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Versions: 00 01 02 03 04 05 06 07 08 09 10               Standards Track
Network Working Group                                            R. Bush
Internet-Draft                                        IIJ, Arrcus, & DRL
Intended status: Standards Track                              R. Austein
Expires: 18 December 2022                           Dragon Research Labs
                                                            16 June 2022


   The Resource Public Key Infrastructure (RPKI) to Router Protocol,
                               Version 2
                     draft-ietf-sidrops-8210bis-10

Abstract

   In order to verifiably validate the origin Autonomous Systems and
   Autonomous System Paths of BGP announcements, routers need a simple
   but reliable mechanism to receive Resource Public Key Infrastructure
   (RFC 6480) prefix origin data and router keys from a trusted cache.
   This document describes a protocol to deliver them.

   This document describes version 2 of the RPKI-Router protocol.  RFC
   6810 describes version 0, and RFC 8210 describes version 1.  This
   document is compatible with both.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 18 December 2022.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.



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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Changes from RFC 8210 . . . . . . . . . . . . . . . . . .   3
   2.  Glossary  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Deployment Structure  . . . . . . . . . . . . . . . . . . . .   5
   4.  Operational Overview  . . . . . . . . . . . . . . . . . . . .   5
   5.  Protocol Data Units (PDUs)  . . . . . . . . . . . . . . . . .   6
     5.1.  Fields of a PDU . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  Serial Notify . . . . . . . . . . . . . . . . . . . . . .  10
     5.3.  Serial Query  . . . . . . . . . . . . . . . . . . . . . .  10
     5.4.  Reset Query . . . . . . . . . . . . . . . . . . . . . . .  11
     5.5.  Cache Response  . . . . . . . . . . . . . . . . . . . . .  12
     5.6.  IPv4 Prefix . . . . . . . . . . . . . . . . . . . . . . .  12
     5.7.  IPv6 Prefix . . . . . . . . . . . . . . . . . . . . . . .  14
     5.8.  End of Data . . . . . . . . . . . . . . . . . . . . . . .  14
     5.9.  Cache Reset . . . . . . . . . . . . . . . . . . . . . . .  15
     5.10. Router Key  . . . . . . . . . . . . . . . . . . . . . . .  16
     5.11. Error Report  . . . . . . . . . . . . . . . . . . . . . .  17
     5.12. ASPA PDU  . . . . . . . . . . . . . . . . . . . . . . . .  18
   6.  Protocol Timing Parameters  . . . . . . . . . . . . . . . . .  20
   7.  Protocol Version Negotiation  . . . . . . . . . . . . . . . .  21
   8.  Protocol Sequences  . . . . . . . . . . . . . . . . . . . . .  23
     8.1.  Start or Restart  . . . . . . . . . . . . . . . . . . . .  23
     8.2.  Typical Exchange  . . . . . . . . . . . . . . . . . . . .  24
     8.3.  No Incremental Update Available . . . . . . . . . . . . .  24
     8.4.  Cache Has No Data Available . . . . . . . . . . . . . . .  25
   9.  Transport . . . . . . . . . . . . . . . . . . . . . . . . . .  25
     9.1.  SSH Transport . . . . . . . . . . . . . . . . . . . . . .  27
     9.2.  TLS Transport . . . . . . . . . . . . . . . . . . . . . .  27
     9.3.  TCP MD5 Transport . . . . . . . . . . . . . . . . . . . .  28
     9.4.  TCP-AO Transport  . . . . . . . . . . . . . . . . . . . .  28
   10. Router-Cache Setup  . . . . . . . . . . . . . . . . . . . . .  29
   11. ROA PDU Race Minimization . . . . . . . . . . . . . . . . . .  30
   12. Deployment Scenarios  . . . . . . . . . . . . . . . . . . . .  30
   13. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . .  31
   14. Security Considerations . . . . . . . . . . . . . . . . . . .  32
   15. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  34
   16. References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     16.1.  Normative References . . . . . . . . . . . . . . . . . .  34
     16.2.  Informative References . . . . . . . . . . . . . . . . .  37



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   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  37
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  38

1.  Introduction

   In order to verifiably validate the origin Autonomous Systems (ASes)
   and AS paths of BGP announcements, routers need a simple but reliable
   mechanism to receive cryptographically validated Resource Public Key
   Infrastructure (RPKI) [RFC6480] prefix origin data and router keys
   from a trusted cache.  This document describes a protocol to deliver
   them.  The design is intentionally constrained to be usable on much
   of the current generation of ISP router platforms.

   This specification documents version 2 of the RPKI-RTR protocol.
   Earlier versions are documented in [RFC6810] and [RFC8210].  Though
   this version is, of course, preferred, the earlier versions are
   expected to continue to be productively deployed indefinitely, and
   Section 7 details how to downgrade from this version to earlier
   versions as needed in order to interoperate.

   Section 3 describes the deployment structure, and Section 4 then
   presents an operational overview.  The binary payloads of the
   protocol are formally described in Section 5, and the expected
   Protocol Data Unit (PDU) sequences are described in Section 8.  The
   transport protocol options are described in Section 9.  Section 10
   details how routers and caches are configured to connect and
   authenticate.  Section 12 describes likely deployment scenarios.  The
   traditional security and IANA considerations end the document.

   The protocol is extensible in order to support new PDUs with new
   semantics, if deployment experience indicates that they are needed.
   PDUs are versioned should deployment experience call for change.

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.

1.2.  Changes from RFC 8210

   This section summarizes the significant changes between [RFC8210] and
   the protocol described in this document.






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   *  A new ASPA (Autonomous System Provider Authorization) PDU type
      (Section 5.12) has been added to support
      [I-D.ietf-sidrops-aspa-profile].

   *  A small Section 11 has been added to handle two possible ROA
      (Route Origination Authorization) PDU race conditions, Break
      Before Make and Shorter Prefix First.

   *  The protocol version number incremented from 1 (one) to 2 (two)
      and Section 7 has been updated accordingly.

2.  Glossary

   The following terms are used with special meaning.

   Global RPKI:  The authoritative data of the RPKI are published in a
      distributed set of servers at the IANA, Regional Internet
      Registries (RIRs), National Internet Registries (NIRs), and ISPs;
      see [RFC6481].

   CA:  The authoritative data of the RPKI are meant to be published by
      a distributed set of Certification Authorities (CAs) at the IANA,
      RIRs, NIRs, and ISPs (see [RFC6481]).

   Cache:  A Cache, AKA Relying Party Cache, is a coalesced copy of the
      published Global RPKI data, periodically fetched or refreshed,
      directly or indirectly, using the rsync protocol [RFC5781] or some
      successor.  Relying Party software is used to gather and validate
      the distributed data of the RPKI into a cache.  Trusting this
      cache further is a matter between the provider of the cache and a
      Relying Party.

   Serial Number:  "Serial Number" is a 32-bit strictly increasing
      unsigned integer which wraps from 2^32-1 to 0.  It denotes the
      logical version of a cache.  A cache increments the value when it
      successfully updates its data from a parent cache or from primary
      RPKI data.  While a cache is receiving updates, new incoming data
      and implicit deletes are associated with the new Serial Number but
      MUST NOT be sent until the fetch is complete.  A Serial Number is
      not commensurate between different caches or different protocol
      versions, nor need it be maintained across resets of the cache
      server.  See [RFC1982] on DNS Serial Number Arithmetic for too
      much detail on the topic.

   Session ID:  When a cache server is started, it generates a Session






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      ID to uniquely identify the instance of the cache and to bind it
      to the sequence of Serial Numbers that cache instance will
      generate.  This allows the router to restart a failed session
      knowing that the Serial Number it is using is commensurate with
      that of the cache.

   Payload PDU:  A payload PDU is a protocol message which contains data
      for use by the router, as opposed to a PDU which conveys the
      control mechanisms of this protocol.  Prefixes and Router Keys are
      examples of payload PDUs.

3.  Deployment Structure

   Deployment of the RPKI to reach routers has a three-level structure
   as follows:

   Global RPKI:  The authoritative data of the RPKI are published in a
      distributed set of servers at the IANA, RIRs, NIRs, and ISPs (see
      [RFC6481]).

