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Versions: (draft-huston-sidr-roa-validation) 00 01 02 03 04 05 06 07 08 09 10 RFC 6483

Secure Inter-Domain Routing (SIDR)                             G. Huston
Internet-Draft                                             G. Michaelson
Intended status: Informational                                     APNIC
Expires: February 7, 2010                                 August 6, 2009


 Validation of Route Origination in BGP using the Resource Certificate
                              PKI and ROAs
                 draft-ietf-sidr-roa-validation-03.txt

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on February 7, 2010.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Abstract

   This document defines an application of the Resource Public Key
   Infrastructure to validate the origination of routes advertised in



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   the Border Gateway Protocol.  The proposed application is intended to
   fit within the requirement for adding security to inter-domain
   routing, including the ability to support incremental and piecemeal
   deployment, and does not require any changes to the specification of
   BGP.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Validation Outcomes of a BGP Route Object  . . . . . . . . . .  3
   3.  Applying Validation Outcomes to BGP Route Selection  . . . . .  4
   4.  Further Considerations . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Partial Deployment Considerations  . . . . . . . . . . . .  6
     4.2.  Disavowal of Routing Origination . . . . . . . . . . . . .  7
     4.3.  BGP Considerations . . . . . . . . . . . . . . . . . . . .  8
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   7.  Change Log . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     7.1.  Changes -02 to -03 . . . . . . . . . . . . . . . . . . . .  9
     7.2.  Changes -01 to -02 . . . . . . . . . . . . . . . . . . . . 10
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11


























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1.  Introduction

   This document defines an application of the Resource Public Key
   Infrastructure (RPKI) [I-D.ietf-sidr-arch] to validate the
   origination of routes advertised in the Border Gateway Protocol (BGP)
   [RFC4271].

   The RPKI is based on a hierarchy of Resource Certificates that are
   aligned to the Internet number resource allocation structure.
   Resource Certificates are X.509 certificates that conform to the PKIX
   profile [RFC5280], and to the extensions for IP addresses and AS
   identifiers [RFC3779].  A Resource Certificate describes an action by
   an issuer that binds a list of IP address blocks and Autonomous
   System (AS) numbers to the Subject of a certificate, identified by
   the unique association of the Subject's private key with the public
   key contained in the Resource Certificate.  The RPKI is structured
   such that each current Resource Certificate matches a current
   resource allocation or assignment.  This is further described in
   [I-D.ietf-sidr-arch].

   Route Origin Authorizations (ROAs) are digitally signed objects that
   bind an address to an AS number, signed by the address holder.  A ROA
   provides a means of verifying that an IP address block holder has
   authorized an AS to originate route objects in the inter-domain
   routing environment for that address block.  ROAs are described in
   [I-D.ietf-sidr-roa-format].  ROAs are intended to fit within the
   requirements for adding security to inter-domain routing.

   This document describes the semantic interpretation of a valid ROA,
   with particular reference to application in BGP relating to the
   origination of route objects.

   This proposed application of validation of ROAs does not require any
   changes to the specification of BGP protocol elements.  The outcomes
   of ROA validation may be used as part of BGP's local route selection
   procedure [RFC4271].


2.  Validation Outcomes of a BGP Route Object

   A BGP "route object" is an address prefix and an associated set of
   attributes.  In terms of validation of the route object the address
   prefix value and the "origin AS" are used in the ROA validation
   operation.  The route object's origin AS is the final element of the
   route object's AS_PATH attribute.  If the final AS_PATH element is an
   AS Set, indicating that the route object is an aggregate, then the
   origin AS is taken as the AS component of the AGGREGATOR attribute
   [RFC4271].



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   A BGP route object does not refer to a specific ROA that should be
   used by a Relying Party (RP) to validate the origination information
   contained in the route object.  The RP needs to match a route object
   to one or more candidate valid ROAs in order to determine a
   validation outcome, which, in turn, can be used to determine the
   appropriate local actions to perform on the route object.  Valid ROAs
   are defined as ROAs that are determined to be syntactically correct
   and are signed using a signature that can be verified using the RPKI,
   as described in [I-D.ietf-sidr-roa-format].  The outcome of this ROA
   validation function is that either the RP has determined that the ROA
   is valid in the context of the RPKI, or the ROA is invalid, in which
   case the ROA is not to be used by the RP.

