[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-madi-sidrops-rp) 00 01 02 03 04 05

SIDROPS                                                            D. Ma
Internet-Draft                                                      ZDNS
Intended status: Informational                                   S. Kent
Expires: October 19, 2019                                    Independent
                                                          April 17, 2019


   Requirements for Resource Public Key Infrastructure (RPKI) Relying
                                Parties
                        draft-ietf-sidrops-rp-05

Abstract

   This document provides a single reference point for requirements for
   Relying Party (RP) software for use in the Resource Public Key
   Infrastructure (RPKI) in the context of securing Internet routing.
   It cites requirements that appear in several RPKI RFCs, making it
   easier for implementers to become aware of these requirements that
   are segmented with orthogonal functionalities.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

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

   This Internet-Draft will expire on October 19, 2019.

Copyright Notice

   Copyright (c) 2019 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



Ma & Kent               Expires October 19, 2019                [Page 1]


Internet-Draft            RPKI RP Requirements                April 2019


   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Fetching and Caching RPKI Repository Objects  . . . . . . . .   3
     2.1.  TAL Acquisition and Processing  . . . . . . . . . . . . .   4
     2.2.  Locating RPKI Objects Using Authority and Subject
           Information Extensions  . . . . . . . . . . . . . . . . .   4
     2.3.  Dealing with Key Rollover . . . . . . . . . . . . . . . .   4
     2.4.  Dealing with Algorithm Transition . . . . . . . . . . . .   4
     2.5.  Strategies for Efficient Cache Maintenance  . . . . . . .   5
   3.  Certificate and CRL Processing  . . . . . . . . . . . . . . .   5
     3.1.  Verifying Resource Certificate and Syntax . . . . . . . .   5
     3.2.  Certificate Path Validation . . . . . . . . . . . . . . .   5
     3.3.  CRL Processing  . . . . . . . . . . . . . . . . . . . . .   6
   4.  Processing RPKI Repository Signed Objects . . . . . . . . . .   6
     4.1.  Basic Signed Object Syntax Checks . . . . . . . . . . . .   6
     4.2.  Syntax and Validation for Each Type of Signed Object  . .   6
       4.2.1.  Manifest  . . . . . . . . . . . . . . . . . . . . . .   6
       4.2.2.  ROA . . . . . . . . . . . . . . . . . . . . . . . . .   7
       4.2.3.  Ghostbusters  . . . . . . . . . . . . . . . . . . . .   7
       4.2.4.  Verifying BGPsec Router Certificate . . . . . . . . .   7
     4.3.  How to Make Use of Manifest Data  . . . . . . . . . . . .   7
     4.4.  What to Do with Ghostbusters Information  . . . . . . . .   8
   5.  Distributing Validated Cache  . . . . . . . . . . . . . . . .   8
   6.  Local Control . . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The RPKI Relying Party (RP) software is used by network operators and
   others to acquire and verify Internet Number Resource (INR) data
   stored in the RPKI repository system.  RPKI data, when verified,
   allow an RP to verify assertions about which Autonomous Systems
   (ASes) are authorized to originate routes for IP address prefixes.
   RPKI data also establishes binding between public keys and BGP
   routers, and indicates the AS numbers that each router is authorized
   to represent.




Ma & Kent               Expires October 19, 2019                [Page 2]


Internet-Draft            RPKI RP Requirements                April 2019


   Noting that the essential requirements imposed on RPs to support
   securing Internet routing ([RFC6480]) are scattered throughout
   numerous RFC documents that are protocol specific or provide best
   practices, as follows:

   RFC 6481 (Repository Structure)
   RFC 6482 (ROA format)
   RFC 6486 (Manifests)
   RFC 6487 (Certificate and CRL profile)
   RFC 6488 (RPKI Signed Objects)
   RFC 6489 (Key Rollover)
   RFC 6810 (RPKI to Router Protocol)
   RFC 6916 (Algorithm Agility)
   RFC 7935 (Algorithms)
   RFC 8209 (Router Certificates)
   RFC 8210 (RPKI to Router Protocol,Version 1)
   RFC 8360 (Certificate Validation Procedure)
   I-D.ietf-sidrops-https-tal (Trust Anchor Locator)

   This makes it hard for an implementer to be confident that he/she has
   addressed all of these generalized requirements.  Besides, software
   engineering calls for how to segment the RP system into components
   with orthogonal functionalities, so that those components could be
   distributed across the operational timeline of the user.  Taxonomy of
   generalized RP requirements is going to help have 'the role of the
   RP' well framed.

