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Independent Submission                                    K. Sriram, Ed.
Internet-Draft                                                  USA NIST
Intended status: Informational                          January 19, 2018
Expires: July 23, 2018


      BGPsec Design Choices and Summary of Supporting Discussions
                 draft-sriram-bgpsec-design-choices-16

Abstract

   This document captures the design rationale of the initial draft of
   the BGPsec protocol specification.  The designers needed to balance
   many competing factors, and this document lists the decisions that
   were made in favor of or against each design choice.  This document
   also presents brief summaries of the arguments that aided the
   decision process.  Where appropriate, this document also provides
   brief notes on design decisions that changed as the specification was
   reviewed and updated by the IETF SIDR working group, resulting in RFC
   8205.  These notes highlight the differences and provide pointers to
   details and rationale about those design changes.

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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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on July 23, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   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



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Creating Signatures and the Structure of BGPsec Update
       Messages  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Origin Validation Using ROA . . . . . . . . . . . . . . .   4
     2.2.  Attributes Signed by an Originating AS  . . . . . . . . .   5
     2.3.  Attributes Signed by an Upstream AS . . . . . . . . . . .   6
     2.4.  What Attributes Are Not Signed  . . . . . . . . . . . . .   7
     2.5.  Receiving Router Actions  . . . . . . . . . . . . . . . .   8
     2.6.  Prepending of ASes in AS Path . . . . . . . . . . . . . .   9
     2.7.  What RPKI Data Need be Included in Updates  . . . . . . .   9
   3.  Withdrawal Protection . . . . . . . . . . . . . . . . . . . .  10
     3.1.  Withdrawals Not Signed  . . . . . . . . . . . . . . . . .  10
     3.2.  Signature Expire Time for Withdrawal Protection (a.k.a.
           Mitigation of Replay Attacks) . . . . . . . . . . . . . .  10
     3.3.  Should Route Expire Time be Communicated in a Separate
           Message . . . . . . . . . . . . . . . . . . . . . . . . .  12
     3.4.  Effect of Expire-Time Updates in BGPsec on RFD  . . . . .  13
   4.  Signature Algorithms and Router Keys  . . . . . . . . . . . .  14
     4.1.  Signature Algorithms  . . . . . . . . . . . . . . . . . .  14
     4.2.  Agility of Signature Algorithms . . . . . . . . . . . . .  15
     4.3.  Sequential Aggregate Signatures . . . . . . . . . . . . .  16
     4.4.  Protocol Extensibility  . . . . . . . . . . . . . . . . .  17
     4.5.  Key Per Router (Rogue Router Problem) . . . . . . . . . .  18
     4.6.  Router ID . . . . . . . . . . . . . . . . . . . . . . . .  18
   5.  Optimizations and Resource Sizing . . . . . . . . . . . . . .  18
     5.1.  Update Packing and Repacking  . . . . . . . . . . . . . .  19
     5.2.  Signature Per Prefix vs. Signature Per Update . . . . . .  19
     5.3.  Maximum BGPsec Update PDU Size  . . . . . . . . . . . . .  20
     5.4.  Temporary Suspension of Attestations and Validations  . .  21
   6.  Incremental Deployment and Negotiation of BGPsec  . . . . . .  22
     6.1.  Downgrade Attacks . . . . . . . . . . . . . . . . . . . .  22
     6.2.  Inclusion of Address Family in Capability Advertisement .  22
     6.3.  Incremental Deployment: Capability Negotiation  . . . . .  23
     6.4.  Partial Path Signing  . . . . . . . . . . . . . . . . . .  23
     6.5.  Consideration of Stub ASes with Resource Constraints:
           Encouraging Early Adoption  . . . . . . . . . . . . . . .  24
     6.6.  Proxy Signing . . . . . . . . . . . . . . . . . . . . . .  25
     6.7.  Multiple Peering Sessions Between ASes  . . . . . . . . .  26
   7.  Interaction of BGPsec with Common BGP Features  . . . . . . .  26
     7.1.  Peer Groups . . . . . . . . . . . . . . . . . . . . . . .  26



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     7.2.  Communities . . . . . . . . . . . . . . . . . . . . . . .  27
     7.3.  Consideration of iBGP Speakers and Confederations . . . .  28
     7.4.  Consideration of Route Servers in IXPs  . . . . . . . . .  28
     7.5.  Proxy Aggregation (a.k.a. AS_SETs)  . . . . . . . . . . .  29
     7.6.  4-Byte AS Numbers . . . . . . . . . . . . . . . . . . . .  30
   8.  BGPsec Validation . . . . . . . . . . . . . . . . . . . . . .  30
     8.1.  Sequence of BGPsec Validation Processing in a Receiver  .  30
     8.2.  Signing and Forwarding Updates when Signatures Failed
           Validation  . . . . . . . . . . . . . . . . . . . . . . .  32
     8.3.  Enumeration of Error Conditions . . . . . . . . . . . . .  32
     8.4.  Procedure for Processing Unsigned Updates . . . . . . . .  33
     8.5.  Response to Syntactic Errors in Signatures and
           Recommendation for Reaction . . . . . . . . . . . . . . .  34
     8.6.  Enumeration of Validation States  . . . . . . . . . . . .  35
     8.7.  Mechanism for Transporting Validation State through iBGP   36
   9.  Operational Considerations  . . . . . . . . . . . . . . . . .  38
     9.1.  Interworking with BGP Graceful Restart  . . . . . . . . .  38
     9.2.  BCP Recommendations for Minimizing Churn: Certificate
           Expiry/Revocation and Signature Expire Time . . . . . . .  39
     9.3.  Outsourcing Update Validation . . . . . . . . . . . . . .  39
     9.4.  New Hardware Capability . . . . . . . . . . . . . . . . .  40
     9.5.  Signed Peering Registrations  . . . . . . . . . . . . . .  40
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  41
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  41
   12. Informative References  . . . . . . . . . . . . . . . . . . .  41
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  46
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  47
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  48

1.  Introduction

   The goal of BGPsec effort is to enhance the security of BGP by
   enabling full AS path validation based on cryptographic principles.
   Standards work on route origin validation based on a Resource
   certificate PKI (RPKI) is already completed or nearing completion in
   the IETF SIDR WG.  The BGPsec effort is aimed at taking advantage of
   the same RPKI infrastructure developed in the SIDR WG to add
   cryptographic signatures to BGP updates, so that routers can perform
   full AS path validation [RFC7132] [RFC7353] [RFC8205].  The BGPsec
   protocol specification RFC was published recently [RFC8205].  The key
   high-level design goals of the BGPsec protocol are as follow
   [RFC7353]:

   o  Rigorous path validation for all announced prefixes; not merely
      showing that a path is not impossible.

   o  Incremental deployment capability; no flag-day requirement for
      global deployment.



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   o  Protection of AS paths only in inter-domain routing (eBGP); not
      applicable to iBGP (or to IGPs).

   o  Aim for no increase in provider's data exposure (e.g., require no
      disclosure of peering relations, etc.).

   This document provides design justifications for the initial draft of
   the BGPsec protocol specification [I-D.lepinski-bgpsec-protocol].
   The designers needed to balance many competing factors, and this
   document lists the decisions that were made in favor of or against
   each design choice.  This document also presents brief summaries of
   the discussions that weighed in the pros and cons and aided the
   decision process.  Where appropriate, this document provides brief
   notes (starting with "Note:") on design decisions that changed from
   the approach taken in the initial draft of the BGPsec protocol
   specification as the specification was reviewed and updated by the
   IETF SIDR working group, resulting in [RFC8205].  The notes provide
   pointers to the details and/or discussion about the design changes.

   The design choices and discussions are presented under the following
   eight broad categories (with many subtopics within each category):
   (1) Creating Signatures and the Structure of BGPsec Update Messages,
   (2) Withdrawal Protection, (3) Signature Algorithms and Router Keys,
   (4) Optimizations and Resource Sizing, (5) Incremental Deployment and
   Negotiation of BGPsec, (6) Interaction of BGPsec with Common BGP
   Features, (7) BGPsec Validation, and (8) Operational Considerations.

2.  Creating Signatures and the Structure of BGPsec Update Messages

2.1.  Origin Validation Using ROA

2.1.1.  Decision

   Route origin validation using Route Origin Authorization (ROA)
   [RFC6482] [RFC6811] is necessary and complements AS path attestation
   based on signed updates.  Thus, BGPsec design makes use of the origin
   validation capability facilitated by the ROAs in RPKI.

   Note: In the finalized BGPsec protocol specification [RFC8205],
   BGPsec is synonymous with cryptographic AS path attestation.  Origin
   validation and BGPsec (path signatures) are the two key pieces of the
   SIDR WG solution for BGP security.

2.1.2.  Discussion

   Route origin validation using RPKI constructs as developed in the
   IETF SIDR WG is a necessary component of BGP security.  It provides




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   cryptographic validation that the first hop AS is authorized to
   originate a route for the prefix in question.

2.2.  Attributes Signed by an Originating AS

2.2.1.  Decision

   An originating AS will sign over the NLRI length, NLRI prefix, its
   own AS number (ASN), the next ASN, the signature algorithm suite ID,
   and a signature Expire Time (see Section 3.2) for the update.  The
   update signatures will be carried in a new optional, non-transitive
   BGP attribute.

   Note: The finalized BGPsec protocol specification [RFC8205] differs
   from the above.  There is no mention of a signature Expire Time field
   in the BGPsec update in RFC 8205.  Further, there are some additional
   details concerning attributes signed by the origin AS that can be
   found in Figure 8 in Section 4.2 of RFC 8205 [RFC8205].  In
   particular, the signed data also includes the Address Family
   Identifier (AFI) in RFC 8205.  By adding the AFI in the data covered
   by signature, a specific security concern was alleviated; see SIDR
   list post [Mandelberg1] and the discussion thread that followed on
   the topic.  The AFI is obtained from the MP_REACH_NLRI attribute in
   the BGPsec update.  It is stated in Section 4.1 of RFC 8205 that
   BGPsec update message MUST use the MP_REACH_NLRI attribute [RFC4760]
   to encode the prefix.

2.2.2.  Discussion

   The next hop ASN is included in the data covered by the signature.
   Without that the AS path cannot be secured; for example, it can be
   shortened (by a MITM) without being detected.

   It was decided that only the originating AS needs to insert a
   signature Expire Time in the update, as it is the originator of the
   route.  The origin AS also will re-originate, i.e., beacon, the
   update prior to the Expire Time of the advertisement (see
   Section 3.2).  (For an explanation of why upstream ASes do not insert
   their respective signature Expire Times, please see Section 3.2.2.)

   Note: Expire Time and beaconing were eventually replaced by router
   key rollover.  The BGPsec protocol [RFC8205] is expected to make use
   of router key rollover to mitigate against replay attacks and
   withdrawal suppression [I-D.ietf-sidrops-bgpsec-rollover]
   [I-D.sriram-replay-protection-design-discussion].

   It was decided that each signed update would include only one NLRI
   prefix.  If more than one NLRI prefix were included, and an upstream



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   AS elected to propagate the advertisement for a subset of the
   prefixes, then the signature(s) on the update would break (see
   Section 5.1 and Section 5.2).  If a mechanism were employed to
   preserve prefixes that were dropped, this would reveal info to later
   ASes that is not revealed in normal BGP operation.  Thus, a tradeoff
   was made to preserve the level of route info exposure that is
   intrinsic to BGP over the performance hit implied by limiting each
   update to carry only one prefix.

