Registration Protocols Extensions                            M. Loffredo
Internet-Draft                                      L. Luconi Trombacchi
Intended status: Standards Track                           M. Martinelli
Expires: 8 September 2022                            IIT-CNR/Registro.it
                                                           J. Romanowski
                                                              M. Machnio
                                                       NASK/.pl Registry
                                                            7 March 2022


       Extensible Provisioning Protocol (EPP) Transport over HTTP
                 draft-loffredo-regext-epp-over-http-01

Abstract

   This document describes how the Extensible Provisioning Protocol
   (EPP) is mapped over the Hypertext Transfer Protocol (HTTP).  This
   mapping requires the use of the Transport Layer Security (TLS)
   protocol to protect information exchanged between an EPP client and
   an EPP server.

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 8 September 2022.

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



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   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   3
   2.  Reasons behind Using HTTP . . . . . . . . . . . . . . . . . .   3
   3.  Message Exchange  . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Session Management  . . . . . . . . . . . . . . . . . . . . .   5
   5.  Return Codes  . . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .   8
     6.1.  IIT-CNR/Registro.it EPP Server  . . . . . . . . . . . . .   8
     6.2.  .pl domain Registry (NASK) EPP Server . . . . . . . . . .   9
   7.  Transport Considerations  . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  Internationalization Considerations . . . . . . . . . . . . .  10
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  10
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     12.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Appendix A.  Notes on Load Balancing  . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Although the Extensible Provisioning Protocol (EPP) core
   specification [RFC5730] does not state the transport protocol, only
   the mapping over TCP [RFC5734] has been standardized thus far.
   Nevertheless, some EPP implementations leverage HTTP due to its ease
   of use and simplicity.  This document describes the reasons behind
   using HTTP as the transport protocol for EPP and how EPP is mapped
   over HTTP preserving the semantics of commands.

   HTTP is defined in some IETF documents according to the versions
   currently in use: HTTP/1.1 [RFC7230], HTTP/2 [RFC7540], HTTP/3
   [I-D.ietf-quic-http].  As the differences among such versions do not
   affect the EPP mapping, hereinafter the version number is omitted
   except for presenting the special features in the underlying layers
   of the HTTP stack.

   Security services beyond those defined in EPP are provided by the
   Transport Layer Security (TLS) protocol [RFC8446].






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1.1.  Conventions Used in This Document

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

2.  Reasons behind Using HTTP

   Unlike TCP, HTTP is loosely coupled with the network and provides
   client-server cross-platform technology communication.  Indeed, since
   an HTTP connection is a higher-level abstraction of a network
   connection, there is no need to take over all of the lower-level
   details of TCP.  For example, while in TCP the data transmission
   between a client and a server starts only after having established a
   connection through a 3-way handshake (i.e.  SYN, SYN-ACK, ACK), HTTP
   uses a one-way communication so that a client can directly issue a
   request to a server and then receive a response.

   All the burden needed to manage the HTTP connections is usually
   performed by an application server, which a service can be deployed
   on.  Service implementors are only required to process the requests
   and return the responses.  Definitively, HTTP ease of use and
   simplicity reduces the development time.

   While TCP is connection-oriented, HTTP is stateless but not session
   less.  This means that, by making an EPP session untied from the
   network connection, the EPP communication over HTTP is more flexible
   and efficient than over TCP.

   The main reason supporting the usage of TCP has always been its
   speed.  TCP has been significantly faster than HTTP as HTTP was
   initially built on top of TCP so that every HTTP request should be
   issued on a new TCP connection.  However, subsequent HTTP versions
   have been defined over time to increase the protocol speed and reduce
   the gap with TCP:

   *  Compared to the original HTTP specification, HTTP/1.1 introduced
      the "keep-alive" connection by default to enable a request-
      response sequence on a single TCP connection without repeating the
      connection handshake at each request;
   *  As opposed to HTTP/1.1, which keeps all requests and responses in
      plain text format, HTTP/2 defined the binary framing layer to
      encapsulate all messages in binary format;
   *  HTTP/3 is based on QUIC transport protocol
      [I-D.ietf-quic-transport].  QUIC uses UDP [RFC768] instead of TCP
      to exchange packets between the client and the server.  It



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      incorporates TLS whereas HTTP/1.1 and HTTP/2 define TLS as an add-
      on.  So doing, HTTP/3 can provide a very quick handshake to
      establish a secure connection.