   Local Caches:  Local caches are a local set of one or more collected
      and verified caches of RPKI data.  A Relying Party, e.g., router
      or other client, MUST have a trust relationship with, and a
      trusted transport channel to, any cache(s) it uses.

   Routers:  A router fetches data from a local cache using the protocol
      described in this document.  It is said to be a client of the
      cache.  There MAY be mechanisms for the router to assure itself of
      the authenticity of the cache and to authenticate itself to the
      cache (see Section 9).

4.  Operational Overview

   A router establishes and keeps open a transport connection to one or
   more caches with which it has client/server relationships.  It is
   configured with a semi-ordered list of caches and establishes a
   connection to the most preferred cache, or set of caches, which
   accept the connections.

   The router MUST choose the most preferred, by configuration, cache or
   set of caches so that the operator may control load on their caches
   and the Global RPKI.

   Periodically, the router sends a Serial Query to the cache the most
   recent Serial Number for which it has received data from that cache,
   i.e., the router's current Serial Number, in the form of a Serial
   Query.  When a router establishes a new session with a cache or
   wishes to reset a current relationship, it sends a Reset Query.



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   The cache responds to the Serial Query with all data changes which
   took place since the given Serial Number.  This may be the null set,
   in which case the End of Data PDU (Section 5.8) is still sent.  Note
   that the Serial Number comparison used to determine "since the given
   Serial Number" MUST take wrap-around into account; see [RFC1982].

   When the router has received all data records from the cache, it sets
   its current Serial Number to that of the Serial Number in the
   received End of Data PDU.

   When the cache updates its database, it sends a Notify PDU to every
   currently connected router.  This is a hint that now would be a good
   time for the router to poll for an update, but it is only a hint.
   The protocol requires the router to poll for updates periodically in
   any case.

   Strictly speaking, a router could track a cache simply by asking for
   a complete data set every time it updates, but this would be very
   inefficient.  The Serial-Number-based incremental update mechanism
   allows an efficient transfer of just the data records which have
   changed since the last update.  As with any update protocol based on
   incremental transfers, the router must be prepared to fall back to a
   full transfer if for any reason the cache is unable to provide the
   necessary incremental data.  Unlike some incremental transfer
   protocols, this protocol requires the router to make an explicit
   request to start the fallback process; this is deliberate, as the
   cache has no way of knowing whether the router has also established
   sessions with other caches that may be able to provide better
   service.

   As a cache server must evaluate certificates and ROAs (Route Origin
   Authorizations; see [RFC6480]), which are time dependent, servers'
   clocks MUST be correct to a tolerance of an hour.

   Barring errors, transport connections remain up as long as the cache
   and router remain up and the router is not reconfigured to no longer
   use the cache.

   Should a transport connection be lost for unknown reasons, the router
   SHOULD try to reestablish one; being careful to not abuse the cache
   with two many failed requests.

5.  Protocol Data Units (PDUs)

   The exchanges between the cache and the router are sequences of
   exchanges of the following PDUs according to the rules described in
   Section 8.




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   Reserved fields (marked "zero" in PDU diagrams) MUST be zero on
   transmission and MUST be ignored on receipt.

5.1.  Fields of a PDU

   PDUs contain the following data elements:

   Protocol Version:  An 8-bit unsigned integer, currently 2, denoting
      the version of this protocol.

   PDU Type:  An 8-bit unsigned integer, denoting the type of the PDU,
      e.g., IPv4 Prefix.

   Serial Number:  A 32-bit unsigned integer serializing the RPKI cache
      epoch when this set of PDUs was received from an upstream cache
      server or gathered from the Global RPKI.  A cache increments its
      Serial Number when completing a validated update from a parent
      cache or the Global RPKI.

   Session ID:  A 16-bit unsigned integer.  When a cache server is
      started, it generates a Session ID to identify the instance of the
      cache and to bind it to the sequence of Serial Numbers that cache
      instance will generate.  This allows the router to restart a
      failed session knowing that the Serial Number it is using is
      commensurate with that of the cache.  If, at any time after the
      protocol version has been negotiated (Section 7), either the
      router or the cache finds that the value of the Session ID is not
      the same as the other's, the party which detects the mismatch MUST
      immediately terminate the session with an Error Report PDU with
      code 0 ("Corrupt Data"), and the router MUST flush all data
      learned from that cache.

      Note that sessions are specific to a particular protocol version.
      That is, if a cache server supports multiple versions of this
      protocol, happens to use the same Session ID value for multiple
      protocol versions, and further happens to use the same Serial
      Number values for two or more sessions using the same Session ID
      but different Protocol Version values, the Serial Numbers are not
      commensurate.  The full test for whether Serial Numbers are
      commensurate requires comparing Protocol Version, Session ID, and
      Serial Number.  To reduce the risk of confusion, cache servers
      SHOULD NOT use the same Session ID across multiple protocol
      versions, but even if they do, routers MUST treat sessions with
      different Protocol Version fields as separate sessions even if
      they do happen to have the same Session ID.

      Should a cache erroneously reuse a Session ID so that a router




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      does not realize that the session has changed (old Session ID and
      new Session ID have the same numeric value), the router may become
      confused as to the content of the cache.  The time it takes the
      router to discover that it is confused will depend on whether the
      Serial Numbers are also reused.  If the Serial Numbers in the old
      and new sessions are different enough, the cache will respond to
      the router's Serial Query with a Cache Reset, which will solve the
      problem.  If, however, the Serial Numbers are close, the cache may
      respond with a Cache Response, which may not be enough to bring
      the router into sync.  In such cases, it's likely but not certain
      that the router will detect some discrepancy between the state
      that the cache expects and its own state.  For example, the Cache
      Response may tell the router to drop a record which the router
      does not hold or may tell the router to add a record which the
      router already has.  In such cases, a router will detect the error
      and reset the session.  The one case in which the router may stay
      out of sync is when nothing in the Cache Response contradicts any
      data currently held by the router.

      Using persistent storage for the Session ID or a clock-based
      scheme for generating Session IDs should avoid the risk of Session
      ID collisions.

      The Session ID might be a pseudorandom value, a strictly
      increasing value if the cache has reliable storage, et cetera.  A
      seconds-since-epoch timestamp value such as the low order 16 bits
      of unsigned integer seconds since 1970-01-01T00:00:00Z ignoring
      leap seconds might make a good Session ID value.

   Length:  A 32-bit unsigned integer which has as its value the count
      of the bytes in the entire PDU, including the 8 bytes of header
      which includes the length field.

   Flags:  An 8-bit binary field, with the lowest-order bit being 1 for
      an announcement and 0 for a withdrawal.  For a Prefix PDU (IPv4 or
      IPv6), the announce/withdraw flag indicates whether this PDU
      announces a new right to announce the prefix or withdraws a
      previously announced right; a withdraw effectively deletes one
      previously announced Prefix PDU with the exact same Prefix,
      Length, Max-Len, and Autonomous System Number (ASN).

      Similarly, for a Router Key PDU, the flag indicates whether this
      PDU announces a new Router Key or deletes one previously announced
      Router Key PDU with the exact same AS Number,
      subjectKeyIdentifier, and subjectPublicKeyInfo.

      The remaining bits in the Flags field are reserved for future use.




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   Prefix Length:  An 8-bit unsigned integer denoting the shortest
      prefix allowed by the Prefix element.

   Max Length:  An 8-bit unsigned integer denoting the longest prefix
      allowed by the Prefix element.  This MUST NOT be less than the
      Prefix Length element.

   Prefix:  The IPv4 or IPv6 prefix of the ROA.

   Autonomous System Number:  A 32-bit unsigned integer representing an
      ASN allowed to announce a prefix or associated with a router key.

   Subject Key Identifier:  The 20-octet Subject Key Identifier (SKI)
      value of a router key, as described in [RFC6487].

   Subject Public Key Info:  A variable length field holding a router
      key's subjectPublicKeyInfo value, as described in [RFC8608].  This
      is the full ASN.1 DER encoding of the subjectPublicKeyInfo,
      including the ASN.1 tag and length values of the
      subjectPublicKeyInfo SEQUENCE.