   The signature data is carried in an optional, non-transitive BGP
   attribute.  The attribute is optional because this is the standard
   mechanism available in BGP to propagate new types of data.  It was
   decided that the attribute should be non-transitive because of
   concern about the impact of sending the (potentially large)
   signatures to routers that don't understand them.  Also, if a router
   that doesn't understand BGPsec somehow gets a message with the
   signatures attribute then it would be undesirable for that router to
   forward the signatures to all its neighbors, especially those who do
   not understand BGPsec and may choke if they receive many updates with
   large optional BGP attributes.  It is envisioned that BGPsec and
   traditional BGP will co-exist while BGPsec is deployed incrementally.

2.3.  Attributes Signed by an Upstream AS

   In the context of BGPsec and throughout this document, an "upstream
   AS" simply refers to an AS that is further along in an AS path
   (origin AS being the nearest to a prefix).  In principle, an AS that
   is upstream from an originating AS would digitally sign the combined
   information including the NLRI length, NLRI prefix, AS path, next
   ASN, signature algorithm suite ID, and Expire Time.  There are
   multiple choices for what is signed by an upstream AS as follows.
   Method 1: Signature protects the combination of NLRI length, NLRI
   prefix, AS path, next ASN, signature algorithm suite ID, and Expire
   Time; or Method 2: Signature protects just the combination of
   previous signature (i.e., signature of the neighbor AS who forwarded
   the update) and next ASN; or Method 3: Signature protects everything
   that was received from preceding AS plus next (i.e., target) ASN;
   thus, ASi signs over NLRI length, NLRI prefix, signature algorithm
   suite ID, Expire Time, {ASi, AS(i-1), AS(i-2), ..., AS2, AS1},
   AS(i+1)(i.e., next ASN), and {Sig(i-1), Sig(i-2), ..., Sig2, Sig1}.

   Note: Please see the notes in Section 2.2.1 and Section 2.2.2 about
   elimination of Expire Time field in the finalized BGPsec protocol
   specification [RFC8205].







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2.3.1.  Decision

   It was decided that that Method 2 will be used.  Please see
   [I-D.lepinski-bgpsec-protocol] for additional protocol details and
   syntax.

   Note: The finalized BGPsec protocol specification [RFC8205]
   essentially uses Method 3 (except for Expire Time).  Additional
   details concerning attributes signed by an upstream AS can be found
   in Figure 8 in Section 4.2 of RFC 8205 [RFC8205].  The decision to go
   with Method 3 (with suitable additions to the data signed) was
   motivated by a security concern that was associated with Method 2;
   see SIDR list post [Mandelberg2] and the discussion thread that
   followed on the topic.  Also, there is a strong rationale for the
   sequence octets to be hashed (as shown in Figure 8 in Section 4.2 of
   RFC 8205) and this sequencing of data is motivated by implementation
   efficiency considerations; see SIDR list post [Borchert] for an
   explanation.

2.3.2.  Discussion

   The rationale for this choice (Method 2) was as follows.  Signatures
   are performed over hash blocks.  When the number of bytes to be
   signed exceeds one hash block, then the remaining bytes will overflow
   into a second hash block, which results in performance penalty.  So
   it is advantageous to minimize the number of bytes being hashed.
   Also, an analysis of the three options noted above did not identify
   any vulnerabilities associated with this approach.

2.4.  What Attributes Are Not Signed

2.4.1.  Decision

   Any attributes other than those identified in Section 2.2 and
   Section 2.3 are not signed.  Examples of such attributes are
   Community Attribute, NO-EXPORT Attribute, Local_Pref, etc.

2.4.2.  Discussion

   The above stated attributes that are not signed are viewed as local
   (e.g., do not need to propagate beyond next hop) or lack clear
   security needs.  NO-EXPORT is sent over a secured next-hop and does
   not need signing.  BGPsec design should work with any transport layer
   protections.  It is well understood that the transport layer must be
   protected hop by hop (if only to prevent malicious session
   termination).





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2.5.  Receiving Router Actions

2.5.1.  Decision

   The expected router actions on receipt of a signed update are
   described by the following example.  Consider an update that was
   originated by AS1 with NLRI prefix p and has traversed the AS path
   [AS(i-1) AS(i-2) .... AS2 AS1] before arriving at ASi.  Let the
   Expire Time (inserted by AS1) for the signature in this update be
   denoted as Te.  Let AlgID represent the ID of the signature algorithm
   suite that is in use.  The update is to be processed at ASi and
   possibly forwarded to AS(i+1).  Let the attestations (signatures)
   inserted by each router in the AS path be denoted by Sig1, Sig2, ...,
   Sig(i-2), and Sig(i-1) corresponding to AS1, AS2, ... , AS(i-2), and
   AS(i-1), respectively.

   The method (#2 in Section 2.3) selected for signing requires a
   receiving router in ASi to perform the following actions:

   o  Validate the route origin pair (p, AS1) by performing a ROA match.

   o  Verify that Te is greater than the clock time at the router
      performing these checks.

   o  Check Sig1 with inputs {NLRI length, p, AlgID, Te, AS1, AS2}.

   o  Check Sig2 with inputs {Sig1, AS3}.

   o  Check Sig3 with inputs {Sig2, AS4}.

   o  ...

   o  ...

   o  Check Sig(i-2) with inputs {Sig(i-3), AS(i-1)}.

   o  Check Sig(i-1) with inputs {Sig(i-2), ASi}.

   o  If the route that has been verified is selected as the best path
      (for prefix p), then generate Sig(i) with inputs {Sig(i-1),
      AS(i+1)}, and generate an update including Sig(i) to AS(i+1).

   Note: The above description of BGPsec update validation and
   forwarding differs in its details from the published BGPsec protocol
   specification [RFC8205].  Please see Sections 4 and 5 of [RFC8205].






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2.5.2.  Discussion

   See Section 8.1 for suggestions regarding efficient sequencing of
   BGPsec validation processing in a receiving router.  Some or all the
   validation actions may be performed by an off-board server (see
   Section 9.3).

2.6.  Prepending of ASes in AS Path

2.6.1.  Decision

   Prepending will be allowed.  Prepending is defined as including more
   than one instance of the AS number (ASN) of the router that is
   signing the update.

   Note: The finalized protocol specification uses a pCount field
   associated with each AS in the path to indicate the number of
   prepends for that AS (see Figure 5, Section 3.1 of [RFC8205]).

2.6.2.  Discussion

   The draft-00 version of the protocol specification calls for a
   signature to be associated with each prepended AS.  The optimization
   of having just one signature for multiple prepended ASes will be
   pursued later (i.e., beyond draft-00 specification).  If such
   optimization is used, a replication count would be included (in the
   signed update) to specify how many times an AS was prepended.

2.7.  What RPKI Data Need be Included in Updates

2.7.1.  Decision

   Concerning inclusion of RPKI data in an update, it was decided that
   only the Subject Key Identifier (SKI) of the router cert must be
   included in a signed update.  This info identifies the router
   certificate, based on the SKI generation criteria defined in
   [RFC6487].

2.7.2.  Discussion

   It was discussed if each router public key certificate should be
   included in a signed update.  Inclusion of this information might be
   helpful for routers that do not have access to RPKI servers or
   temporarily lose connectivity to them.  It is safe to assume that in
   majority of network environments, intermittent connectivity would not
   be a problem.  So it is best to avoid this complexity because
   majority of the use environments do not have connectivity
   constraints.  Because the SKI of a router certificate is a hash of



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   the public key of that certificate, it suffices to select the public
   key from that certificate.  This design assumes that each BGPsec
   router has access to a cache containing the relevant data from
   (validated) router certificates.

3.  Withdrawal Protection

3.1.  Withdrawals Not Signed

3.1.1.  Decision

   Withdrawals are not signed.

3.1.2.  Discussion

   In the current BGP protocol, any AS can withdraw, at any time, any
   prefix it previously announced.  The rationale for not signing
   withdrawals is that BGPsec assumes use of transport security between
   neighboring BGPsec routers.  Thus, no external entity can inject an
   update that withdraws a route or replay a previously transmitted
   update containing a withdrawal.  Because the rationale for
   withdrawing a route is not visible to a neighboring BGPsec router,
   there are residual vulnerabilities associated with withdrawals.  For
   example, a router that advertised a (valid) route may fail to
   withdraw that route when it is no longer viable.  A router also might
   re-advertise a route that it previously withdrew, before the route is
   again viable.  This latter vulnerability is mitigated by the Expire
   Time value in an AS path signature (see Section 3.2).

   Repeated withdrawals and announcements for a prefix can run up the
   BGP RFD penalty and may result in unreachability for that prefix at
   upstream routers.  But what can the attacker gain from doing so?
   This phenomenon is intrinsic to the design and operation of RFD.

3.2.  Signature Expire Time for Withdrawal Protection (a.k.a.
      Mitigation of Replay Attacks)

3.2.1.  Decision

   Note: As mentioned earlier in Section 2.2.2, the Expire Time approach
   to mitigation of replay attacks and withdrawal suppression was
   subsequently changed to an approach based on router key rollover
   [I-D.ietf-sidrops-bgpsec-rollover]
   [I-D.sriram-replay-protection-design-discussion].

   Only the originating AS inserts a signature Expire Time in the
   update; all other ASes along an AS path do not insert Expire Times
   associated with their respective signatures.  Further, the



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   originating AS will re-originate a route sufficiently in advance of
   the Expire Time of its signature so that other ASes along an AS path
   will typically receive the re-originated route well ahead of the
   current Expire Time for that route.

   The duration of the signature Expire Time is recommended to be on the
   order of days (preferably) but it may be on the order of hours (about
   4 to 8 hours) in some cases, where extra replay protection is
   perceived to be critical.

   Each AS should stagger the Expire Time values in the routes it
   originates.  Re-origination will be done, say, at time Tb after
   origination or the last re-origination, where Tb will equal a certain
   percentage of the Expire Time, Te (for example, Tb = 0.75 x Te).  The
   percentage will be configurable and additional guidance can be
   provided via an operational considerations document later.  Further,
   the actual re-origination time should to be jittered with a uniform
   random distribution over a short interval {Tb1, Tb2} centered at Tb.

   It is also recommended that a receiving BGPsec router should detect
   if the only attribute change in an announcement (relative to the
   current best path) is the expire time (besides, of course, the
   signatures).  In that case, assuming that the update is found valid,
   the route processor should not re-announce the route to non-BGPsec
   peers.  (It should sign and re-announce the route to only BGPsec
   speakers.)  This procedure will reduce BGP chattiness for the non-
   BGPsec border routers.

3.2.2.  Discussion

   Mitigation of BGPsec update replay attacks can be thought of as
   protection against malicious re-advertisement of withdrawn routes.
   If each AS along a path were to insert its own signature Expire Time,
   then there would be much additional BGP chattiness and increase in
   BGP processing load due to the need to detect and react to multiple
   (possibly redundant) signature Expire Times.  Furthermore, there
   would be no extra benefit from the point of view of mitigation of
   replay attacks as compared to having a single Expire Time
   corresponding to the signature of the originating AS.

   The recommended Expire Time value is on the order of days but 4 to 8
   hours may used in some cases on the basis of perceived need for extra
   protection from replay attacks.  Thus, different ASes may choose
   different values based on the perceived need to protect against
   malicious route replays.  (A shorter Expire Time reduces the window
   during which an AS can maliciously replay the route.  However,
   shorter Expire Time values cause routes to be refreshed more often,
   and thus causes more BGP chatter.)  Even a 4 hours duration seems



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   long enough to keep the re-origination workload manageable.  For
   example, if 500K routes are re-originated every 4 hours, it amounts
   to an increase in BGP update load of 35 updates per second; this can
   be considered reasonable.  However, further analysis is needed to
   confirm these recommendations.

