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 [inter-domain-ps].¶

Inter-domain SAVNET [savnet] 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 [inter-domain-ps]. As illustrated in the Section 9.2 of [savnet], 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 [savnet]. 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 Content Type

The content-type for a SiSPI object is defined as SAVNETAuthz, which has the numerical value of 1.2.840.113549.1.9.16.1.52 (suggested). This OID MUST appear both within the eContentType in the encapContentInfo structure as well as the content-type 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 [savnet] for inter-domain SAV. The eContent of a SiSPI object is an instance of SAVNETAttestation, formally defined by the following ASN.1 [X.680] module:¶

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

ASID ::= INTEGER (0..4294967295)
IPFamilyAddresses ::= SEQUENCE {
  IPFamily ADDRESS-FAMILY.&afi ({AddressFamilySet}),
  IPAddresses ADDRESS-FAMILY.&ip ({AddressFamilySet}{@addressFamily}) }

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

AddressFamilySet ADDRESS-FAMILY ::= { addressFamilyIPv4 | addressFamilyIPv6 }

addressFamilyIPv4 ADDRESS-FAMILY ::= { AFI afi-IPv4 IP IPv4ip }
addressFamilyIPv6 ADDRESS-FAMILY ::= { AFI afi-IPv6 IP IPv6ip }

afi-IPv4 OCTET STRING ::= '0001'H
afi-IPv6 OCTET STRING ::= '0002'H

IPv4ip ::= SEQUENCE (SIZE(1..MAX)) OF ipAddress{ub-IPv4}
IPv6ip ::= SEQUENCE (SIZE(1..MAX)) OF ipAddress{ub-IPv6}

ub-IPv4 INTEGER ::= 32
ub-IPv6 INTEGER ::= 128

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

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

4. SiSPI Validation

Before, a relying party can use a SiSPI object to validate a routing announcement, the relying party MUST first validate the SiSPI object. To validate a SiSPI object, the relying party MUST perform all the validation checks specified in [RFC6488] as well as the following additional specific validation steps of the Signed AS List.¶

• 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 == SAVNETAuthzOID:
        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: Ensure the version number is explicitly set to 2.
    if not (sispiContent.version exists and sispiContent.version==2):
        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
---------------------------------------------
Signed SAVNET-Peering Information | 1.2.840.113549.1.9.16.1.52 (suggested)

Filename
Extension | RPKI Object                       | Reference
------------------------------------------------------------------------
   .sav   | Signed SAVNET-Peering Information | draft-chen-sidrops-sispi

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.¶

   • Ensure that the AS paths conform to the customer-provider relationships indicated by the ASPAs, thereby validating the correctness of the routing information.¶

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, rank those according to their frequency in an descending order, since the frequency indicates the weight of traffic from the local AS and higher frequency represents more volume of traffic to transmit for the local AS.¶

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.¶

Based on the above steps, a description of the detailed procedure to establish SAVNET peering relationships is as follows:¶

1. Let the set of selected AS paths to all the potential destinations be denoted as ASPaths.¶

2. Let i = 1. Validate ASPaths(i) using ASPA objects.¶

3. Let the set of validated AS paths be denoted as ASPaths-V.¶

4. If ASPaths(i) passes the validation of ASPA objects, add it to ASPaths-V.¶

5. Increment i to i+1.¶

6. If ASPaths(i) is null, then set i_max = i - 1 and go to Step 7. Else, go to Step 4.¶

7. Let j = 1 and k = 1. Initialize AS-set S(1) = ASPaths-V(1)(1) and N(ASPaths-V(1)(1)) = 1.¶

8. If ASPaths-V(j)(k) belongs to S, N(ASPaths-V(j)(k)) = N(ASPaths-V(j)(k)) + 1. Else, N(ASPaths-V(j)(k)) = 1 and S(J * k) = ASPaths-V(j)(k).¶

9. Increment k to k+1.¶

10. If ASPaths-V(j)(k) is null, then go to Step 11. Else, go to Step 8.¶

11. Increment j to j+1.¶

12. If ASPaths-V(j)(k) is null, then go to Step 13. Else, go to Step 8.¶

13. Rank the AS-set N according to its values in descending order.¶

14. Retrieve SiSPI objects from the RPKI repository and let the set of ASes within the SiSPI objects be denoted as O.¶

15. Let m = 1. Create a SAVNET neighbor candidate set C.¶

16. If N(m) belongs to O, add N(1) to C.¶

17. Increate m to m + 1.¶

18. If N(m) is null or the number of ASes in set C exceeds 4000, go to Step 19. Else, go to Step 16.¶

19. Establish SAVNET peering relationship with the selected candidate ASes in set C.¶

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], [RFC6485], and [RFC6488] also apply to the SiSPI object.¶

9. References

Authors' Addresses