   It is assumed here that ROAs are managed and distributed
   independently of the operation of BGP itself, and that a local BGP
   speaker has access to a local cache of the complete set of valid ROAs
   when performing a route object validation operation.

   Route object validation is defined by the following procedure:


      1.  Select all valid ROAs that include a ROAIPAddress value that
          either matches, or is a covering aggregate of, the address
          prefix in the route object.

      2.  If the set of candidate ROAs is empty then the validation
          procedure stops with an outcome of "unknown".

      3.  If any ROA has an asID value that matches the origin AS in the
          route object, and either the route object's address prefix
          precisely matches a ROAIPAddress in the ROA, or the route
          object's address prefix is a more specific prefix of a
          ROAIPAddress and the route object's prefix length value is
          less than or equal to the ROAIPAddress' maxLength value, then
          the validation procedure stops with an outcome of "valid".

      4.  Otherwise, the validation procedure stops with an outcome of
          "invalid".


3.  Applying Validation Outcomes to BGP Route Selection

   Within the framework of the abstract model of BGP operation, a
   received prefix announcement from a BGP speaking peer is compared to
   all announcements for this prefix received from other BGP peers and a
   route selection procedure is used to select the "best" route object
   from this candidate set.  This route object is then used locally by
   installing it in the loc-RIB [RFC4271], and is announced to peers as



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   the local "best" route.

   The route object validation outcome, described in Section 2, of
   "unknown", "valid" or "invalid" may be used as part of the
   determination of the local degree of preference as defined in section
   9.1.1 of the BGP specification [RFC4271].  The local degree of
   preference is as follows:
      "valid" is to be preferred over
      "unknown", which itself is to be preferred over
      "invalid".

   This preference ranking is performed prior to the steps described in
   section 9.1.1 of [RFC4271].

   It is a matter of local BGP selection policy as to the actions to be
   undertaken by a BGP instance in processing route objects with
   "unknown" validation outcomes.  Due to considerations of partial use
   of ROAs in heterogeneous environments, such as in the public
   Internet, it is advised that local policy settings should not result
   in "unknown" validation outcomes being considered as sufficient
   grounds to reject a route object outright from further consideration
   as a local "best" route.

   It is a matter of local BGP selection policy as to whether "invalid"
   route objects are considered to be ineligible for further
   consideration in the route selection process.  The consideration here
   is one of potential circularity of dependence.  If the authoritative
   publication point of the repository of ROAs, or that of any
   certificate used in relation to an address prefix, is located at an
   address that lies within the address prefix described in a ROA, then
   the repository can only be accessed once a route for the prefix has
   been accepted by the RP's local routing domain.  It is also noted
   that the propagation time of RPKI objects may be different to the
   propagation time of route objects in BGP, and that route objects may
   be received before the RP's local repository cache picks up the
   associated ROAs and recognises them as valid within the RPKI.

   A local policy setting may be considered such that "invalid"
   validation outcomes would be sufficient grounds to reject the route
   object.  However, due to these considerations of circular dependence
   and differing propagation times of ROAs and route objects, an
   alternate local policy setting may be considered that would involve
   the use of a local timer to accept the route object as feasible for
   an interim period of time, until there is an acceptable level of
   assurance that all reasonable efforts to obtain a valid ROA for the
   route object have been undertaken.





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4.  Further Considerations

4.1.  Partial Deployment Considerations

   This approach to route object origination validation uses a model of
   "positive security" attestations, where information that cannot be
   validated within the RPKI framework is intended to interpreted by a
   RP as invalid information.

   However, the considerations of accommodating environments of partial
   adoption, where only a subset of valid route objects have associated
   ROAs within the structure of the RPKI, imply some modification to
   this model of positive security.  Here it is assumed that once an
   address prefix is described in a ROA, then this ROA encompasses all
   address prefixes that are more specific than that described in the
   ROA.  Thus, any more specific address prefix and originating AS
   combination of a valid ROA, that does not have a matching valid ROA
   is considered to be "invalid".

   Routes objects that describe address prefixes that are not fully
   described by any single ROA, i.e., those address prefixes that may be
   an aggregate of a ROA, or have no intersection with any ROA, and are
   not matched by any ROA and are not a more specific of any ROA cannot
   be reliably classified as "invalid" in a partial deployment scenario,
   and are therefore described as "unknown".