   Refresh Interval:  A 32-bit interval in seconds between normal cache
      polls.  See Section 6.

   Retry Interval:  A 32-bit interval in seconds between cache poll
      retries after a failed cache poll.  See Section 6.

   Expire Interval:  A 32-bit interval in seconds during which data
      fetched from a cache remains valid in the absence of a successful
      subsequent cache poll.  See Section 6.

   AFI Flags:  An 8-bit field of the ASPA PDU where the low order bit
      denotes whether the AS relationships are for IPv4 (0) or IPv6 (1)
      AFI.

   Provider AS Count:  A 16-bit count of Provider Autonomous System
      Numbers in the PDU.

   Customer Autonomous System Number:  The 32-bit AS number of the
      Autonomous System that authorizes the upstream providers listed in
      the Provider Autonomous System list to propagate prefixes of the
      specified address family to other ASes.

   Provider Autonomous System Numbers:  The set of 32-bit AS numbers
      authorized to propagate prefixes of the specified AFI which were
      received from the customer AS.





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5.2.  Serial Notify

   The cache notifies the router that the cache has new data.

   The Session ID reassures the router that the Serial Numbers are
   commensurate, i.e., the cache session has not been changed.

   Upon receipt of a Serial Notify PDU, the router MAY issue an
   immediate Serial Query (Section 5.3) or Reset Query (Section 5.4)
   without waiting for the Refresh Interval timer (see Section 6) to
   expire.

   Serial Notify is the only message that the cache can send that is not
   in response to a message from the router.

   If the router receives a Serial Notify PDU during the initial startup
   period where the router and cache are still negotiating to agree on a
   protocol version, the router MUST simply ignore the Serial Notify
   PDU, even if the Serial Notify PDU is for an unexpected protocol
   version.  See Section 7 for details.

   0          8          16         24        31
   .-------------------------------------------.
   | Protocol |   PDU    |                     |
   | Version  |   Type   |     Session ID      |
   |    2     |    0     |                     |
   +-------------------------------------------+
   |                                           |
   |                Length=12                  |
   |                                           |
   +-------------------------------------------+
   |                                           |
   |               Serial Number               |
   |                                           |
   `-------------------------------------------'

5.3.  Serial Query

   The router sends a Serial Query to ask the cache for all
   announcements and withdrawals which have occurred since the Serial
   Number specified in the Serial Query.

   The cache replies to this query with a Cache Response PDU
   (Section 5.5) if the cache has a (possibly null) record of the
   changes since the Serial Number specified by the router, followed by
   zero or more payload PDUs and an End Of Data PDU (Section 5.8).





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   When replying to a Serial Query, the cache MUST return the minimum
   set of changes needed to bring the router into sync with the cache.
   That is, if a particular prefix or router key underwent multiple
   changes between the Serial Number specified by the router and the
   cache's current Serial Number, the cache MUST merge those changes to
   present the simplest possible view of those changes to the router.
   In general, this means that, for any particular prefix or router key,
   the data stream will include at most one withdrawal followed by at
   most one announcement, and if all of the changes cancel out, the data
   stream will not mention the prefix or router key at all.

   The rationale for this approach is that the entire purpose of the
   RPKI-Router protocol is to offload work from the router to the cache,
   and it should therefore be the cache's job to simplify the change
   set, thus reducing work for the router.

   If the cache does not have the data needed to update the router,
   perhaps because its records do not go back to the Serial Number in
   the Serial Query, then it responds with a Cache Reset PDU
   (Section 5.9).

   The Session ID tells the cache what instance the router expects to
   ensure that the Serial Numbers are commensurate, i.e., the cache
   session has not been changed.

   0          8          16         24        31
   .-------------------------------------------.
   | Protocol |   PDU    |                     |
   | Version  |   Type   |     Session ID      |
   |    2     |    1     |                     |
   +-------------------------------------------+
   |                                           |
   |                 Length=12                 |
   |                                           |
   +-------------------------------------------+
   |                                           |
   |               Serial Number               |
   |                                           |
   `-------------------------------------------'

5.4.  Reset Query

   The router tells the cache that it wants to receive the total active,
   current, non-withdrawn database.  The cache responds with a Cache
   Response PDU (Section 5.5), followed by zero or more payload PDUs and
   an End of Data PDU (Section 5.8).





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   0          8          16         24        31
   .-------------------------------------------.
   | Protocol |   PDU    |                     |
   | Version  |   Type   |         zero        |
   |    2     |    2     |                     |
   +-------------------------------------------+
   |                                           |
   |                 Length=8                  |
   |                                           |
   `-------------------------------------------'

5.5.  Cache Response

   The cache responds to queries with zero or more payload PDUs.  When
   replying to a Serial Query (Section 5.3), the cache sends the set of
   announcements and withdrawals that have occurred since the Serial
   Number sent by the client router.  When replying to a Reset Query
   (Section 5.4), the cache sends the set of all data records it has; in
   this case, the announce/withdraw field in the payload PDUs MUST have
   the value 1 (announce).

   In response to a Reset Query, the new value of the Session ID tells
   the router the instance of the cache session for future confirmation.
   In response to a Serial Query, the Session ID being the same
   reassures the router that the Serial Numbers are commensurate, i.e.,
   the cache session has not been changed.

   0          8          16         24        31
   .-------------------------------------------.
   | Protocol |   PDU    |                     |
   | Version  |   Type   |     Session ID      |
   |    2     |    3     |                     |
   +-------------------------------------------+
   |                                           |
   |                 Length=8                  |
   |                                           |
   `-------------------------------------------'

5.6.  IPv4 Prefix












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   0          8          16         24        31
   .-------------------------------------------.
   | Protocol |   PDU    |                     |
   | Version  |   Type   |         zero        |
   |    2     |    4     |                     |
   +-------------------------------------------+
   |                                           |
   |                 Length=20                 |
   |                                           |
   +-------------------------------------------+
   |          |  Prefix  |   Max    |          |
   |  Flags   |  Length  |  Length  |   zero   |
   |          |   0..32  |   0..32  |          |
   +-------------------------------------------+
   |                                           |
   |                IPv4 Prefix                |
   |                                           |
   +-------------------------------------------+
   |                                           |
   |         Autonomous System Number          |
   |                                           |
   `-------------------------------------------'

   This PDU carries an [RFC6811] Validated ROA Payload (VRP) for an IPv4
   ROA.

   The lowest-order bit of the Flags field is 1 for an announcement and
   0 for a withdrawal.

   In the RPKI, nothing prevents a signing certificate from issuing two
   identical ROAs.  In this case, there would be no semantic difference
   between the objects, merely a process redundancy.

   In the RPKI, there is also an actual need for what might appear to a
   router as identical IPvX PDUs.  This can occur when an upstream
   certificate is being reissued or there is an address ownership
   transfer up the validation chain.  The ROA would be identical in the
   router sense, i.e., have the same {Prefix, Len, Max-Len, ASN}, but it
   would have a different validation path in the RPKI.  This is
   important to the RPKI but not to the router.

   The cache server MUST ensure that it has told the router client to
   have one and only one IPvX PDU for a unique {Prefix, Len, Max-Len,
   ASN} at any one point in time.  Should the router client receive an
   IPvX PDU with a {Prefix, Len, Max-Len, ASN} identical to one it
   already has active, it SHOULD raise a Duplicate Announcement Received
   error.




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5.7.  IPv6 Prefix

   0          8          16         24        31
   .-------------------------------------------.
   | Protocol |   PDU    |                     |
   | Version  |   Type   |         zero        |
   |    2     |    6     |                     |
   +-------------------------------------------+
   |                                           |
   |                 Length=32                 |
   |                                           |
   +-------------------------------------------+
   |          |  Prefix  |   Max    |          |
   |  Flags   |  Length  |  Length  |   zero   |
   |          |  0..128  |  0..128  |          |
   +-------------------------------------------+
   |                                           |
   +---                                     ---+
   |                                           |
   +---            IPv6 Prefix              ---+
   |                                           |
   +---                                     ---+
   |                                           |
   +-------------------------------------------+
   |                                           |
   |         Autonomous System Number          |
   |                                           |
   `-------------------------------------------'

   This PDU carries an [RFC6811] Validated ROA Payload (VRP) for an IPv6
   ROA.