   It was stated above that originating AS will re-originate a route
   sufficiently in advance of its Expire Time.  What is considered
   sufficiently in advance?  For this, modeling should be performed to
   determine the 95th-percentile convergence time of update propagation
   in BGPsec enabled Internet.

   Each BGPsec router should stagger the Expire Time values in the
   updates it originates, especially during table dumps to a neighbor or
   during its own recovery from a BGP session failure.  By doing this,
   the re-origination (i.e., beaconing) workload at the router will be
   dispersed.

3.3.  Should Route Expire Time be Communicated in a Separate Message

3.3.1.  Decision

   The idea of sending a new signature expire time in a special message
   (rather than re-transmitting the entire update with signatures) was
   considered.  However, it was decided not to do this.  Re-origination
   to communicate a new signature Expire Time will be done by
   propagation of a normal update message; no special type of message
   will be required.

3.3.2.  Discussion

   It was suggested that if re-beaconing of signature Expire Time is
   carried in a separate special message, then update processing load
   may be reduced.  But it was recognized that such re-beaconing message
   necessarily entails AS path and prefix information, and hence cannot
   be separated from the update.

   It was observed that at the edge of the Internet, there are frequent
   updates that may result from simple situations like BGP session being
   switched from one interface to another (e.g., from primary to backup)
   between two peering ASes (e.g., customer and provider).  With
   traditional BGP, these updates do not propagate beyond the two ASes
   involved.  But with BGPsec, the customer AS will put in a new
   signature Expire Time each time such an event happens, and hence the
   update will need to propagate throughout the Internet (limited only
   by best path selection process).  It was accepted that this cost of
   added churn will be unavoidable.




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3.4.  Effect of Expire-Time Updates in BGPsec on RFD

3.4.1.  Decision

   With regard to the Route Flap Damping (RFD) protocol
   [RFC2439][JunOS][CiscoIOS], no differential treatment is required for
   Expire-Time triggered (re-beaconed) BGPsec updates.

   However, it was noted that it would be preferable if these updates
   did not cause route churn (and perhaps not even require any RFD
   related processing), since they are identical except for the change
   in the Expire Time value.  The way this can be accomplished is by not
   assigning RFD penalty to Expire-Time triggered updates.  If the
   community agrees, this could be accommodated, but a change to the
   BGP-RFD protocol specification will be required.

3.4.2.  Discussion

   Summary:

   The decision is supported by the following observations: (1) Expire
   Time-triggered updates are generally not preceded by withdrawals, and
   hence the path hunting and associated RFD exacerbation
   [Mao02][RIPE580] problems are not anticipated; (2) Such updates would
   not normally change the best path (unless another concurrent event
   impacts the best path); (3) Expire Time-triggered updates would have
   negligible impact on RFD penalty accumulation because the re-
   advertisement interval is much longer relative to the half-time of
   decay of RFD penalty.  Elaborating further on reason #3 above, it may
   be noted that the re-advertisements (i.e., beacons) of a route for a
   given address prefix from a given peer will be received at intervals
   of a few or several hours (see Section 3.2).  During that time
   period, any incremental contribution to RFD penalty due to a Expire
   Time-triggered update would decay sufficiently to have negligible (if
   any) impact on damping the address prefix in consideration.
   Additional details of this analysis and justification can be found
   below.

   Further Details of the Analysis and Justification:

   The frequency with which RFD penalty increments may be triggered for
   a given prefix from a given peer is the same as the re-beaconing
   frequency for that prefix from its origin AS.  The re-beaconing
   frequency is on the order of once every few or several hours (see
   Section 3.2).  The incremental RFD penalty assigned to a prefix due
   to a re-beaconed update varies depending on the implementation.  For
   example, it appears that JunOS implementation [JunOS] would assign a
   penalty of 1000 or 500 depending on whether the re-beaconed update is



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   regarded as a re-advertisement or an attribute change, respectively.
   Normally, a re-beaconed update would be treated as a case of
   attribute change.  The Cisco implementation [CiscoIOS] on the other
   hand assigns an RFD penalty only in the case of an actual flap (i.e.,
   a route is available, then unavailable, or vice versa).  So it
   appears that Cisco implementation of RFD would not assign any penalty
   for a re-beaconed update (i.e., a route was already advertised
   previously; not withdrawn; and the re-beaconed update is merely
   updating the expire time attribute).  Even if one assumes that an RFD
   penalty of 500 is assigned (corresponding to attribute change in
   JunOS RFD implementation), it can be illustrated that the incremental
   affect it would have on damping the prefix in consideration would be
   negligible.  The reason for this is as follows.  The half-time of RFD
   penalty decay is normally set to 15 minutes, whereas the re-beaconing
   frequency is on the order of once every few or several hours.  An
   incremental penalty of 500 would decay to 31.25 in one hour; 0.12 in
   two hours; 3x10^(-5) in three hours.  It may also be noted that the
   threshold for route suppression is 3000 in JunOS and 2000 in Cisco
   IOS.  Based on the foregoing analysis, it may be concluded that
   routine re-beaconing by itself would not result in RFD suppression of
   routes in the BGPsec protocol.

4.  Signature Algorithms and Router Keys

4.1.  Signature Algorithms

4.1.1.  Decision

   Initially, ECDSA with Curve P-256 and SHA-256 will be used for
   generating BGPsec path signatures.  One other signature algorithm,
   e.g., RSA-2048 will also be used during prototyping and testing.  The
   use of a second signature algorithm is needed to verify the ability
   of the BGPsec implementations to change from a current algorithm to
   the next algorithm.

   Note: The BGPsec cryptographic algorithms document [RFC8208]
   specifies only ECDSA with Curve P-256 and SHA-256.

4.1.2.  Discussion

   Initially, choice of RSA-2048 algorithm for BGPsec update signatures
   was considered because it is being used ubiquitously in the RPKI
   system.  However, the use of ECDSA P-256 algorithm was decided
   because it yields a smaller signature size, and hence the update size
   and in turn the RIB size needed in BGPsec routers would be much
   smaller [RIB_size].





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   Testing with two different signature algorithms (e.g., ECDSA P-256
   and RSA-2048) for transition from one to the other will increase
   confidence in prototype implementations.

   For Elliptic Curve Cryptography (ECC) algorithms, according to
   [RFC6090], optimizations and specialized algorithms (e.g., for speed-
   ups) have active IPR, but the basic (unoptimized) algorithms do not
   have IPR encumbrances.

   Note: Recently, even open source implementations have incorporated
   certain cryptographic optimizations and demonstrated significant
   performance speedup [Gueron].  Researchers continue to devote
   significant efforts to demonstrate substantial speedup for ECDSA as
   part of BGPsec implementations [Mehmet1] [Mehmet2].

4.2.  Agility of Signature Algorithms

4.2.1.  Decision

   During the transition period from one algorithm, i.e., current
   algorithm, to the next (new) algorithm, the updates will carry two
   sets of signatures (i.e., two Signature-List Blocks), one
   corresponding to each algorithm.  Each Signature-List Block will be
   preceded by its type-length field and an algorithm-suite identifier.
   A BGPsec speaker that has been upgraded to handle the new algorithm
   should validate both Signature-List Blocks, and then add its
   corresponding signature to each Signature-List Block for forwarding
   the update to the next AS.  A BGPsec speaker that has not been
   upgraded to handle the new algorithm will strip off the Signature-
   List Block of the new algorithm, and forward the update after adding
   its own sig to the Signature-List Block of the current algorithm.

   It was decided that there will be at most two Signature-List Blocks
   per update.

   Note: Signature-List Block is Signature_Block in RFC 8205.  The
   algorithm agility scheme described in the published BGPsec protocol
   specification is consistent with the above; see Section 6.1 of
   [RFC8205].

4.2.2.  Discussion

   A length field in the Signature-List Block allows for delineation of
   the two signature blocks.  Hence, a BGPsec router that doesn't know
   about a particular algorithm suite (and hence doesn't know how long
   signatures were for that algorithm suite) could still skip over the
   corresponding Signature-List Block when parsing the message.




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   The overlap period between the two algorithms is expected to last two
   to four years.  The RIB memory and cryptographic processing capacity
   will have to be sized to cope with such overlap periods when updates
   would contain two sets of signatures [RIB_size].

   The lifetime of a signature algorithm is anticipated to be much
   longer than the duration of a transition period from current to new
   algorithm.  It is fully expected that all ASes will have converted to
   the required new algorithm within a certain amount of time that is
   much shorter than the interval in which a subsequent newer algorithm
   may be investigated and standardized for BGPsec.  Hence, the need for
   more than two Signature-List Blocks per update is not envisioned.

4.3.  Sequential Aggregate Signatures

4.3.1.  Decision

   There is currently weak or no support for the Sequential Aggregate
   Signature (SAS) approach.  Please see in the discussion section below
   for a brief description of what SAS is and what its pros and cons
   are.

4.3.2.  Discussion

   In Sequential Aggregate Signature (SAS) method, there would be only
   one (aggregated) signature per signature block, irrespective of the
   number of AS hops.  For example, ASn (nth AS) takes as input the
   signatures of all previous ASes [AS1, ..., AS(n-1)] and produces a
   single composite signature.  This composite signature has the
   property that a recipient who has the public keys for AS1, ..., ASn
   can verify (using only the single composite signature) that all of
   the ASes actually signed the message.  SAS could potentially result
   in savings in bandwidth, PDU size, and maybe in RIB size but the
   signature generation and validation costs will be higher as compared
   to one signature per AS hop.

   SAS schemes exist in the literature, typically based on RSA or
   equivalent.  For SAS with RSA and for the cryptographic strength
   needed for BGPsec signatures, a 2048-bit signature size (RSA-2048)
   would be required.  However, without SAS, ECDSA with 512-bit
   signature (256-bit key) would suffice for equivalent cryptographic
   strength.  The larger signature size of RSA used with SAS undermines
   the advantages of SAS, because the average hop count, i.e., number of
   ASes, for a route is about 3.8.  In the end, it may turn out that SAS
   has more complexity and does not provide sufficient savings in PDU
   size or RIB size to merit its use.  Further exploration of this is
   needed to better understand SAS properties and applicability for




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   BGPsec.  There is also a concern that SAS is not a time-tested
   cryptographic technique and thus its adoption is potentially risky.

4.4.  Protocol Extensibility

   There is a clearly a need to specify a transition path from a current
   protocol specification to a new version.  When changes to the
   processing of the BGPsec path signatures are required, that will
   require a new version of BGPsec.  Examples of this include changes to
   the data that is protected by the BGPsec signatures or adoption of a
   signature algorithm in which the number of signatures in the
   signature block may not correspond to one signature per AS in the AS-
   PATH (e.g., aggregate signatures).

4.4.1.  Decision

   The protocol-version transition mechanism here is analogous to the
   algorithm transition discussed in Section 4.2.  During the transition
   period from one protocol version (i.e., current version) to the next
   (new) version, updates will carry two sets of signatures (i.e., two
   Signature-List Blocks), one corresponding to each version.  A
   protocol-version identifier is associated with each Signature-List
   Block.  Hence, each Signature-List Block will be preceded by its
   type-length field and a protocol-version identifier.  A BGPsec
   speaker that has been upgraded to handle the new version should
   validate both Signature-List Blocks, and then add its corresponding
   signature to each Signature-List Block for forwarding the update to
   the next AS.  A BGPsec speaker that has not been upgraded to handle
   the new protocol version will strip off the Signature-List Block of
   the new version, and forward the update with an attachment of its own
   signature to the Signature-List Block of the current version.