   The match condition of a route object against a single ROA is
   summarized in the following table:


   Prefix      matching   non-matching
               AS         AS
              +---------+-------------+
   Covering   | unknown | unknown     |
   Aggregate  |         |             |
              +---------+-------------+
   match ROA  | valid   | invalid     |
   prefix     |         |             |
              +---------+-------------+
   More       | invalid | invalid     |
   Specific   |         |             |
   than ROA   |         |             |
              +---------+-------------+

   In an environment of a collection of ROAs, a route object is
   considered to be "valid" if any ROA provides a "valid" outcome, and
   "invalid" if one or more ROAs provide an "invalid" outcome and no
   ROAs provide a "valid" outcome.  The "unknown" outcome occurs when no



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   ROA produces either a "valid" or an "invalid" outcome.

4.2.  Disavowal of Routing Origination

   A ROA is a positive attestation that a prefix holder has authorized
   an AS to originate a route for this prefix into the inter-domain
   routing system.  It is possible for a prefix holder to attest that no
   AS has been granted any such authority by using a ROA where the ROA'S
   subject AS is one that will not be used in a routing context.
   Specifically, AS 0 is reserved by the IANA such that it "may be use
   [sic] to identify non-routed networks" [IANA.AS-Registry].

   A ROA with a subject of AS 0 is an attestation by the holder of a
   prefix that the prefix described in the ROA, and any more specific
   prefix, should not be used in a routing context.

   The route object validation procedure, described in Section 2, will
   provide a "valid" outcome if any ROA matches the address prefix and
   origin AS, even if other valid ROAs would provide an "invalid"
   validation outcome if used in isolation.  Consequently, an AS0 ROA
   has a lower preference than any other ROA that has a routeable AS as
   its subject.  This allows a prefix holder to use an AS0 ROA to
   declare a default condition that any route object that is equal to,
   or more specific than the prefix to be considered to be invalid,
   while also allowing other concurrently issued ROAs to describe valid
   origination authorizations for more specific prefixes.

   For example, the holder of prefix 203.0.113.0/24 may wish to
   authorise the origination of a route object of 203.0.113.196/26 by
   64496, and explicitly declare that all other use of prefixes from
   this block should be considered invalid.  This could be achieved
   through the issuing of a ROA for Address=203.0.113.0/24,
   maxLength=32, AS = 0 and a second ROA for Address=203.0.113.196/26,
   maxLength=26, AS=64496.

   By convention, an AS 0 ROA should have a maxLength value of 32 for
   IPv4 addresses and 128 for IPv6 addresses, although in terms of route
   object validation the same outcome would be achieved with any valid
   maxLength value, or even if the maxLength element were to be omitted
   from the ROA.  Also by convention, an AS 0 ROA should be the only ROA
   issued for a given address prefix, although again this is not a
   strict requirement.  An AS 0 ROA can coexist with ROAs that have
   different subject AS values, although in such cases the presence of
   the AS 0 ROA does not alter the route object validation outcome in
   any way.






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4.3.  BGP Considerations

   This document provides a description of how ROAs could be used by a
   BGP speaker.

   It is noted that the proposed procedure requires no changes to the
   operation of BGP.  However, there are a number of considerations
   about this approach to origination validation that are relevant to
   the operation of a BGP speaker that are not specified here.

   These considerations include:


      *  It is not specified when validation of an advertised prefix
         should be performed by a BGP speaker.  It is considered to be a
         matter of local policy whether it is strictly required to
         perform validation at a point prior to loading the object into
         the Adj-RIB-In structure [RFC4271], or once the object has been
         loaded into Adj-RIB-In, or at a later time that is determined
         by a local configuration setting.  It is also not specified
         whether origination validation should be performed each time a
         route object is updated by a peer even when the origin AS has
         not altered.

      *  The lifetime of a validation outcome is not specified here.
         This specifically refers to the time period during which the
         original validation outcome can be still applied, at the
         expiration of which the routing object should be re-tested for
         validity.  It is a matter of local policy setting as to whether
         a validation outcome be regarded as valid until the route
         object is withdrawn or further updated, or whether validation
         of a route object should occur at more frequent intervals.

