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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: April 9, 2009                                   October 6, 2008


 Validation of Route Origination in BGP using the Resource Certificate
                                  PKI
                 draft-ietf-sidr-roa-validation-01.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on April 9, 2009.

Abstract

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







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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Validation Outcomes of a BGP Route Object  . . . . . . . . . .  3
     2.1.  Decoupled Validation . . . . . . . . . . . . . . . . . . .  4
     2.2.  Linked Validation  . . . . . . . . . . . . . . . . . . . .  6
   3.  Applying Validation Outcomes to BGP Route Selection  . . . . .  6
     3.1.  Validation Outcomes and Rejection of BGP Route Objects . .  9
   4.  Further Considerations . . . . . . . . . . . . . . . . . . . .  9
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   7.  Normative References . . . . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
   Intellectual Property and Copyright Statements . . . . . . . . . . 13





































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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].

   Bogon Origin Attestations (BOAs) are digitally signed objects that
   describe a collection of address prefixes and AS numbers that are not
   authorised by the right-of-use holder to be advertised in the inter-
   domain routing system [I-D.ietf-sidr-boa].

   This document describes how ROA and BOA validation outcomes can be
   used in the BGP route selection process, and how the proposed
   application of ROAs and BOAs are intended to fit within the
   requirements for adding security to inter-domain routing
   [ID.ietf-rpsec-bgpsecrec], 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



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   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.

   BOA validation is described in [I-D.ietf-sidr-boa], and the outcome
   of the validation operation is that the BOA is valid in the context
   of the RPKI, or validation has failed.

   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 to match a route object to one or more candidate
   valid ROAs and BOAs in order to determine the appropriate local
   actions to perform on the route object.

   The relying party selects the set of 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 and
   greater then or equal to the ROA's corresponding maxLength attribute.

   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.








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   Covering Match:
      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.

   Exact 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.

   Covering 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.

   No ROA:
      There are no Exact Matches, Covering Matches, no Exact Mismatches
      or Covering Mismatches in the RPKI repository.

   The ROA to be used for the validation function is selected from the
   set of ROAs in the order given above.  In other words an Exact Match
   is preferred over a Covering Match, which, in turn, is preferred over
   an Exact Mismatch which is preferred over a Covering Mismatch.

   The set of BOAs that are used for the validation function are
   composed of the set of valid BOAs where the origin AS of the route
   object matches an AS described in a BOA, or where an address prefix
   in a valid BOA that is an exact match or a covering aggregate of the
   route object.  In the case that the validation outcome using ROAs is
   one of Exact Mismatch, Covering Mismatch or No ROA, then the
   validation outcome of the BOA changes the overall validation result
   to "Bogon".

   Bogon:
      A valid BOA exists where an address prefix in the BOA is a an
      exact match for the prefix in the route object, or is a covering
      aggregate of the prefix in the route object, or an AS in the BOA
      matches the originating AS in the BOA.  In addition, there is no
      valid ROA that is an Exact Match or a Covering Match with the
      route object.




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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, giving one of five possible results: Exact Match,
   Covering Match, Exact Mismatch, Covering Mismatch, and No Match,
   which is defined as:

   No Match:
      The valid ROA does not comtain any address prefix that exactly
      matches the address prefix in the route object, or is a covering
      aggregate of the address prefix in the route object.

   In the case of a Mismatch or a No Match condition, the relying party
   should check for the presence of valid BOAs where the origin AS of
   the route object matches an AS described in a BOA, or where an
   address prefix in a valid BOA that is an exact match or a covering
   aggregate of the route object.  If a valid BOA can be found that
   matches either of these conditions that the overall route object
   validation of a route object with a linked ROA is changed to "Bogon".


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 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].

   In the case of partial deployment of ROAs there are a very limited
   set of circumstances where the outcome of ROA validation can be used
   as grounds to reject all consideration of the route object as an
   invalid advertisement.  While the presence of a valid ROA that
   matches the advertisement is a strong indication that an
   advertisement matches the authority provided by the prefix holder to
   advertise the prefix into the routing system, the absence of a ROA or
   the invalidity of a covering ROA does not provide a conclusive



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   indication that the advertisement has been undertaken without the
   address holder's permission, unless the object is described in a BOA.

   In the case of a partial deployment scenario of RPKI route
   attestation objects, where some address prefixes and AS numbers are
   described in ROAs or BOAs and others are not, then the relative
   ranking of validation outcomes from the highest (most preferred) to
   the lowest (least preferred) degree of preference are proposed to be
   as specified int he following list.  The exact values to apply to a
   Local Preference setting are left as a matter of local policy and
   local configuration.

