Network Working Group                                       P. Mohapatra
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                              J. Scudder
Expires: October 19, November 23, 2012                              Juniper Networks
                                                                 D. Ward
                                                           Cisco Systems
                                                                 R. Bush
                                         Internet Initiative Japan, Inc.
                                                              R. Austein
                                                    Dragon Research Labs
                                                          April 17,
                                                            May 22, 2012

                      BGP Prefix Origin Validation


   To help reduce well-known threats against BGP including prefix mis-
   announcing and monkey-in-the-middle attacks, one of the security
   requirements is the ability to validate the origination AS of BGP
   routes.  More specifically, one needs to validate that the AS number
   claiming to originate an address prefix (as derived from the AS_PATH
   attribute of the BGP route) is in fact authorized by the prefix
   holder to do so.  This document describes a simple validation
   mechanism to partially satisfy this requirement.

Status of this Memo

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   This Internet-Draft will expire on October 19, November 23, 2012.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  5
   2.  Prefix-to-AS Mapping Database  . . . . . . . . . . . . . . . .  5
     2.1.  Pseudo-Code  . . . . . . . . . . . . . . . . . . . . . . .  7
   3.  Policy Control . . . . . . . . . . . . . . . . . . . . . . . .  7  8
   4.  Interaction with Local Cache . . . . . . . . . . . . . . . . .  8
   5.  Deployment Considerations  . . . . . . . . . . . . . . . . . .  8
   6.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  8  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9 10
     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  9 10
     9.2.  Informational References . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10

1.  Introduction

   A BGP route associates an address prefix with a set of autonomous
   systems (AS) that identify the interdomain path the prefix has
   traversed in the form of BGP announcements.  This set is represented
   as the AS_PATH attribute in BGP [RFC4271] and starts with the AS that
   originated the prefix.  To help reduce well-known threats against BGP
   including prefix mis-announcing and monkey-in-the-middle attacks, one
   of the security requirements is the ability to validate the
   origination AS of BGP routes.  More specifically, one needs to
   validate that the AS number claiming to originate an address prefix
   (as derived from the AS_PATH attribute of the BGP route) is in fact
   authorized by the prefix holder to do so.  This document describes a
   simple validation mechanism to partially satisfy this requirement.

   The Resource Public Key Infrastructure (RPKI) describes an approach
   to build a formally verifiable database of IP addresses and AS
   numbers as resources.  The overall architecture of RPKI as defined in
   [RFC6480] consists of three main components:

   o  A public key infrastructure (PKI) with the necessary certificate

   o  Digitally signed routing objects,

   o  A distributed repository system to hold the objects that would
      also support periodic retrieval.

   The RPKI system is based on resource certificates that define
   extensions to X.509 to represent IP addresses and AS identifiers
   [RFC3779], thus the name RPKI.  Route Origin Authorizations (ROA)
   [RFC6482] are separate digitally signed objects that define
   associations between ASes and IP address blocks.  Finally the
   repository system is operated in a distributed fashion through the
   IANA, RIR hierarchy, and ISPs.

   In order to benefit from the RPKI system, it is envisioned that
   relying parties either at AS or organization level obtain a local
   copy of the signed object collection, verify the signatures, and
   process them.  The cache must also be refreshed periodically.  The
   exact access mechanism used to retrieve the local cache is beyond the
   scope of this document.

   Individual BGP speakers can utilize the processed data contained in
   the local cache to validate BGP announcements.  The protocol details
   to retrieve the processed data from the local cache to the BGP
   speakers is beyond the scope of this document (refer to
   [I-D.ietf-sidr-rpki-rtr] for such a mechanism).  This document
   proposes a means by which a BGP speaker can make use of the processed
   data in order to assign a "validation state" to each prefix in a
   received BGP UPDATE message.

   Note that the complete path attestation against the AS_PATH attribute
   of a route is outside the scope of this document.

   Although RPKI provides the context for this draft, it is equally
   possible to use any other database which is able to map prefixes to
   their authorized origin ASes.  Each distinct database will have its
   own particular operational and security characteristics; such
   characteristics are beyond the scope of this document.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Prefix-to-AS Mapping Database

   The BGP speaker loads validated objects from the cache into local
   storage.  The objects loaded have the content (IP address, prefix
   length, maximum length, origin AS number).  We refer to such a
   locally stored object as a "Validated ROA Payload" or "VRP".