   In the perspective of moving to the cloud to achieve scalability and
   cost reduction, it should be further noted that application protocols
   that aren't based on HTTP can be hardly migrated by using cloud-
   native features, both on client side and server side.  In addition,
   from the security point of view, registries would be limited in terms
   of the third-party security services available to protect their EPP
   servers.

   Finally, some considerations should be done about load balancing
   which is generally used by EPP operators to distribute the requests
   across a pool of servers and, consequently, provide an efficient
   domains registration and maintenance service.  While HTTP load
   balancers are very common and are quite often software, TCP load
   balancers are usually implemented in dedicated hardware.  In
   addition, HTTP load balancers don't merely forward the traffic but
   can make high-level routing decisions based on the message content.
   With regard to the performance, although HTTP load balancers do more
   work, their throughput is evaluated considerably fast.

   Additional notes on how EPP sessions can be managed in HTTP load
   balancing are included in Appendix A.

3.  Message Exchange

   EPP describes client-server interaction as a command-response
   exchange where the client sends one command to the server and the
   server returns one response to the client.  A client MUST use the
   POST method (Section 3.3 of [RFC7231]) to issue an EPP command
   through the request body.  A server receiving a request MUST return
   an EPP message in the response body using the "Content-Length"
   entity-header field to indicate the length in decimal number of
   OCTETs of the entity-body.  No EPP message information MUST be issued
   through any other part of the request or the response.  If the HTTP
   connection is closed after a server receives and successfully
   processes a command but before the response can be returned to the
   client, the server MAY attempt to undo the effects of the command to
   ensure a consistent state between the client and the server.

   Commands MUST be processed independently and in the same order as
   received from the server.  An EPP client MAY issue multiple EPP
   commands to an EPP server on an HTTP connection by relying on the
   HTTP keep-alive capability.  A server SHOULD limit a client to a
   maximum number of HTTP connections based on server capabilities and
   operational load.



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   A client might be able to realize a slight performance gain by
   pipelining the requests, but this feature does not change the basic
   single command, single response operating mode of the EPP protocol.
   A server SHOULD limit the amount of time required for a client to
   issue a well-formed EPP command and, consequently close an open HTTP
   connection.

4.  Session Management

   The EPP session is implemented by using the mechanism described in
   [RFC6265].  An EPP session is started by the client issuing an EPP
   <login> command.  A server receiving an EPP <login> command MUST use
   the "Set-Cookie" response header to send the client a token that the
   client will return in future requests within the scope of the EPP
   session.  For example (Figure 1), the server can send the client a
   "session identifier" (a.k.a "session ID") named SID.  The client then
   returns the session ID in the "Cookie" header of the subsequent
   requests.

      == Server -> Client ==

      Set-Cookie: SID=52ceb07c2a824f09a1c6f9c45574097d

      == Client -> Server ==

      Cookie: SID=52ceb07c2a824f09a1c6f9c45574097d


                                  Figure 1

   The name of the cookie attribute identifying the session ID is not
   relevant and depends on the implementations.  Examples of the names
   that some programming languages use to represent the session ID
   include JSESSIONID (Java EE), PHPSESSID (PHP), and ASPSESSIONID
   (Microsoft ASP).

   An EPP session is ended by the client issuing an EPP <logout>
   command.  A server receiving an EPP <logout> command MUST end the EPP
   session invalidating it after having issued the <logout> response.

   A client MAY open multiple EPP sessions and distribute commands from
   a single EPP session over multiple HTTP connections.  A server SHOULD
   limit a client to a maximum number of EPP sessions based on server
   capabilities and operational load.

   EPP sessions that are inactive for more than a server-defined period
   MAY be ended by a server invalidating the session.




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   Clients MAY issue the <hello> command outside an EPP session.  In
   such a case, servers MUST return the <greeting> response without
   starting a session.  To accomplish this, a server MAY return no
   cookie at all or provide the client with an expired cookie so that it
   cannot be used for further communication with the server.  Clients
   MAY also issue the <hello> command within an EPP session to keep it
   alive.

   The mechanism implemented by a server to maintain the relationship
   between a session and the EPP information negotiated with the client
   through the <login> command (e.g. the language, the namespace URIs
   representing both the objects and the extensions to be managed during
   the session) is out of the scope of this document.

