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Versions: (draft-huston-sidr-roa-validation) 00 01 02 03 04 05 06 07 08 09 10 RFC 6483

Individual Submission                                          G. Huston
Internet-Draft                                             G. Michaelson
Intended status: Informational                                     APNIC
Expires: February 8, 2009                                 August 7, 2008


 Validation of Route Origination in BGP using the Resource Certificate
                                  PKI
                 draft-ietf-sidr-roa-validation-00.txt

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Copyright Notice

   Copyright (C) The IETF Trust (2008).

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  . . . . . . . . . . . . . . . . . . . .  5
   3.  Applying Validation Outcomes to BGP Route Selection  . . . . .  6
     3.1.  Using Validation Outcomes to reject BGP advertisements . .  7
   4.  Open Issues  . . . . . . . . . . . . . . . . . . . . . . . . .  8
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   7.  Normative References . . . . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
   Intellectual Property and Copyright Statements . . . . . . . . . . 11





































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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:

   o  An "exact match" is a valid ROA where the address prefix in the
      route object exactly matches a prefix listed in the ROA and the
      origin AS in the route object matches the origin AS listed in the
      ROA.

   o  A "covering match" is a valid ROA where the 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 or equal to
      the ROA's maxLength attribute, and the origin AS in the route
      object matches the AS listed in the ROA.





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   o  An "exact mismatch" is a ROA where the address prefix in the route
      object exactly matches a prefix listed in the ROA and the origin
      AS of the route object does not match the AS listed in the ROA.

   o  A "covering mismatch" is a ROA where the 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 or equal to the
      ROA's maxLength attribute, and the origin AS of the route object
      does not match the AS listed in the ROA.

   o  "ROA missing" is where there are no exact or covering matches, no
      exact or covering mismatches and no exact of covering failures in
      the RPKI repository.

   In this case the ROA that would be used for the validation function
   is selected from the set such that the most specific valid ROA that
   matches or covers the route object address prefix and where the route
   object origin AS matches the ROA AS.  If there is no such ROA in the
   set, then the most specific valid ROA is selected.  If there is no
   such ROA in the set then the most specific ROA is selected.

   The set of BOAs that are used in validation are composed of the set
   of valid BOAs where the origin AS matches an AS described in a BOA,
   or where the BOA's address prefix 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 "ROA missing"), then the validation outcome of the BOA changes the
   overall validation result to "bogon match".

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.  The relying party will
   still need check for BOAs that refer to this route object in the case
   that an exact match or a covering match is not present.  The set of
   possible outcomes of linked validation is as follows:

   o  "exact match"

   o  "covering match"

   o  "exact mismatch"

   o  "covering mismatch"





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   o  "bogon match"

   o  "ROA missing"


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 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
   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 or RPKI route
   attestation objects, when some prefixes 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 as follows:

   1.  "exact match"

       An exact match indicates that 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"

       A covering match 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, and both the
       aggregate address holder and the prefix holder have signed ROAs



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       and are advertising the prefix.

   3.  "ROA missing"

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

   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.  An "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
       announcement by inference.

   6.  "bogon match"

       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 prefix should be ranked at a level
       commensurate with rejecting the route object.

   In the case of comprehensive deployment of ROAs the absence of a
   specific origination authority for the route object should render it
   as an unusable for routing.  In this case the relative degree of
   preference the relative local degree of preference can be adjusted
   such that cases 3 through 5 of the above list have an equal level of
   lesser preference.

3.1.  Using Validation Outcomes to reject BGP advertisements

   The use of a validation outcome of a missing ROA, or a covering or
   exact mismatch 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 to related to an



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   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.  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.


4.  Open Issues

   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 questions about this approach that are not
   resolved here.

   Some open issues at this point are:

   o  When should validation of an advertised prefix be performed by a
      BGP speaker?  Is it 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?  Should
      validation be performed each time a route object is updated by a
      peer even when the origin AS has not altered?

   o  What is the lifetime of a validation outcome?  When should the
      routing object be revalidated?  Should the validation outcome be
      regarded as valid until the route object is withdrawn or further
      updated, or should validation occur at more frequent intervals?

   o  Are there 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?



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   o  Can ROA validation be performed on a per-AS basis rather than a
      per-BGP speaker?  What BGP mechanisms would be appropriate to
      support such a mode of operation?

   o  If a relying party had access to RPKI signed objects with
      comparable semantics to a Route Registry's Route Object (RRRO),
      namely the acknowledgement by an AS holder that it intends to
      originate an advertisement for a specified address prefix, how
      would this validation procedure be altered.  Presumably these
      signed RRROs would need to describe the complete set of address
      prefixes that may be announced by this originating AS in order to
      be of use in this context.  Failure to match a valid RPKI RRRO
      would then be commensurate with a "bogon match", namely rejection
      of the route object, in a manner similar to the operation of a
      filter list constructed from a Route Registry.


5.  Security Considerations

   [To be Completed - the intent of this validation approach is to
   improve the level of confidence in route objects in the IDR domain.
   It is noted that this approach does not allow for 'comprehensive'
   validation 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, and issues of treatment of unauthorised route objects in
   the scenario of partial use of the RPKI.  The consequence is that
   ROAs can increase the confidence in the validity of route objects
   that match a valid ROA, but cannot perform the opposite of explicitly
   rejecting invalid route objects.  To assist in the case of rejecting
   invalid route objects the BOA has been used as a means of explicit
   rejection of certain classes route objects.  The implication is that
   RRs should issue 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 at this stage.
   Later iterations of this draft may propose to add a ROA identifier
   into the BGP attribute set]


7.  Normative References

   [I-D.ietf-sidr-arch]
              Lepinski, M., Kent, S., and R. Barnes, "An Infrastructure



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              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.


Authors' Addresses

   Geoff Huston
   Asia Pacific Network Information Centre

   Email: gih@apnic.net
   URI:   http://www.apnic.net


   George Michaelson
   Asia Pacific Network Information Centre

   Email: ggm@apnic.net
   URI:   http://www.apnic.net







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