   To consolidate RP requirements in one document, with pointers to all
   the relevant RFCs, this document outlines a set of baseline
   requirements imposed on RPs and provides a single reference point for
   requirements for RP software for use in the RPKI, as segmented with
   orthogonal functionalities:

   o Fetching and Caching RPKI Repository Objects
   o Processing Certificates and CRLs
   o Processing RPKI Repository Signed Objects
   o Distributing Validated Cache of the RPKI Data

   This document will be update to reflect new or changed requirements
   as these RFCs are updated, or new RFCs are written.

2.  Fetching and Caching RPKI Repository Objects

   RP software uses synchronization mechanisms supported by targeted
   repositories (e.g., [rsync], RRDP [RFC8182]) to download all RPKI
   changed data objects in the repository system and cache them locally.
   The software validates the RPKI data and uses it to generate
   authenticated data identifying which ASes are authorized to originate



Ma & Kent               Expires October 19, 2019                [Page 3]


Internet-Draft            RPKI RP Requirements                April 2019


   routes for address prefixes, and which routers are authorized to sign
   BGP updates on behalf of ASes.

2.1.  TAL Acquisition and Processing

   In the RPKI, each RP chooses its own set of trust anchors (TAs).
   Consistent with the extant INR allocation hierarchy, the IANA and/or
   the five RIRs are obvious candidates to be default TAs for the RP.

   An RP does not retrieve TAs directly.  A set of Trust Anchor Locators
   (TALs) is used by each RP to retrieve and verify the authenticity of
   each TA.

   TAL acquisition and processing are specified in Section 3 of
   [I-D.ietf-sidrops-https-tal].

2.2.  Locating RPKI Objects Using Authority and Subject Information
      Extensions

   The RPKI repository system is a distributed one, consisting of
   multiple repository instances.  Each repository instance contains one
   or more repository publication points.  An RP discovers publication
   points using the Subject Information Access (SIA) and the Authority
   Information Access (AIA) extensions from (validated) certificates.

   Section 5 of [RFC6481] specifies how an RP locates all RPKI objects
   by using the SIA and AIA extensions.  Detailed specifications of SIA
   and AIA extensions in a resource certificate are described in
   Section 4 of [RFC6487].

2.3.  Dealing with Key Rollover

   An RP takes the key rollover period into account with regard to its
   frequency of synchronization with RPKI repository system.

   RP requirements in dealing with key rollover are described in
   Section 3 of [RFC6489] and Section 3 of
   [I-D.ietf-sidrops-bgpsec-rollover].

2.4.  Dealing with Algorithm Transition

   The set of cryptographic algorithms used with the RPKI is expected to
   change over time.  Each RP is expected to be aware of the milestones
   established for the algorithm transition and what actions are
   required at every juncture.

   RP requirements for dealing with algorithm transition are specified
   in Section 4 of [RFC6916].



Ma & Kent               Expires October 19, 2019                [Page 4]


Internet-Draft            RPKI RP Requirements                April 2019


2.5.  Strategies for Efficient Cache Maintenance

   Each RP is expected to maintain a local cache of RPKI objects.  The
   cache needs to be as up to date and consistent with repository
   publication point data as the RP's frequency of checking permits.

   The last paragraph of Section 5 of [RFC6481] provides guidance for
   maintenance of a local cache.

3.  Certificate and CRL Processing

   The RPKI make use of X.509 certificates and CRLs, but it profiles
   these standard formats [RFC6487].  The major change to the profile
   established in [RFC5280] is the mandatory use of a new extension to
   X.509 certificate [RFC3779].

3.1.  Verifying Resource Certificate and Syntax

   Certificates in the RPKI are called resource certificates, and they
   are required to conform to the profile [RFC6487].  An RP is required
   to verify that a resource certificate adheres to the profile
   established by Section 4 of [RFC6487].  This means that all
   extensions mandated by Section 4.8 of [RFC6487] must be present and
   value of each extension must be within the range specified by this
   RFC.  Moreover, any extension excluded by Section 4.8 of [RFC6487]
   must be omitted.

   Section 7.1 of [RFC6487] gives the procedure that the RP should
   follow to verify resource certificate and syntax.

