶

The SiSPI object makes use of the template for RPKI digitally signed objects [RFC6488], which defines a Crytopgraphic Message Syntax (CMS) [RFC5652] wrapper for the SiSPI content as well as a generic validation procedure for RPKI signed objects. In accordance with Section 4 of [RFC6488], this document defines:¶

1. The object identifier (OID) that identifies the SiSPI object. This OID appears in the eContentType field of the enCapContentInfo object as well as the content-type signed attribute within the signerInfo structure.¶

2. The ASN.1 syntax for the SiSPI eContent, which is the payload that specifies the AS deploying SAVNET. The SiSPI eContent is encoded using the ASN.1 Distinguished Encoding Rules (DER) [X.690].¶

3. The steps required to validate a SiSPI beyond the validation steps specified in [RFC6488].¶

2. The SiSPI ContentType

The content-type for a SiSPI object is defined as id-ct-rpkiSiSPI, which has the numerical value of 1.2.840.113549.1.9.16.1.TBD. This OID MUST appear both within the eContentType in the encapContentInfo structure as well as the ContentType signed attribute within the signerInfo structure (see [RFC6488]).¶

3. The SiSPI eContent

The content of a SiSPI object identifies a single AS that has deployed SAVNET [I-D.ietf-savnet-inter-domain-architecture] for inter-domain SAV and a list of its IP addresses. The eContent of a SiSPI object is an instance of SAVNETAttestation, formally defined by the following ASN.1 [X.680] module:¶

RpkiSiSPI-2026
     { iso(1) member-body(2) us(840) rsadsi(113549)
       pkcs(1) pkcs9(9) smime(16) mod(0)
       id-mod-rpkiSiSPI-2026-2026(TBD0) }

DEFINITIONS EXPLICIT TAGS ::=
BEGIN

IMPORTS
  CONTENT-TYPE
  FROM CryptographicMessageSyntax-2010 -- in [RFC6268]
    { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
      pkcs-9(9) smime(16) modules(0) id-mod-cms-2009(58) } ;

ct-rpkiSiSPI CONTENT-TYPE ::=
  { TYPE SAVNETAttestation IDENTIFIED BY id-ct-rpkiSiSPI }

id-ct-rpkiSiSPI OBJECT IDENTIFIER ::=
  { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
    pkcs-9(9) id-smime(16) id-ct(1) TBD1 }

SAVNETAttestation ::= SEQUENCE {
  version [0]   INTEGER DEFAULT 0,
  asID          ASID,
  addresses     SEQUENCE OF IPFamilyAddresses }

ASID ::= INTEGER (0..4294967295)

IPFamilyAddresses ::= SEQUENCE {
  ipFamily    IP-ADDRESS-FAMILY.&afi ({IPAddressFamilySet}),
  ipAddresses IP-ADDRESS-FAMILY.&IPAddresses ({IPAddressFamilySet}{@ipFamily}) }

IP-ADDRESS-FAMILY ::= CLASS {
     &afi          OCTET STRING (SIZE(2)) UNIQUE,
     &IPAddresses
   } WITH SYNTAX { AFI &afi IP &IPAddresses }

IPAddressFamilySet IP-ADDRESS-FAMILY ::= { ipAddressFamilyIPv4 | ipAddressFamilyIPv6 }

ipAddressFamilyIPv4 IP-ADDRESS-FAMILY ::= { AFI afi-IPv4 IP IPv4Addresses }

ipAddressFamilyIPv6 IP-ADDRESS-FAMILY ::= { AFI afi-IPv6 IP IPv6Addresses }

afi-IPv4 OCTET STRING ::= '0001'H

afi-IPv6 OCTET STRING ::= '0002'H

IPv4Addresses ::= SEQUENCE (SIZE(1..MAX)) OF IPAddress{ub-IPv4}

IPv6Addresses ::= SEQUENCE (SIZE(1..MAX)) OF IPAddress{ub-IPv6}

ub-IPv4 INTEGER ::= 32

ub-IPv6 INTEGER ::= 128

IPAddress {INTEGER: ub} ::= BIT STRING (SIZE(0..ub))