   We define several terms in addition to "VRP".  Where these terms are
   used, they are capitalized:

   o  Prefix: (IP address, prefix length), interpreted as is customary
      (see [RFC4632]).

   o  Route: Data derived from a received BGP UPDATE, as defined in
      [RFC4271], Section 1.1.  The Route includes one Prefix and an
      AS_PATH; it may include other attributes to characterize the

   o  VRP Prefix: The Prefix from a VRP.

   o  VRP ASN: The origin AS number from a VRP.

   o  Route Prefix: The Prefix derived from a route.

   o  Route Origin ASN: The origin AS number derived from a Route.  The
      origin AS number is Route as

      *  the rightmost AS in the final segment of the AS_PATH attribute
         in the Route if that segment is of type AS_SEQUENCE, or

      *  the BGP speaker's own AS number if that segment is of type
         AS_CONFED_SEQUENCE or AS_CONFED_SET or if the AS_PATH is empty,

      *  the distinguished value "NONE" if the final segment of the
         AS_PATH attribute is of any type other than
      AS_SEQUENCE. type.

   o  Covered: A Route Prefix is said to be Covered by a VRP when the
      VRP prefix length is less than or equal to the Route prefix length
      length, and the VRP prefix address matches and the Route prefix address
      are identical for all bits specified by the VRP prefix length.  (This
      length.(I.e. the Route prefix is simply either identical to the VRP
      prefix or a
      statement more specific of the well-known concept of determining a prefix
      match.) VRP prefix.)

   o  Matched: A Route Prefix is said to be Matched by a VRP when the
      Route Prefix is Covered by that VRP and in addition, the Route
      prefix length is less than or equal to the VRP maximum length and
      the Route Origin ASN is equal to the VRP ASN.

   Given these definitions, any given BGP Route will be found to have
   one of the following "validation states":

   o  NotFound: No VRP Covers the Route Prefix.

   o  Valid: At least one VRP Matches the Route Prefix.

   o  Invalid: At least one VRP Covers the Route Prefix, but no VRP
      Matches it.

   We observe that no VRP can have the value "NONE" as its VRP ASN.
   Thus a Route whose Origin ASN is "NONE" cannot be Matched by any VRP.
   Similarly, no valid Route can have an Origin ASN of zero
   [I-D.ietf-idr-as0].  Thus no Route can be Matched by a VRP whose ASN
   is zero.

   When a BGP speaker receives an UPDATE from a neighbor, it SHOULD
   perform a lookup as described above for each of the Routes in the
   UPDATE message.  The lookup SHOULD also be applied to routes which
   are redistributed into BGP from another source, such as another
   protocol or a locally defined static route.  An implementation MAY
   provide configuration options to control which routes the lookup is
   applied to.  The "validation state" of the Route MUST be set to
   reflect the result of the lookup.  The implementation should consider
   the "validation state" as described in the document as a local
   property or attribute of the Route.  If validation is not performed
   on a Route, the implementation SHOULD initialize the "validation
   state" of such a route to "NotFound".

   Use of the validation state is discussed in Section 3 and Section 5.
   An implementation MUST NOT exclude a route from the Adj-RIB-In or
   from consideration in the decision process as a side-effect of its
   validation state, unless explicitly configured to do so.

   We observe that a Route can be Matched or Covered by more than one
   VRP.  This procedure does not mandate an order in which VRPs must be
   visited; however, the "validation state" output is fully determined.

2.1.  Pseudo-Code

   The following pseudo-code illustrates the procedure above.  In case
   of ambiguity, the procedure above, rather than the pseudo-code,
   should be taken as authoritative.


   //Iterate through all the Covering entries in the local VRP
   //database, pfx_validate_table.
   entry = next_lookup_result(pfx_validate_table, route_prefix);

   while (entry != NULL) {
     prefix_exists = TRUE;

     if (route_prefix_length <= entry->max_length) {
       if (route_origin_as != NONE
           && entry->origin_as != 0
           && route_origin_as == entry->origin_as) {
         result = BGP_PFXV_STATE_VALID;
         return (result);
     entry = next_lookup_result(pfx_validate_table, input.prefix);

   //If one or more VRP entries Covered the route prefix, but
   //no one Matched, return "Invalid" validation state.
   if (prefix_exists == TRUE) {

   return (result);

3.  Policy Control

   An implementation MUST provide the ability to match and set the
   validation state of routes as part of its route policy filtering
   function.  Use of validation state in route policy is elaborated in
   Section 5.  For more details on operational policy considerations,
   see [I-D.ietf-sidr-origin-ops].

