Internet DRAFT - draft-huston-sidr-roa-validation

draft-huston-sidr-roa-validation






Secure Inter-Domain Routing (SIDR)                             G. Huston
Internet-Draft                                             G. Michaelson
Intended status: Informational                                     APNIC
Expires: November 27, 2009                                  May 26, 2009


 Validation of Route Origination in BGP using the Resource Certificate
                                  PKI
                draft-huston-sidr-roa-validation-01.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
     2.1.  Decoupled Validation  . . . . . . . . . . . . . . . . . . . 4
     2.2.  Linked Validation . . . . . . . . . . . . . . . . . . . . . 5
   3.  Applying Validation Outcomes to BGP Route
       Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     3.1.  Validation Outcomes and Rejection of BGP Route
           Objects . . . . . . . . . . . . . . . . . . . . . . . . . . 6
   4.  Further Considerations  . . . . . . . . . . . . . . . . . . . . 6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
   7.  Changes from draft-ietf-sidr-roa-validation-01  . . . . . . . . 8
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9




























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1.  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].

   This document describes how ROA validation outcomes can be used in
   the BGP route selection process, and how the proposed application of
   ROAs is intended to fit within the requirements for adding security
   to inter-domain routing, including the ability to support incremental
   and piecemeal deployment.  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].


2.  Validation Outcomes of a BGP Route Object

   A BGP Route Object is an address prefix and a set of attributes.  In
   terms of ROA and BOA validation the prefix value and the origin AS
   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
   context of the RPKI, or validation has failed.




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   There appears to be two means of matching a route object to a ROA:
   decoupled and linked.

2.1.  Decoupled Validation

   The decoupled approach is where the ROAs are managed and distributed
   independently of the operation of the routing protocol 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.

   In this case the BGP route object does not refer to a specific ROA.
   The relying party 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.

   The relying party selects a set of valid ROAs where the address
   prefix in the route object either exactly matches an ROAIPAddress
   (matching both the address prefix value and the prefix length), or
   where the route object spans a block of addresses that is included in
   the span described by the ROA's address prefix value and length and
   where the route object's prefix length is less than the ROA's prefix
   length.

   If the set of ROAs is empty then the validation outcome can be
   classified as "unknown".

   Otherwise the route object should be tested against the set of valid
   ROAS.  The following outcomes are possible using the defined ROA
   validation procedure for each ROA in this set:

   Exact Match:
      A valid ROA exists, where the address prefix in the route object
      exactly matches a prefix listed in the ROA, or the ROA contains a
      covering aggregate and the prefix length of the route object is
      smaller than or equal to the ROA's associated maxLength attribute,
      and the origin AS in the route object matches the origin AS listed
      in the ROA.

   More Specific:
      A valid ROA exists, where an address prefix in the ROA is a
      covering aggregate of the prefix in the route object, and the
      prefix length of the route object is greater than the ROA's
      associated maxLength attribute, and the origin AS in the route
      object matches the AS listed in the ROA.







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   AS Mismatch:
      A valid ROA exists where the address prefix in the route object
      exactly matches a prefix listed in the ROA, or the ROA contains a
      covering aggregate and the prefix length of the route object is
      smaller than or equal to the ROA's associated maxLength attribute,
      and the origin AS of the route object does not match the AS listed
      in the ROA.

   More Specific AS Mismatch:
      A valid ROA exists where an address prefix in the ROA is a
      covering aggregate of the prefix in the route object, the prefix
      length of the route object is greater than the ROA's associated
      maxLength attribute, and the origin AS of the route object does
      not match the AS listed in the ROA.


   If any of the ROAs in the set provide an "Exact Match" outcome then
   the BGP route object can be interpreted by the Relying Party as
   "valid", otherwise the route object can be regarded as "invalid".

2.2.  Linked Validation

   The linked approach requires the route object to reference a ROA
   either by inclusion of the ROA as an attribute of the route object,
   or inclusion of a identity field in an attribute of the route object
   as a means of identifying a particular ROA.

   If the ROA can be located is valid within the context of the RPKI
   then the route object can be compared against the ROA, as per the
   previous section, and can be validated if there is an "Exact Match"
   and otherwise be regarded as 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 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 placing it in the
   loc-RIB, and is announced to peers as the local "best" route.

   It is proposed here that the validation outcome (or "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].

   The proposed addition to the local degree of preference is "valid" is



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   to be preferred over "unknown" over "invalid".

3.1.  Validation Outcomes and Rejection of BGP Route
      Objects

   It is a matter of local preference 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, even in the case of
   comprehensive deployment of ROAs, "unknown" and "invalid" validations
   should not be considered as sufficient grounds to reject a route
   advertisement outright.  Alternate approaches may involve the use of
   a local timer to accept the route for an interim period of time until
   there is an acceptable level of assurance that all reasonable efforts
   to local a valid ROA have been undertaken.


4.  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.

   It is also noted that the decoupled and linked approach are not
   mutually exclusive, and the same procedure can be applied to route
   objects that contain an explicit pointer to the associated ROA and
   route objects where the local BGP speaker has to create a set of
   candidate ROAs that could be applied to a route object.  However,
   there are a number of considerations about this approach to
   origination validation 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.  Is is considered to be a matter of
      local policy whether it is considered to be strictly necessary to
      perform validation at a point prior to loading the object into the
      Adj-RIB-In structure, 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, and the time when the
      routing object be revalidated.  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 policy as to whether there are
      circumstances that would allow a route object to be removed from
      further consideration in route selection upon a validation
      failure, similar to the actions of Route Flap Damping.

   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 BGP mechanisms to support such a per-AS iBGP route
      validation service are not considered here.



5.  Security Considerations

   This approach to origination validation does not allow for
   'deterministic' validation in terms of the ability of a BGP speaker
   to accept or reject an advertised route object outright, given that
   there remains some issues of potential circularity of dependence and
   time lags between the propagation of information in the routing
   system and propagation of information in the RPKI.

   There are also issues of the most appropriate interpretation of
   outcomes where validation of the authenticity of the route object has
   not been possible in the context of partial adoption of the RPKI,
   where the absence of validation information does not necessarily
   constitute sufficient grounds to interpret the route object as an
   invalidly originated object.




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6.  IANA Considerations

   [There are no IANA considerations in this document.]


7.  Changes from draft-ietf-sidr-roa-validation-01

   Following WG discussion at IETF 74 on the appropriate means of
   specification of denial in routing authorizations in the context of
   the RPKI, it appears to the authors that there is no general WG
   support for the inclusion of an explicit denial capability.  Instead,
   the authors are of the view there was visible WG support, to the
   level of some form of rough consensus, for the approach where a valid
   ROA acts as an implicit "denial" for those route objects that have
   address prefixes that are more specific than the set of prefixes
   specified in the ROA, and for those route objects which have
   originating AS numbers other than those listed in valid ROAs that
   span the address prefix listed in the route object.  This draft has
   been revised to remove all references to the use of an explicit
   denial object in ROA validation, and uses only the semantics of a ROA
   to define an "invalid" route object in this context.  The remainder
   of the WG internet draft has been left largely intact.


8.  Normative References

   [I-D.ietf-sidr-arch]
              Lepinski, M., Kent, S., and R. Barnes, "An Infrastructure
              to Support Secure Internet Routing", draft-ietf-sidr-arch
              (work in progress), March 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),
              nOVEMBER 2008.

   [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.




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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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