Internet Engineering Task Force (IETF)                         K. Sriram
Internet-Draft                                                  USA NIST
Updates: RFC8704 (if approved)                               I. Lubashev
Intended status: Best Current Practice                            Akamai
Expires: 17 December 2022                                  D. Montgomery
                                                                USA NIST
                                                            15 June 2022


  Source Address Validation Using BGP UPDATEs, ASPA, and ROA (BAR-SAV)
                    draft-sriram-sidrops-bar-sav-00

Abstract

   Designing an efficient source address validation (SAV) filter
   requires minimizing false positives (i.e., avoiding dropping
   legitimate traffic) while maintaining directionality (see RFC8704).
   This document advances the technology for SAV filter design through a
   method that makes use of BGP UPDATE messages, Autonomous System
   Provider Authorization (ASPA), and Route Origin Authorization (ROA).
   The proposed method's name is abbreviated as BAR-SAV.  BAR-SAV can be
   used by network operators to derive more robust SAV filters and thus
   improve network resilience.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 17 December 2022.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.






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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Same Procedure Applies to Customers and Lateral Peers . . . .   3
   3.  SAV Using ASPA and ROA (Procedure X)  . . . . . . . . . . . .   4
   4.  SAV using BGP UPDATE Messages, ASPA, and ROA (BAR-SAV)  . . .   5
   5.  Operational Recommendations . . . . . . . . . . . . . . . . .   6
     5.1.  Considerations for the CDN and DSR Scenario . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Spoofed source addresses are often used in Denial of Service (DoS)
   and Distributed DoS (DDoS) attacks.  Source address validation (SAV)
   filtering is used to drop packets with spoofed source addresses (see
   BCP 84 [RFC3704] [RFC8704]).  A detailed review of unicast Reverse
   Path Forwarding (uRPF) techniques for SAV is provided in [RFC8704]).
   Also, [RFC8704] describes enhanced feasible-path uRPF (EFP-uRPF)
   methods that aim to minimize false positives (i.e., avoid dropping
   legitimate traffic) while maintaining directionality (see definitions
   in [RFC3704]).

   New technology for securing the Border Gateway Protocol (BGP)
   [RFC4271] using Resource Public Key Infrastructure (RPKI) [RFC6480]
   is seeing increasing adoption.  Two of the currently existing or
   proposed types of signed objects in the RPKI can be leveraged for a
   more accurate SAV filter design as well.  These are the Route Origin
   Authorization (ROA) and the Autonomous System Provider Authorizations
   (ASPA) objects.  A ROA is a cryptographically signed attestation by
   an IP address-resource holder listing their prefixes that are
   authorized to be originated in BGP by a specific autonomous system
   (AS) [RFC6482].  ROAs are currently used for Route Origin Validation



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   (ROV) [RFC6811].  An ASPA is a cryptographically signed attestation
   by an AS listing its transit provider AS numbers (ASNs)
   [I-D.ietf-sidrops-aspa-profile].  The ASPA data is designed to be
   used for a form of AS path validation that can detect and mitigate
   route leaks [I-D.ietf-sidrops-aspa-verification] [sriram1] [sriram2].
   See [RFC7908] for the definition of route leaks.

   This document advances the technology for SAV filter design using
   methods that make use of ASPA, ROA, and/or BGP UPDATE data.  A method
   is presented in Section 3 that makes use of only ASPA and ROA data to
   design the SAV filter.  This method is for use in the future when the
   adoption of ROA and ASPA is considered to be ubiquitous.  However,
   for use in the period before that, another method for SAV is
   presented in Section 4 that makes complementary use of BGP UPDATE
   messages along with ASPA and ROA data.  Accordingly, the latter
   method's name is abbreviated as BAR-SAV.  It is hoped that just as
   the adoption of ROAs is growing at present [Monitor], the adoption of
   ASPA will also gain momentum in the near future.  The BAR-SAV method
   additionally incorporates a refined version of Algorithm A of the
   EFP-uRPF technique (Section 3.1 of [RFC8704]).  BAR-SAV can be used
   by network operators to derive more robust SAV filters and thus
   improve network resilience.

   The focus of this document is on the design of ingress SAV filters
   for an interface facing a customer or lateral peer AS.  The same
   procedure applies in both cases (Section 2).