   Analogous to the IPv4 Prefix PDU, it has 96 more bits and no magic.

5.8.  End of Data

   The cache tells the router it has no more data for the request.

   The Session ID and Protocol Version MUST be the same as that of the
   corresponding Cache Response which began the (possibly null) sequence
   of payload PDUs.










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   0          8          16         24        31
   .-------------------------------------------.
   | Protocol |   PDU    |                     |
   | Version  |   Type   |     Session ID      |
   |    2     |    7     |                     |
   +-------------------------------------------+
   |                                           |
   |                 Length=24                 |
   |                                           |
   +-------------------------------------------+
   |                                           |
   |               Serial Number               |
   |                                           |
   +-------------------------------------------+
   |                                           |
   |              Refresh Interval             |
   |                                           |
   +-------------------------------------------+
   |                                           |
   |               Retry Interval              |
   |                                           |
   +-------------------------------------------+
   |                                           |
   |              Expire Interval              |
   |                                           |
   `-------------------------------------------'

   The Refresh Interval, Retry Interval, and Expire Interval are all
   32-bit elapsed times measured in seconds.  They express the timing
   parameters which the cache expects the router to use in deciding when
   to send subsequent Serial Query or Reset Query PDUs to the cache.
   See Section 6 for an explanation of the use and the range of allowed
   values for these parameters.

   Note that the End of Data PDU changed significantly between versions
   0 and 1.  Version 2 End of Data is the same as Version 1.

5.9.  Cache Reset

   The cache may respond to a Serial Query informing the router that the
   cache cannot provide an incremental update starting from the Serial
   Number specified by the router.  The router must decide whether to
   issue a Reset Query or switch to a different cache.








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   0          8          16         24        31
   .-------------------------------------------.
   | Protocol |   PDU    |                     |
   | Version  |   Type   |         zero        |
   |    2     |    8     |                     |
   +-------------------------------------------+
   |                                           |
   |                 Length=8                  |
   |                                           |
   `-------------------------------------------'

5.10.  Router Key

   0          8          16         24        31
   .-------------------------------------------.
   | Protocol |   PDU    |          |          |
   | Version  |   Type   |   Flags  |   zero   |
   |    2     |    9     |          |          |
   +-------------------------------------------+
   |                                           |
   |                  Length                   |
   |                                           |
   +-------------------------------------------+
   |                                           |
   +---                                     ---+
   |          Subject Key Identifier           |
   +---                                     ---+
   |                                           |
   +---                                     ---+
   |                (20 octets)                |
   +---                                     ---+
   |                                           |
   +-------------------------------------------+
   |                                           |
   |                 AS Number                 |
   |                                           |
   +-------------------------------------------+
   |                                           |
   |          Subject Public Key Info          |
   |                                           |
   `-------------------------------------------'

   The Router Key PDU transports an [RFC8635] Router key.

   The lowest-order bit of the Flags field is 1 for an announcement and
   0 for a withdrawal.





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   The cache server MUST ensure that it has told the router client to
   have one and only one Router Key PDU for a unique {SKI, ASN, Subject
   Public Key} at any one point in time.  Should the router client
   receive a Router Key PDU with a {SKI, ASN, Subject Public Key}
   identical to one it already has active, it SHOULD raise a Duplicate
   Announcement Received error.

   Note that a particular ASN may appear in multiple Router Key PDUs
   with different Subject Public Key values, while a particular Subject
   Public Key value may appear in multiple Router Key PDUs with
   different ASNs.  In the interest of keeping the announcement and
   withdrawal semantics as simple as possible for the router, this
   protocol makes no attempt to compress either of these cases.

   Also note that it is possible, albeit very unlikely, for multiple
   distinct Subject Public Key values to hash to the same SKI.  For this
   reason, implementations MUST compare Subject Public Key values as
   well as SKIs when detecting duplicate PDUs.

   As the Subject Public Key Info is a variable length field, it must be
   decoded to determine where the PDU terminates.

5.11.  Error Report

   This PDU is used by either party to report an error to the other.

   Error reports are only sent as responses to other PDUs, not to report
   errors in Error Report PDUs.

   Error codes are described in Section 13.

   The Erroneous PDU field is a binary copy of the PDU causing the error
   condition, including all fields.

   If the error is generic (e.g., "Internal Error") and not associated
   with the PDU to which it is responding, the Erroneous PDU field MUST
   be empty and the Length of Encapsulated PDU field MUST be zero.

   An Error Report PDU MUST NOT be sent for an Error Report PDU.  If an
   erroneous Error Report PDU is received, the session SHOULD be
   dropped.

   If the error is associated with a PDU of excessive length, i.e., too
   long to be any legal PDU other than another Error Report, or a
   possibly corrupt length, the Erroneous PDU field MAY be truncated.






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   The Arbitrary Text field is optional; if not present, the Length of
   Arbitrary text field MUST be zero.  If Arbitrary Text is present, it
   MUST be a string in UTF-8 encoding (see [RFC3629]) in the Queen's
   English.

   0          8          16         24        31
   .-------------------------------------------.
   | Protocol |   PDU    |                     |
   | Version  |   Type   |     Error Code      |
   |    2     |    10    |                     |
   +-------------------------------------------+
   |                                           |
   |                  Length                   |
   |                                           |
   +-------------------------------------------+
   |                                           |
   |       Length of Encapsulated PDU          |
   |                                           |
   +-------------------------------------------+
   |                                           |
   ~               Erroneous PDU               ~
   |                                           |
   +-------------------------------------------+
   |                                           |
   |         Length of Arbitrary Text          |
   |                                           |
   +-------------------------------------------+
   |                                           |
   |              Arbitrary Text               |
   ~                    of                     ~
   |          Error Diagnostic Message         |
   |                                           |
   `-------------------------------------------'

5.12.  ASPA PDU
















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   0          8          16         24        31
   .-------------------------------------------.
   | Protocol |   PDU    |                     |
   | Version  |   Type   |        zero         |
   |    2     |    11    |                     |
   +-------------------------------------------+
   |                                           |
   |                 Length                    |
   |                                           |
   +-------------------------------------------+
   |          |          |                     |
   |  Flags   | AFI Flags|  Provider AS Count  |
   |          |          |                     |
   +-------------------------------------------+
   |                                           |
   |    Customer Autonomous System Number      |
   |                                           |
   +-------------------------------------------+
   |                                           |
   ~    Provider Autonomous System Numbers     ~
   |                                           |
   ~-------------------------------------------~

   The ASPA PDU supports [I-D.ietf-sidrops-aspa-profile].  An ASPA PDU
   represents one single customer AS and its provider ASes for a
   particular Address Family.  Receipt of an ASPA PDU announcement
   (announce/withdraw flag == 1) when the router already has an ASPA PDU
   with the same Customer Autonomous System Number and the same Address
   Family (see AFI Flags field), replaces the previous one.  The cache
   MUST deliver the complete data of an ASPA record in a single ASPA
   PDU.

   The router MUST see at most one ASPA for a given AFI from a cache for
   a particular Customer Autonomous System Number active at any time.
   As a number of conditions in the global RPKI may present multiple
   valid ASPA RPKI records for a single customer to a particular RP
   cache, this places a burden on the cache to form the union of
   multiple ASPA records it has received from the global RPKI into one
   ASPA PDU.

   The Flags field is as described in Section 5.

   For the ASPA PDU, the announce/withdraw Flag is set to 1 to indicate
   either the announcement of a new ASPA record or a replacement for a
   previously announced record with the same Customer Autonomous System
   Number and AFI.





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   If the announce/withdraw flag is set to 0, it indicates removal of
   the entire ASPA record for the specified AFI and Customer AS.  Here,
   the AFI and the customer AS of the ASPA record MUST be provided, the
   Provider AS Count must be zero, the Provider AS Numbers list MUST be
   null, and these last two fields MUST be ignored by the router.

   The AFI Flags field is defined in Section 15.

   The Provider AS Count is the number of 32-bit Provider Autonomous
   System Numbers in the PDU.