   1.  Exact Match

       The prefix has been allocated and is routeable, and that the
       prefix right-of-use holder has authorized the originating AS to
       originate precisely this announcement.

   2.  Covering Match

       This is slightly less preferred because it is possible that the
       address holder of the aggregate has allocated the prefix in
       question to a different party.  It is also possible that the
       originating AS is using more specific advertisements as part of a
       traffic engineering scenario.

   3.  No ROA

       In the case of partial deployment of ROAs, the absence of
       validation credentials is a neutral outcome, in that there is no
       grounds to increase or decrease the relative degree of preference
       for the route object.

   4.  Covering Mismatch

       A Covering Mismatch is considered to be less preferable than a
       neutral position in that the address holder of a covering
       aggregate has indicated an originating AS that is not the
       originating AS of this announcement.  On the other hand it may be
       the case that this prefix has been validly allocated to another
       party who has not generated a ROA for this prefix even through
       the announcement is valid.

   5.  Exact Mismatch

       Here the exact match prefix holder has validly provided an
       authority for origination by an AS that is not the AS that is
       originating this announcement.  This would appear to be a bogus



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       announcement by inference.

   6.  No Match

       Here the route object has referenced a ROA that is not valid, or
       does not include an address prefix that matcehs the route object,
       or the referenced ROA could not be located.  This could be an
       attempt to create a false route object and use an invalid ROA.

   7.  Bogon

       Here the right-of-use holder of the AS or address prefix has
       explicitly tagged the address prefix or the AS as a "bogon".
       This implies that the announcement has been made without the
       appropriate authority, and the local preference of the route
       object should be ranked at a level commensurate with rejecting
       the route object.

   In the case of comprehensive deployment of RPKI route attestion
   objects the absence of a specific ROA origination authority for the
   route object should render it as an unusable for routing.  In this
   case the local preference setting for the route object is as follows:

   1.  Exact Match

       The prefix has been allocated and is routeable, and that the
       prefix right-of-use holder has authorized the originating AS to
       originate precisely this announcement.

   2.  Covering Match, No ROA, Covering Mismatch, Exact Mismatch, No
       Match

       The local preference of the route object should be ranked at a
       level of least preferred, due to the constraints noted in the
       following section.

   3.  Bogon

       Here the right-of-use holder of the AS or address prefix has
       explicitly tagged the address prefix or the AS as a "bogon".
       This implies that the announcement has been made without the
       appropriate authority, and the local preference of the route
       object should be ranked at a level commensurate with rejecting
       the route object.







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3.1.  Validation Outcomes and Rejection of BGP Route Objects

   In the case of comprehensive deployment of ROAs, the use of a
   validation outcome other than an Exact Match as sufficient grounds to
   reject a route object should be undertaken with care.

   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 proposed that, even in the case of
   comprehensive deployment of ROAs, a missing ROA or a mismatch 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 and BOAs 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:

   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



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      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 whther 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 whther 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 orgination validation does not allow for
   'deterministic' validation in terms of the ability of a BGP speker 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 appropirate 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 absense of validation information does not necessarily
   constitute sufficient grounds to interpret the route object as an
   invalidly originated object.

   The consequence of these considerations is that while the use of ROAs
   can increase the confidence in the validity of origination of route
   objects that match a valid ROA, ROAs cannot perform the opposite,
   namely the rejection of route objects that cannot be validated by



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   ROAs.  To assist in the case of rejecting some forms of route objects
   that cannot be explicitly validated, the BOA has been used as a means
   of explicit rejection of certain classes route objects.  The
   implication is that publishers in the RPKI should publish both ROAs
   and BOAs in order to provide the greatest level of information that
   will allow relying parties to make appropriate choices in terms of
   route preference selection.


6.  IANA Considerations

   [There are no IANA considerations in this document.]


7.  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), February 2008.

   [I-D.ietf-sidr-boa]
              Huston, G., Manderson, T., and G. Michaelson, "Profile for
              Bogon Origin Attestations (BOAs)", draft-ietf-sidr-bogons
              (work in progress), August 2008.

   [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 2008.

   [ID.ietf-rpsec-bgpsecrec]
              Christian, B. and T. Tauber, "BGP Security Requirements",
              draft-ietf-sidr-roa-format (work in progress),
              November 2007.

   [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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Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

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