Secure Inter-Domain Routing (SIDR)                             G. Huston
Internet-Draft                                             G. Michaelson
Intended status: Informational                                     APNIC
Expires: September 4, 2010                                 March 3, 2010

 Validation of Route Origination using the Resource Certificate PKI and


   This document defines the semantics of a Route Origin Authorization
   in terms of the context of an application of the Resource Public Key
   Infrastructure to validate the origination of routes advertised in
   the Border Gateway Protocol.

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   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  ROA Validation Outcomes for a Route . . . . . . . . . . . . . . 3
   3.  Applying Validation Outcomes to Route Selection . . . . . . . . 6
   4.  Disavowal of Routing Origination  . . . . . . . . . . . . . . . 6
   5.  Route Validation Lifetime . . . . . . . . . . . . . . . . . . . 7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     9.2.  Informative References  . . . . . . . . . . . . . . . . . . 9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9

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1.  Introduction

   This document defines the semantics of a Route Origin Authorization
   (ROA) in terms of the context of 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)

   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

   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 a particular
   AS to originate routes 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 ROA, with
   particular reference to application in inter-domain routing relating
   to the origination of routes, and the intended scope of the authority
   that is conveyed in the ROA.

2.  ROA Validation Outcomes for a Route

   A "route" is unit of information that associates a set of
   destinations described by an IP address prefix with a set of
   attributes of a path to those destinations, as defined in section 1.1
   of [RFC4271].

   A route'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 is an aggregate, then the origin AS is
   taken as the AS component of the AGGREGATOR attribute [RFC4271].  In
   the case where there is an AS Set as the final AS_PATH element and no
   AGGREGATOR attribute is present then the origin AS is the AS

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   immediately preceding the AS Set in the AS_PATH, and if there is no
   such AS then the route's origin AS cannot be determined.

   In terms of validation of a route in the context of a routing
   environment, the address prefix value and the origin AS are used in
   the ROA validation operation.

   It is assumed here that a Relying Party (RP) has access to a local
   cache of the complete set of valid ROAs when performing validation of
   a route.  (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 RP needs to match a route 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.

   This approach to route origination validation uses a model of
   "positive" attestations, with an associated inference that route that
   cannot be validated within the RPKI framework would conventionally be
   interpreted by a RP as "invalid".  However, the considerations of
   accommodating environments of partial adoption of the use of ROAs,
   where only a subset of validly advertised address prefixes have
   associated published ROAs within the structure of the RPKI, imply
   some modification to this model of positive attestation.  In the
   context of route validation it is assumed that once an address prefix
   is described in a ROA, then this ROA specifically encompasses all
   address prefixes that are more specific than that described in the
   ROA.  Thus, any route for more specific address prefix than that
   described by any valid ROA that does not itself have a matching valid
   ROA is considered to be "invalid".  However, routes objects for
   address prefixes that are not fully described by any single ROA,
   i.e., those route objects whose address prefixes may be an aggregate
   of address prefixes described in a valid ROA, or have address
   prefixes where there is 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.
   Such routes have a validation outcome of "unknown".

   The validation condition of a route with a prefix and an origin AS
   when using single ROA for validation is summarized in the following

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   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 is considered to
   be "valid" if any ROA provides a "valid" outcome.  It is considered
   to be "invalid" if one (or more) ROAs provide an "invalid" outcome
   and no ROAs provide a "valid" outcome.  It is considered to be
   "unknown" when no ROA produces either a "valid" or an "invalid"

   Route 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.

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

      3.  If any of the selected ROAs has an asID value that matches the
          origin AS in the route, and the route object's address prefix
          matches a ROAIPAddress in the ROA (where "match" is defined as
          where the route object's address precisely matches the
          ROAIPAddress, or where the ROAIPAddress includes a maxLength
          element, and the route's address prefix is a more specific
          prefix of the ROAIPAddress, and the route's address 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

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3.  Applying Validation Outcomes to Route Selection

   Within the framework of the abstract model of the operation of inter-
   domain routing using BGP [RFC4271], a received prefix announcement
   from a routing peer is compared to all announcements for this prefix
   received from other routing peers and a route selection procedure is
   used to select the "best" route from this candidate set.

   The route 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, in which case the local order of
   preference is as follows:
      "valid" is to be preferred over
      "unknown", which itself is to be preferred over

   It is a matter of local routing policy as to the actions to be
   undertaken by a routing entity in processing routes 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 outright from further consideration as a local "best" route.

   It is a matter of local routing policy as to whether "invalid" routes
   are considered to be ineligible for further consideration in a route
   selection process.  A possible 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 by the RP 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
   routes, and that routes may be learned by an RP's routing system
   before the RP's local RPKI repository cache picks up the associated
   ROAs and recognises them as valid within the RPKI.

4.  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 construct an
   authorization where no valid AS has been granted any such authority
   to originate a route for an address prefix.  This is achieved by
   using a ROA where the ROA's subject AS is one that must never be used
   in any routing context.  Specifically, AS 0 is reserved by the IANA

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   such that it "may be use [sic] to identify non-routed networks"

   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 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 AS 0 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 AS 0 ROA to declare a default
   condition that any route 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.

   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
   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 validation outcome in any way.

5.  Route Validation Lifetime

   The "lifetime" of a validation outcome refers to the time period
   during which the original validation outcome can be still applied.
   The implicit assumption here is that when the validation lifetime
   expires the routing object SHOULD be re-tested for validity.

   The validation lifetime for a ROA is controlled by the Valid times
   specified in the End Entity (EE) Certificate used to sign the ROA,
   and the valid times of those certificates in the certification path
   used to validate the EE Certificate.  A ROA validation "expires" at
   the Validity To field of the signing EE certificate, or at such a
   time when there is no certification path that can validate the ROA.
   A ROA issuer may prematurely invalidate a ROA by revoking the EE
   certificate that was used to sign the ROA.

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6.  Security Considerations

   ROA issuers should be aware of the validation implication in issuing
   a ROA, in that a ROA implicitly invalidates all route objects that
   have 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 for this prefix.

   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 routes during ROA

   ROA issuers should also be aware that if they generate a ROA for one
   origin AS, then if the address prefix holder authorises multiple AS's
   to originate routes for a given address prefix, then is necessary for
   a ROA be generated for every such authorized AS.

7.  IANA Considerations

   [There are no IANA Considerations.]

8.  Acknowledgements

   The authors would like to acknowledge the helpful contributions of
   John Scudder and Stephen Kent in preparing this document, and also
   the contributions of many members of the SIDR Working Group in
   response to presentations of this material in SIDR WG sessions.  The
   authors also acknowledge prior work undertaken by Tony Bates, Randy
   Bush, Tony Li, and Yakov Rekhter as the validation outcomes described
   here reflect the authentication outcomes and semantics of origin AS
   verification described in [exI-D.bates].

9.  References

9.1.  Normative References

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

              Lepinski, M., Kent, S., and D. Kong, "An Infrastructure to

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              Support Secure Internet Routing",
              draft-ietf-sidr-roa-format (work in progress),
              October 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.

9.2.  Informative References

              IANA, "IANA Autonomous System Number Registry",
              March 2010.

              Bates, T., Bush, R., Li, T., and Y. Rekhter, "DNS-based
              NLRI origin AS verification in BGP",
              draft-bates-bgp4-nlri-orig-verif-00.txt (work in
              progress), January 1998.

Authors' Addresses

   Geoff Huston
   Asia Pacific Network Information Centre


   George Michaelson
   Asia Pacific Network Information Centre


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