   The Customer Autonomous System Number is the 32-bit Autonomous System
   Number of the customer which authenticated the ASPA RPKI data.  For a
   given AFI, there MUST be one and only one ASPA for a Customer
   Autonomous System Number active in the router at any time.

   There are zero or more 32-bit Provider Autonomous System Number
   fields as indicated in the Provider AS Count; see
   [I-D.ietf-sidrops-aspa-profile].

6.  Protocol Timing Parameters

   Since the data the cache distributes via the RPKI-Router protocol are
   retrieved from the Global RPKI system at intervals which are only
   known to the cache, only the cache can really know how frequently it
   makes sense for the router to poll the cache, or how long the data
   are likely to remain valid (or, at least, unchanged).  For this
   reason, as well as to allow the cache some control over the load
   placed on it by its client routers, the End Of Data PDU includes
   three values that allow the cache to communicate timing parameters to
   the router:

   Refresh Interval:  This parameter tells the router how long to wait
      before next attempting to poll the cache and between subsequent
      attempts, using a Serial Query or Reset Query PDU.  The router
      SHOULD NOT poll the cache sooner than indicated by this parameter.
      Note that receipt of a Serial Notify PDU overrides this interval
      and suggests that the router issue an immediate query without
      waiting for the Refresh Interval to expire.  Countdown for this
      timer starts upon receipt of the containing End Of Data PDU.

      Minimum allowed value:  1 second.

      Maximum allowed value:  86400 seconds (1 day).

      Recommended default:  3600 seconds (1 hour).

   Retry Interval:  This parameter tells the router how long to wait



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      before retrying a failed Serial Query or Reset Query.  The router
      SHOULD NOT retry sooner than indicated by this parameter.  Note
      that a protocol version mismatch overrides this interval: if the
      router needs to downgrade to a lower protocol version number, it
      MAY send the first Serial Query or Reset Query immediately.
      Countdown for this timer starts upon failure of the query and
      restarts after each subsequent failure until a query succeeds.

      Minimum allowed value:  1 second.

      Maximum allowed value:  7200 seconds (2 hours).

      Recommended default:  600 seconds (10 minutes).

   Expire Interval:  This parameter tells the router how long it can
      continue to use the current version of the data while unable to
      perform a successful subsequent query.  The router MUST NOT retain
      the data past the time indicated by this parameter.  Countdown for
      this timer starts upon receipt of the containing End Of Data PDU.

      Minimum allowed value:  600 seconds (10 minutes).

      Maximum allowed value:  172800 seconds (2 days).

      Recommended default:  7200 seconds (2 hours).

   If the router has never issued a successful query against a
   particular cache, it SHOULD retry periodically using the default
   Retry Interval, above.

   Caches MUST set Expire Interval to a value larger than both the
   Refresh Interval and the Retry Interval.

7.  Protocol Version Negotiation

   A router MUST start each transport connection by issuing either a
   Reset Query or a Serial Query.  This query MUST tell the cache the
   highest version of this protocol the router implements.

   If a cache which supports version N receives a Reset Query with
   Version Q < N, the cache MUST downgrade to protocol version Q
   [RFC6810] or [RFC8210].  If the router's Reset Request was Q > N, the
   cache MUST send a version 2 Error Report PDU with Error Code 4
   ("Unsupported Protocol Version"), and the router MUST send another
   Reset Query with a lower Version Q.  Yjis MAY repeat.  If the router
   requests Q == 0 and it still fails, then the router MUST abort the
   session, sending a version 2 Error Report PDU with Error Code 4
   ("Unsupported Protocol Version").



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   If a router which supports version N sends a query to a cache which
   only supports version C < N, one of two things will happen:

   1.  The cache may terminate the connection, perhaps with a version 2
       Error Report PDU with Error Code 4 ("Unsupported Protocol
       Version").  In this case, the router MAY retry the connection
       using protocol version C.

   2.  The cache may reply with a version C response.  In this case, the
       router MUST either downgrade to version C or terminate the
       connection.

   In any of the downgraded combinations above, the new features of the
   higher version will not be available, and all PDUs MUST have the
   negotiated lower version number in their version fields.

   If either party receives a PDU containing an unrecognized Protocol
   Version (neither 0, 1, nor 2) during this negotiation, it MUST either
   downgrade to a known version or terminate the connection, with an
   Error Report PDU unless the received PDU is itself an Error Report
   PDU.

   The router MUST ignore any Serial Notify PDUs it might receive from
   the cache during this initial startup period, regardless of the
   Protocol Version field in the Serial Notify PDU.  Since Session ID
   and Serial Number values are specific to a particular protocol
   version, the values in the notification are not useful to the router.
   Even if these values were meaningful, the only effect that processing
   the notification would have would be to trigger exactly the same
   Reset Query or Serial Query that the router has already sent as part
   of the not-yet-complete version negotiation process, so there is
   nothing to be gained by processing notifications until version
   negotiation completes.

   Caches SHOULD NOT send Serial Notify PDUs before version negotiation
   completes.  Routers, however, MUST handle such notifications (by
   ignoring them) for backwards compatibility with caches serving
   protocol version 0.

   Once the cache and router have agreed upon a Protocol Version via the
   negotiation process above, that version is stable for the life of the
   session.  See Section 5.1 for a discussion of the interaction between
   Protocol Version and Session ID.








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   If either party receives a PDU for a different Protocol Version once
   the above negotiation completes, that party MUST drop the session;
   unless the PDU containing the unexpected Protocol Version was itself
   an Error Report PDU, the party dropping the session SHOULD send an
   Error Report with an error code of 8 ("Unexpected Protocol Version").

8.  Protocol Sequences

   The sequences of PDU transmissions fall into four conversations as
   follows:

8.1.  Start or Restart

   Cache                         Router
     ~                             ~
     | <----- Reset Query -------- | R requests data (or Serial Query)
     |                             |
     | ----- Cache Response -----> | C confirms request
     | ------- Payload PDU ------> | C sends zero or more
     | ------- Payload PDU ------> |   IPv4 Prefix, IPv6 Prefix,
     | ------- Payload PDU ------> |   ASPA, or Router Key PDUs
     | ------- End of Data ------> | C sends End of Data
     |                             |   and sends new serial
     ~                             ~

   When a transport connection is first established, the router MUST
   send either a Reset Query or a Serial Query.  A Serial Query would be
   appropriate if the router has unexpired data from a broken session
   with the same cache and remembers the Session ID of that session, in
   which case a Serial Query containing the Session ID from the previous
   session will allow the router to bring itself up to date while
   ensuring that the Serial Numbers are commensurate and that the router
   and cache are speaking compatible versions of the protocol.  In all
   other cases, the router lacks the necessary data for fast
   resynchronization and therefore MUST fall back to a Reset Query.

   The Reset Query sequence is also used when the router receives a
   Cache Reset, chooses a new cache, or fears that it has otherwise lost
   its way.

   See Section 7 for details on version negotiation.

   To limit the length of time a cache must keep the data necessary to
   generate incremental updates, a router MUST send either a Serial
   Query or a Reset Query periodically.  This also acts as a keep-alive
   at the application layer.  See Section 6 for details on the required
   polling frequency.




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8.2.  Typical Exchange

   Cache                         Router
     ~                             ~
     | -------- Notify ----------> |  (optional)
     |                             |
     | <----- Serial Query ------- | R requests data
     |                             |
     | ----- Cache Response -----> | C confirms request
     | ------- Payload PDU ------> | C sends zero or more
     | ------- Payload PDU ------> |   IPv4 Prefix, IPv6 Prefix,
     | ------- Payload PDU ------> |   ASPA. or Router Key PDUs
     | ------- End of Data ------> | C sends End of Data
     |                             |   and sends new serial
     ~                             ~

   The cache server SHOULD send a Notify PDU with its current Serial
   Number when the cache's serial changes, with the expectation that the
   router MAY then issue a Serial Query earlier than it otherwise might.
   This is analogous to DNS NOTIFY in [RFC1996].  The cache MUST rate-
   limit Serial Notifies to no more frequently than one per minute.

   When the transport layer is up and either a timer has gone off in the
   router or the cache has sent a Notify PDU, the router queries for new
   data by sending a Serial Query, and the cache sends all data newer
   than the serial in the Serial Query.