   The state machine described in Section 2 of [RFC5730] is updated as
   shown in Figure 2.



































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                |
                V
       +-----------------+     <hello>      +-----------------+
       |   Waiting for   |----------------->|     Prepare     |
       |      Client     |<-----------------|     Greeting    |
       +-----------------+       Send       +-----------------+
                  ^ | ^ |      Greeting
                  | | | |
                  | | | |  Other command    +-----------------+
                  | | | +------------------>|     Prepare     |
                  | | +---------------------|  Fail Response  |
                  | |   Send 2002 Response  +-----------------+
                  | |
        Send 2200 | +-------------------------------+
        Response  |       +---------------+         |
                  +-------| Prepare Auth  |         | <login>
                          | Fail Response |         |
                          +---------------+         V
       +-----------------+        ^         +-----------------+
       |       End       |        |         |   Processing    |
       |     Session     |        +---------|     <login>     |
       +-----------------+        Auth Fail +-----------------+
          ^    ^                                   |
          |    |            Timeout                | Auth OK
          |    +-------------------------------+   | Start
          |                                    |   | Session
          |                                    |   V
          |   +-----------------+  <hello>  +-----------------+
          |   |     Prepare     |<----------|   Waiting for   |
          |   |     Greeting    |---------->|   Command or    |
          |   +-----------------+   Send    |   <hello> or    |
          |                       Greeting  |    <logout>     |
          | Send 1500                       +-----------------+
          | Response                           |   ^  |
       +-----------------+                     |   |  |
       |   Processing    |      <logout>       |   |  |
       |    <logout>     |<--------------------+   |  | Command
       +-----------------+                         |  | Received
                      +-----------------+  Send    |  |
                      |     Prepare     | Response |  |
                      |     Response    |----------+  |
                      +-----------------+             V
                                 ^          +-----------------+
                         Command |          |   Processing    |
                       Processed +----------|     Command     |
                                            +-----------------+

                                  Figure 2



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5.  Return Codes

   Servers MUST NOT use HTTP return codes to signal clients about the
   failure of the EPP commands.  The HTTP code 200 MUST be used for both
   successful and unsuccessful EPP requests.  Servers MUST use HTTP
   codes to signal clients about the failure of the HTTP requests.

   Servers MUST return a 2002 response (i.e.  Command use error) if the
   client issues an EPP command other than the <hello> and the <login>
   commands through HTTP requests including either an empty or an
   invalid session ID.  Servers receiving a <login> command through an
   HTTP request including a session ID MAY return a 2002 response (i.e.
   Command use error) or simply ignore the incoming session ID.

6.  Implementation Status

   NOTE: Please remove this section and the reference to RFC 7942 prior
   to publication as an RFC.

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to RFC 7942, "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

6.1.  IIT-CNR/Registro.it EPP Server

   *  Responsible Organization: Institute of Informatics and Telematics
      of National Research Council (IIT-CNR)/Registro.it
   *  Location: https://epp.nic.it/ EPP endpoint available only "per IP
      address" basis.






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   *  Description: The .it EPP server is deployed on WildFly Application
      Server.  TLS versions supported are 1.2 and 1.3.  Load balancing
      is implemented with NGINX.  EPP sessions are maintained on a Redis
      cluster.
   *  Level of Maturity: This is a live implementation.
   *  Coverage: This implementation includes all of the features
      described in this specification except for the media type that is
      currently set to "text/xml".
   *  Contact Information: Mario Loffredo, mario.loffredo@iit.cnr.it

6.2.  .pl domain Registry (NASK) EPP Server

   *  Responsible Organization: .pl domain Registry (NASK)/dns.pl
   *  Location: https://dns.pl EPP endpoint available only "per IP
      address" basis.
   *  Description: It is an implementation of the EPP protocol that is
      used by .pl Registry.
   *  Level of Maturity: This is a live implementation.
   *  Coverage: This implementation includes all of the features
      described in this specification.
   *  Contact Information: Marcin Machnio, info@dns.pl

7.  Transport Considerations

   Section 2.1 of the EPP core specification [RFC5730] describes
   considerations to be addressed by protocol transport mappings.  This
   document addresses each of the considerations using a combination of
   features described in this document and features provided by HTTP as
   follows:

   *  Sections 3.3.3 and 3.9.3 of [RFC8095] includes features to provide
      reliability, flow control, ordered delivery, and congestion
      control of, respectively, UDP and HTTP over TCP as
      Pseudotransport.
   *  Section 3 and Section 4 of this document describe how the stateful
      nature of EPP is preserved through controlled message exchanges
      and managed sessions.
   *  Section 3 of this document notes that command pipelining is
      possible with HTTP, though batch-oriented processing (combining
      multiple EPP commands in a single HTTP request) is not permitted.

