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Route Leak Prevention and Detection Using Roles in UPDATE and OPEN Messages
RFC 9234

Document Type RFC - Proposed Standard (May 2022)
Authors Alexander Azimov , Eugene Bogomazov , Randy Bush , Keyur Patel , Kotikalapudi Sriram
Last updated 2022-05-06
Replaces draft-ymbk-idr-bgp-open-policy
Stream Internet Engineering Task Force (IETF)
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OPSDIR Early Review Incomplete, due 2021-02-01
Stream WG state Submitted to IESG for Publication
Document shepherd Susan Hares
Shepherd write-up Show Last changed 2022-01-25
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Responsible AD Alvaro Retana
Send notices to Susan Hares <shares@ndzh.com>, aretana.ietf@gmail.com
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RFC 9234


Internet Engineering Task Force (IETF)                         A. Azimov
Request for Comments: 9234                          Qrator Labs & Yandex
Category: Standards Track                                   E. Bogomazov
ISSN: 2070-1721                                              Qrator Labs
                                                                 R. Bush
                                                            IIJ & Arrcus
                                                                K. Patel
                                                                  Arrcus
                                                               K. Sriram
                                                                USA NIST
                                                                May 2022

   Route Leak Prevention and Detection Using Roles in UPDATE and OPEN
                                Messages

Abstract

   Route leaks are the propagation of BGP prefixes that violate
   assumptions of BGP topology relationships, e.g., announcing a route
   learned from one transit provider to another transit provider or a
   lateral (i.e., non-transit) peer or announcing a route learned from
   one lateral peer to another lateral peer or a transit provider.
   These are usually the result of misconfigured or absent BGP route
   filtering or lack of coordination between autonomous systems (ASes).
   Existing approaches to leak prevention rely on marking routes by
   operator configuration, with no check that the configuration
   corresponds to that of the External BGP (eBGP) neighbor, or
   enforcement of the two eBGP speakers agreeing on the peering
   relationship.  This document enhances the BGP OPEN message to
   establish an agreement of the peering relationship on each eBGP
   session between autonomous systems in order to enforce appropriate
   configuration on both sides.  Propagated routes are then marked
   according to the agreed relationship, allowing both prevention and
   detection of route leaks.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9234.

Copyright Notice

   Copyright (c) 2022 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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Requirements Language
   3.  Terminology
     3.1.  Peering Relationships
   4.  BGP Role
     4.1.  BGP Role Capability
     4.2.  Role Correctness
   5.  BGP Only to Customer (OTC) Attribute
   6.  Additional Considerations
   7.  IANA Considerations
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgments
   Contributors
   Authors' Addresses

1.  Introduction

   Route leaks are the propagation of BGP prefixes that violate
   assumptions of BGP topology relationships, e.g., announcing a route
   learned from one transit provider to another transit provider or a
   lateral (i.e., non-transit) peer or announcing a route learned from
   one lateral peer to another lateral peer or a transit provider
   [RFC7908].  These are usually the result of misconfigured or absent
   BGP route filtering or lack of coordination between autonomous
   systems (ASes).

   Existing approaches to leak prevention rely on marking routes by
   operator configuration, with no check that the configuration
   corresponds to that of the eBGP neighbor, or enforcement of the two
   eBGP speakers agreeing on the relationship.  This document enhances
   the BGP OPEN message to establish an agreement of the relationship on
   each eBGP session between autonomous systems in order to enforce
   appropriate configuration on both sides.  Propagated routes are then
   marked according to the agreed relationship, allowing both prevention
   and detection of route leaks.

   This document specifies a means of replacing the operator-driven
   configuration-based method of route leak prevention, described above,
   with an in-band method for route leak prevention and detection.

   This method uses a new configuration parameter, BGP Role, which is
   negotiated using a BGP Role Capability in the OPEN message [RFC5492].
   An eBGP speaker may require the use of this capability and
   confirmation of the BGP Role with a neighbor for the BGP OPEN to
   succeed.

   An optional, transitive BGP Path Attribute, called "Only to Customer
   (OTC)", is specified in Section 5.  It prevents ASes from creating
   leaks and detects leaks created by the ASes in the middle of an AS
   path.  The main focus/applicability is the Internet (IPv4 and IPv6
   unicast route advertisements).

2.  Requirements Language

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

3.  Terminology

   The terms "local AS" and "remote AS" are used to refer to the two
   ends of an eBGP session.  The "local AS" is the AS where the protocol
   action being described is to be performed, and "remote AS" is the AS
   at the other end of the eBGP session in consideration.