   To limit the length of time a cache must keep old withdraws, a router
   MUST send either a Serial Query or a Reset Query periodically.  See
   Section 6 for details on the required polling frequency.

8.3.  No Incremental Update Available

   Cache                         Router
     ~                             ~
     | <------ Serial Query ------ | R requests data
     | ------- Cache Reset ------> | C cannot supply update
     |                             |   from specified serial
     | <------ Reset Query ------- | R requests new data
     | ----- Cache Response -----> | C confirms request
     | ------- Payload PDU ------> | C sends zero or more
     | ------- Payload PDU ------> |   IPv4 Prefix, IPv6 Prefix,
     | ------- Payload PDU ------> |   ASPA, or Router Key PDUs
     | ------- End of Data ------> | C sends End of Data
     |                             |   and sends new serial
     ~                             ~





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   The cache may respond to a Serial Query with a Cache Reset, informing
   the router that the cache cannot supply an incremental update from
   the Serial Number specified by the router.  This might be because the
   cache has lost state, or because the router has waited too long
   between polls and the cache has cleaned up old data that it no longer
   believes it needs, or because the cache has run out of storage space
   and had to expire some old data early.  Regardless of how this state
   arose, the cache replies with a Cache Reset to tell the router that
   it cannot honor the request.  When a router receives this, the router
   SHOULD attempt to connect to any more-preferred caches in its cache
   list.  If there are no more-preferred caches, it MUST issue a Reset
   Query and get an entire new load from the cache.

8.4.  Cache Has No Data Available

   Cache                         Router
     ~                             ~
     | <------ Serial Query ------ | R requests data
     | ---- Error Report PDU ----> | C No Data Available
     ~                             ~

   Cache                         Router
     ~                             ~
     | <------ Reset Query ------- | R requests data
     | ---- Error Report PDU ----> | C No Data Available
     ~                             ~

   The cache may respond to either a Serial Query or a Reset Query
   informing the router that the cache cannot supply any update at all.
   The most likely cause is that the cache has lost state, perhaps due
   to a restart, and has not yet recovered.  While it is possible that a
   cache might go into such a state without dropping any of its active
   sessions, a router is more likely to see this behavior when it
   initially connects and issues a Reset Query while the cache is still
   rebuilding its database.

   When a router receives this kind of error, the router SHOULD attempt
   to connect to any other caches in its cache list, in preference
   order.  If no other caches are available, the router MUST issue
   periodic Reset Queries until it gets a new usable load from the
   cache; maybe once a minute so as not to DoS the cache.

9.  Transport

   The transport-layer session between a router and a cache carries the
   binary PDUs in a persistent session.





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   To prevent cache spoofing and DoS attacks by illegitimate routers, it
   is highly desirable that the router and the cache be authenticated to
   each other.  Integrity protection for payloads is also desirable to
   protect against monkey-in-the-middle (MITM) attacks.  Unfortunately,
   there is no protocol to do so on all currently used platforms.
   Therefore, as of the writing of this document, there is no mandatory-
   to-implement transport which provides authentication and integrity
   protection.

   To reduce exposure to dropped but non-terminated sessions, both
   caches and routers SHOULD enable keep-alives when available in the
   chosen transport protocol.

   It is expected that, when the TCP Authentication Option (TCP-AO)
   [RFC5925] is available on all platforms deployed by operators, it
   will become the mandatory-to-implement transport.

   Caches and routers MUST implement unprotected transport over TCP
   using a port, rpki-rtr (323); see Section 15.  Operators SHOULD use
   procedural means, e.g., access control lists (ACLs), to reduce the
   exposure to authentication issues.

   If unprotected TCP is the transport, the cache and routers MUST be on
   the same trusted and controlled network.

   If available to the operator, caches and routers MUST use one of the
   following more protected protocols:

   *  Caches and routers SHOULD use TCP-AO transport [RFC5925] over the
      rpki-rtr port.

   *  Caches and routers MAY use Secure Shell version 2 (SSHv2)
      transport [RFC4252] using the normal SSH port.  For an example,
      see Section 9.1.

   *  Caches and routers MAY use TCP MD5 transport [RFC2385] using the
      rpki-rtr port if no other protected transport is available.  Note
      that TCP MD5 has been obsoleted by TCP-AO [RFC5925].

   *  Caches and routers MAY use TCP over IPsec transport [RFC4301]
      using the rpki-rtr port.

   *  Caches and routers MAY use Transport Layer Security (TLS)
      transport [RFC8446] using port rpki-rtr-tls (324); see Section 15.
      Conformance to [RFC7525] modern cipher suites is REQUIRED.






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9.1.  SSH Transport

   To run over SSH, the client router first establishes an SSH transport
   connection using the SSHv2 transport protocol, and the client and
   server exchange keys for message integrity and encryption.  The
   client then invokes the "ssh-userauth" service to authenticate the
   application, as described in the SSH authentication protocol
   [RFC4252].  Once the application has been successfully authenticated,
   the client invokes the "ssh-connection" service, also known as the
   SSH connection protocol.

   After the ssh-connection service is established, the client opens a
   channel of type "session", which results in an SSH session.

   Once the SSH session has been established, the application invokes
   the application transport as an SSH subsystem called "rpki-rtr".
   Subsystem support is a feature of SSHv2 and is not included in SSHv1.
   Running this protocol as an SSH subsystem avoids the need for the
   application to recognize shell prompts or skip over extraneous
   information, such as a system message that is sent at shell startup.

   It is assumed that the router and cache have exchanged keys out of
   band by some reasonably secured means.

   Cache servers supporting SSH transport MUST accept RSA authentication
   and SHOULD accept Elliptic Curve Digital Signature Algorithm (ECDSA)
   authentication.  User authentication "publickey") MUST be supported;
   host authentication "hostbased") MAY be supported.  Implementations
   MAY support password authentication "password").  "None"
   authentication MUST NOT be used.  Client routers SHOULD verify the
   public key of the cache to avoid MITM attacks.

9.2.  TLS Transport

   Client routers using TLS transport MUST present client-side
   certificates to authenticate themselves to the cache in order to
   allow the cache to manage the load by rejecting connections from
   unauthorized routers.  In principle, any type of certificate and
   Certification Authority (CA) may be used; however, in general, cache
   operators will wish to create their own small-scale CA and issue
   certificates to each authorized router.  This simplifies credential
   rollover; any unrevoked, unexpired certificate from the proper CA may
   be used.








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   Certificates used to authenticate client routers in this protocol
   MUST include a subjectAltName extension [RFC5280] containing one or
   more iPAddress identities; when authenticating the router's
   certificate, the cache MUST check the IP address of the TLS
   connection against these iPAddress identities and SHOULD reject the
   connection if none of the iPAddress identities match the connection.

   Routers MUST also verify the cache's TLS server certificate, using
   subjectAltName dNSName identities as described in [RFC6125], to avoid
   MITM attacks.  The rules and guidelines defined in [RFC6125] apply
   here, with the following considerations:

   *  Support for the DNS-ID identifier type (that is, the dNSName
      identity in the subjectAltName extension) is REQUIRED in rpki-rtr
      server and client implementations which use TLS.  Certification
      authorities which issue rpki-rtr server certificates MUST support
      the DNS-ID identifier type, and the DNS-ID identifier type MUST be
      present in rpki-rtr server certificates.

   *  DNS names in rpki-rtr server certificates SHOULD NOT contain the
      wildcard character "*".

   *  rpki-rtr implementations which use TLS MUST NOT use Common Name
      (CN-ID) identifiers; a CN field may be present in the server
      certificate's subject name but MUST NOT be used for authentication
      within the rules described in [RFC6125].

   *  The client router MUST set its "reference identifier" (see
      Section 6.2 of [RFC6125]) to the DNS name of the rpki-rtr cache.

9.3.  TCP MD5 Transport

   If TCP MD5 is used, implementations MUST support key lengths of at
   least 80 printable ASCII bytes, per Section 4.5 of [RFC2385].
   Implementations MUST also support hexadecimal sequences of at least
   32 characters, i.e., 128 bits.