   Note: Signature-List Block is Signature_Block in RFC 8205.  The
   details of protocol extensibility (i.e., transition to a new version
   of BGPsec) in the published BGPsec protocol specification (see
   Section 6.3 in [RFC8205]) differ somewhat from the above.  In
   particular, the protocol-version identifier is not part of the BGPsec
   update.  Instead, it is negotiated during BGPsec capability exchange
   during the BGPsec session negotiation.

4.4.2.  Discussion

   In the case that change to BGPsec is deemed desirable, it is expected
   that a subsequent version of BGPsec would be created and that this
   version of BGPsec would specify a new BGP Path Attribute, let's call
   it BGPsec_PATH_SIG_TWO, which is designed to accommodate the desired
   changes to BGPsec.  At this point a transition would begin which is
   analogous to the algorithm transition discussed in Section 4.2.



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   During the transition period, all BGPsec speakers will simultaneously
   include both the BGPsec_Path_Signatures (current) attribute and the
   new BGPsec_PATH_SIG_TWO attribute.  Once the transition is complete,
   the use of BGPsec_Path_Signatures could then be deprecated, at which
   point BGPsec speakers will include only the new BGPsec_PATH_SIG_TWO
   attribute.  Such a process could facilitate a transition to a new
   BGPsec semantics in a backwards compatible fashion.

4.5.  Key Per Router (Rogue Router Problem)

4.5.1.  Decision

   Within each AS, each individual BGPsec router can have a unique pair
   of private and public keys [RFC8207].

4.5.2.  Discussion

   Given unique key pair per router, if a router is compromised, its key
   pair can be revoked independently, without disrupting the other
   routers in the AS.  Each per-router key-pair will be represented in
   an end-entity certificate issued under the CA cert of the AS.  The
   Subject Key Identifier (SKI) in the signature points to the router
   certificate (and thus the unique public key) of the router that
   affixed its signature, so that a validating router can reliably
   identify the public key to use for signature verification.

4.6.  Router ID

4.6.1.  Decision

   The router certificate Subject name will be the string "router"
   followed by a decimal representation of a 4-byte AS number followed
   by the router ID.  See the current RFCs for preferred standard
   textual representations for 4-byte ASNs [RFC5396] and router IDs
   [RFC6891].

4.6.2.  Discussion

   Every X.509 certificate requires a Subject name.  The stylized
   Subject name adopted here is intended to facilitate debugging, by
   including the ASN and router ID.

5.  Optimizations and Resource Sizing








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5.1.  Update Packing and Repacking

   With traditional BGP protocol [RFC4271], an originating BGP router
   normally packs multiple prefix announcements into one update if the
   prefixes all share the same BGP attributes.  When an upstream BGP
   router forwards eBGP updates to its peers, it can also pack multiple
   prefixes (based on shared AS path and attributes) into one update.
   The update propagated by the upstream BGP router may include only a
   subset of the prefixes that were packed in a received update.

5.1.1.  Decision

   Each update contains exactly one prefix.  This avoids the complexity
   that would be otherwise inevitable if the origin had packed and
   signed multiple prefixes in an update and an upstream AS decided to
   propagate an update containing only a subset of the prefixes in that
   update.  BGPsec recommendation regarding packing and repacking may be
   be revisited when optimizations are considered in the future.

5.1.2.  Discussion

   Currently, with traditional BGP, there are, on average, approximately
   4 prefixes announced per update [RIB_size].  So the number of BGP
   updates (carrying announcements) is about 4 times fewer, on average,
   as compared to the number of prefixes announced.

   The current decision is to include only one prefix per secured update
   (see Section 2.2 and Section 2.3).  When optimizations are considered
   in the future, the possibility of packing multiple prefixes into an
   update can be considered.  (Please see Section 5.2 for a discussion
   of signature per prefix vs. signature per update.)  Repacking could
   be performed if signatures were generated on a per prefix basis.
   However, one problem regarding this approach, i.e., multiple prefixes
   in a BGP update but with a separate signature for each prefix, is
   that the resulting BGP update violates the basic definition of a BGP
   update.  That is because the different prefixes will have different
   signature and expire-time attributes, while a BGP update (by
   definition) must have the same set of shared attributes for all
   prefixes it carries.

5.2.  Signature Per Prefix vs. Signature Per Update

5.2.1.  Decision

   The initial design calls for including exactly one prefix per update,
   hence there is only one signature in each secured update (modulo
   algorithm transition conditions).  Optimizations will be examined
   later.



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5.2.2.  Discussion

   Some notes to assist in future optimization discussions: In the
   general case of one signature per update, multiple prefixes may be
   signed with one signature together with their shared AS path, next
   ASN, and Expire Time.  If signature per update is used, then there
   are potentially savings in update PDU size as well as RIB memory
   size.  But if there are any changes made to the announced prefix set
   along the AS path, then the AS where the change occurs would need to
   insert an Explicit Path Attribute (EPA)[I-D.draft-clynn-s-bgp].  The
   EPA conveys information regarding what the prefix set contained prior
   to the change.  There would be one EPA for each AS that made such a
   modification, and there would be a way to associate each EPA with its
   corresponding AS.  This enables an upstream AS to be able to know and
   to verify what was announced and signed by prior ASes in the AS path
   (in spite of changes made to the announced prefix set along the way).
   The EPA adds complexity to processing (signature generation and
   validation), further increases the size of updates and, thus of the
   RIB, and exposes data to downstream ASes that would not otherwise be
   exposed.  Not all the pros and cons of packing and repacking in the
   context of signature per prefix vs.  signature per update (with
   packing) have been evaluated.  But the current recommendation is for
   having only one prefix per update (no packing); so there is no need
   for the EPA attribute.

5.3.  Maximum BGPsec Update PDU Size

   The current BGP update message PDU size is limited to 4096 bytes
   [RFC4271].  The question was raised if BGPsec would require a larger
   update PDU size.

5.3.1.  Decision

   The current thinking is that the max PDU size should be increased to
   64 KB [I-D.ietf-idr-bgp-extended-messages] so that there is
   sufficient room to accommodate two signature-list blocks (i.e., one
   block with a current algorithm and another block with a new signature
   algorithm during a future transition period) for long AS paths.

   Note: RFC 8205 states the following: "All BGPsec update messages MUST
   conform to BGP's maximum message size.  If the resulting message
   exceeds the maximum message size, then the guidelines in Section 9.2
   of RFC 4271 [RFC4271] MUST be followed."








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5.3.2.  Discussion

   The current maximum message size for BGP updates is 4096 octets.
   There is effort underway in the IETF to extend it to a larger size
   [I-D.ietf-idr-bgp-extended-messages].  BGPsec will conform to
   whatever maximum message size that is available for BGP while
   adhering to the guidelines in Section 9.2 of RFC 4271 [RFC4271].

   Note: Estimates for the average and maximum sizes anticipated for
   BGPsec update messages are provided in [MsgSize].

5.4.  Temporary Suspension of Attestations and Validations

5.4.1.  Decision

   If a BGPsec-capable router needs to temporarily suspend/defer signing
   and/or validation of BGPsec updates during periods of route processor
   overload, the router may do so even though such suspension/deferment
   is not desirable.  The specification does not forbid that.  Following
   any temporary suspension, the router should subsequently send signed
   updates corresponding to the updates for which validation and signing
   were skipped.  The router also may choose to skip only validation but
   still sign and forward updates during periods of congestion.

5.4.2.  Discussion

   In some situations, a BGPsec router may be unable to keep up with the
   workload of performing signing and/or validation.  This can happen,
   for example, during BGP session recovery when a router has to send
   the entire routing table to a recovering router in a neighboring AS
   (see [CPUworkload]).  So it is possible that a BGPsec router
   temporarily pauses performing validation or signing of updates.  When
   the work load eases, the BGPsec router should clear the validation or
   signing backlog, and send signed updates corresponding to the updates
   for which validation and signing were skipped.  During periods of
   overload, the router may simply send unsigned updates (with
   signatures dropped), or may sign and forward the updates with
   signatures (even though the router itself has not yet verified the
   signatures it received).

   A BGPsec-capable AS may request (out-of-band) a BGPsec-capable peer
   AS never to downgrade a signed update to an unsigned update.
   However, in partial deployment scenarios, it is not possible for a
   BGPsec router to require a BGPsec-capable eBGP peer to send only
   signed updates, except for prefixes originated by the peer's AS.

   Note: If BGPsec has not been negotiated with a peer, then a BGPsec
   router forwards only unsigned updates to that peer.  For this, the



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   sending router follows the reconstruction procedure of Section 4.4 in
   [RFC8205] to generate an AS_PATH attribute corresponding to the
   BGPsec_PATH attribute in a received signed update.  If the above
   mentioned temporary suspension is ever applied, then the same AS_PATH
   reconstruction procedure should be utilized.

6.  Incremental Deployment and Negotiation of BGPsec

6.1.  Downgrade Attacks

6.1.1.  Decision

   No attempt will be made in BGPsec design to prevent downgrade
   attacks, i.e., a BGPsec-capable router sending unsigned updates when
   it is capable of sending signed updates.

6.1.2.  Discussion

   BGPsec allows routers to temporarily suspend signing updates (see
   Section 5.4).  Therefore, it would be contradictory if we were to try
   to incorporate in the BGPsec protocol a way to detect and reject
   downgrade attacks.  One proposed way for detecting downgrade attacks
   was considered, based on signed peering registrations (see
   Section 9.5).

6.2.  Inclusion of Address Family in Capability Advertisement

6.2.1.  Decision

   It was decided that during capability negotiation, the address family
   for which the BGPsec speaker is advertising support for BGPsec will
   be shared using the Address Family Identifier (AFI).  Initially, two
   address families would be included, namely, IPv4 and IPv6.  BGPsec
   for use with other address families may be specified in the future.
   Simultaneous use of the two (i.e., IPv4 and IPv6) address families
   for the same BGPsec session will require that the BGPsec speaker must
   include two instances of this capability (one for each address
   family) during BGPsec capability negotiation.

6.2.2.  Discussion

   If new address families are supported in the future, they will be
   added in future versions of the specification.  A comment was made
   that too many version numbers are bad for interoperability.  Re-
   negotiation on the fly to add a new address family (i.e., without
   changeover to new version number) is desirable.





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6.3.  Incremental Deployment: Capability Negotiation

6.3.1.  Decision

   BGPsec will be incrementally deployable.  BGPsec routers will use
   capability negotiation to agree to run BGPsec between them.  If a
   BGPsec router's peer does not agree to run BGPsec, then the BGPsec
   router will run only traditional BGP with that peer, i.e., it will
   not send BGPsec (i.e., signed) updates to the peer.

   Note: See Section 7.9 of [RFC8205] for a discussion of incremental/
   partial deployment considerations.  Also, see Section 6 of [RFC8207]
   where it is described that edge sites (stub ASes) can sign updates
   that they originate but receive only unsigned updates.  This
   facilitates less expensive upgrade to BGPsec in resource-limited stub
   ASes, and expedites incremental deployment.

6.3.2.  Discussion

   During partial deployment, there will be BGPsec islands as a result
   of this approach to incremental deployment.  Updates that originate
   within a BGPsec island will generally propagate with signed AS paths
   to the edges of that island.  As BGPsec adoption grows, the BGPsec
   islands will expand outward (subsuming non-BGPsec portions of the
   Internet) and/or pairs of islands may join to form larger BGPsec
   islands.

6.4.  Partial Path Signing

   Partial path signing means that a BGPsec AS can be permitted to sign
   an update that was received unsigned from a downstream neighbor.
   That is, the AS would add its ASN to the AS path and sign the
   (previously unsigned) update to other neighboring (upstream) BGPsec
   ASes.  It was decided that this should not be permitted.