   The reader is encouraged to be familiar with [RFC8704], [RFC6811],
   and [I-D.ietf-sidrops-aspa-profile].


1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Same Procedure Applies to Customers and Lateral Peers

   The same procedure applies for the construction of a permissible
   ingress SAV filter for a customer or lateral peer interface.
   Customers and lateral peers should only transmit data packets with
   source addresses belonging to only the prefixes that are authorized
   to be used by the ASes in their respective customer cones (CC).  The
   CC includes the AS belonging to the customer or lateral peer.



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3.  SAV Using ASPA and ROA (Procedure X)

   The method/procedure (called Procedure X) described in this section
   is for future scenarios when ASPA and ROA adoption is ubiquitous.  In
   that scenario, robust SAV filters can be generated from the RPKI
   information (ASPA and ROA data) alone.  The procedure is applicable
   for ingress SAV filter design for customer and lateral peer
   interfaces.  An ISP may use Procedure X on customer interfaces if it
   requires all its customers to register ROAs and ASPAs.

   A description of Procedure X (one that makes use of only ASPA and ROA
   data):

   *  Step A: Compute the set of ASNs in the Customer's or Lateral
      Peer's customer cone using ASPA data.

   *  Step B: Compute from ROA data the set of unique prefixes
      authorized to be announced by the ASNs found in Step A.  Keep only
      the unique prefixes.  This set is the permissible prefix list for
      SAV for the interface in consideration.

   A detailed description of Procedure X is as follows:

   1.  Let the Customer or Lateral Peer ASN be denoted as AS-k.

   2.  Let i = 1.  Initialize: AS-set S(1) = {AS-k}.

   3.  Increment i to i+1.

   4.  Create AS-set S(i) of all ASNs whose ASPA data declares at least
       one ASN in AS-set S(i-1) as a Provider.

   5.  If AS-set S(i) is null, then set i_max = i - 1 and go to Step 6.
       Else, go to Step 3.

   6.  Form the union of the sets, S(i), i = 1, 2, ..., i_max, and name
       this union as AS-set A.

   7.  Select all ROAs in which the authorized origin ASN is equal to
       any ASN in AS-set A.  Form the union of the sets of prefixes
       listed in the selected ROAs.  Name this union set of prefixes as
       P-set.

   8.  Apply P-set as the list of permissible prefixes for SAV.







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4.  SAV using BGP UPDATE Messages, ASPA, and ROA (BAR-SAV)

   SAV using BGP UPDATE Messages, ASPA, and ROA (BAR-SAV) is described
   in this section and is meant for the period when there is a partial
   deployment of ROAs and ASPAs.  To compensate for incomplete RPKI
   information, BAR-SAV augments ASPA data with BGP UPDATE AS_PATH data
   for discovering CC ASes, and it augments ROA data with BGP UPDATE
   data for discovering all prefixes associated with ASes in the CC.
   The details of this procedure are described below.

   BAR-SAV additionally incorporates a refined version of Algorithm A of
   EFP-uRPF (Section 3.1 of [RFC8704]).  Algorithm A in [RFC8704] picked
   only the originating ASes from AS_PATHs received on the customer or
   lateral peer interface in consideration and included them for SAV
   filter computation.  The variant of Algorithm A in [RFC8704] used
   here includes all ASes in the AS_PATHs for the SAV filter
   computation.  Unless there is a route leak [RFC7908], each AS is a
   customer of the AS added next in AS_PATHs of BGP UPDATE messages
   received from a customer or lateral peer.  Further customer-provider
   AS relations within the CC are discovered by examining all unique
   ASes in the AS_PATHs in BGP UPDATEs received on all interfaces (from
   transit providers, customers, lateral peers, and IBGP peers).  This
   is described in the step-by-step procedure later in this section.

   Note that if a multi-homed AS is present in an above-mentioned
   AS_PATH and did not originate any prefix in the CC in consideration
   but originated a prefix into an overlapping neighboring CC, then the
   AS and prefix will still be detected and included in the design of
   the SAV filter.  This improves the accuracy of the SAV filter in the
   BAR-SAV method in comparison to Algorithm A in [RFC8704].