3.2.  Certificate Path Validation

   The INRs in issuer's certificate are required to encompass the INRs
   in the subject's certificate.  This is one of necessary principles of
   certificate path validation in addition to cryptographic verification
   i.e., verification of the signature on each certificate using the
   public key of the parent certificate).

   Section 7.2 of [RFC6487] gives the procedure that the RP should
   follow to perform certificate path validation.

   Certificate Authorities that want to reduce aspects of operational
   fragility will migrate to the new OIDs [RFC8360], informing the RP of
   using an alternative RPKI validation algorithm.  An RP is expected to
   support the amended procedure to handle with accidental over-claim.






Ma & Kent               Expires October 19, 2019                [Page 5]


Internet-Draft            RPKI RP Requirements                April 2019


3.3.  CRL Processing

   The CRL processing requirements imposed on CAs and RP are described
   in Section 5 of [RFC6487].  CRLs in the RPKI are tightly constrained;
   only the AuthorityKeyIndetifier and CRLNumber extensions are allowed,
   and they are required to be present.  No other CRL extensions are
   allowed, and no CRLEntry extensions are permitted.  RPs are required
   to verify that these constraints have been met.  Each CRL in the RPKI
   must be verified using the public key from the certificate of the CA
   that issued the CRL.

   In the RPKI, RPs are expected to pay extra attention when dealing
   with a CRL that is not consistent with the Manifest associated with
   the publication point associated with the CRL.

   Processing of a CRL that is not consistent with a manifest is a
   matter of local policy, as described in the fourth paragraph of
   Section 6.6 of [RFC6486].

4.  Processing RPKI Repository Signed Objects

4.1.  Basic Signed Object Syntax Checks

   Before an RP can use a signed object from the RPKI repository, the RP
   is required to check the signed object syntax.

   Section 3 of [RFC6488] lists all the steps that the RP is required to
   execute in order to validate the top level syntax of a repository
   signed object.

   Note that these checks are necessary, but not sufficient.  Additional
   validation checks must be performed based on the specific type of
   signed object.

4.2.  Syntax and Validation for Each Type of Signed Object

4.2.1.  Manifest

   To determine whether a manifest is valid, the RP is required to
   perform manifest-specific checks in addition to those specified in
   [RFC6488].

   Specific checks for a Manifest are described in Section 4 of
   [RFC6486].  If any of these checks fails, indicating that the
   manifest is invalid, then the manifest will be discarded and treated
   as though no manifest were present.





Ma & Kent               Expires October 19, 2019                [Page 6]


Internet-Draft            RPKI RP Requirements                April 2019


4.2.2.  ROA

   To validate a ROA, the RP is required perform all the checks
   specified in [RFC6488] as well as the additional ROA-specific
   validation steps.  The IP address delegation extension [RFC3779]
   present in the end-entity (EE) certificate (contained within the
   ROA), must encompass each of the IP address prefix(es) in the ROA.

   More details for ROA validation are specified in Section 4 of
   [RFC6482].

4.2.3.  Ghostbusters

   The Ghostbusters Record is optional; a publication point in the RPKI
   can have zero or more associated Ghostbuster Records.  If a CA has at
   least one Ghostbuster Record, RP is required to verify that this
   Ghostbusters Record conforms to the syntax of signed object defined
   in [RFC6488].

   The payload of this signed object is a (severely) profiled vCard.  An
   RP is required to verify that the payload of Ghostbusters conforms to
   format as profiled in [RFC6493].

4.2.4.  Verifying BGPsec Router Certificate

   A BGPsec Router Certificate is a resource certificate, so it is
   required to comply with [RFC6487].  Additionally, the certificate
   must contain an AS Identifier Delegation extension, and must not
   contain an IP Address Delegation extension.  The validation procedure
   used for BGPsec Router Certificates is identical to the validation
   procedure described in Section 7 of [RFC6487], but using the
   constraints applied come from specification of Section 7 of
   [RFC8209].

   Note that the cryptographic algorithms used by BGPsec routers are
   found in [RFC8208].  Currently, the algorithms specified in
   [RFC8208]and [RFC7935] are different.  BGPsec RPs will need to
   support algorithms that are used to validate BGPsec signatures as
   well as the algorithms that are needed to validate signatures on
   BGPsec certificates, RPKI CA certificates, and RPKI CRLs.

