Skip to main content

Extensible Provisioning Protocol (EPP) Transport Over TCP

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 3734.
Author Scott Hollenbeck
Last updated 2015-10-14 (Latest revision 2003-01-29)
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state (None)
Document shepherd (None)
IESG IESG state RFC 3734 (Proposed Standard)
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD Ted Hardie
Send notices to (None)
Internet Engineering Task Force                            S. Hollenbeck
Internet-Draft                                            VeriSign, Inc.
January 29, 2003                                  Expires: July 29, 2003

          Extensible Provisioning Protocol Transport Over TCP

Status of this Memo

  This document is an Internet-Draft and is in full conformance with all
  provisions of Section 10 of RFC2026.

  Internet-Drafts are working documents of the Internet Engineering Task
  Force (IETF), its areas, and its working groups.  Note that other
  groups may also distribute working documents as Internet-Drafts.

  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".

  The list of current Internet-Drafts can be accessed at

  The list of Internet-Draft Shadow Directories can be accessed at


  This document describes how an Extensible Provisioning Protocol (EPP)
  session is mapped onto a single Transmission Control Protocol (TCP)
  connection.  This mapping requires use of the Transport Layer Security
  (TLS) protocol to protect information exchanged between an EPP client
  and an EPP server.

Conventions Used In This Document

  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
  document are to be interpreted as described in [RFC2119].

Hollenbeck               Expires July 29, 2003                  [Page 1]
Internet-Draft             EPP TCP Transport            January 29, 2003

Table of Contents

  1. Introduction .................................................    3
  2. Session Management ...........................................    4
  3. Message Exchange .............................................    5
  4. Data Unit Format .............................................    7
  5. Transport Considerations .....................................    8
  6. Internationalization Considerations ..........................    9
  7. IANA Considerations ..........................................    9
  8. Security Considerations ......................................   10
  9. Acknowledgements .............................................   11
  10. References ..................................................   11
  11. Author's Address ............................................   11
  A. Revisions From Previous Version ..............................   12
  B. Full Copyright Statement .....................................   13

Hollenbeck               Expires July 29, 2003                  [Page 2]
Internet-Draft             EPP TCP Transport            January 29, 2003

1. Introduction

  This document describes how the Extensible Provisioning Protocol (EPP)
  is mapped onto a single client-server TCP connection.  Security
  services beyond those defined in EPP are provided by the Transport
  Layer Security (TLS) Protocol [RFC2246].  EPP is described in [EPP].
  TCP is described in [RFC793].

Hollenbeck               Expires July 29, 2003                  [Page 3]
Internet-Draft             EPP TCP Transport            January 29, 2003

2. Session Management

  Mapping EPP session management facilities onto the TCP service is
  straight forward.  An EPP session first requires creation of a TCP
  connection between two peers, one that initiates the connection
  request and one that responds to the connection request.  The
  initiating peer is called the "client", and the responding peer is
  called the "server".  An EPP server MUST listen for TCP connection
  requests on a standard TCP port assigned by IANA.

  The client MUST issue an active OPEN call, specifying the TCP port
  number on which the server is listening for EPP connection attempts.
  The server MUST respond with a passive OPEN call, which the client
  MUST acknowledge to establish the connection.  The EPP server MUST
  return an EPP <greeting> to the client after the TCP session has been

  An EPP session is normally ended by the client issuing an EPP <logout>
  command.  A server receiving an EPP <logout> command MUST end the EPP
  session and close the TCP connection through an active CLOSE call.
  The client MUST respond with a passive CLOSE call.

  A client MAY end an EPP session by issuing an active CLOSE call.  A
  server SHOULD respond with a passive CLOSE call.

  A server MAY limit the life span of an established TCP connection.
  EPP sessions that are inactive for more than a server-defined period
  MAY be ended by a server issuing an active CLOSE call.  A server MAY
  also close TCP connections that have been open and active for longer
  than a server-defined period.

  Peers SHOULD respond to an active CLOSE call with a passive CLOSE
  call.  The closing peer MAY issue an ABORT call if the responding peer
  does not respond to the active CLOSE call.

Hollenbeck               Expires July 29, 2003                  [Page 4]
Internet-Draft             EPP TCP Transport            January 29, 2003

3. Message Exchange

  With the exception of the EPP server greeting, EPP messages are
  initiated by the EPP client in the form of EPP commands.  An EPP
  server MUST return an EPP response to an EPP command on the same TCP
  connection that carried the command.  If the TCP 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.  EPP commands are idempotent,
  so processing a command more than once produces the same net effect on
  the repository as successfully processing the command once.

  An EPP client streams EPP commands to an EPP server on an established
  TCP connection.  A client MAY but SHOULD NOT establish multiple TCP
  connections to create multiple command exchange channels.  A server
  SHOULD limit a client to a maximum number of TCP connections based on
  server capabilities and operational load.