   An implementation MUST support Four-Octet AS Numbers, [RFC4893].

4.  Interaction with Local Cache

   Each BGP speaker supporting prefix validation as described in this
   document is expected to communicate with one or more RPKI caches,
   each of which stores a local copy of the global RPKI database.  The
   protocol mechanisms used to gather and validate these data and
   present them to BGP speakers are described in

   The prefix-to-AS mappings used by the BGP speaker are expected to be
   updated over time.  When a mapping is added or deleted, the
   implementation MUST re-validate any affected prefixes.  An "affected
   prefix" is any prefix that was matched by a deleted or updated
   mapping, or could be matched by an added mapping.

5.  Deployment Considerations

   Once a Route is selected for validation, it is categorized according
   the procedure given in Section 2.  Subsequently, routing policy as
   discussed in Section 3 can be used to take action based on the
   validation state.

   Policies which could be implemented include filtering routes based on
   validation state (for example, rejecting all "invalid" routes) or
   adjusting a route's degree of preference in the selection algorithm
   based on its validation state.  The latter could be accomplished by
   adjusting the value of such attributes as LOCAL_PREF.  Considering
   invalid routes for BGP decision process is a pure local policy matter
   and should be done with utmost care.

   In some cases (particularly when the selection algorithm is
   influenced by the adjustment of a route property that is not
   propagated into IBGP) it could be necessary for routing correctness
   to propagate the validation state to the IBGP peer.  This can be
   accomplished on the sending side by setting a community or extended
   community based on the validation state, and on the receiving side by
   matching the (extended) community and setting the validation state.

6.  Acknowledgments

   The authors wish to thank Rex Fernando, Hannes Gredler, Mouhcine
   Guennoun, Russ Housley, Junaid Israr, Miya Kohno, Shin Miyakawa, Taka
   Mizuguchi, Hussein Mouftah, Keyur Patel, Tomoya Yoshida, Kannan
   Varadhan, and Wes George. George, Jay Borkenhagen, and Sandra Murphy.  The
   authors are grateful for the feedback from the members of the SIDR
   working group.

   Junaid Israr's contribution to this specification was part of his PhD
   research work and thesis at University of Ottawa.

7.  IANA Considerations

8.  Security Considerations

   Although this specification discusses one portion of a system to
   validate BGP routes, it should be noted that it relies on a database
   (RPKI or other) to provide validation information.  As such, the
   security properties of that database must be considered in order to
   determine the security provided by the overall solution.  If
   "invalid" routes are blocked as this specification suggests, the
   overall system provides a possible denial-of-service vector, for
   example if an attacker is able to inject or remove one or more
   records in the validation database, it could lead an otherwise valid
   route to be marked as invalid.

   In addition, this system is only able to provide limited protection
   against a determined attacker -- the attacker need only prepend the
   "valid" source AS to a forged BGP route announcement in order to
   defeat the protection provided by this system.

   This mechanism does not protect against "AS in the middle attacks" or
   provide any path validation.  It only attempts to verify the origin.
   In general, this system should be thought of more as a protection
   against misconfiguration than as true "security" in the strong sense.

9.  References
9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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.

   [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing
              (CIDR): The Internet Address Assignment and Aggregation
              Plan", BCP 122, RFC 4632, August 2006.

   [RFC4893]  Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
              Number Space", RFC 4893, May 2007.

   [RFC6482]  Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
              Origin Authorizations (ROAs)", RFC 6482, February 2012.

9.2.  Informational References

              Kumari, W., Bush, R., Schiller, H., and K. Patel,
              "Codification of AS 0 processing.", draft-ietf-idr-as0-03 draft-ietf-idr-as0-04
              (work in progress), January May 2012.

              Bush, R., "RPKI-Based Origin Validation Operation",
              draft-ietf-sidr-origin-ops-15 (work in progress),
              March 2012.

              Bush, R. and R. Austein, "The RPKI/Router Protocol",
              draft-ietf-sidr-rpki-rtr-26 (work in progress),
              February 2012.

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, February 2012.

Authors' Addresses

   Pradosh Mohapatra
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134


   John Scudder
   Juniper Networks
   1194 N. Mathilda Ave
   Sunnyvale, CA  94089


   David Ward
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134


   Randy Bush
   Internet Initiative Japan, Inc.
   5147 Crystal Springs
   Bainbridge Island, Washington  98110


   Rob Austein
   Dragon Research Labs