4.3.  How to Make Use of Manifest Data

   For a given publication point, the RP ought to perform tests, as
   specified in Section 6.1 of [RFC6486], to determine the state of the
   Manifest at the publication point.  A Manifest can be classified as
   either valid or invalid, and a valid Manifest is either current and




Ma & Kent               Expires October 19, 2019                [Page 7]


Internet-Draft            RPKI RP Requirements                April 2019


   stale.  An RP decides how to make use of a Manifest based on its
   state, according to local (RP) policy.

   If there are valid objects in a publication point that are not
   present on a Manifest, [RFC6486] does not mandate specific RP
   behavior with respect to such objects.  However, most RP software
   ignores such objects and the authors of this document suggest this
   behavior be adopted uniformly.

   In the absence of a Manifest, an RP is expected to accept all valid
   signed objects present in the publication point.  If a Manifest is
   stale or invalid (see [RFC6486]) and an RP has no way to acquire a
   more recently valid Manifest, the RP is expected to contact the
   repository manager via Ghostbusters record and thereafter make
   decision according to local (RP) policy.

4.4.  What to Do with Ghostbusters Information

   An RP may encounter a stale Manifest or CRL, or an expired CA
   certificate or ROA at a publication point.  An RP is expected to use
   the information from the Ghostbusters record to contact the
   maintainer of the publication point where any stale/expired objects
   were encountered.  The intent here is to encourage the relevant CA
   and/or repository manager to update the slate or expired objects.

5.  Distributing Validated Cache

   On a periodic basis, BGP speakers within an AS request updated
   validated origin AS data and router/ASN data from the validated cache
   of RPKI data.  The RP may either transfer the validated data to the
   BGP speakers directly, or it may transfer the validated data to a
   cache server that is responsible for provisioning such data to BGP
   speakers.  The specification of the protocol designed to deliver
   validated cache data to a BGP Speaker is provided in [RFC6810] and
   [RFC8210].

6.  Local Control

   ISPs may want to establish a local view of exceptions to the RPKI
   data in the form of local filters and additions.  For instance, a
   network operator might wish to make use of a local override
   capability to protect routes from adverse actions [RFC8211] . The
   mechanisms developed to provide this capability to network operators
   are called "Simplified Local Internet Number Resource Management with
   the RPKI (SLURM).  If an ISP wants to implement SLURM, its RP system
   can follow the instruction specified in [RFC8416] .





Ma & Kent               Expires October 19, 2019                [Page 8]


Internet-Draft            RPKI RP Requirements                April 2019


7.  Security Considerations

   The RP links the RPKI provisioning side and the routing system,
   establishing the local view of global RPKI data to BGP speakers.  The
   security of the RP is critical to BGP messages exchanging.  The RP
   implementation is expected to offer cache backup management to
   facilitate recovery from outage state.  The RP implementation also
   should support application of secure transport (e.g., IPsec
   [RFC4301]) that is able to protect validated cache delivery in a
   unsafe environment.

8.  IANA Considerations

   This document has no actions for IANA.

9.  Acknowledgements

   The authors thank David Mandelberg, Wei Wang, Tim Bruijnzeels, George
   Michaelson and Oleg Muravskiy for their review, feedback and
   editorial assistance in preparing this document.

10.  References

10.1.  Normative References

   [I-D.ietf-sidrops-https-tal]
              Huston, G., Weiler, S., Michaelson, G., Kent, S., and T.
              Bruijnzeels, "Resource Public Key Infrastructure (RPKI)
              Trust Anchor Locator", draft-ietf-sidrops-https-tal-07
              (work in progress), March 2019.

   [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>.

   [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>.

   [RFC6481]  Huston, G., Loomans, R., and G. Michaelson, "A Profile for
              Resource Certificate Repository Structure", RFC 6481,
              DOI 10.17487/RFC6481, February 2012,
              <https://www.rfc-editor.org/info/rfc6481>.





Ma & Kent               Expires October 19, 2019                [Page 9]


Internet-Draft            RPKI RP Requirements                April 2019


   [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>.

   [RFC6486]  Austein, R., Huston, G., Kent, S., and M. Lepinski,
              "Manifests for the Resource Public Key Infrastructure
              (RPKI)", RFC 6486, DOI 10.17487/RFC6486, February 2012,
              <https://www.rfc-editor.org/info/rfc6486>.

   [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>.