  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 might be able to realize
  a slight performance gain by pipelining (sending more than one command
  before a response for the first command is received) commands with TCP
  transport, but this feature does not change the basic single command,
  single response operating mode of the core protocol.  The amount of
  data that can be outstanding is limited to the current TCP window

  Each EPP data unit MUST contain a single EPP message.  Commands MUST
  be processed independently and in the same order as sent from the

  A server SHOULD impose a limit on the amount of time required for a
  client to issue a well-formed EPP command.  A server SHOULD end an EPP
  session and close an open TCP connection if a well-formed command is
  not received within the time limit.

  A general state machine for an EPP server is described in section 2 of
  [EPP].  General client-server message exchange using TCP transport is
  illustrated in Figure 1.

Hollenbeck               Expires July 29, 2003                  [Page 5]
Internet-Draft             EPP TCP Transport            January 29, 2003

                      Client                  Server
                 |                                     |
                 |                Connect              |
                 | >>------------------------------->> |
                 |                                     |
                 |             Send Greeting           |
                 | <<-------------------------------<< |
                 |                                     |
                 |             Send <login>            |
                 | >>------------------------------->> |
                 |                                     |
                 |             Send Response           |
                 | <<-------------------------------<< |
                 |                                     |
                 |             Send Command            |
                 | >>------------------------------->> |
                 |                                     |
                 |             Send Response           |
                 | <<-------------------------------<< |
                 |                                     |
                 |            Send Command X           |
                 | >>------------------------------->> |
                 |                                     |
                 |    Send Command Y                   |
                 | >>---------------+                  |
                 |                  |                  |
                 |                  |                  |
                 |            Send Response X          |
                 | <<---------------(---------------<< |
                 |                  |                  |
                 |                  |                  |
                 |                  +--------------->> |
                 |                                     |
                 |            Send Response Y          |
                 | <<-------------------------------<< |
                 |                                     |
                 |             Send <logout>           |
                 | >>------------------------------->> |
                 |                                     |
                 |     Send Response & Disconnect      |
                 | <<-------------------------------<< |
                 |                                     |

               Figure 1: TCP Client-Server Message Exchange

Hollenbeck               Expires July 29, 2003                  [Page 6]
Internet-Draft             EPP TCP Transport            January 29, 2003

4. Data Unit Format

  The data field of the TCP header MUST contain an EPP data unit.  The
  EPP data unit contains two fields: a 32-bit header that describes the
  total length of the data unit, and the EPP XML instance.

  EPP Data Unit Format (one tick mark represents one bit position):

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |                           Total Length                        |
     |                         EPP XML Instance                      |

  Total Length (32 bits): The total length of the EPP data unit measured
  in octets in network (big endian) byte order.  The octets contained in
  this field MUST be included in the total length calculation.

  EPP XML Instance (variable length): The EPP XML instance carried in
  the data unit.

Hollenbeck               Expires July 29, 2003                  [Page 7]
Internet-Draft             EPP TCP Transport            January 29, 2003

5. Transport Considerations

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

  - TCP includes features to provide reliability, flow control, ordered
  delivery, and congestion control.  Section 1.5 of RFC 793 [RFC793]
  describes these features in detail; congestion control principles are
  described further in RFC 2581 [RFC2581] and RFC 2914 [RFC2914].  TCP
  is a connection-oriented protocol, and Section 2 of this mapping
  describes how EPP sessions are mapped to TCP connections.

  - Sections 2 and 3 of this mapping describe how the stateful nature of
  EPP is preserved through managed sessions and controlled message

  - Section 3 of this mapping notes that command pipelining is possible
  with TCP, though batch-oriented processing (combining multiple EPP
  commands in a single data unit) is not permitted.

  - Section 4 of this mapping describes features to frame data units by
  explicitly specifying the number of octets used to represent a data

Hollenbeck               Expires July 29, 2003                  [Page 8]
Internet-Draft             EPP TCP Transport            January 29, 2003

6. Internationalization Considerations

  This mapping does not introduce or present any internationalization or
  localization issues.

7. IANA Considerations

  Mapping EPP onto TCP requires a TCP port assignment from IANA for
  public operation.  TCP port 3121 (a port number in the user port
  range) has been assigned by IANA for development and test purposes.  A
  system port will need to be assigned, and this user port assignment
  will need to be reclaimed, if this document advances to RFC status.

  System Port number XXX - TBA by IANA.

Hollenbeck               Expires July 29, 2003                  [Page 9]
Internet-Draft             EPP TCP Transport            January 29, 2003

8. Security Considerations

  EPP as-is provides only simple client authentication services using
  identifiers and plain text passwords.  A passive attack is sufficient
  to recover client identifiers and passwords, allowing trivial command
  forgery.  Protection against most other common attacks MUST be
  provided by other layered protocols.