END

Note that this content appears as the eContent within the encapContentInfo as specified in [RFC6488].¶

4. SiSPI Validation

Before using a SiSPI object, a relying party MUST validate the object. In addition to all validation checks specified in [RFC6488], a relying party MUST perform the SiSPI-specific validation checks defined below.¶

• The CMS eContent MUST conform to the ASN.1 syntax and constraints specified in Section 3.¶

• The AS Identifier Delegation Extension [RFC3779] MUST be present in the end-entity (EE) certificate (contained within the SiSPI object), and the asID in the SiSPI object eContent MUST be contained within the set of AS numbers specified by the EE certificate's AS Identifier Delegation Extension.¶

• The EE certificate's AS Identifier Delegation Extension MUST NOT contain any ''inherit'' elements.¶

• The IP Address Delegation Extension [RFC3779] MUST be absent.¶

The pseudocode for SiSPI validation is as follows:¶

function ValidateSiSPI(sispiObject, eeCertificate):
    // Step 1: Validate the SiSPI object using the generic RPKI
    //         validation procedure.
    // This includes checking the CMS wrapper, signature, and
    //         certification path.
    if not IsValidRPKISignedObject(sispiObject):
        return False, "Invalid RPKI Signed Object"

    // Step 2: Check the content-type of the SiSPI object.
    if not sispiObject.eContentType == id-ct-rpkiSiSPI:
        return False, "Invalid content-type"

    // Step 3: Parse the eContent of the SiSPI object as
    //         SAVNETAttestation.
    sispiContent = ParseSAVNETAttestation(sispiObject.eContent)
    if sispiContent is None:
        return False, "Unable to parse SAVNETAttestation"

    // Step 4: Verify the SAVNETAttestation version.
    if not (sispiContent.version exists and sispiContent.version==0):
        return False, "Invalid version"

    // Step 5: Validate the AS Identifier Delegation Extension in
    //         the EE certificate.
    if not ValidateASIdExt(eeCertificate, sispiContent.asID):
        return False, "AS Identifier Extension validation failed"

    // Step 6: Ensure the EE certificate's AS Identifier Delegation
    //         Extension does not contain 'inherit'.
    if "inherit" in eeCertificate.asIdentifiers:
        return False,
               "AS Identifier Delegation Extension contains 'inherit'"

    // Step 7: Ensure the IP Address Delegation Extension is absent.
    if HasIPAddressDelegationExtension(eeCertificate):
        return False, "IP Address Delegation Extension is present"

    // Step 8: Determine if all validation checks are successful.
    return True, "SiSPI object is valid"

function ValidateASIdentifierExtension(eeCertificate, asID):
    // Check if the asID is within the set of AS numbers
    //   specified by the AS Identifier Delegation Extension.
    return asID in eeCertificate.asIdentifiers

function HasIPAddressDelegationExtension(eeCertificate):
    // Check for the presence of the IP Address Delegation
    //   Extension.
    return "ipAddresses" in eeCertificate.extensions

5. IANA Considerations

Name                              | OID                                    | Reference
-----------------------------------------------------------------------------------------------------
Signed SAVNET-Peering Information | 1.2.840.113549.1.9.16.1.TBD            | draft-chen-sidrops-sispi

Filename
Extension | RPKI Object                       | Reference
------------------------------------------------------------------------
   .sav   | Signed SAVNET-Peering Information | This document

Decimal | Description                | Reference
---------------------------------------------------------------
TBD     | id-mod-rpkiSiSPI-2026-2026 | This document

