Secure Inter-Domain Routing (SIDR)                             G. Huston
Internet-Draft                                             G. Michaelson
Intended status: Informational                                     APNIC
Expires: February 5, 2010                                 August 4, 2009


 Validation of Route Origination in BGP using the Resource Certificate
                                  PKI
                 draft-ietf-sidr-roa-validation-02.txt

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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 requirements 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  . . . . . . . . . . . . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   7.  Changes -01 to -02  . . . . . . . . . . . . . . . . . . . . . . 7
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8

































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.  Introduction

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

   The RPKI is based on Resource Certificates.  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 PKI is structured such that each current Resource
   Certificate matches a current resource allocation or assignment.
   This is 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, including
   the ability to support incremental and piecemeal deployment.

   This document describes the semantic interpretation of a valid ROA,
   with particular reference to application in BGP relating to the
   origination of route objects.  The document does not describe any
   application of a ROA to validation of the AS Path.

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


.  Validation Outcomes of a BGP Route Object

   A BGP "Route Object" is an address prefix and a set of attributes.
   In terms of validation of the Route Object the prefix value and the
   origin AS attribute are used in the validation operation.

   If the route object is an aggregate and the AS Path contains an AS
   Set, then the origin AS is considered to be the AS described as the
   AGGREGATOR [RFC4271] of the route object.

   ROA validation is described in [I-D.ietf-sidr-roa-format], and the
   outcome of the validation operation is that the ROA is valid in the



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   context of the RPKI, or validation has failed.

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

   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, nor does it refer to the set of
   certificates that the RP should use to validate the ROA's digital
   signature.  The RP needs to match a route object to one or more
   candidate valid ROAs in order to determine the appropriate local
   actions to perform on the route object.

   To validate a route object the RP would undertake the following
   steps:

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


.  Applying Validation Outcomes to BGP Route Selection

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

   It is proposed here that the ROA validation outcome of "unknown",
   "valid" or "invalid" 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].




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   The proposed addition to the local degree of preference is "valid" is
   to be preferred over "unknown" over "invalid".

   It is a matter of local BGP selection policy in setting whether
   "invalid" route objects are discarded from further consideration in
   the route selection process, however the following consideration
   should be taken into account in such a situation.

   The consideration here is one of potential circularity of dependence.
   If the authoritative publication point of the repository of ROAs or
   any certificates used in relation to an address prefix is stored at a
   location 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 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 relying party's local repository cache picks up the
   associated ROAs and recognises them as valid within the RPKI.

   For these reasons 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
   consideration as a local "best" route.

   A local policy setting may be considered such that "invalid"
   validation outcomes would be sufficient grounds to reject the route
   object.  However, due to the considerations of circular dependence
   and differing propagation times as noted above, a local policy
   setting may be considered that would involve the use of a local timer
   to accept the route 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 object have been undertaken.


.  Further 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:






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   o  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.

   o  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.

   o  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.



.  Security Considerations

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

   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 the
   model of positive security.  Here it is assumed that once an address
   prefix is described in a ROA, then this ROA "protects" 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".

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





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   Prefix      match AS   mismatch 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 "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
   ROA produces a "valid" or an "invalid" outcome.


.  IANA Considerations

   [There are no IANA considerations in this document.]


.  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 ROA's 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.



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   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.


.  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.

   [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.


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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