   [RFC6488]  Lepinski, M., Chi, A., and S. Kent, "Signed Object
              Template for the Resource Public Key Infrastructure
              (RPKI)", RFC 6488, DOI 10.17487/RFC6488, February 2012,
              <https://www.rfc-editor.org/info/rfc6488>.

   [RFC6493]  Bush, R., "The Resource Public Key Infrastructure (RPKI)
              Ghostbusters Record", RFC 6493, DOI 10.17487/RFC6493,
              February 2012, <https://www.rfc-editor.org/info/rfc6493>.

   [RFC6810]  Bush, R. and R. Austein, "The Resource Public Key
              Infrastructure (RPKI) to Router Protocol", RFC 6810,
              DOI 10.17487/RFC6810, January 2013,
              <https://www.rfc-editor.org/info/rfc6810>.

   [RFC7935]  Huston, G. and G. Michaelson, Ed., "The Profile for
              Algorithms and Key Sizes for Use in the Resource Public
              Key Infrastructure", RFC 7935, DOI 10.17487/RFC7935,
              August 2016, <https://www.rfc-editor.org/info/rfc7935>.

   [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>.

   [RFC8209]  Reynolds, M., Turner, S., and S. Kent, "A Profile for
              BGPsec Router Certificates, Certificate Revocation Lists,
              and Certification Requests", RFC 8209,
              DOI 10.17487/RFC8209, September 2017,
              <https://www.rfc-editor.org/info/rfc8209>.







Ma & Kent               Expires October 19, 2019               [Page 10]


Internet-Draft            RPKI RP Requirements                April 2019


   [RFC8210]  Bush, R. and R. Austein, "The Resource Public Key
              Infrastructure (RPKI) to Router Protocol, Version 1",
              RFC 8210, DOI 10.17487/RFC8210, September 2017,
              <https://www.rfc-editor.org/info/rfc8210>.

   [RFC8360]  Huston, G., Michaelson, G., Martinez, C., Bruijnzeels, T.,
              Newton, A., and D. Shaw, "Resource Public Key
              Infrastructure (RPKI) Validation Reconsidered", RFC 8360,
              DOI 10.17487/RFC8360, April 2018,
              <https://www.rfc-editor.org/info/rfc8360>.

10.2.  Informative References

   [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.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <https://www.rfc-editor.org/info/rfc4301>.

   [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>.

   [RFC6489]  Huston, G., Michaelson, G., and S. Kent, "Certification
              Authority (CA) Key Rollover in the Resource Public Key
              Infrastructure (RPKI)", BCP 174, RFC 6489,
              DOI 10.17487/RFC6489, February 2012,
              <https://www.rfc-editor.org/info/rfc6489>.

   [RFC6916]  Gagliano, R., Kent, S., and S. Turner, "Algorithm Agility
              Procedure for the Resource Public Key Infrastructure
              (RPKI)", BCP 182, RFC 6916, DOI 10.17487/RFC6916, April
              2013, <https://www.rfc-editor.org/info/rfc6916>.

   [RFC8182]  Bruijnzeels, T., Muravskiy, O., Weber, B., and R. Austein,
              "The RPKI Repository Delta Protocol (RRDP)", RFC 8182,
              DOI 10.17487/RFC8182, July 2017,
              <https://www.rfc-editor.org/info/rfc8182>.

   [RFC8211]  Kent, S. and D. Ma, "Adverse Actions by a Certification
              Authority (CA) or Repository Manager in the Resource
              Public Key Infrastructure (RPKI)", RFC 8211,
              DOI 10.17487/RFC8211, September 2017,
              <https://www.rfc-editor.org/info/rfc8211>.




Ma & Kent               Expires October 19, 2019               [Page 11]


Internet-Draft            RPKI RP Requirements                April 2019


   [RFC8416]  Ma, D., Mandelberg, D., and T. Bruijnzeels, "Simplified
              Local Internet Number Resource Management with the RPKI
              (SLURM)", RFC 8416, DOI 10.17487/RFC8416, August 2018,
              <https://www.rfc-editor.org/info/rfc8416>.

   [rsync]    "rsync web page", <http://rsync.samba.org/>.

Authors' Addresses

   Di Ma
   ZDNS
   4 South 4th St. Zhongguancun
   Haidian, Beijing  100190
   China

   Email: madi@zdns.cn


   Stephen Kent
   Independent

   Email: kent@alum.mit.edu





























Ma & Kent               Expires October 19, 2019               [Page 12]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/