   Key rollover with TCP MD5 is problematic.  Cache servers SHOULD
   support [RFC4808].

9.4.  TCP-AO Transport

   Implementations MUST support key lengths of at least 80 printable
   ASCII bytes.  Implementations MUST also support hexadecimal sequences
   of at least 32 characters, i.e., 128 bits.  Message Authentication
   Code (MAC) lengths of at least 96 bits MUST be supported, per
   Section 5.1 of [RFC5925].




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   The cryptographic algorithms and associated parameters described in
   [RFC5926] MUST be supported.

10.  Router-Cache Setup

   A cache has the public authentication data for each router it is
   configured to support.

   A router may be configured to peer with a selection of caches, and a
   cache may be configured to support a selection of routers.  Each must
   have the name of, and authentication data for, each peer.  In
   addition, in a router, this list has a non-unique preference value
   for each cache.  This preference is intended to be based on
   proximity, a la RTT, not trust, preferred belief, et cetera.  The
   client router attempts to establish a session with each potential
   serving cache in preference order and then starts to load data from
   the most preferred cache to which it can connect and authenticate.
   The router's list of caches has the following elements:

   Preference:  An unsigned integer denoting the router's preference to
      connect to that cache; the lower the value, the more preferred.

   Name:  The IP address or fully qualified domain name of the cache.

   Cache Credential(s):  Any credential (such as a public key) needed to
      authenticate the cache's identity to the router.

   Router Credential(s):  Any credential (such as a private key or
      certificate) needed to authenticate the router's identity to the
      cache.

   Due to the distributed nature of the RPKI, caches simply cannot be
   rigorously synchronous.  A client may hold data from multiple caches
   but MUST keep the data marked as to source, as later updates MUST
   affect the correct data.

   Just as there may be more than one covering ROA from a single cache,
   there may be multiple covering ROAs from multiple caches.  The
   results are as described in [RFC6811].

   If data from multiple caches are held, implementations MUST NOT
   distinguish between data sources when performing validation of BGP
   announcements.

   When a more-preferred cache becomes available, if resources allow, it
   would be prudent for the client to start fetching from that cache.





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   The client SHOULD attempt to maintain at least one set of data,
   regardless of whether it has chosen a different cache or established
   a new connection to the previous cache.

   A client MAY drop the data from a particular cache when it is fully
   in sync with one or more other caches.

   See Section 6 for details on what to do when the client is not able
   to refresh from a particular cache.

   If a client loses connectivity to a cache it is using or otherwise
   decides to switch to a new cache, it SHOULD retain the data from the
   previous cache until it has a full set of data from one or more other
   caches.  Note that this may already be true at the point of
   connection loss if the client has connections to more than one cache.

11.  ROA PDU Race Minimization

   When a cache is sending ROA (IPv4 or IPv6) PDUs to a router,
   especially an initial full load in response to a Reset Query PDU, two
   undesirable race conditions are possible:

   Break Before Make:  For some prefix P, an AS may announce two (or
      more) ROAs because they are in the process of changing what
      provider AS is announcing P.  This is a case of "make before
      break."  If a cache is feeding a router and sends the one not yet
      in service a significant time before sending the one currently in
      service, then BGP data could be marked invalid during the
      interval.  To minimize that interval, the cache SHOULD announce
      all ROAs for the same prefix as close to sequentially as possible.

   Shorter Prefix First:  If an AS has issued a ROA for P0, and another
      AS (likely their customer) has issued a ROA for P1 which is a sub-
      prefix of P0, a router which receives the ROA for P0 before that
      for P1 is likely to mark a BGP prefix P1 invalid.  Therefore, the
      cache SHOULD announce the sub-prefix P1 before the covering prefix
      P0.

12.  Deployment Scenarios

   For illustration, we present three likely deployment scenarios:

   Small End Site:  The small multihomed end site may wish to outsource








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      the RPKI cache to one or more of their upstream ISPs.  They would
      exchange authentication material with the ISP using some out-of-
      band mechanism, and their router(s) would connect to the cache(s)
      of one or more upstream ISPs.  The ISPs would likely deploy caches
      intended for customer use separately from the caches with which
      their own BGP speakers peer.

   Large End Site:  A larger multihomed end site might run one or more
      caches, arranging them in a hierarchy of client caches, each
      fetching from a serving cache which is closer to the Global RPKI.
      They might configure fallback peerings to upstream ISP caches.

   ISP Backbone:  A large ISP would likely have one or more redundant
      caches in each major point of presence (PoP), and these caches
      would fetch from each other in an ISP-dependent topology so as not
      to place undue load on the Global RPKI.

   Experience with large DNS cache deployments has shown that complex
   topologies are ill-advised, as it is easy to make errors in the
   graph, e.g., not maintain a loop-free condition.

   Of course, these are illustrations, and there are other possible
   deployment strategies.  It is expected that minimizing load on the
   Global RPKI servers will be a major consideration.

   To keep load on Global RPKI services from unnecessary peaks, it is
   recommended that caches which fetch from the Global RPKI not do so
   all at the same times, e.g., on the hour.  Choose a random time,
   perhaps the ISP's AS number modulo 60, and jitter the inter-fetch
   timing.

13.  Error Codes

   This section describes the meaning of the error codes.  There is an
   IANA registry where valid error codes are listed; see [iana-err].
   Errors which are considered fatal MUST cause the session to be
   dropped.

   0: Corrupt Data (fatal):  The receiver believes the received PDU to
      be corrupt in a manner not specified by another error code.

   1: Internal Error (fatal):  The party reporting the error experienced
      some kind of internal error unrelated to protocol operation (ran
      out of memory, a coding assertion failed, et cetera).

   2: No Data Available:  The cache believes itself to be in good





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      working order but is unable to answer either a Serial Query or a
      Reset Query because it has no useful data available at this time.
      This is likely to be a temporary error and most likely indicates
      that the cache has not yet completed pulling down an initial
      current data set from the Global RPKI system after some kind of
      event that invalidated whatever data it might have previously held
      (reboot, network partition, et cetera).

   3: Invalid Request (fatal):  The cache server believes the client's
      request to be invalid.

   4: Unsupported Protocol Version (fatal):  The Protocol Version is not
      known by the receiver of the PDU.

   5: Unsupported PDU Type (fatal):  The PDU Type is not known by the
      receiver of the PDU.

   6: Withdrawal of Unknown Record (fatal):  The received PDU has
      Flag=0, but a matching record ({Prefix, Len, Max-Len, ASN} tuple
      for an IPvX PDU, or {SKI, ASN, Subject Public Key} tuple for a
      Router Key PDU), or Customer Autonomous System for an ASPA PDU
      does not exist in the receiver's database.

   7: Duplicate Announcement Received (fatal):  The received PDU has
      Flag=1, but a matching record ({Prefix, Len, Max-Len, ASN} tuple
      for an IPvX PDU or {SKI, ASN, Subject Public Key} tuple for a
      Router Key PDU), or Customer Autonomous System for an ASPA PDU is
      already active in the router.

   8: Unexpected Protocol Version (fatal):  The received PDU has a
      Protocol Version field that differs from the protocol version
      negotiated in Section 7.

14.  Security Considerations

   As this document describes a security protocol, many aspects of
   security interest are described in the relevant sections.  This
   section points out issues which may not be obvious in other sections.

   Cache Validation:  In order for a collection of caches as described
      in Section 12 to provide a consistent view, they need to be given
      consistent trust anchors of the Certification Authorities to use
      in their internal validation process.  Distribution of a
      consistent trust anchor set to validating caches is assumed to be
      out of band.

   Cache Peer Identification:  The router initiates a transport




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      connection to a cache, which it identifies by either IP address or
      fully qualified domain name.  Be aware that a DNS or address
      spoofing attack could make the correct cache unreachable.  No
      session would be established, as the authorization keys would not
      match.

   Transport Security:  The RPKI relies on object, not server or
      transport, trust.  That is, the IANA root trust anchor is
      distributed to all caches through some out-of-band means and can
      then be used by each cache to validate certificates and ROAs all
      the way down the tree.  The inter-cache relationships are based on
      this object security model; hence, the inter-cache transport can
      be lightly protected.