   One should not compute a customer cone by separately processing ASPA
   data and AS_PATH data and then merging the two sets of ASes at the
   end.  Doing so is likely to miss ASes from the customer cone.
   Instead, both ASPAs and AS_PATHs should be used to iteratively expand
   the discovered customer cone.  When new ASes are discovered, both
   ASPA and AS_PATH data should be used to discover customers of those
   ASes.  This process is repeated for newly discovered customer ASes
   until there are no new ASes to be found.

   If a transit provider-to-customer relationship, e.g., from AS X to AS
   Y, is deduced from AS_PATH data but the ASPA data contradicts it
   (i.e., AS Y has ASPA and it does not include AS X as a transit
   provider), then the ASPA data prevails, and AS Y must not be
   considered to be a customer of X.  This design principle is reflected
   in Step 5 of the procedure described below.  (Please see discussion
   about route leaks in Section 7.)




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   A detailed description of the BAR-SAV procedure is as follows:

   1.   Let the Customer or Lateral Peer ASN be denoted as AS-k.

   2.   Let i = 1.  Initialize: AS-set Z(1) = {AS-k}.

   3.   Increment i to i+1.

   4.   Create AS-set A(i) of all ASNs whose ASPA data declares at least
        one ASN in AS-set Z(i-1) as a Provider.

   5.   Create AS-set B(i) of all "non-ASPA" customer ASNs each of which
        is a customer of at least one ASN in AS-set Z(i-1) according to
        unique AS_PATHs in Adj-RIBs-In [RFC4271] of all interfaces at
        the BGP speaker computing the SAV filter.  "Non-ASPA" ASN are
        ASNs that declare no provider in ASPA data.

   6.   Form the union of AS-sets A(i) and B(i) and call it AS-set C.
        From AS-set C, remove any ASNs that are present in Z(j), for j=1
        to j=(i-1).  Call the resulting set Z(i).

   7.   If AS-set Z(i) is null, then set i_max = i - 1 and go to Step 8.
        Else, go to Step 3.

   8.   Form the union of the AS-sets, Z(i), i = 1, 2, ..., i_max, and
        name this union as AS-set D.

   9.   Select all ROAs in which the authorized origin ASN is in AS-set
        D.  Form the union of the sets of prefixes listed in the
        selected ROAs.  Name this union set of prefixes as Prefix-set
        P1.

   10.  Using the routes in Adj-RIBs-In of all interfaces, create a list
        of all prefixes originated by any ASN in AS-set D.  Name this
        set of prefixes as Prefix-set P2.

   11.  Form the union of Prefix-sets P1 and P2.  Apply this union set
        as the list of permissible prefixes for SAV.

5.  Operational Recommendations

   Network operators SHOULD implement the BAR-SAV method (Section 4) for
   computing the permissible ingress prefix list for SAV on interfaces
   facing customers and lateral peers.  BAR-SAV offers immediate
   incremental benefits to early adopters.






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   The operational recommendations provided in Section 3.2 of [RFC8704]
   are applicable and helpful for BAR-SAV (Section 4).  Since Procedure
   X (Section 3) and the BAR-SAV procedure (Section 4) benefit from the
   registration of ROAs, network operators are RECOMMENDED to register
   ROAs and enable ROV in their ASes.  When ASPA becomes available,
   network operators are also RECOMMENDED to register ASPAs at that
   time.

   The registration of ROAs and ASPAs helps with the detection and
   inclusion of otherwise hidden prefixes in the permissible list for
   SAV.  As mentioned earlier, prefixes hidden in other techniques often
   arise from the use of multi-homing in conjunction with limited
   propagation of prefixes in a given CC (for example, by attaching
   NO_EXPORT to all prefixes announced from a customer AS to a transit
   provider AS).  In these situations, the registration of ASPAs helps
   improve the accuracy of SAV.

5.1.  Considerations for the CDN and DSR Scenario

   Direct Server Return (DSR) is a common asymmetric routing scenario
   that is not supported by existing BCP-84 uRPF [RFC3704] and EFP-uRPF
   [RFC8704] SAV methods.  DSR is commonly used by Content Delivery
   Networks (CDNs) that wish to use anycast service addresses but
   deliver data from edge locations that do not announce anycast
   addresses.