8.  IANA Considerations

   This document has no actions for IANA.







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9.  Internationalization Considerations

   Servers MUST use the "charset" attribute in the HTTP "Content-Type"
   response header field to specify the UTF-8 character encoding (e.g.
   Content-Type: application/epp+xml; charset=UTF-8).

10.  Security Considerations

   Since clients credentials are included in the EPP <login> command,
   the HTTP over TLS [RFC8740] MUST be used to protect them from
   disclosure while in transit.  As well, the transfer over TLS prevents
   from sniffing the session ID and, consequently, impersonating a
   client to perform actions on registrars' objects.

   Anyway, servers are RECOMMENDED to implement additional measures to
   verify the client.  These measures include IP whitelisting and
   locking the session ID to the client's IP address.

   As a further measure to enforce the security, servers MAY require
   clients to present a digital certificate.  Clients who possess and
   present a valid X.509 digital certificate, issued by a recognized
   Certification Authority (CA), could be identified and authenticated
   by a server who trusts the corresponding CA.  This certificate-based
   mechanism is supported by HTTPS and can be used with EPP over HTTP.
   The TLS protocol describes the specification of a client certificate
   in Section 7.4.6 of [RFC8446].

   With regard to sessions, session IDs SHOULD be randomly generated to
   mitigate the risk of obtaining a valid one through a brute-force
   search.  A session ID SHOULD be at least 128 bits or 16 bytes long.
   An example of a reliable session ID is the Universally Unique
   Identifier (UUID).  Servers MAY limit the lifetime of active sessions
   to avoid them being exchanged for a long time.

   The following measures MAY also be taken to control cookies usage:

   *  restricting their scope through the "Domain" and "Path"
      attributes;
   *  limiting their lifetime through the "Max-Age" and "Expire"
      attributes.

   Other attributes that are normally used to secure the cookies and
   prevent them to be accessed from unintended parties or scripts, such
   as "HttpOnly" and "Secure", are meaningless in this context.







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   Finally, servers are RECOMMENDED to perform additional checks to
   limit the rate of open EPP sessions and HTTP connections to mitigate
   the risk of congestion of requests.  Here again, IP whitelisting
   could also be implemented to prevent DDoS attacks.

   If the EPP server is configured as a load balancer routing the
   requests to a pool of backend servers, some of the aforementioned
   checks SHOULD be implemented on the load balancer side.

11.  Acknowledgements

   The authors would like to acknowledge the following individuals for
   their contributions to this document: Cristian Lucchesi, Stefano
   Ruberti, Luca Vasarelli, Roberto Ravazzolo from IIT-CNR/Registro.it
   and Adrian Prokop, S&#322;awomir Mateuszczyk from NASK/.pl Registry.

12.  References

12.1.  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>.

   [RFC3470]  Hollenbeck, S., Rose, M., and L. Masinter, "Guidelines for
              the Use of Extensible Markup Language (XML) within IETF
              Protocols", BCP 70, RFC 3470, DOI 10.17487/RFC3470,
              January 2003, <https://www.rfc-editor.org/info/rfc3470>.

   [RFC5730]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
              STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,
              <https://www.rfc-editor.org/info/rfc5730>.

   [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
              DOI 10.17487/RFC6265, April 2011,
              <https://www.rfc-editor.org/info/rfc6265>.

   [RFC6839]  Hansen, T. and A. Melnikov, "Additional Media Type
              Structured Syntax Suffixes", RFC 6839,
              DOI 10.17487/RFC6839, January 2013,
              <https://www.rfc-editor.org/info/rfc6839>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.