   The use of the term "route is ineligible" in this document has the
   same meaning as in [RFC4271], i.e., "route is ineligible to be
   installed in Loc-RIB and will be excluded from the next phase of
   route selection."

3.1.  Peering Relationships

   The terms for peering relationships defined and used in this document
   (see below) do not necessarily represent business relationships based
   on payment agreements.  These terms are used to represent
   restrictions on BGP route propagation, sometimes known as the Gao-
   Rexford model [GAO-REXFORD].  The terms "Provider", "Customer", and
   "Peer" used here are synonymous to the terms "transit provider",
   "customer", and "lateral (i.e., non-transit) peer", respectively,
   used in [RFC7908].

   The following is a list of BGP Roles for eBGP peering and the
   corresponding rules for route propagation:

   Provider:  MAY propagate any available route to a Customer.

   Customer:  MAY propagate any route learned from a Customer, or that
      is locally originated, to a Provider.  All other routes MUST NOT
      be propagated.

   Route Server (RS):  MAY propagate any available route to a Route
      Server Client (RS-Client).

   Route Server Client (RS-Client):  MAY propagate any route learned
      from a Customer, or that is locally originated, to an RS.  All
      other routes MUST NOT be propagated.

   Peer:  MAY propagate any route learned from a Customer, or that is
      locally originated, to a Peer.  All other routes MUST NOT be
      propagated.

   If the local AS has one of the above Roles (in the order shown), then
   the corresponding peering relationship with the remote AS is
   Provider-to-Customer, Customer-to-Provider, RS-to-RS-Client, RS-
   Client-to-RS, or Peer-to-Peer (i.e., lateral peers), respectively.
   These are called normal peering relationships.

   If the local AS has more than one peering Role with the remote AS,
   such a peering relation is called "Complex".  An example is when the
   peering relationship is Provider-to-Customer for some prefixes while
   it is Peer-to-Peer for other prefixes [GAO-REXFORD].

   A BGP speaker may apply policy to reduce what is announced, and a
   recipient may apply policy to reduce the set of routes they accept.

   Violation of the route propagation rules listed above may result in
   route leaks [RFC7908].  Automatic enforcement of these rules should
   significantly reduce route leaks that may otherwise occur due to
   manual configuration mistakes.

   As specified in Section 5, the OTC Attribute is used to identify all
   the routes in the AS that have been received from a Peer, a Provider,
   or an RS.

4.  BGP Role

   The BGP Role characterizes the relationship between the eBGP speakers
   forming a session.  One of the Roles described below SHOULD be
   configured at the local AS for each eBGP session (see definitions in
   Section 3) based on the local AS's knowledge of its Role.  The only
   exception is when the eBGP connection is Complex (see Section 6).
   BGP Roles are mutually confirmed using the BGP Role Capability
   (described in Section 4.1) on each eBGP session.

   Allowed Roles for eBGP sessions are:

   Provider:  the local AS is a transit provider of the remote AS;

   Customer:  the local AS is a transit customer of the remote AS;

   RS:  the local AS is a Route Server (usually at an Internet exchange
      point), and the remote AS is its RS-Client;

   RS-Client:  the local AS is a client of an RS and the RS is the
      remote AS; and

   Peer:  the local and remote ASes are Peers (i.e., have a lateral
      peering relationship).

4.1.  BGP Role Capability

   The BGP Role Capability is defined as follows:

   Code:  9

   Length:  1 (octet)

   Value:  integer corresponding to the speaker's BGP Role (see Table 1)

                 +=======+==============================+
                 | Value | Role name (for the local AS) |
                 +=======+==============================+
                 |   0   | Provider                     |
                 +-------+------------------------------+
                 |   1   | RS                           |
                 +-------+------------------------------+
                 |   2   | RS-Client                    |
                 +-------+------------------------------+
                 |   3   | Customer                     |
                 +-------+------------------------------+
                 |   4   | Peer (i.e., Lateral Peer)    |
                 +-------+------------------------------+
                 | 5-255 | Unassigned                   |
                 +-------+------------------------------+

                   Table 1: Predefined BGP Role Values

   If the BGP Role is locally configured, the eBGP speaker MUST
   advertise the BGP Role Capability in the BGP OPEN message.  An eBGP
   speaker MUST NOT advertise multiple versions of the BGP Role
   Capability.  The error handling when multiple BGP Role Capabilities
   are received is described in Section 4.2.

4.2.  Role Correctness

   Section 4.1 describes how the BGP Role encodes the relationship on
   each eBGP session between ASes.