   For example, in Figure 1, the CDN announces an anycast prefix P3
   (from AS3) from a well-connected location with CDN control
   infrastructure.  When a User from prefix P1 (AS1) establishes a
   connection to the anycast address and requests an object, an Anycast
   Server at the CDN may determine that the best location to serve the
   object is an Edge Server in a location close to the User.  The Edge
   Server is reachable only via prefix P2 (AS2).  The Anycast Server can
   forward packets arriving from the User to the Edge Server (via IP-IP
   tunneling or similar means), but the bulk data transmission would
   need to happen directly from the Edge Server to the User with an
   anycast source address (a P3 address).














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                    +----------+   P3[AS5 AS3]  +------------+
                    |    AS4   |<---------------|     AS5    |
                    +----------+      (P2P)     +------------+
                        /\   /\                        /\
                        /     \                         \
                P1[AS1]/       \P2[AS2]                  \P3[AS3]
                 (C2P)/         \(C2P)                    \(C2P)
                     /           \                         \
              +----------+    +----------+           +----------+
              |  AS1 (P1)|    | AS2 (P2) |           | AS3 (P3) |
              +-----+----+    +----+-----+           +-----+----+
                    +              +                       +
                  User       Edge Server (DSR)      Anycast Server

              Consider AS4 generating its SAV list
              CDN's ROAs: {P3 AS3}, {P3, AS2}, {P2, AS2}
              AS2 should not/does not announce P3
              With the SAV methods in this document,
                AS4 correctly includes P2 and P3 in its SAV list

     Figure 1: Illustration of how the solution functions for the CDN/
                               DSR scenario.

   Existing SAV methods of [RFC3704] and EFP-uRPF [RFC8704] would not
   allow AS4 to include P3 as a legitimate SA prefix on the interface to
   AS2.  However, if the CDN (owner of prefix P3) registers a ROA object
   authorizing AS2 to originate P3, and AS4 uses an SAV procedure
   specified in this draft, then AS4 will use that ROA object to include
   P3 as a valid source prefix for the AS2 customer interface.  The CDN
   may never want to announce a route to P3 from AS2, but the existence
   of this ROA would result in the construction of an SAV filter that
   would permit AS2 to send data packets with source addresses belonging
   to P3.

   The CDN example above is just one DSR scenario.  There are other
   cloud-based DSR scenarios that include low-latency gaming, mobile
   roaming, corporate networks of global enterprises, and others.

   Recommendation: In a DSR scenario, a network operator SHOULD register
   ROAs authorizing edge server ASes to announce anycast service
   prefixes.  This is in addition to registering a ROA authorizing the
   anycast server AS to announce the anycast prefix.

6.  IANA Considerations

   This document includes no request to IANA.





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7.  Security Considerations

   The security considerations described in [RFC8704], [RFC6811], and
   [I-D.ietf-sidrops-aspa-profile] also apply to this document.

   The security and robustness of BAR-SAV are strengthened by supporting
   mechanisms for detecting and dropping routes that are misoriginations
   or leaks.  It is advised that the BGP UPDATEs received at BGP
   speakers are vetted using ROV (using ROAs and/or trusted IRR route
   objects) and prefix filtering (see [RFC6811] [RFC7454]
   [NIST-800-189]).  It is also advised that one or more of the
   available methods to prevent, detect, and mitigate route leaks are
   also deployed (e.g., [RFC9234]
   [I-D.ietf-grow-route-leak-detection-mitigation]
   [I-D.ietf-sidrops-aspa-verification] [sriram1] [sriram2]).

8.  References

8.1.  Normative References

   [I-D.ietf-sidrops-aspa-profile]
              Azimov, A., Uskov, E., Bush, R., Patel, K., Snijders, J.,
              and R. Housley, "A Profile for Autonomous System Provider
              Authorization", Work in Progress, Internet-Draft, draft-
              ietf-sidrops-aspa-profile-07, 31 January 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-sidrops-
              aspa-profile-07>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
              Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March
              2004, <https://www.rfc-editor.org/info/rfc3704>.






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   [RFC8704]  Sriram, K., Montgomery, D., and J. Haas, "Enhanced
              Feasible-Path Unicast Reverse Path Forwarding", BCP 84,
              RFC 8704, DOI 10.17487/RFC8704, February 2020,
              <https://www.rfc-editor.org/info/rfc8704>.

