Detecting RRDP Session Desynchronization
draft-ietf-sidrops-rrdp-desynchronization-00

SIDROPS                                                      J. Snijders
Internet-Draft                                                    Fastly
Intended status: Informational                                T. de Kock
Expires: 7 October 2024                                         RIPE NCC
                                                            5 April 2024

                Detecting RRDP Session Desynchronization
              draft-ietf-sidrops-rrdp-desynchronization-00

Abstract

   This document describes an approach for Resource Public Key
   Infrastructure (RPKI) Relying Parties to detect a particular form of
   RPKI Repository Delta Protocol (RRDP) session desynchronization and
   how to recover.

Status of This Memo

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   This Internet-Draft will expire on 7 October 2024.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  Immutability of RRDP files  . . . . . . . . . . . . . . . . .   2
   3.  Detection of Desynchronization  . . . . . . . . . . . . . . .   3
     3.1.  Example . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Recovery after Desynchronization  . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   7
   Appendix B.  Implementation status  . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The Resource Public Key Infrastructure (RPKI) Repository Delta
   Protocol (RRDP) [RFC8182] is a one-way synchronization protocol for
   distributing RPKI data in the form of _differences_ (deltas) between
   sequential repository states.  Relying Parties apply a contiguous
   chain of deltas to synchronize their local copy of the repository
   with the current state of the remote Repository Server.  Delta files
   for any given session_id and serial number are expected to contain an
   immutable record of the state of the Repository Server at that given
   point in time, but this is not always the case.

   This document describes an approach for Relying Parties (RPs) to
   detect a particular form of RRDP session desynchronization and how to
   recover.

1.1.  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 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Immutability of RRDP files

   Section 3.1 of [RFC8182] describes how discrete publication events
   such as the addition, modification, or deletion of one or more
   repository objects _can_ be communicated as immutable files,
   highlighting advantages for publishers such as the ability to pre-
   calculate files and make use of caching infrastructure.

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   However, if an RRDP server over time serves differing data for a
   given session_id and serial number, distinct RP instances (depending
   on the moment they connected to the RRDP server) would end up with
   divergent local repositories.  Comparing the server-provided
   session_id and serial numbers across distinct RP instances would not
   bring such divergence to light.

   While the global RPKI is understood to present a loosely consistent
   view, depending on timing, updating, fetching (see Section 6 of
   [RFC7115]), different caches having different data for the same RRDP
   session at the same serial violates the principle of least
   astonishment.

   The [RFC8182] specification does allude to immutability being a
   property of RRDP files, but doesn't make it clear immutability is an
   absolute requirement for the RRDP protocol to work well.  A future
   update to [RFC8182] should set a hard rule to establish that the
   immutability of RRDP files must not be violated after publication,
   and RPs should check for unexpected mutations.

3.  Detection of Desynchronization

   Relying Parties can implement a mechanism to keep a record of the
   serial and hash attribute values in delta elements of the previous
   successful fetch of an Update Notification File.  Then, after the
   fetch of a new Update Notification File, the Relying Party should
   compare if the serial and hash values of previously seen serials
   match those in the newly fetched file.  If any difference is
   detected, Delta files were unexpectedly mutated, and the RP should
   proceed to Section 4.

   RP implementations decide how many Delta Files to maximally process
   before switching to downloading the latest Snapshot File.  The same
   upper bound can be used as a limit to the number of delta element
   serial and hash values to track.

3.1.  Example

   This section contains two versions of a Update Notification File to
   demonstrate an unexpected mutation.  The initial Update Notification
   File is as following:

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   <notification xmlns="http://www.ripe.net/rpki/rrdp" version="1"
                 session_id="fe528335-db5f-48b2-be7e-bf0992d0b5ec"
                 serial="1774">
     <snapshot uri="https://rrdp.example.net/1774/snapshot.xml"
          hash="4b5f27b099737b8bf288a33796bfe825fb2014a69fd6aa99080380299952f2e2"/>
     <delta serial="1774"
            hash="effac94afd30bbf1cd6e180e7f445a4d4653cb4c91068fa9e7b669d49b5aaa00"
            uri="https://rrdp.example.net/1774/delta.xml" />
     <delta serial="1773"
            hash="731169254dd5de0ede94ba6999bda63b0fae9880873a3710e87a71bafb64761a"
            uri="https://rrdp.example.net/1773/delta.xml" />
     <delta serial="1772"
            hash="d4087585323fd6b7fd899ebf662ef213c469d39f53839fa6241847f4f6ceb939"
            uri="https://rrdp.example.net/1772/delta.xml />
   </notification>

   Based on the above Update Notification File, an RP implementation
   could record the following state:

   fe528335-db5f-48b2-be7e-bf0992d0b5ec
   1774 effac94afd30bbf1cd6e180e7f445a4d4653cb4c91068fa9e7b669d49b5aaa00
   1773 731169254dd5de0ede94ba6999bda63b0fae9880873a3710e87a71bafb64761a
   1772 d4087585323fd6b7fd899ebf662ef213c469d39f53839fa6241847f4f6ceb939

   A new version of the Update Notification File is published, as
   following:

   <notification xmlns="http://www.ripe.net/rpki/rrdp" version="1"
                 session_id="fe528335-db5f-48b2-be7e-bf0992d0b5ec"
                 serial="1775">
     <snapshot uri="https://rrdp.example.net/1775/snapshot.xml"
          hash="cd430c386deacb04bda55301c2aa49f192b529989b739f412aea01c9a77e5389"/>
     <delta serial="1775"
            hash="d199376e98a9095dbcf14ccd49208b4223a28a1327669f89566475d94b2b08cc"
            uri="https://rrdp.example.net/1775/delta.xml />
     <delta serial="1774"
            hash="10ca28480a584105a059f95df5ca8369142fd7c8069380f84ebe613b8b89f0d3"
            uri="https://rrdp.example.net/1774/delta.xml" />
     <delta serial="1773"
            hash="731169254dd5de0ede94ba6999bda63b0fae9880873a3710e87a71bafb64761a"
            uri="https://rrdp.example.net/1773/delta.xml" />
   </notification>

   Using its previously recorded state (Section 3.1), the RP can compare
   the hash values for serials 1773 and 1774.  For serial 1774, compared
   to the earlier version of the Update Notification File, a different
   hash value is now listed, meaning an unexpected delta mutation
   occurred.