      *  It is a matter of local configuration as to whether ROA
         validation is performed on a per-AS basis rather than a per-BGP
         speaker, and the appropriate mechanisms to support a de-coupled
         framework of validation of ROAs and the loading of outcomes
         into BGP speakers are not considered here.



5.  Security Considerations

   ROA issuers should be aware of the validation implication in issuing
   a ROA, in that a ROA will implicitly invalidate all route objects for
   more specific prefixes with a prefix length greater than maxLength,
   and all originating AS's other than the AS listed in the collection
   of ROAs.



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   A conservative operational practice would be to ensure the issuing of
   ROAs for all more specific prefixes with distinct origination AS's
   prior to the issuing of ROAs for larger encompassing address blocks,
   in order to avoid inadvertent invalidation of valid route objects
   during ROA generation.

   ROA issuers should also be aware that if they generate a ROA for one
   origin AS, then if the prefix is authorised by multiple AS's then
   ROAs should be generated for all such authorized AS's.


6.  IANA Considerations

   Dear IANA,

   The AS number registry [IANA.AS-Registry] contains the following
   annotation against AS 0: "may be use to identify non-routed
   networks."  Could you please add a 'd' as appropriate to this text?

   Thank you,

   the authors.


7.  Change Log

   Note: This section is NOT to be included in final version of this
   document.

7.1.  Changes -02 to -03

   Further Considerations section now has a subsection describing the
   assumptions that ROA validation is making about the precise nature of
   partial deployment, noting that a ROA has an implicit scope of
   application for all prefixes that are equal to or more specific than
   the prefix listed in the ROA

   Moved the table of validation outcomes from the Security
   Considerations section to the section on Further Considerations.

   Added consideration about disavowal and the use of an AS 0 ROA and
   its interpretation in the context of validation of route objects, and
   proposed conventions of use of an AS 0 ROA.

   Noted hierarchical dependence of ROA issuance in the Security
   Considerations section.





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7.2.  Changes -01 to -02

   Following WG review of the means of specification of denial in
   routing authorizations in the context of the RPKI at IETF 74 and IETF
   75, it appears that there is no general WG support for the use of an
   explicit denial object (termed a 'BOA').  The alternative approach,
   explored in previous iterations of this draft, used a more restricted
   interpretation of a ROA that yielded only "valid" or "unknown"
   outcomes (by using "unknown" where "invalid" is used in this revision
   of the document).  To allow for "invalid" outcomes the draft used the
   BOA to undertake the role of a 'disavow' constraint, where a route
   object was considered to be "invalid" if it was the subject of a
   valid BOA and was not considered to be "valid" by any valid ROA.  The
   reasons advanced to support the dropping of the BOA was the increased
   complexity of RP systems through the use of a second object in route
   validation, a potentially confusing mismatch in the interpretation
   scope between the ROA and the BOA, where the ROAs scope was limited
   to set of prefixes described in the ROA, while the BOA's scope
   included all possible more specifics of the prefixes listed in the
   BOA, and the ability to reconstruct the semantic equivalent of a BOA
   through the use of a ROA that used a restricted-use AS as its asID.
   Accordingly, this draft has been revised to remove all references to
   the use of an explicit denial object and uses the implicit semantics
   of denial in a ROA object.

   There appears to be no WG interest in consideration of validation in
   a "linked" model, where a ROA is bound to the route object that it is
   intended to validate.  Accordingly this section of the text has also
   been dropped from this version.


8.  References

8.1.  Normative References

   [I-D.ietf-sidr-arch]
              Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", draft-ietf-sidr-arch (work in
              progress), July 2009.

   [I-D.ietf-sidr-roa-format]
              Lepinski, M., Kent, S., and D. Kong, "An Infrastructure to
              Support Secure Internet Routing",
              draft-ietf-sidr-roa-format (work in progress), July 2009.

   [RFC3779]  Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
              Addresses and AS Identifiers", RFC 3779, June 2004.




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   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.

   [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, May 2008.

8.2.  Informative References

   [IANA.AS-Registry]
              IANA, "IANA Autonomous System Number Registry",
              August 2009.


Authors' Addresses

   Geoff Huston
   Asia Pacific Network Information Centre

   Email: gih@apnic.net


   George Michaelson
   Asia Pacific Network Information Centre

   Email: ggm@apnic.net
























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