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rfc:rfc6483

Internet Engineering Task Force (IETF) G. Huston Request for Comments: 6483 G. Michaelson Category: Informational APNIC ISSN: 2070-1721 February 2012

               Validation of Route Origination Using
    the Resource Certificate Public Key Infrastructure (PKI) and
                 Route Origin Authorizations (ROAs)

Abstract

 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 to validate the origination of routes
 advertised in the Border Gateway Protocol.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6483.

Copyright Notice

 Copyright (c) 2012 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
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  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 Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Huston & Michaelson Informational [Page 1] RFC 6483 Route Validation February 2012

Table of Contents

 1. Introduction ....................................................2
 2. ROA Validation Outcomes for a Route .............................3
 3. Applying Validation Outcomes to Route Selection .................5
 4. Disavowal of Routing Origination ................................6
 5. Route Validation Lifetime .......................................6
 6. Security Considerations .........................................7
 7. Acknowledgements ................................................7
 8. References ......................................................8
    8.1. Normative References .......................................8
    8.2. Informative References .....................................8

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) [RFC6480] 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
 [RFC6480].
 ROAs are digitally signed objects that bind an address to an AS
 number, and are 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 [RFC6482].
 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.

Huston & Michaelson Informational [Page 2] RFC 6483 Route Validation February 2012

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 defined as follows: If the final path
 segment of the AS_PATH is of type AS_SEQUENCE, the origin AS is the
 first element of the sequence (i.e., the AS in the rightmost position
 with respect to the position of octets in the protocol message).  If
 the AS_PATH contains a path segment of type AS_SET, indicating that
 the route is an aggregate, then the 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 [RFC6482].)  The RP needs to
 match a route to one or more valid candidate 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 generic model of
 "positive" attestation that has an associated inference that routes
 that cannot be validated within the RPKI framework would
 conventionally be interpreted by an 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 a more specific address
 prefix than that described by any valid ROA that does not itself have
 a matching valid ROA can be considered "invalid".  However, routes
 for address prefixes that are not fully described by any single ROA
 (i.e., those routes 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 valid ROA), and are not
 matched by any valid ROA and do not have an address prefix that is a
 more specific address prefix described in any valid ROA, cannot be
 reliably classified as "invalid" in a partial deployment scenario.
 Such routes have a validation outcome of "unknown".

Huston & Michaelson Informational [Page 3] RFC 6483 Route Validation February 2012

 An abstract attribute of a route can be determined as the outcome of
 this validation procedure, namely a "validity state" [BGP-PFX].  The
 validity state of a route, with a prefix and an origin AS as defined
 above, when using single ROA for determining this validity state, is
 summarized in the following table:
         Route    matching  non-matching
    Prefix   AS->   AS         AS
     V           +---------+---------+
    Non-         | unknown | unknown |
    Intersecting |         |         |
                 +---------+---------+
    Covering     | unknown | unknown |
    Aggregate    |         |         |
                 +---------+---------+
    match ROA    | valid   | invalid |
    prefix       |         |         |
                 +---------+---------+
    More         |         |         |
    Specific     | invalid | invalid |
    than ROA     |         |         |
                 +---------+---------+
                Route's Validity State
 In an environment of a collection of valid ROAs, a route's validity
 state is considered to be "valid" if any ROA provides a "valid"
 outcome.  It's validity state is considered to be "invalid" if one
 (or more) ROAs provide an "invalid" outcome and no ROAs provide a
 "valid" outcome.  Its validity state is considered to be "unknown"
 (or, synonymously, "not found" [BGP-PFX]) when no valid ROA can
 produce either a "valid" or an "invalid" validity state outcome.
 A route validity state 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.  This selection forms the set of
       "candidate ROAs".
    2. If the set of candidate ROAs is empty, then the procedure stops
       with an outcome of "unknown" (or, synonymously, "not found", as
       used in [BGP-PFX]).
    3. If the route's origin AS can be determined and any of the set
       of candidate ROAs has an asID value that matches the origin AS
       in the route, and the route's address prefix matches a
       ROAIPAddress in the ROA (where "match" is defined as where the

Huston & Michaelson Informational [Page 4] RFC 6483 Route Validation February 2012

       route'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 procedure
       halts with an outcome of "valid".
    4. Otherwise, the procedure halts with an outcome of "invalid".

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's validity state, described in Section 2, of "valid",
 "invalid", or "unknown" 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 is to be preferred over
    "invalid".
 It is a matter of local routing policy as to the actions to be
 undertaken by a routing entity in processing those routes with
 "unknown" validity states.  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" validity state 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 routes with an
 "invalid" validity state are considered to be ineligible for further
 consideration in a route selection process.  Potential circular
 dependence is a consideration here: 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

Huston & Michaelson Informational [Page 5] RFC 6483 Route Validation February 2012

 associated ROAs and recognizes them as having a validity state of
 "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 not be used
 in any routing context.  Specifically, AS 0 is reserved by the IANA
 such that it may be used to identify non-routed networks [IANA-AS].
 A ROA with a subject of AS 0 (AS 0 ROA) 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
 relative preference than any other ROA that has a routable 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 "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 a maxlength value of 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 may coexist with ROAs that have different
 subject AS values; although in such cases, the presence or lack of
 presence of the AS 0 ROA does not alter the route's validity state 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 route should be re-tested for validity.

Huston & Michaelson Informational [Page 6] RFC 6483 Route Validation February 2012

 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
 notAfter 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 elect to prematurely invalidate a ROA by revoking the EE
 certificate that was used to sign the ROA.

6. Security Considerations

 ROA issuers should be aware of the validation implication in issuing
 a ROA, in that a ROA implicitly invalidates all routes 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 ASes
 prior to the issuing of ROAs for larger encompassing address blocks,
 in order to avoid inadvertent invalidation of valid routes during ROA
 generation.
 ROA issuers should also be aware that if they generate a ROA for one
 origin AS, then if the address prefix holder authorizes multiple ASes
 to originate routes for a given address prefix, then is necessary for
 a ROA be generated for every such authorized AS.

7. 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 [NLRI-ORIG].  A number of validation
 concepts relating to a route's validity state presented in [BGP-PFX],
 edited by Pradosh Mohapatra, et al., have be used in this document.

Huston & Michaelson Informational [Page 7] RFC 6483 Route Validation February 2012

8. References

8.1. Normative References

 [RFC3779]   Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
             Addresses and AS Identifiers", RFC 3779, June 2004.
 [RFC4271]   Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "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.
 [RFC6480]   Lepinski, M. and S. Kent, "An Infrastructure to Support
             Secure Internet Routing", RFC 6480, February 2012.
 [RFC6482]   Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
             Origin Authorizations (ROAs)", RFC 6482, February 2012.

8.2. Informative References

 [BGP-PFX]   Mohapatra, P., Ed., Scudder, J., Ed., Ward, D., Ed.,
             Bush, R., Ed., and R. Austein, Ed., "BGP Prefix Origin
             Validation", Work in Progress, October 2011.
 [IANA-AS]  IANA, "Autonomous System (AS) Numbers",
             http://http://www.iana.org/assignments/as-numbers
 [NLRI-ORIG] Bates, T., Bush, R., Li, T., and Y. Rekhter, "DNS-based
             NLRI origin AS verification in BGP", Work in Progress,
             January 1998.

Authors' Addresses

 Geoff Huston
 APNIC
 EMail: gih@apnic.net
 George Michaelson
 APNIC
 EMail: ggm@apnic.net

Huston & Michaelson Informational [Page 8]

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