6.4.1.  Decision

   It was decided that partial path signing in BGPsec will not be
   allowed.  A BGPsec update must be fully signed, i.e., each AS in the
   AS-PATH must sign the update.  So in a signed update there must be a
   signature corresponding each AS in the AS path.

6.4.2.  Discussion

   Partial path signing (as described above) implies that the AS path is
   not rigorously protected.  Rigorous AS path protection is a key
   requirement of BGPsec [RFC7353].  Partial path signing clearly re-
   introduces the following attack vulnerability: If a BGPsec speaker is



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   allowed to sign an unsigned update, and if signed (i.e., partially or
   fully signed) updates would be preferred to unsigned updates, then a
   faulty, misconfigured or subverted BGPsec speaker can manufacture any
   unsigned update it wants (with insertion of a valid origin AS) and
   add a signature to it to increase the chance that its update will be
   preferred.

6.5.  Consideration of Stub ASes with Resource Constraints: Encouraging
      Early Adoption

6.5.1.  Decision

   The protocol permits each pair of BGPsec-capable ASes to negotiate
   BGPsec use asymmetrically.  Thus, a stub AS (or downstream customer
   AS) can agree to perform BGPsec only in the transmit direction and
   speak traditional BGP in the receive direction.  In this arrangement,
   the ISP's (upstream) AS will not send signed updates to this stub or
   customer AS.  Thus, the stub AS can avoid the need to hardware
   upgrade its route processor and RIB memory to support BGPsec update
   validation.

6.5.2.  Discussion

   Various other options were also considered for accommodating a
   resource-constrained stub AS as discussed below:

   1.  An arrangement that can be effected outside of BGPsec
       specification is as follows.  Through a private arrangement
       (invisible to other ASes), an ISP's AS (upstream AS) can truncate
       the stub AS (or downstream AS) from the path and sign the update
       as if the prefix is originating from ISP's AS (even though the
       update originated unsigned from the customer AS).  This way the
       path will appear fully signed to the rest of the network.  This
       alternative will require the owner of the prefix at the stub AS
       to issue a ROA for the upstream AS, so that the upstream AS is
       authorized to originate routes for the prefix.

   2.  Another type of arrangement that can also be effected outside of
       the BGPsec specification is as follows.  Stub AS does not sign
       updates but obtains an RPKI (CA) certificate, issues a router
       certificate under that CA certificate.  It passes on the private
       key for the router certificate to its upstream provider.  That
       ISP (i.e., the second hop AS) would insert a signature on behalf
       the stub AS using the private key obtained from the stub AS.
       This arrangement is called proxy signing (see Section 6.6).

   3.  An extended ROA is created that includes the stub AS as the
       originator of the prefix and the upstream provider as the second



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       hop AS, and partial signatures would be allowed (i.e., stub AS
       need not sign the updates).  It is recognized that this approach
       is also authoritative and not trust based.  It was observed that
       the extended ROA is not much different from what is done with ROA
       (in its current form) when a PI address is originated from a
       provider's AS.  This approach was rejected due to possible
       complications with creation and use of a new RPKI object, namely,
       the extended ROA.  Also, the validating BGPsec router has to
       perform a level of indirection with approach, i.e., it must
       detect if an update is not fully signed and then look for the
       extended ROA to validate.

   4.  Another method based on a different form of indirection would be
       as follows: Customer (stub) AS registers something like a Proxy
       Signer Authorization, which authorizes the second hop (i.e.,
       provider) AS to sign on behalf of the customer AS using the
       provider's own key [Dynamics].  This method allows for fully
       signed updates (unlike the Extended ROA based approach).  But
       this approach also requires the creation of a new RPKI object,
       namely, the Proxy Signer Authorization.  In this approach, the
       second hop AS and validating ASes have to perform a level of
       indirection.  This approach was also rejected.

   The various inputs regarding ISP preferences were taken into
   consideration, and eventually the decision in favor of asymmetric
   BGPsec was reached (Section 6.5.1).  A stub AS that does asymmetric
   BGPsec has the advantage that it needs to minimally upgrade to BGPsec
   so it can sign updates to its upstream while it receives only
   unsigned updates.  Thus,it can avoid the cost of increased processing
   and memory needed to perform update validations and to store signed
   updates in the RIBs, respectively.

6.6.  Proxy Signing

6.6.1.  Decision

   An ISP's AS (or upstream AS) can proxy sign BGP announcements for a
   customer (downstream) AS provided that the customer AS obtains an
   RPKI (CA) certificate, issues a router certificate under that CA
   certificate, and it passes on the private key for that certificate to
   its upstream provider.  That ISP (i.e., the second hop AS) would
   insert a signature on behalf the customer AS using the private key
   provided by the customer AS.  This is a private arrangement between
   the two ASes, and is invisible to other ASes.  Thus, this arrangement
   is not part of the BGPsec protocol specification.






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   BGPsec will not make any special provisions for an ISP to use its own
   private key to proxy sign updates for a customer's AS.  This type of
   proxy signing is considered a bad idea.

6.6.2.  Discussion

   Consider a scenario when a customer's AS (say, AS8) is multi-homed to
   two ISPs, i.e., AS8 peers with AS1 and AS2 of ISP-1 and ISP-2,
   respectively.  In this case AS8 would have an RPKI (CA) certificate;
   it issues two separate router certificates (corresponding to AS1 and
   AS2) under that CA certificate; and it passes on the respective
   private keys for those two certificates to its upstream providers AS1
   and AS2.  Thus,AS8 has proxy signing service from both its upstream
   ASes.  In the future, if the customer AS8 disconnects from ISP-2,
   then it would revoke the router certificate corresponding to AS2.

6.7.  Multiple Peering Sessions Between ASes

6.7.1.  Decision

   No problems are anticipated when BGPsec capable ASes have multiple
   peering sessions between them (between distinct routers).

6.7.2.  Discussion

   In traditional BGP, multiple peering sessions, between different
   pairs of routers (between two neighboring ASes) may be simultaneously
   used for load sharing.  Similarly, BGPsec capable ASes can also have
   multiple peering sessions between them.  Because routers in an AS can
   have distinct private keys, the same update when propagated over
   these multiple peering sessions will result in multiple updates that
   may differ in their signatures.  The peer (upstream) AS will apply
   its normal procedures for selecting a best path from those multiple
   updates (and updates from other peers).

   This decision regarding load balancing (vs. using one peering as
   primary for carrying data and another as backup) is entirely local
   and is up to the two neighboring ASes.

7.  Interaction of BGPsec with Common BGP Features

7.1.  Peer Groups

   In the traditional BGP, the idea of peer groups is used in BGP
   routers to save on processing when generating and sending updates.
   Multiple peers for whom the same policies apply can be organized into
   peer groups.  A peer group can typically have tens (maybe as high as
   300) of ASes in it.



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7.1.1.  Decision

   It was decided that BGPsec updates are generated to target unique AS
   peers, so there is no support for peer groups in BGPsec.

7.1.2.  Discussion

   BGPsec router processing can make use of peer groups preceding the
   signing of updates to peers.  Some of the update processing prior to
   forwarding to members of a peer group can be done only once per
   update as is done in traditional BGP.  Prior to forwarding the
   update, a BGPsec speaker adds the peer's ASN to the data that needs
   to be signed and signs the update for each peer AS in the group
   individually.

   If updates were to be signed per peer group, that would require
   divulging information about the forward AS-set that constitutes a
   peer group (since the ASN of each peer would have to be included in
   the update).  Some ISPs do not like to share this kind of information
   globally.

7.2.  Communities

   The need to provide protection in BGPsec for the community attribute
   was discussed.

7.2.1.  Decision

   Community attribute(s) will not be included in what is signed in
   BGPsec.

7.2.2.  Discussion

   The community attribute - in its current definition - may be
   inherently defective, from a security standpoint.  A substantial
   amount of work is needed on semantics of the community attribute, and
   additional work on its security aspects also needs to be done.  The
   community attribute is not necessarily transitive; it is often used
   only between neighbors.  In those contexts, transport security
   mechanisms suffice to provide integrity and authentication.  (There
   is no need to sign data when it is passed only between peers.)  It
   was suggested that one could include only the transitive community
   attributes in what is signed and propagated (across the AS path).  It
   was noted that there is a flag available (i.e., unused) in the
   community attribute, and it might be used by BGPsec (in some
   fashion).  However, little information is available at this point
   about the use and function of this flag.  It was speculated that
   potentially this flag could be used to indicate to BGPsec if the



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   community attribute needs protection.  For now, community attributes
   will not be secured by BGPsec path signatures.

7.3.  Consideration of iBGP Speakers and Confederations

7.3.1.  Decision

   An iBGP speaker that is also an eBGP speaker, and that executes
   BGPsec, will necessarily carry BGPsec data and perform eBGPsec
   functions.  Confederations are eBGP clouds for administrative
   purposes and contain multiple Member-ASes.  A Member-AS is not
   required to sign updates sent to another Member-AS within the same
   confederation.  However, if BGPsec signing is applied in eBGP within
   a confederation, i.e., each Member-AS signs to the next Member-AS in
   the path within the confederation, then upon egress from the
   confederation, the Member-AS at the boundary must remove any and all
   signatures applied within the confederation.  The Member-AS at the
   boundary of the confederation will sign the update to an external
   eBGPsec peer using the public AS number of the confederation and its
   private key.  The BGPsec specification will not specify how to
   perform this process.

   Note: In RFC 8205, signing a BGPsec update between Member-ASes within
   a confederation is required if the update were to propagate with
   signatures within the confederation.  A Confed_Segment flag exists in
   each Secure_Path segment, and when set, it indicates that the
   corresponding signature belongs to a Member-AS.  At the confederation
   boundary, all signatures with Confed_Segment flags set are removed
   from the update.  RFC 8205 specifies in detail how all of this done.
   Please see Section 3.1 (Figure 5) and Section 4.3 in [RFC8205] for
   the details.

7.3.2.  Discussion

   This topic may need to be revisited to flesh out the details
   carefully.

7.4.  Consideration of Route Servers in IXPs

7.4.1.  Decision

   BGPsec (individual draft-00) makes no special provisions to
   accommodate route servers in Internet Exchange Points (IXPs) .

   Note: The above decision changed subsequently.  RFC 8205 allows
   accommodation for IXPs, especially for the case of transparent route
   servers.  The pCount (AS prepend count) field is set to 0 for
   transparent route servers (see Section 4.2 of [RFC8205]).  The



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   operational guidance for preventing misuse of pCount=0 is given in
   Section 7.2 of RFC 8205.  Also, see Section 8.4 for a discussion of
   security considerations concerning pCount=0.

7.4.2.  Discussion

   There are basically three methods that an IXP may use to propagate
   routes: (A) Direct bilateral peering through the IXP, (B) BGP peering
   between clients via a peering with a route server at the IXP (without
   IXP inserting its ASN in the path), and (C) BGP peering with an IXP
   route server, where the IXP inserts its ASN in the path.  (Note:
   IXP's route server does not change the NEXT_HOP attribute even if it
   inserts its ASN in the path.)  It is very rare for an IXP to use
   Method C because it is less attractive for the clients if their AS
   path length increases by one due to the IXP.  A measure of the extent
   of use of Method A vs.  Method B is given in terms of the
   corresponding IP traffic load percentages.  As an example, at a major
   European IXP, these percentages are about 80% and 20% for Methods A
   and B, respectively (this data is based on private communication with
   IXPs circa 2011).  However, as the IXP grows (in terms of number of
   clients), it tends to migrate more towards Method B, because of the
   difficulties of managing up to n x (n-1)/2 direct inter-connections
   between n peers in Method A.