   The mere receipt of the BGP Role Capability does not automatically
   guarantee the Role agreement between two eBGP neighbors.  If the BGP
   Role Capability is advertised, and one is also received from the
   peer, the Roles MUST correspond to the relationships in Table 2.  If
   the Roles do not correspond, the BGP speaker MUST reject the
   connection using the Role Mismatch Notification (code 2, subcode 11).

                    +===============+================+
                    | Local AS Role | Remote AS Role |
                    +===============+================+
                    | Provider      | Customer       |
                    +---------------+----------------+
                    | Customer      | Provider       |
                    +---------------+----------------+
                    | RS            | RS-Client      |
                    +---------------+----------------+
                    | RS-Client     | RS             |
                    +---------------+----------------+
                    | Peer          | Peer           |
                    +---------------+----------------+

                      Table 2: Allowed Pairs of Role
                               Capabilities

   For backward compatibility, if the BGP Role Capability is sent but
   one is not received, the BGP Speaker SHOULD ignore the absence of the
   BGP Role Capability and proceed with session establishment.  The
   locally configured BGP Role is used for the procedures described in
   Section 5.

   An operator may choose to apply a "strict mode" in which the receipt
   of a BGP Role Capability from the remote AS is required.  When
   operating in the "strict mode", if the BGP Role Capability is sent
   but one is not received, the connection is rejected using the Role
   Mismatch Notification (code 2, subcode 11).  See comments in
   Section 8.

   If an eBGP speaker receives multiple but identical BGP Role
   Capabilities with the same value in each, then the speaker considers
   them to be a single BGP Role Capability and proceeds [RFC5492].  If
   multiple BGP Role Capabilities are received and not all of them have
   the same value, then the BGP speaker MUST reject the connection using
   the Role Mismatch Notification (code 2, subcode 11).

   The BGP Role value for the local AS (in conjunction with the OTC
   Attribute in the received UPDATE message) is used in the route leak
   prevention and detection procedures described in Section 5.

5.  BGP Only to Customer (OTC) Attribute

   The OTC Attribute is an optional transitive Path Attribute of the
   UPDATE message with Attribute Type Code 35 and a length of 4 octets.
   The purpose of this attribute is to enforce that once a route is sent
   to a Customer, a Peer, or an RS-Client (see definitions in
   Section 3.1), it will subsequently go only to the Customers.  The
   attribute value is an AS number (ASN) determined by the procedures
   described below.

   The following ingress procedure applies to the processing of the OTC
   Attribute on route receipt:

   1.  If a route with the OTC Attribute is received from a Customer or
       an RS-Client, then it is a route leak and MUST be considered
       ineligible (see Section 3).

   2.  If a route with the OTC Attribute is received from a Peer (i.e.,
       remote AS with a Peer Role) and the Attribute has a value that is
       not equal to the remote (i.e., Peer's) AS number, then it is a
       route leak and MUST be considered ineligible.

   3.  If a route is received from a Provider, a Peer, or an RS and the
       OTC Attribute is not present, then it MUST be added with a value
       equal to the AS number of the remote AS.

   The following egress procedure applies to the processing of the OTC
   Attribute on route advertisement:

   1.  If a route is to be advertised to a Customer, a Peer, or an RS-
       Client (when the sender is an RS), and the OTC Attribute is not
       present, then when advertising the route, an OTC Attribute MUST
       be added with a value equal to the AS number of the local AS.

   2.  If a route already contains the OTC Attribute, it MUST NOT be
       propagated to Providers, Peers, or RSes.

   The above-described procedures provide both leak prevention for the
   local AS and leak detection and mitigation multiple hops away.  In
   the case of prevention at the local AS, the presence of an OTC
   Attribute indicates to the egress router that the route was learned
   from a Peer, a Provider, or an RS, and it can be advertised only to
   the Customers.  The same OTC Attribute that is set locally also
   provides a way to detect route leaks by an AS multiple hops away if a
   route is received from a Customer, a Peer, or an RS-Client.  For
   example, if an AS sets the OTC Attribute on a route sent to a Peer
   and the route is subsequently received by a compliant AS from a
   Customer, then the receiving AS detects (based on the presence of the
   OTC Attribute) that the route is a leak.

   The OTC Attribute might be set at the egress of the remote AS or at
   the ingress of the local AS, i.e., if the remote AS is non-compliant
   with this specification, then the local AS will have to set the OTC
   Attribute if it is absent.  In both scenarios, the OTC value will be
   the same.  This makes the scheme more robust and benefits early
   adopters.

   The OTC Attribute is considered malformed if the length value is not
   4.  An UPDATE message with a malformed OTC Attribute SHALL be handled
   using the approach of "treat-as-withdraw" [RFC7606].