8.2.  Informative References

   [I-D.ietf-sidrops-aspa-verification]
              Azimov, A., Bogomazov, E., Bush, R., Patel, K., and J.
              Snijders, "Verification of AS_PATH Using the Resource
              Certificate Public Key Infrastructure and Autonomous
              System Provider Authorization", Work in Progress,
              Internet-Draft, draft-ietf-sidrops-aspa-verification-08,
              25 August 2021, <https://datatracker.ietf.org/doc/html/
              draft-ietf-sidrops-aspa-verification-08>.

   [I-D.ietf-grow-route-leak-detection-mitigation]
              Sriram, K. and A. Azimov, "Methods for Detection and
              Mitigation of BGP Route Leaks", Work in Progress,
              Internet-Draft, draft-ietf-grow-route-leak-detection-
              mitigation-07, 26 April 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-grow-
              route-leak-detection-mitigation-07>.

   [sriram1]  Sriram, K. and J. Heitz, "On the Accuracy of Algorithms
              for ASPA Based Route Leak Detection", IETF SIDROPS
              Meeting, Proceedings of the IETF 110, March 2021,
              <https://datatracker.ietf.org/meeting/110/materials/
              slides-110-sidrops-sriram-aspa-alg-accuracy-01>.

   [sriram2]  Sriram, K., "ASPA Verification Procedures: Enhancements
              and RS Considerations", IETF SIDROPS Meeting, Proceedings
              of the IETF 113, March 2022,
              <https://datatracker.ietf.org/meeting/113/materials/
              slides-113-sidrops-aspa-verification-procedures-01>.

   [Monitor]  "NIST RPKI Monitor", National Institute of Standards and
              Technology, accessed June 2022,
              <https://rpki-monitor.antd.nist.gov/>.

   [NIST-800-189]
              Sriram, K. and D. Montgomery, "Resilient Interdomain
              Traffic Exchange: BGP Security and DDoS Mitigation", NIST
              Special Publication, NIST SP 800-189, December 2019,
              <https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
              NIST.SP.800-189.pdf>.





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   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
              February 2012, <https://www.rfc-editor.org/info/rfc6480>.

   [RFC6482]  Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
              Origin Authorizations (ROAs)", RFC 6482,
              DOI 10.17487/RFC6482, February 2012,
              <https://www.rfc-editor.org/info/rfc6482>.

   [RFC6811]  Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
              Austein, "BGP Prefix Origin Validation", RFC 6811,
              DOI 10.17487/RFC6811, January 2013,
              <https://www.rfc-editor.org/info/rfc6811>.

   [RFC7454]  Durand, J., Pepelnjak, I., and G. Doering, "BGP Operations
              and Security", BCP 194, RFC 7454, DOI 10.17487/RFC7454,
              February 2015, <https://www.rfc-editor.org/info/rfc7454>.

   [RFC7908]  Sriram, K., Montgomery, D., McPherson, D., Osterweil, E.,
              and B. Dickson, "Problem Definition and Classification of
              BGP Route Leaks", RFC 7908, DOI 10.17487/RFC7908, June
              2016, <https://www.rfc-editor.org/info/rfc7908>.

   [RFC9234]  Azimov, A., Bogomazov, E., Bush, R., Patel, K., and K.
              Sriram, "Route Leak Prevention and Detection Using Roles
              in UPDATE and OPEN Messages", RFC 9234,
              DOI 10.17487/RFC9234, May 2022,
              <https://www.rfc-editor.org/info/rfc9234>.

Acknowledgements

   The authors would like to thank Oliver Borchert for comments and
   discussion.

Authors' Addresses

   Kotikalapudi Sriram
   USA National Institute of Standards and Technology
   100 Bureau Drive
   Gaithersburg, MD 20899
   United States of America
   Email: ksriram@nist.gov









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   Igor Lubashev
   Akamai Technologies
   145 Broadway
   Cambridge , MA 02142
   United States of America
   Email: ilubashe@akamai.com


   Doug Montgomery
   USA National Institute of Standards and Technology
   100 Bureau Drive
   Gaithersburg, MD 20899
   United States of America
   Email: dougm@nist.gov





































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