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   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/info/rfc7231>.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <https://www.rfc-editor.org/info/rfc7540>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [RFC8095]  Fairhurst, G., Ed., Trammell, B., Ed., and M. Kuehlewind,
              Ed., "Services Provided by IETF Transport Protocols and
              Congestion Control Mechanisms", RFC 8095,
              DOI 10.17487/RFC8095, March 2017,
              <https://www.rfc-editor.org/info/rfc8095>.

   [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>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8740]  Benjamin, D., "Using TLS 1.3 with HTTP/2", RFC 8740,
              DOI 10.17487/RFC8740, February 2020,
              <https://www.rfc-editor.org/info/rfc8740>.

12.2.  Informative References

   [I-D.ietf-quic-http]
              Bishop, M., "Hypertext Transfer Protocol Version 3
              (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
              quic-http-34, 2 February 2021,
              <https://www.ietf.org/archive/id/draft-ietf-quic-http-
              34.txt>.

   [I-D.ietf-quic-transport]
              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", Work in Progress, Internet-Draft,
              draft-ietf-quic-transport-34, 14 January 2021,
              <https://www.ietf.org/internet-drafts/draft-ietf-quic-
              transport-34.txt>.



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   [RFC5734]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
              Transport over TCP", STD 69, RFC 5734,
              DOI 10.17487/RFC5734, August 2009,
              <https://www.rfc-editor.org/info/rfc5734>.

   [RFC768]   Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,
              <https://www.rfc-editor.org/info/rfc768>.

Appendix A.  Notes on Load Balancing

   An EPP server should be able to serve a large number of concurrent
   requests from clients and return the responses in a fast and reliable
   manner.  In addition, since EPP is extensible, EPP servers might be
   updated and the replacement of an EPP server with a new version
   should take place in accordance with the service level agreement
   negotiated between the registry and the registrars.  To
   cost-effectively scale high volumes of requests and redeploy a server
   without affecting its functioning, best practice in providing a
   software service generally requires using load balancing.  This
   section presents two possible approaches to the implementation of a
   HTTP load balancing solution for an EPP server.

   An EPP server made up of a server pool must always operate with
   respect to the constraint that, once an EPP session is established,
   all the requests related to that session should be processed by the
   servers in the pool as long as the session is alive.

   One possible approach is using sticky sessions.  In this case, the
   load balancer assigns an identifier to each client issuing a request.
   Then, according to such identifier, the load balancer can route all
   of the requests of a given client to the backend server that started
   the session for its entire duration.  This approach requires each
   backend server to maintain the EPP information connected to the
   sessions opened by that server.  This means that when a backend
   server is stopped and then restarted after its update, all the
   sessions currently active and managed by that server are lost.














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   A more efficient solution consists in releasing the sessions from the
   server pool.  According to this approach, every session is stored
   somewhere outside the server pool.  The load balancer distributes the
   request based on the load of each backend server and according to a
   specific algorithm.  When a server receives a request, it first
   retrieves the session information by the session ID and, if any,
   processes the request.  Sessions are normally stored in a cluster of
   NO-SQL databases so that performance and efficiency requirements are
   fulfilled.  In this approach, only the ongoing requests are lost when
   a backend server is stopped and restarted.  Moreover, maintaining the
   sessions on a persistent data storage results in supporting a
   virtually unlimited number of concurrent sessions.

Authors' Addresses

   Mario Loffredo
   IIT-CNR/Registro.it
   Via Moruzzi,1
   56124 Pisa
   Italy
   Email: mario.loffredo@iit.cnr.it
   URI:   https://www.iit.cnr.it


   Lorenzo Luconi Trombacchi
   IIT-CNR/Registro.it
   Via Moruzzi,1
   56124 Pisa
   Italy
   Email: lorenzo.luconi@iit.cnr.it
   URI:   https://www.iit.cnr.it


   Maurizio Martinelli
   IIT-CNR/Registro.it
   Via Moruzzi,1
   56124 Pisa
   Italy
   Email: maurizio.martinelli@iit.cnr.it
   URI:   https://www.iit.cnr.it


   Jan Romanowski
   NASK/.pl Registry
   Kolska 12
   01-045 Warszawa
   Poland
   Email: jan.romanowski@nask.pl



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   URI:   https://www.dns.pl/


   Marcin Machnio
   NASK/.pl Registry
   Kolska 12
   01-045 Warszawa
   Poland
   Email: info@dns.pl
   URI:   https://www.dns.pl/









































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