   The BGP Role negotiation and OTC-Attribute-based procedures specified
   in this document are NOT RECOMMENDED to be used between autonomous
   systems in an AS Confederation [RFC5065].  If an OTC Attribute is
   added on egress from the AS Confederation, its value MUST equal the
   AS Confederation Identifier.  Also, on egress from the AS
   Confederation, an UPDATE MUST NOT contain an OTC Attribute with a
   value corresponding to any Member-AS Number other than the AS
   Confederation Identifier.

   The procedures specified in this document in scenarios that use
   private AS numbers behind an Internet-facing ASN (e.g., a data-center
   network [RFC7938] or stub customer) may be used, but any details are
   outside the scope of this document.  On egress from the Internet-
   facing AS, the OTC Attribute MUST NOT contain a value other than the
   Internet-facing ASN.

   Once the OTC Attribute has been set, it MUST be preserved unchanged
   (this also applies to an AS Confederation).

   The described ingress and egress procedures are applicable only for
   the address families AFI 1 (IPv4) and AFI 2 (IPv6) with SAFI 1
   (unicast) in both cases and MUST NOT be applied to other address
   families by default.  The operator MUST NOT have the ability to
   modify the procedures defined in this section.

6.  Additional Considerations

   Roles MUST NOT be configured on an eBGP session with a Complex
   peering relationship.  If multiple eBGP sessions can segregate the
   Complex peering relationship into eBGP sessions with normal peering
   relationships, BGP Roles SHOULD be used on each of the resulting eBGP
   sessions.

   An operator may want to achieve an equivalent outcome by configuring
   policies on a per-prefix basis to follow the definitions of peering
   relations as described in Section 3.1.  However, in this case, there
   are no in-band measures to check the correctness of the per-prefix
   peering configuration.

   The incorrect setting of BGP Roles and/or OTC Attributes may affect
   prefix propagation.  Further, this document does not specify any
   special handling of an incorrect AS number in the OTC Attribute.

   In AS migration scenarios [RFC7705], a given router may represent
   itself as any one of several different ASes.  This should not be a
   problem since the egress procedures in Section 5 specify that the OTC
   Attribute is to be attached as part of route transmission.
   Therefore, a router is expected to set the OTC value equal to the ASN
   it is currently representing itself as.

   Section 6 of [RFC7606] documents possible negative impacts of "treat-
   as-withdraw" behavior.  Such negative impacts may include forwarding
   loops or dropped traffic.  It also discusses debugging considerations
   related to this behavior.

7.  IANA Considerations

   IANA has registered a new BGP Capability (Section 4.1) in the
   "Capability Codes" registry within the "IETF Review" range [RFC5492].
   The description for the new capability is "BGP Role".  IANA has
   assigned the value 9.  This document is the reference for the new
   capability.

   IANA has created and now maintains a new subregistry called "BGP Role
   Value" within the "Capability Codes" registry.  Registrations should
   include a value, a role name, and a reference to the defining
   document.  IANA has registered the values in Table 3.  Future
   assignments may be made by the "IETF Review" policy as defined in
   [RFC8126].

         +=======+===============================+===============+
         | Value | Role name (for the local AS)  |   Reference   |
         +=======+===============================+===============+
         |   0   | Provider                      | This document |
         +-------+-------------------------------+---------------+
         |   1   | RS                            | This document |
         +-------+-------------------------------+---------------+
         |   2   | RS-Client                     | This document |
         +-------+-------------------------------+---------------+
         |   3   | Customer                      | This document |
         +-------+-------------------------------+---------------+
         |   4   | Peer (i.e., Lateral Peer)     | This document |
         +-------+-------------------------------+---------------+
         | 5-255 | To be assigned by IETF Review |               |
         +-------+-------------------------------+---------------+

                    Table 3: IANA Registry for BGP Role

   IANA has registered a new OPEN Message Error subcode named "Role
   Mismatch" (see Section 4.2) in the "OPEN Message Error subcodes"
   registry.  IANA has assigned the value 11.  This document is the
   reference for the new subcode.

   Due to improper use of the values 8, 9, and 10, IANA has marked
   values 8-10 as "Deprecated" in the "OPEN Message Error subcodes"
   registry.  This document is listed as the reference.

   IANA has also registered a new Path Attribute named "Only to Customer
   (OTC)" (see Section 5) in the "BGP Path Attributes" registry.  IANA
   has assigned code value 35.  This document is the reference for the
   new attribute.

8.  Security Considerations

   The security considerations of BGP (as specified in [RFC4271] and
   [RFC4272]) apply.