   To the extent an IXP is providing direct bilateral peering between
   clients (Method A), that model works naturally with BGPsec.  Also, if
   the route server in the IXP plays the role of a regular BGPsec
   speaker (minus the routing part for payload) and inserts its own ASN
   in the path (Method C), then that model would also work well in the
   BGPsec Internet and this case is trivially supported in BGPsec.

7.5.  Proxy Aggregation (a.k.a.  AS_SETs)

7.5.1.  Decision

   Proxy aggregation (i.e., use of AS_SETs in the AS path) will not be
   supported in BGPsec.  There is no provision in BGPsec to sign an
   update when an AS_SET is part of an AS path.  If a BGPsec capable
   router receives an update that contains an AS_SET and also finds that
   the update is signed, then the router will consider the update
   malformed (i.e., protocol error).

   Note: In Section 5.2 of RFC 8205, it is specified that a receiving
   BGPsec router MUST handle any syntactical or protocol errors in the
   BGPsec_PATH attribute by using the "treat-as-withdraw" approach as
   defined in RFC 7606 [RFC7606].





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7.5.2.  Discussion

   Proxy aggregation does occur in the Internet today, but is it very
   rare.  Only a very small fraction (about 0.1%) of observed updates
   contain AS_SETs in the AS path [ASset].  Since traditional BGP
   currently allows for proxy aggregation with inclusion of AS_SETs in
   the AS path, it is necessary that BGPsec specify what action a
   receiving router must take in case such an update is received with
   attestation.  BCP 172 [RFC6472] recommends against the use of AS_SETs
   in updates, so it is anticipated that the use of AS_SETs will
   diminish over time.

7.6.  4-Byte AS Numbers

   Not all (currently deployed) BGP speakers are capable of dealing with
   4-byte ASNs [RFC4893].  The standard mechanism used to accommodate
   such speakers requires a peer AS to translate each 4-byte ASN in the
   AS path to a reserved 2-byte ASN (23456) before forwarding the
   update.  This mechanism is incompatible with use of BGPsec, since the
   ASN translation is equivalent to a route modification attack and will
   cause signatures corresponding to the translated 4-byte ASNs to fail
   validation.

7.6.1.  Decision

   BGP speakers that are BGPsec-capable are required to process 4-byte
   ASNs.

7.6.2.  Discussion

   It is reasonable to assume that upgrades for 4-byte ASN support will
   be in place prior to deployment of BGPsec.

8.  BGPsec Validation

8.1.  Sequence of BGPsec Validation Processing in a Receiver

   It is natural to ask in what sequence a receiver must perform BGPsec
   update validation so that if a failure were to occur (i.e., update
   was determined to be invalid) the processor would have spent the
   least amount of processing or other resources.

8.1.1.  Decision

   There was agreement that the following sequence of receiver
   operations is quite meaningful, and are included in the individual
   draft-00 BGPsec specification [I-D.lepinski-bgpsec-protocol].




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   However, the ordering of validation processing steps is not a
   normative part of the BGPsec specification.

   1.  Verify that the signed update is syntactically correct.  For
       example, check if the number of signatures match with the number
       of ASes in the AS path (after duly accounting for AS prepending).

   2.  Verify that the origin AS is authorized to advertise the prefix
       in question.  This verification is based on data from ROAs, and
       does not require any crypto operations.

   3.  Verify that the advertisement has not yet expired.

   4.  Verify that the target ASN in the signature data matches the ASN
       of the router that is processing the advertisement.  Note that
       the target ASN check is also a non-crypto operation and is fast.

   5.  Validate the signature data starting from the most recent AS to
       the origin.

   6.  Locate the public key for the router from which the advertisement
       was received, using the SKI from the signature data.

   7.  Hash the data covered by the signature algorithm.  Invoke the
       signature validation algorithm on the following three inputs: the
       locally computed hash, the received signature, and the public
       key.  There will be one output: valid or invalid.

   8.  Repeat steps 5 and 6 for each preceding signature in the
       Signature-List Block, until the signature data for the origin AS
       is encountered and processed, or until either of these steps
       fails.

   Note: Significant refinements to the above list occurred in the
   progress towards RFC 8205.  The detailed syntactic error checklist is
   presented and explained in Section 5.2 of [RFC8205].  Also, a logical
   sequence of steps to be followed in the validation of
   Signature_Blocks is described in Section 5.2 of [RFC8205].

8.1.2.  Discussion

   The suggested sequence of receiver operations described above were
   discussed and are viewed as appropriate, if the goal is to minimize
   computational costs associated with cryptographic operations.  One
   additional interesting suggestion was that when there are two
   Signature-List Blocks in an update, the validating router can first
   verify whichever of the two algorithms is cheaper to save on




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   processing.  If that Signature-List Block verifies, then the router
   can skip validating the other Signature-List Block.

8.2.  Signing and Forwarding Updates when Signatures Failed Validation

8.2.1.  Decision

   A BGPsec router should sign and forward a signed update to upstream
   peers if it selected the update as the best path, regardless of
   whether the update passed or failed validation (at this router).

8.2.2.  Discussion

   The availability of RPKI data at different routers (in the same or
   different ASes) may differ, depending on the sources used to acquire
   RPKI data.  Hence an update may fail validation in one AS and the
   same update may pass validation in another AS.  Also, an update may
   fail validation at one router in an AS and the same update may pass
   validation at another router in the same AS.

   A BCP may be published later in which some conditions of update
   failure are identified which may be unambiguous cases for rejecting
   the update, in which case the router must not select the AS path in
   the update.  These cases are TBD.

8.3.  Enumeration of Error Conditions

   Enumeration of error conditions and the recommendations for reactions
   to them are still under discussion.

8.3.1.  Decision

   TBD.  Also, please see Section 8.5 for the decision and discussion
   specifically related to syntactic errors in signatures.

   Note: Section 5.2 of RFC 8205 describes detection of syntactic and
   protocol errors in BGPsec updates as well as how the updates with
   such errors are to be handled.

8.3.2.  Discussion

   The list here is a first cut at some possible error conditions and
   recommended receiver reactions in response to detection of those
   errors.  Refinements will follow after further discussions.

   E1  Abnormalities that a peer (i.e., preceding AS) should definitely
       not have propagated to a receiving eBGPsec router.  Examples: (A)
       The number of signatures does not match the number of ASes in the



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       AS path (after accounting for AS prepending); (B) There is an
       AS_SET in the received update and the update has signatures; (C)
       Other syntactic errors with signatures.

      Reaction: See Section 8.5.

   E2  Situations where a receiving eBGPsec router cannot find the cert
       for an AS in the AS_PATH.

      Reaction: Mark the update as "Invalid".  It is acceptable to
      consider the update in best path selection.  If it is chosen, then
      the router should sign and propagate the update.

   E3  Situations where a receiving eBGPsec router cannot find a ROA for
       the {prefix, origin} pair in the update.

      Reaction: Same as in (E2) above.

   E4  The receiving eBGPsec router verifies signatures and finds that
       the update is Invalid (even though its peer might not have known,
       e.g., due to RPKI skew).

      Reaction: Same as in (E2) above.

      In some networks, best path selection policy may specify choosing
      an unsigned update over one with invalid signature(s).  Hence, the
      signatures must not be stripped even if the update is "Invalid".
      No evil bit is set in the update (when it is Invalid) because an
      upstream peer may not get that same answer when it tries to
      validate.

8.4.  Procedure for Processing Unsigned Updates

   An update may come in unsigned from an eBGP peer or internally (e.g.,
   as an iBGP update).  In the latter case, the route is being
   originated from within the AS in consideration.

8.4.1.  Decision

   If an unsigned route is received from an eBGP peer, and if it is
   selected, then the route will be forwarded unsigned to other eBGP
   peers, even BGPsec-capable peers.  If the route originated in this AS
   (IGP or iBGP) and is unsigned, then it should be signed and announced
   to external BGPsec-capable peers.







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8.4.2.  Discussion

   There is also a possibility that an update received in IGP (or iBGP)
   may have private AS numbers in the AS path.  These private AS numbers
   would normally appear in the right most portion of the AS path.  It
   was noted that in this case, the private AS numbers to the right
   would be removed (as done in traditional BGP), and then the update
   will be signed by the originating AS and announced to BGPsec-capable
   eBGP peers.

   Note: See Section 7.5 [RFC8205] for operational considerations for
   BGPsec in the context of private AS numbers.

8.5.  Response to Syntactic Errors in Signatures and Recommendation for
      Reaction

   Note: The contents in this subsection (i.e., Section 8.5) differ
   substantially from the syntactic and protocol error handling
   recommendations for BGPsec in RFC 8205.  Hence, the reader may skip
   reading this subsection and instead read Section 5.2 of [RFC8205].
   This section (Section 8.5) is kept here for the sake of archival
   value concerning design discussions.

   Different types of error conditions were discussed in Section 8.3.
   Here the focus is only on syntactic error conditions in signatures.

8.5.1.  Decision

   If there are syntactic error conditions such as (a) AS_SET and
   Signature-List Block (or Signature_Block per RFC 8205) both appear in
   an update, or (b) the number of signatures does not match the number
   of ASes (after accounting for any AS prepending), or (c) a parsing
   issue occurs with the BGPsec_Path_Signatures attribute, then the
   update (with the signatures stripped) will still be considered in the
   best path selection algorithm (**Note: This is not true in RFC
   8205**).  If the update is selected as the best path, then the update
   will be propagated unsigned.  The error condition will be logged
   locally.

   A BGPsec router will follow whatever the current IETF (IDR WG)
   recommendations are for notifying a peer that it is sending malformed
   messages.

   In the case when there are two Signature-List Blocks in an update,
   and one or more syntactic errors are found to occur within one of
   them but the other one is free of any syntactic errors, then the
   update will still be considered in the best path selection algorithm
   after the syntactically bad Signature-List Block has been removed



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   (**Note: This is not true in RFC 8205**).  If the update is selected
   as the best path, then the update will be propagated with only one
   (i.e., the error-free) Signature-List Block.  The error condition
   will be logged locally.

8.5.2.  Discussion

   As stated above, a BGPsec router will follow whatever the current
   IETF (IDR WG) recommendations are for notifying a peer that it is
   sending malformed messages.  Question: If the error is persistent,
   and there is a full BGP table dump occurring, then would there be
   500K such errors resulting in 500K notify messages sent to the erring
   peer?  The answer was that rate limiting would be applied to the
   notify messages which should prevent any overload due to these
   messages.

8.6.  Enumeration of Validation States

   Various validation conditions are possible which can be mapped to
   validation states for possible input to BGPsec decision process.
   These conditions can be related to whether an update is signed,
   Expire Time checked, route origin validation checked against a ROA,
   signatures verification passed, etc.

8.6.1.  Decision

   It was decided that BGPsec validation outcomes will be mapped to one
   of only two validation states: (1) Valid - passed all validation
   checks (i.e., Expire Time check, route origin and Signature-List
   Block validation), and (2) Invalid - all other possibilities.
   "Invalid" would include situations such as (1) did not perform
   validation due to lack of or insufficient RPKI data, (2) signature
   Expire Time check failed, (3) route origin validation failed, and (4)
   signature checks were performed and one or more of them failed.

   Note: Expire Time is obsolete (see the notes in Section 2.2.1 and
   Section 2.2.2).  RFC 8205 uses the states 'Valid' and 'Not Valid',
   but only with respect to AS path validation (i.e., not including the
   result of origin validation); see Section 5.1 of [RFC8205]).  'Not
   Valid' includes all conditions in which path validation was attempted
   but a 'Valid' result could not be reached (note: path validation is
   not attempted in case of syntactic or protocol errors in a BGPsec
   update; see Section 5.2 of [RFC8205]).  Each Relying Party (RP) is
   expected to devise its own policy to suitably factor in the results
   from origin validation [RFC6811] and path validation [RFC8205] in its
   path selection decision.