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4.  Recovery after Desynchronization

   Following the detection of RRDP session desynchronization, the RP
   implementation SHOULD issue a warning and SHOULD download the latest
   Snapshot File and process it as described in Section 3.4.3 of
   [RFC8182].

5.  Security Considerations

   Due to the lifetime of RRDP sessions (often measured in months),
   desynchronization can persist for an extended period.

   Caches in a desynchronized state pose a risk by emitting a different
   set of Validated Payloads than they would otherwise emit with a
   consistent repository copy.  Through the interaction of the
   desynchronization and the _failed fetch_ mechanism described in
   Section 6.6 of [RFC9286], Relying Parties could spuriously omit
   Validated Payloads or emit Validated Payloads that the Certification
   Authority intended to withdrawn.  In a desynchronized state, all bets
   are off.

   Missing Validated Payloads negatively impact the ability to validate
   BGP announcements using mechanisms such as described in [RFC6811] and
   [I-D.ietf-sidrops-aspa-verification].

   Section 6.6 of [RFC9286] advises RP implementations to continue to
   use cached versions of objects, but only until such time as they
   become stale.  By detecting whether the remote Repository Server is
   in an inconsistent state and then immediately switching to using the
   latest Snapshot File, RPs increase the probability to successfully
   replace objects before they become stale.

6.  IANA Considerations

   No IANA actions required.

7.  References

7.1.  Normative References

   [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>.

   [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>.

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   [RFC8182]  Bruijnzeels, T., Muravskiy, O., Weber, B., and R. Austein,
              "The RPKI Repository Delta Protocol (RRDP)", RFC 8182,
              DOI 10.17487/RFC8182, July 2017,
              <https://www.rfc-editor.org/info/rfc8182>.

7.2.  Informative References

   [FORT-validator]
              Leiva, A., "FORT validator 1.7.0", March 2024,
              <https://github.com/NICMx/FORT-validator/compare/
              main...draft-spaghetti-sidrops-rrdp-desynchronization>.

   [I-D.ietf-sidrops-aspa-verification]
              Azimov, A., Bogomazov, E., Bush, R., Patel, K., Snijders,
              J., and K. Sriram, "BGP AS_PATH Verification Based on
              Autonomous System Provider Authorization (ASPA) Objects",
              Work in Progress, Internet-Draft, draft-ietf-sidrops-aspa-
              verification-17, 29 February 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-sidrops-
              aspa-verification-17>.

   [RFC6811]  Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
              Austein, "BGP Prefix Origin Validation", RFC 6811,
              DOI 10.17487/RFC6811, January 2013,
              <https://www.rfc-editor.org/info/rfc6811>.

   [RFC7115]  Bush, R., "Origin Validation Operation Based on the
              Resource Public Key Infrastructure (RPKI)", BCP 185,
              RFC 7115, DOI 10.17487/RFC7115, January 2014,
              <https://www.rfc-editor.org/info/rfc7115>.

   [RFC9286]  Austein, R., Huston, G., Kent, S., and M. Lepinski,
              "Manifests for the Resource Public Key Infrastructure
              (RPKI)", RFC 9286, DOI 10.17487/RFC9286, June 2022,
              <https://www.rfc-editor.org/info/rfc9286>.

   [rpki-client]
              Jeker, C., Snijders, J., Dzonsons, K., and T. Buehler,
              "rpki-client 8.5", July 2023,
              <https://www.rpki-client.org/>.

   [rpki-prover]
              Puzanov, M., "rpki-prover 0.9.0", February 2024,
              <https://github.com/lolepezy/rpki-prover>.

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Appendix A.  Acknowledgements

   During the hallway track at RIPE 86, Ties de Kock shared the idea for
   detecting this particular form of RRDP desynchronization, after which
   Claudio Jeker, Job Snijders, and Theo Buehler produced an
   implementation based on rpki-client.  Equipped with tooling to detect
   this particular error condition, in subsequent months it became
   apparent that unexpected delta mutations in the global RPKI
   repositories do happen from time to time.

   The authors wish to thank Theo Buehler, Mikhail Puzanov, and Alberto
   Leiva for their careful review and feedback on this document.

Appendix B.  Implementation status

   This section is to be removed before publishing as an RFC.

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in RFC 7942.
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to RFC 7942, "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

   *  OpenBSD [rpki-client] 8.5 and higher

   *  Mikhail Puzanov's [rpki-prover] 0.9.0 and higher

   *  FORT project's [FORT-validator] 1.7.0 and higher

Authors' Addresses

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   Job Snijders
   Fastly
   Amsterdam
   Netherlands
   Email: job@fastly.com

   Ties de Kock
   RIPE NCC
   Amsterdam
   Netherlands
   Email: tdekock@ripe.net

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