Type name: application
Subtype name: rpki-sispi
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: binary
Security considerations: Carries Signed SAVNET-Peering Information.
  This media type contains no active content. See
  Section 4 of draft-chen-sidrops-sispi for further information.
Interoperability considerations: None
Published specification: draft-chen-sidrops-sispi
Applications that use this media type: RPKI operators
Additional information:
  Content: This media type is a signed object, as defined
      in {{RFC6488}}, which contains a payload of an AS identifer
      as defined in draft-chen-sidrops-sispi.
Magic number(s): None
File extension(s): .sav
Macintosh file type code(s):
Person & email address to contact for further information:
Li Chen <lichen@zgclab.edu.cn>
Intended usage: COMMON
Restrictions on usage: None
Change controller: IETF

6. Using SiSPI

A router can use the AS_Path from BGP announcements, ASPA objects, and SiSPI to find the closest ASes to set up SAVNET peering, as described below:¶

1. BGP AS_Paths Analysis:¶

   • Collect AS paths from BGP announcements.¶

   • Determine the frequency or preference of certain AS paths based on routing policies, which may involve path attributes like AS path length, origin type, local preference, and MED (Multi-Exit Discriminator).¶

2. ASPA Verification:¶

   • Use ASPA objects to verify the legitimacy of customer-provider AS relationships.¶

   • Where ASPA information is available, ASPA-based path verification MAY be used as an additional signal for assessing candidate AS paths. The absence of sufficient ASPA information does not imply that an AS path is invalid.¶

3. Peering Candidates Determination:¶

   • Identify the ASes that frequently appear on the preferred paths to various destinations, implying they are topologically 'close' or significant transit providers.¶

   • Among these ASes, an operator MAY rank candidates according to routing-related metrics, such as their occurrence across selected AS paths or their AS-path distance from the local AS. Such metrics indicate routing relevance but do not by themselves represent traffic volume. Traffic-aware ranking requires additional local traffic measurements.¶

4. SiSPI Objects Utilization:¶

   • Retrieve SiSPI objects from the RPKI repository to determine which ASes have deployed SAVNET.¶

   • Filter the previously identified candidate ASes by checking whether they have a valid SiSPI object, which would indicate their readiness to establish SAVNET peering.¶

5. Peering Candidates Selection:¶

   • From the set of candidate ASes with valid SiSPI objects, select candidates for SAVNET peering based on their rankings.¶

   • The selection criteria may include additional factors such as existing peering policies, traffic volumes, and peering agreements.¶

6. Peering Establishment:¶

   • Initiate peering negotiations with the selected candidate ASes.¶

   • Upon successful negotiation, establish SAVNET peering relationships and configure the necessary SAVNET protocols.¶

A SAVNET implementation MAY use validated SiSPI objects together with locally available routing and policy information to identify candidate SAVNET peers. One possible procedure is:¶

1. Obtain locally selected BGP routes and their AS paths.¶

2. Optionally apply available routing-security information, such as ASPA validation results.¶

3. Identify ASes of operational interest according to local policy.¶

4. Retain ASes for which valid SiSPI objects are available.¶

5. Obtain the SAVNET agent endpoints from the corresponding SiSPI objects.¶

6. Apply local policy and establish SAVNET peering using the authentication and connection procedures defined by the applicable SAVNET protocol.¶

The specific ranking or selection algorithm is a matter of local policy and is outside the scope of this document.¶

7. Newly SAVNET-adopting ASes

The newly SAVNET-adopting ASes need to register the SiSPI object proactively to help other SAVNET-adopting ASes find it and establish SAVNET peering relationships, as well as using the SiSPI objects to establish SAVNET peering relationships with other SAVNET-adopting ASes.¶

To register the SiSPI object, the newly SAVNET-adopting ASes should share its information as described in Section 3.¶

To establish SAVNET peering relationships with other SAVNET-adopting ASes, the newly SAVNET-adopting ASes should collect BGP announcements, ASPA objects, and SiSPI objects, and run the procedures described in Section 6.¶

8. Security Considerations

The security considerations of [RFC6481], [RFC7935], and [RFC6488] also apply to the SiSPI object.¶

9. References

Authors' Addresses