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8.6.2.  Discussion

   It may be noted that the result of update validation is just an
   additional input for the BGP decision process.  The router's local
   policy ultimately has control over what action (regarding BGP path
   selection) is taken.

   Initially, four validation states were considered: (1) Update is not
   signed; (2) Update is signed but router does not have corresponding
   RPKI data to perform validation check; (3) Invalid (validation check
   performed and failed); (4) Valid (validation check performed and
   passed).  Later, it was decided that BGPsec validation outcomes will
   be mapped to one of only two validation states as stated above.  It
   was observed that an update can be invalid for many different
   reasons.  To begin to differentiate these numerous reasons and to try
   to enumerate different flavors of the Invalid state is not likely to
   be constructive in route selection decision, and may even introduce
   to new vulnerability in the system.  However, some questions remain
   such as the following.

   Question: Is there a need to define a separate validation state for
   the case when update is not signed but {prefix, origin} pair matched
   with ROA information?  This question was discussed, and a tentative
   conclusion was that this is in principle similar to validation based
   on partial path signatures and that was ruled out earlier (see
   Section 6.4).  So there is no need to add another validation state
   for this case; treat it as "Unverified" (i.e., "Invalid") considering
   that it is unsigned.  Questions still remain, e.g., would the relying
   party want to give the update in consideration a higher preference
   over another unsigned update that failed origin validation or over a
   signed update that failed both signature and ROA validation?

8.7.  Mechanism for Transporting Validation State through iBGP

8.7.1.  Decision

   BGPsec validation need be performed only at eBGP edges.  The
   validation status of a BGP signed/unsigned update may be conveyed via
   iBGP from an ingress edge router to an egress edge router.  Local
   policy in the AS will determine how the validation status is conveyed
   internally, using various pre-existing mechanisms, e.g., setting a
   BGP community, or modifying a metric value such as Local_Pref or MED.
   A signed update that cannot be validated (except those with syntax
   errors) should be forwarded with signatures from the ingress to the
   egress router, where it is signed when propagated towards other
   eBGPsec speakers in neighboring ASes.  Based entirely on local policy
   settings, an egress router may trust the validation status conveyed
   by an ingress router or it may perform its own validation.  The



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   latter approach may be used at an operator's discretion, under
   circumstances when RPKI skew is known to happen at different routers
   within an AS.

   Note: An extended community for carrying origin validation state in
   iBGP has been specified in RFC 8097 [RFC8097]).

8.7.2.  Discussion

   The attribute used to represent the validation state can be carried
   between ASes if desired.  ISPs may like to carry it over their eBGP
   links between their own ASes (e.g., sibling ASes).  A peer (or
   customer) may receive it over an eBGP link from a provider, and may
   want to use it to shortcut their own validation check.  However, the
   peer (or customer) should be aware that this validation-state
   attribute is just a preview of a neighbor's validation and must
   perform their own validation check to be sure of the actual state of
   update's validation.  Question: Should validation state propagation
   be protected by attestation in case it has utility for diagnostics
   purposes?  It was decided not to protect the validation state
   information using signatures.

   The following are intended only as suggestions to be considered by AS
   operators.

   The following Validation states may be needed for propagation via
   iBGP between edge routers in an AS:

   o  Validation states communicated in iBGP for an unsigned update
      (route origin validation result): (1) Valid, (2) Invalid, (3) 'Not
      Found' (see [RFC6811]), (4) Validation Deferred.

      *  An update could be unsigned for two reasons but they need not
         be distinguished: (a) Because it had no signatures (came in
         unsigned from an eBGP peer), or (b) Signatures were present but
         stripped.

   o  Validation states communicated in iBGP for a Signed update: (1)
      Valid, (2) Invalid, (3) Validation Deferred.

   The reason for conveying the additional "Validation Deferred" state
   may be stated as follows.  An ingress edge Router A receiving an
   update from an eBGPsec peer may not attempt to validate signatures
   (e.g., in a processor overload situation), and in that case Router A
   should convey "Validation Deferred" state for that signed update (if
   selected for best path) in iBGP to other edge routers.  Then an
   egress edge Router B upon receiving the update from ingress Router A
   would be able to perform its own validation (origin validation for



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   unsigned update or origin/signature validation for signed update).
   As stated before, the egress Router B may always choose to perform
   its own validation when it receives an update from iBGP (independent
   of the validation status conveyed in iBGP) to account for the
   possibility of RPKI data skew at different routers.  These various
   choices are local and entirely up to operator discretion.

9.  Operational Considerations

   Note: Significant thought has been devoted to operations and
   management considerations post publication of individual draft-00 of
   BGPsec specification.  For this, the reader is referred to [RFC8207]
   and Section 7 of [RFC8205].

9.1.  Interworking with BGP Graceful Restart

   BGP Graceful Restart (BGP-GR) [RFC4724] is a mechanism currently used
   to facilitate non-stop packet forwarding when the control plane is
   recovering from a fault (i.e., BGP session is restarted), but the
   data plane is functioning.  A question was asked regarding if there
   are any special concerns about how BGP-GR works while BGPsec is
   operational?  Also, what happens if the BGP router operation
   transitions from traditional BGP operation to BGP-GR to BGPsec, in
   that order?

9.1.1.  Decision

   No decision was made relative to this issue (at the time of
   publication of individual draft-00 of BGPsec specification).

   Note: See Section 7.7 of [RFC8205] for comments concerning the
   operation of Graceful Restart with BGPsec.  They are consistent with
   the discussion below.

9.1.2.  Discussion

   BGP-GR can be implemented with BGPsec just as it is currently
   implemented with traditional BGP.  The Restart State bit, Forwarding
   State bit, End-of-RIB marker, Staleness marker (in RIB-in), and
   Selection_Deferral_Timer are key parameters associated with BGP-GR
   [RFC4724].  These parameters would apply to BGPsec just as they do
   with traditional BGP.

   Regarding what happens if the BGP router transitions from traditional
   BGP to BGP-GR to BGPsec, the answer would simply be as follows.  If
   there is software upgrade to BGPsec during BGP-GR (assuming upgrade
   is being done on a live BGP speaker), then the BGP-GR session should
   be terminated before a BGPsec session is initiated.  Once the eBGPsec



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   peering session is established, then the receiving eBGPsec speaker
   will see signed updates from the sending (newly upgraded) eBGPsec
   speaker.  There is no apparent harm (it may, in fact, be desirable)
   if the receiving speaker continues to use previously-learned unsigned
   BGP routes from the sending speaker until they are replaced by new
   BGPsec routes.  However, if the Forwarding State bit is set to zero
   by the sending speaker (i.e., the newly upgraded speaker) during
   BGPsec session negotiation, then the receiving speaker would mark all
   previously-learned unsigned BGP routes from that sending speaker as
   "Stale" in its RIB-in.  Then, as BGPsec updates are received
   (possibly interspersed with unsigned BGP updates), the "Stale" routes
   will be replaced or refreshed.

9.2.  BCP Recommendations for Minimizing Churn: Certificate Expiry/
      Revocation and Signature Expire Time

9.2.1.  Decision

   This is still work in progress.

9.2.2.  Discussion

   BCP recommendations for minimizing churn in BGPsec have been
   discussed.  There are potentially various strategies on how routers
   should react to events such as certificate expiry/revocation,
   signature Expire Time exhaustion, etc.  [Dynamics].  The details will
   be documented in the near future after additional work is completed.

9.3.  Outsourcing Update Validation

9.3.1.  Decision

   Update signature validation and signing can be outsourced to an off-
   board server or processor.

9.3.2.  Discussion

   Possibly an off-router box (one or more per AS) can be used that
   performs path validation.  For example, these capabilities might be
   incorporated into a route reflector.  At an ingress router, one needs
   the RIB-in entries validated; not the RIB-out entries.  So the off-
   router box is probably unlike the traditional route reflector; it
   sits at the network edge and validates all incoming BGPsec updates.
   Thus,it appears that each router passes each BGPsec update it
   receives to the off-router box and receives a validation result
   before it stores the route in the RIB-in.  Question: What about
   failure modes here?  They would be dependent on (1) How much of the
   control plane is outsourced; (2) Reliability of the off-router box



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   (or, equivalently communication to and from it); and (3) How
   centralized vs. distributed is this arrangement?  When any kind of
   outsourcing is done, the user needs to be watchful and ensure that
   the outsourcing does not cross trust/security boundaries.

9.4.  New Hardware Capability

9.4.1.  Decision

   It is assumed that BGPsec routers (PE routers and route reflectors)
   will require significantly upgraded hardware - much more memory for
   RIBs and hardware crypto assistance.  However, stub ASes would not
   need to make such upgrades because they can negotiate asymmetric
   BGPsec capability with their upstream ASes, i.e., they sign updates
   to the upstream AS but receive only unsigned BGP updates (see
   Section 6.5).

9.4.2.  Discussion

   It is accepted that it might take several years to go beyond test
   deployment of BGPsec, because of the need for additional route
   processor CPU and memory.  However, because BGPsec deployment will be
   incremental, and because signed updates are not sent outside of a set
   of contiguous BGPsec-enabled ASes, it is not clear how much
   additional (RIB) memory will be required during initial deployment.
   See (see [RIB_size]) for preliminary results on modeling and
   estimation of BGPsec RIB size and its projected growth.  Hardware
   cryptographic support reduces the computation burden on the route
   processor, and offers good security for router private keys.
   However, given the incremental deployment model, it also is not clear
   how substantial a cryptographic processing load will be incurred,
   initially.

   Note: There are recent detailed studies that considered software
   optimizations for BGPsec.  In [Mehmet1] and [Mehmet2], computational
   optimizations for cryptographic processing (i.e., ECDSA speedup) are
   considered for BGPsec implementations on general purpose CPUs.  In
   [V_Sriram], software optimizations at the level of update processing
   and path selection are proposed and quantified for BGPsec
   implementations.

9.5.  Signed Peering Registrations

9.5.1.  Decision

   The idea of signed BGP peering registrations (for the purpose of path
   validation) was rejected.




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9.5.2.  Discussion

   The idea of using a secure map of AS relationships to "validate"
   updates was discussed and rejected.  The reason for not pursuing such
   solutions was that they cannot provide strong guarantees about the
   validity of updates.  Using these techniques, one can say only that
   an update is 'plausible', but cannot say it is 'definitely' valid
   (based on signed peering relations alone).

10.  Security Considerations

   This document requires no security considerations.  See [RFC8205] for
   security considerations for the BGPsec protocol.

11.  IANA Considerations

   This document includes no request to IANA.

12.  Informative References

   [ASset]    Sriram, K. and D. Montgomery, "Measurement Data on AS_SET
              and AGGREGATOR: Implications for {Prefix, Origin}
              Validation Algorithms", IETF SIDR WG presentation, IETF
              78, July 2010, <http://www.nist.gov/itl/antd/upload/
              AS_SET_Aggregator_Stats.pdf>.

   [Borchert]
              Borchert, O. and M. Baer, "Subject: Modification request:
              draft-ietf-sidr-bgpsec-protocol-14", message to the IETF
              SIDR WG Mailing List, 10 February 2016,
              <https://www.ietf.org/mail-archive/web/sidr/current/
              msg07509.html>.

   [CiscoIOS]
              "Cisco IOS RFD implementation",
              <http://www.cisco.com/en/US/docs/ios/12_2/ip/
              configuration/guide/1cfbgp.html#wp1002395>.