   This document proposes a mechanism that uses the BGP Role for the
   prevention and detection of route leaks that are the result of BGP
   policy misconfiguration.  A misconfiguration of the BGP Role may
   affect prefix propagation.  For example, if a downstream (i.e.,
   towards a Customer) peering link were misconfigured with a Provider
   or Peer Role, it would limit the number of prefixes that can be
   advertised in this direction.  On the other hand, if an upstream
   provider were misconfigured (by a local AS) with the Customer Role,
   it may result in propagating routes that are received from other
   Providers or Peers.  But the BGP Role negotiation and the resulting
   confirmation of Roles make such misconfigurations unlikely.

   Setting the strict mode of operation for BGP Role negotiation as the
   default may result in a situation where the eBGP session will not
   come up after a software update.  Implementations with such default
   behavior are strongly discouraged.

   Removing the OTC Attribute or changing its value can limit the
   opportunity for route leak detection.  Such activity can be done on
   purpose as part of an on-path attack.  For example, an AS can remove
   the OTC Attribute on a received route and then leak the route to its
   transit provider.  This kind of threat is not new in BGP, and it may
   affect any Attribute (note that BGPsec [RFC8205] offers protection
   only for the AS_PATH Attribute).

   Adding an OTC Attribute when the route is advertised from Customer to
   Provider will limit the propagation of the route.  Such a route may
   be considered as ineligible by the immediate Provider or its Peers or
   upper-layer Providers.  This kind of OTC Attribute addition is
   unlikely to happen on the Provider side because it will limit the
   traffic volume towards its Customer.  On the Customer side, adding an
   OTC Attribute for traffic-engineering purposes is also discouraged
   because it will limit route propagation in an unpredictable way.

9.  References

9.1.  Normative References

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

   [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>.

   [RFC5065]  Traina, P., McPherson, D., and J. Scudder, "Autonomous
              System Confederations for BGP", RFC 5065,
              DOI 10.17487/RFC5065, August 2007,
              <https://www.rfc-editor.org/info/rfc5065>.

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <https://www.rfc-editor.org/info/rfc5492>.

   [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>.

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

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

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

9.2.  Informative References

   [GAO-REXFORD]
              Gao, L. and J. Rexford, "Stable Internet routing without
              global coordination", IEEE/ACM Transactions on Networking,
              Volume 9, Issue 6, pp. 689-692, DOI 10.1109/90.974523,
              December 2001,
              <https://ieeexplore.ieee.org/document/974523>.

   [RFC4272]  Murphy, S., "BGP Security Vulnerabilities Analysis",
              RFC 4272, DOI 10.17487/RFC4272, January 2006,
              <https://www.rfc-editor.org/info/rfc4272>.

   [RFC7705]  George, W. and S. Amante, "Autonomous System Migration
              Mechanisms and Their Effects on the BGP AS_PATH
              Attribute", RFC 7705, DOI 10.17487/RFC7705, November 2015,
              <https://www.rfc-editor.org/info/rfc7705>.

   [RFC7938]  Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of
              BGP for Routing in Large-Scale Data Centers", RFC 7938,
              DOI 10.17487/RFC7938, August 2016,
              <https://www.rfc-editor.org/info/rfc7938>.

   [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>.

Acknowledgments

   The authors wish to thank Alvaro Retana, Bruno Decraene, Jeff Haas,
   John Scudder, Sue Hares, Ben Maddison, Andrei Robachevsky, Daniel
   Ginsburg, Ruediger Volk, Pavel Lunin, Gyan Mishra, and Ignas Bagdonas
   for their reviews, comments, and suggestions during the course of
   this work.  Thanks are also due to many IESG reviewers whose comments
   greatly helped improve the clarity, accuracy, and presentation in the
   document.

Contributors

   Brian Dickson
   Independent
   Email: brian.peter.dickson@gmail.com

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

Authors' Addresses

   Alexander Azimov
   Qrator Labs & Yandex
   Ulitsa Lva Tolstogo 16
   Moscow
   119021
   Russian Federation
   Email: a.e.azimov@gmail.com

   Eugene Bogomazov
   Qrator Labs
   1-y Magistralnyy tupik 5A
   Moscow
   123290
   Russian Federation
   Email: eb@qrator.net

   Randy Bush
   Internet Initiative Japan & Arrcus, Inc.
   5147 Crystal Springs
   Bainbridge Island, Washington 98110
   United States of America
   Email: randy@psg.com

   Keyur Patel
   Arrcus
   2077 Gateway Place
   Suite #400
   San Jose, CA 95119
   United States of America
   Email: keyur@arrcus.com

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