      However, this protocol document assumes that the routers cannot do
      the validation cryptography.  Hence, the last link, from cache to
      router, SHOULD be secured by server authentication and transport-
      level security to prevent monkey in the middle attacks; though it
      might not be.  Not using transport security is dangerous, as
      server authentication and transport have very different threat
      models than object security.

      So the strength of the trust relationship and the transport
      between the router(s) and the cache(s) are critical.  You're
      betting your routing on this.

      While we cannot say the cache must be on the same LAN, if only due
      to the issue of an enterprise wanting to offload the cache task to
      their upstream ISP(s), locality, trust, and control are very
      critical issues here.  The cache(s) really SHOULD be as close, in
      the sense of controlled and protected (against DDoS, MITM)
      transport, to the router(s) as possible.  It also SHOULD be
      topologically close so that a minimum of validated routing data
      are needed to bootstrap a router's access to a cache.

      Authenticating transport protocols (i.e. not raw TCP) will
      authenticate the identity of the cache server to the router
      client, and vice versa, before any data are exchanged.

      Transports which cannot provide the necessary authentication and
      integrity (see Section 9) must rely on network design and
      operational controls to provide protection against spoofing/
      corruption attacks.  As pointed out in Section 9, TCP-AO is the
      long-term plan.  Protocols which provide integrity and
      authenticity SHOULD be used, and if they cannot, i.e., TCP is used
      as the transport, the router and cache MUST be on the same
      trusted, controlled network.




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15.  IANA Considerations

   This section only discusses updates required in the existing IANA
   protocol registries to accommodate version 2 of this protocol.  See
   [RFC8210] for IANA considerations of the previous (version 1)
   protocol.

   All of the PDU types in the IANA "rpki-rtr-pdu" registry [iana-pdu]
   in protocol versions 0 and 1 are also allowed in protocol version 2,
   with the addition of the new ASPA PDU.

   The "rpki-rtr-pdu" registry [iana-pdu] has been updated as follows:

              Protocol   PDU
              Version    Type  Description
              --------   ----  ---------------
                 0-2       0   Serial Notify
                 0-2       1   Serial Query
                 0-2       2   Reset Query
                 0-2       3   Cache Response
                 0-2       4   IPv4 Prefix
                 0-2       6   IPv6 Prefix
                 0-2       7   End of Data
                 0-2       8   Cache Reset
                  0        9   Reserved
                 1-2       9   Router Key
                 0-2      10   Error Report
                 0-1      11   Reserved
                  2       11   ASPA
                 0-2     255   Reserved

   This document requests the IANA to create a registry for ASPA AFI
   Flags 0 to 7.  The name of the registry should be rpki-rtr-afi.  The
   policy for adding to the registry is Expert Review per [RFC8126],
   where the responsible IESG area director should appoint the Expert
   Reviewer.  The initial entries should be as follows:

             Bit     Bit Name
             ----    -------------------
              0      AFI (IPv4 == 0, IPv6 == 1)
              1-7    Reserved, MUST be zero

16.  References

16.1.  Normative References






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   [I-D.ietf-sidrops-aspa-profile]
              Azimov, A., Uskov, E., Bush, R., Patel, K., Snijders, J.,
              and R. Housley, "A Profile for Autonomous System Provider
              Authorization", Work in Progress, Internet-Draft, draft-
              ietf-sidrops-aspa-profile-07, 31 January 2022,
              <https://www.ietf.org/archive/id/draft-ietf-sidrops-aspa-
              profile-07.txt>.

   [iana-err] IANA, "rpki-rtr-error",
              <https://www.iana.org/assignments/rpki#rpki-rtr-error>.

   [iana-pdu] IANA, "rpki-rtr-pdu",
              <https://www.iana.org/assignments/rpki#rpki-rtr-pdu>.

   [RFC1982]  Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
              DOI 10.17487/RFC1982, August 1996,
              <https://www.rfc-editor.org/info/rfc1982>.

   [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>.

   [RFC2385]  Heffernan, A., "Protection of BGP Sessions via the TCP MD5
              Signature Option", RFC 2385, DOI 10.17487/RFC2385, August
              1998, <https://www.rfc-editor.org/info/rfc2385>.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
              2003, <https://www.rfc-editor.org/info/rfc3629>.

   [RFC4252]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
              January 2006, <https://www.rfc-editor.org/info/rfc4252>.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <https://www.rfc-editor.org/info/rfc4301>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.



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   [RFC5926]  Lebovitz, G. and E. Rescorla, "Cryptographic Algorithms
              for the TCP Authentication Option (TCP-AO)", RFC 5926,
              DOI 10.17487/RFC5926, June 2010,
              <https://www.rfc-editor.org/info/rfc5926>.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <https://www.rfc-editor.org/info/rfc6125>.

   [RFC6487]  Huston, G., Michaelson, G., and R. Loomans, "A Profile for
              X.509 PKIX Resource Certificates", RFC 6487,
              DOI 10.17487/RFC6487, February 2012,
              <https://www.rfc-editor.org/info/rfc6487>.

   [RFC6810]  Bush, R. and R. Austein, "The Resource Public Key
              Infrastructure (RPKI) to Router Protocol", RFC 6810,
              DOI 10.17487/RFC6810, January 2013,
              <https://www.rfc-editor.org/info/rfc6810>.

   [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>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

   [RFC8210]  Bush, R. and R. Austein, "The Resource Public Key
              Infrastructure (RPKI) to Router Protocol, Version 1",
              RFC 8210, DOI 10.17487/RFC8210, September 2017,
              <https://www.rfc-editor.org/info/rfc8210>.





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   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8608]  Turner, S. and O. Borchert, "BGPsec Algorithms, Key
              Formats, and Signature Formats", RFC 8608,
              DOI 10.17487/RFC8608, June 2019,
              <https://www.rfc-editor.org/info/rfc8608>.

   [RFC8635]  Bush, R., Turner, S., and K. Patel, "Router Keying for
              BGPsec", RFC 8635, DOI 10.17487/RFC8635, August 2019,
              <https://www.rfc-editor.org/info/rfc8635>.

16.2.  Informative References

   [RFC1996]  Vixie, P., "A Mechanism for Prompt Notification of Zone
              Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
              August 1996, <https://www.rfc-editor.org/info/rfc1996>.

   [RFC4808]  Bellovin, S., "Key Change Strategies for TCP-MD5",
              RFC 4808, DOI 10.17487/RFC4808, March 2007,
              <https://www.rfc-editor.org/info/rfc4808>.

   [RFC5781]  Weiler, S., Ward, D., and R. Housley, "The rsync URI
              Scheme", RFC 5781, DOI 10.17487/RFC5781, February 2010,
              <https://www.rfc-editor.org/info/rfc5781>.

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
              February 2012, <https://www.rfc-editor.org/info/rfc6480>.

   [RFC6481]  Huston, G., Loomans, R., and G. Michaelson, "A Profile for
              Resource Certificate Repository Structure", RFC 6481,
              DOI 10.17487/RFC6481, February 2012,
              <https://www.rfc-editor.org/info/rfc6481>.

Acknowledgements

   The authors wish to thank Nils Bars, Steve Bellovin, Oliver Borchert,
   Mohamed Boucadair, Tim Bruijnzeels, Roman Danyliw, Rex Fernando,
   Richard Hansen, Martin Hoffmann, Paul Hoffman, Fabian Holler, Russ
   Housley, Pradosh Mohapatra, Keyur Patel, David Mandelberg, Sandy
   Murphy, Robert Raszuk, Andreas Reuter, Thomas Schmidt, John Scudder,
   Ruediger Volk, Matthias Waehlisch, and David Ward.  Particular thanks
   go to Hannes Gredler for showing us the dangers of unnecessary
   fields.





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   No doubt this list is incomplete.  We apologize to any contributor
   whose name we missed.

Authors' Addresses

   Randy Bush
   IIJ, Arrcus, & DRL
   5147 Crystal Springs
   Bainbridge Island, Washington 98110
   United States of America
   Email: randy@psg.com


   Rob Austein
   Dragon Research Labs
   Email: sra@hactrn.net



































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