   [CPUworkload]
              Sriram, K. and R. Bush, "Estimating CPU Cost of BGPSEC on
              a Router", Presented at RIPE-63; also at IETF-83 SIDR WG
              Meeting, March 2012,
              <http://www.ietf.org/proceedings/83/slides/
              slides-83-sidr-7.pdf>.







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   [Dynamics]
              Sriram, K. and et al., "Potential Impact of BGPSEC
              Mechanisms on Global BGP Dynamics", December 2009, <Work
              in progress, Presentation slides available on request>.

   [Gueron]   Gueron, S. and V. Krasnov, "Fast and side channel
              protected implementation of the NIST P-256 Elliptic Curve
              for x86-64 platforms", OpenSSL patch ID 3149, October
              2013, <https://rt.openssl.org/>.

   [I-D.draft-clynn-s-bgp]
              Lynn, C., Mukkelson, J., and K. Seo, "Secure BGP (S-BGP)",
              June 2003, <http://tools.ietf.org/html/
              draft-clynn-s-bgp-protocol-01>.

   [I-D.ietf-idr-bgp-extended-messages]
              Bush, R., Patel, K., and D. Ward, "Extended Message
              support for BGP", draft-ietf-idr-bgp-extended-messages-24
              (work in progress), November 2017.

   [I-D.ietf-sidrops-bgpsec-rollover]
              Weis, B., Gagliano, R., and K. Patel, "BGPsec Router
              Certificate Rollover", draft-ietf-sidrops-bgpsec-
              rollover-04 (work in progress), December 2017.

   [I-D.lepinski-bgpsec-protocol]
              Lepinski, M., "BGPSEC Protocol Specification", draft-
              lepinski-bgpsec-protocol-00 (work in progress), March
              2011.

   [I-D.sriram-replay-protection-design-discussion]
              Sriram, K. and D. Montgomery, "Design Discussion and
              Comparison of Protection Mechanisms for Replay Attack and
              Withdrawal Suppression in BGPsec", draft-sriram-replay-
              protection-design-discussion-09 (work in progress),
              October 2017.

   [JunOS]    "Juniper JunOS RFD implementation",
              <http://www.juniper.net/techpubs/en_US/junos10.4/topics/
              usage-guidelines/policy-using-routing-policies-to-damp-
              bgp-route-flapping.html>.










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   [Mandelberg1]
              Mandelberg, D., "Subject: wglc for draft-ietf-sidr-bgpsec-
              protocol-11 (Specific topic: Include Address Family
              Identifier in the data protected under signature -- to
              alleviate security concern)", message to the IETF SIDR WG
              Mailing List, 10 February 2015, <https://www.ietf.org/
              mail-archive/web/sidr/current/msg06930.html>.

   [Mandelberg2]
              Mandelberg, D., "Subject: draft-ietf-sidr-bgpsec-protocol-
              13's security guarantees (Specific topic: Sign all of the
              preceding signed data (rather than just the immediate,
              previous signature) -- to alleviate security concern)",
              message to the IETF SIDR WG Mailing List, 26 August 2015,
              <https://www.ietf.org/mail-archive/web/sidr/current/
              msg07241.html>.

   [Mao02]    Mao, Z. and et al., "Route-flap Damping Exacerbates
              Internet Routing Convergence", August 2002,
              <http://www.eecs.umich.edu/~zmao/Papers/sig02.pdf>.

   [Mehmet1]  Adalier, M., "Efficient and Secure Elliptic Curve
              Cryptography Implementation of Curve P-256", NIST Workshop
              on ECC Standards , June 2015,
              <http://csrc.nist.gov/groups/ST/ecc-workshop-2015/papers/
              session6-adalier-Mehmet.pdf>.

   [Mehmet2]  Adalier, M., Sriram, K., Borchert, O., Lee, K., and D.
              Montgomery, "High Performance BGP Security: Algorithms and
              Architectures", North American Network Operator Group
              Meeting NANOG-69, February 2017,
              <https://www.nanog.org/meetings/abstract?id=3043>.

   [MsgSize]  Sriram, K., "Decoupling BGPsec Documents and Extended
              Messages draft", Presented in the IETF SIDROPS WG
              Meeting, IETF-98, March 2017,
              <https://www.ietf.org/proceedings/98/slides/slides-98-
              sidrops-decoupling-bgpsec-documents-and-extended-messages-
              draft-00.pdf>.

   [RFC2439]  Villamizar, C., Chandra, R., and R. Govindan, "BGP Route
              Flap Damping", RFC 2439, DOI 10.17487/RFC2439, November
              1998, <https://www.rfc-editor.org/info/rfc2439>.

   [RFC3779]  Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
              Addresses and AS Identifiers", RFC 3779,
              DOI 10.17487/RFC3779, June 2004,
              <https://www.rfc-editor.org/info/rfc3779>.



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   [RFC4055]  Schaad, J., Kaliski, B., and R. Housley, "Additional
              Algorithms and Identifiers for RSA Cryptography for use in
              the Internet X.509 Public Key Infrastructure Certificate
              and Certificate Revocation List (CRL) Profile", RFC 4055,
              DOI 10.17487/RFC4055, June 2005,
              <https://www.rfc-editor.org/info/rfc4055>.

   [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>.

   [RFC4724]  Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y.
              Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724,
              DOI 10.17487/RFC4724, January 2007,
              <https://www.rfc-editor.org/info/rfc4724>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <https://www.rfc-editor.org/info/rfc4760>.

   [RFC4893]  Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
              Number Space", RFC 4893, DOI 10.17487/RFC4893, May 2007,
              <https://www.rfc-editor.org/info/rfc4893>.

   [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, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC5396]  Huston, G. and G. Michaelson, "Textual Representation of
              Autonomous System (AS) Numbers", RFC 5396,
              DOI 10.17487/RFC5396, December 2008,
              <https://www.rfc-editor.org/info/rfc5396>.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,
              <https://www.rfc-editor.org/info/rfc5652>.

   [RFC6090]  McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
              Curve Cryptography Algorithms", RFC 6090,
              DOI 10.17487/RFC6090, February 2011,
              <https://www.rfc-editor.org/info/rfc6090>.






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   [RFC6472]  Kumari, W. and K. Sriram, "Recommendation for Not Using
              AS_SET and AS_CONFED_SET in BGP", BCP 172, RFC 6472,
              DOI 10.17487/RFC6472, December 2011,
              <https://www.rfc-editor.org/info/rfc6472>.

   [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>.

   [RFC6483]  Huston, G. and G. Michaelson, "Validation of Route
              Origination Using the Resource Certificate Public Key
              Infrastructure (PKI) and Route Origin Authorizations
              (ROAs)", RFC 6483, DOI 10.17487/RFC6483, February 2012,
              <https://www.rfc-editor.org/info/rfc6483>.

   [RFC6487]  Huston, G., Michaelson, G., and R. Loomans, "A Profile for
              X.509 PKIX Resource Certificates", RFC 6487,
              DOI 10.17487/RFC6487, February 2012,
              <https://www.rfc-editor.org/info/rfc6487>.

   [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>.

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891,
              DOI 10.17487/RFC6891, April 2013,
              <https://www.rfc-editor.org/info/rfc6891>.

   [RFC7132]  Kent, S. and A. Chi, "Threat Model for BGP Path Security",
              RFC 7132, DOI 10.17487/RFC7132, February 2014,
              <https://www.rfc-editor.org/info/rfc7132>.

   [RFC7353]  Bellovin, S., Bush, R., and D. Ward, "Security
              Requirements for BGP Path Validation", RFC 7353,
              DOI 10.17487/RFC7353, August 2014,
              <https://www.rfc-editor.org/info/rfc7353>.

   [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
              Patel, "Revised Error Handling for BGP UPDATE Messages",
              RFC 7606, DOI 10.17487/RFC7606, August 2015,
              <https://www.rfc-editor.org/info/rfc7606>.



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   [RFC8097]  Mohapatra, P., Patel, K., Scudder, J., Ward, D., and R.
              Bush, "BGP Prefix Origin Validation State Extended
              Community", RFC 8097, DOI 10.17487/RFC8097, March 2017,
              <https://www.rfc-editor.org/info/rfc8097>.

   [RFC8205]  Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
              Specification", RFC 8205, DOI 10.17487/RFC8205, September
              2017, <https://www.rfc-editor.org/info/rfc8205>.

   [RFC8207]  Bush, R., "BGPsec Operational Considerations", BCP 211,
              RFC 8207, DOI 10.17487/RFC8207, September 2017,
              <https://www.rfc-editor.org/info/rfc8207>.

   [RFC8208]  Turner, S. and O. Borchert, "BGPsec Algorithms, Key
              Formats, and Signature Formats", RFC 8208,
              DOI 10.17487/RFC8208, September 2017,
              <https://www.rfc-editor.org/info/rfc8208>.

   [RIB_size]
              Sriram, K. and et al., "RIB Size Estimation for BGPSEC",
              June 2011, <http://www.nist.gov/itl/antd/upload/
              BGPSEC_RIB_Estimation.pdf>.

   [RIPE580]  Bush, R. and et al., "RIPE-580: RIPE Routing Working Group
              Recommendations on Route-flap Damping", January 2013,
              <http://www.ripe.net/ripe/docs/ripe-580>.

   [V_Sriram]
              Sriram, V. and D. Montgomery, "Design and analysis of
              optimization algorithms to minimize cryptographic
              processing in BGP security protocols", Computer
              Communications, Vol. 106, pp. 75-85, July 2017,
              <http://www.sciencedirect.com/science/article/pii/
              S0140366417303365>.

Acknowledgements

   The authors would like to thank Jeff Haas and Wes George for serving
   as reviewers for this document for the Independent Submissions
   stream.  The authors are grateful to Nevil Brownlee for shepherding
   this document through the Independent Submissions review process.
   Many thanks are also due to Michael Baer, Oliver Borchert, David
   Mandelberg, Sean Turner, Alvaro Retana, Matthias Waehlisch, Tim Polk,
   Russ Mundy, Wes Hardaker, Sharon Goldberg, Ed Kern, Chris Hall, Shane
   Amante, Luke Berndt, Doug Maughan, Pradosh Mohapatra, Mark Reynolds,
   Heather Schiller, Jason Schiller, Ruediger Volk, and David Ward for
   their review, comments, and suggestions during the course of this
   work.



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Contributors

   The following people have made significant contributions to this
   document and should be considered co-authors:

   Rob Austein
   Dragon Research Labs
   Email: sra@hactrn.net

   Steven Bellovin
   Columbia University
   Email: smb@cs.columbia.edu

   Randy Bush
   Internet Initiative Japan, Inc.
   Email: randy@psg.com

   Russ Housley
   Vigil Security, LLC
   Email: housley@vigilsec.com

   Stephen Kent
   BBN Technologies
   Email: kent@alum.mit.edu

   Warren Kumari
   Google
   Email: warren@kumari.net

   Matt Lepinski
   New College of Florida
   mlepinski@ncf.edu

   Doug Montgomery
   USA National Institute of Standards and Technology
   Email: dougm@nist.gov

   Chris Morrow
   Google, Inc.
   Email: morrowc@google.com

   Sandy Murphy
   SPARTA, Inc., a Parsons Company
   Email: sandy@tislabs.com

   Keyur Patel
   Arrcus
   Email: keyur@arrcus.com



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   John Scudder
   Juniper Networks
   Email: jgs@juniper.net

   Samuel Weiler
   W3C/MIT
   Email: weiler@csail.mit.edu

Author's Address

   Kotikalapudi Sriram (editor)
   USA NIST
   100 Bureau Drive
   Gaithersburg, MD  20899
   USA

   Email: ksriram@nist.gov


































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