  EPP provides protection against replay attacks through command
  idempotency.  A replayed or repeated command will not change the state
  of any object in any way, though denial of service through consumption
  of connection resources is a possibility.

  When layered over TCP, the Transport Layer Security (TLS) Protocol
  described in [RFC2246] MUST be used to prevent eavesdropping,
  tampering, and command forgery attacks.  Implementations of TLS often
  contain a US-exportable cryptographic mode that SHOULD NOT be used to
  protect EPP.  Clients and servers desiring high security SHOULD
  instead use TLS with cryptographic algorithms that are less
  susceptible to compromise.

  Mutual client and server authentication using the TLS Handshake
  Protocol is REQUIRED.  Signatures on the complete certificate chain
  for both client machine and server machine MUST be validated as part
  of the TLS handshake.  Information included in the client and server
  certificates, such as validity periods and machine names, MUST also be
  validated.  EPP service MUST NOT be granted until successful
  completion of a TLS handshake and certificate validation, ensuring
  that both the client machine and the server machine have been
  authenticated and cryptographic protections are in place.

  Authentication using the TLS Handshake Protocol confirms the identity
  of the client and server machines.  EPP uses an additional client
  identifier and password to identify and authenticate the client's user
  identity to the server, supplementing the machine authentication
  provided by TLS.  The identity described in the client certificate and
  the identity described in the EPP client identifier can differ, as a
  server can assign multiple user identities for use from any particular
  client machine.

  EPP TCP servers are vulnerable to common TCP denial of service attacks
  including TCP SYN flooding.  Servers SHOULD take steps to minimize the
  impact of a denial of service attack using combinations of easily
  implemented solutions, such as deployment of firewall technology and
  border router filters to restrict inbound server access to known,
  trusted clients.

Hollenbeck               Expires July 29, 2003                 [Page 10]
Internet-Draft             EPP TCP Transport            January 29, 2003

9. Acknowledgements

  This document was originally written as an individual submission
  Internet-Draft.  The provreg working group later adopted it as a
  working group document and provided many invaluable comments and
  suggested improvements.  The author wishes to acknowledge the efforts
  of WG chairs Edward Lewis and Jaap Akkerhuis for their process and
  editorial contributions.

  Specific suggestions that have been incorporated into this document
  were provided by Chris Bason, Randy Bush, Patrik Faltstrom, Ned Freed,
  James Gould, Dan Manley, and John Immordino.

10. References

  Normative References:

  [EPP] S. Hollenbeck: "Extensible Provisioning Protocol", work in

  [RFC793] J. Postel: "Transmission Control Protocol", STD 7, RFC 793,
  September 1981.

  [RFC2119] S. Bradner: "Key Words for Use in RFCs to Indicate
  Requirement Levels", BCP 14, RFC 2119, March 1997.

  [RFC2246] T. Dierks and C. Allen: "The TLS Protocol Version 1.0", RFC
  2246, January 1999.

  [RFC2581] M. Allman et al.: "TCP Congestion Control", RFC 2581, April

  [RFC2914] S. Floyd: "Congestion Control Principles", BCP 41, RFC 2914,
  September 2000.

  Informative References:


11. Author's Address

  Scott Hollenbeck
  VeriSign Global Registry Services
  21345 Ridgetop Circle
  Dulles, VA 20166-6503

Hollenbeck               Expires July 29, 2003                 [Page 11]
Internet-Draft             EPP TCP Transport            January 29, 2003

A. Revisions From Previous Version

  (Note to RFC editor: please remove this section completely before
  publication as an RFC.)

  -05 to -06 (IESG review):

  Removed "This document is being discussed" paragraph from section 1.

  Modified MAY/SHOULD text in section 3, paragraph 2.

  More text in section 8 to describe the relationship between TLS
  authentication and EPP ID/password authentication.

  Added references to RFCs 2581 and 2914.

Hollenbeck               Expires July 29, 2003                 [Page 12]
Internet-Draft             EPP TCP Transport            January 29, 2003

B. Full Copyright Statement

  Copyright (C) The Internet Society 2002.  All Rights Reserved.

  This document and translations of it may be copied and furnished to
  others, and derivative works that comment on or otherwise explain it
  or assist in its implementation may be prepared, copied, published and
  distributed, in whole or in part, without restriction of any kind,
  provided that the above copyright notice and this paragraph are
  included on all such copies and derivative works.  However, this
  document itself may not be modified in any way, such as by removing
  the copyright notice or references to the Internet Society or other
  Internet organizations, except as needed for the purpose of developing
  Internet standards in which case the procedures for copyrights defined
  in the Internet Standards process must be followed, or as required to
  translate it into languages other than English.

  The limited permissions granted above are perpetual and will not be
  revoked by the Internet Society or its successors or assigns.

  This document and the information contained herein is provided on an


  Funding for the RFC Editor function is currently provided by the
  Internet Society.

Hollenbeck               Expires July 29, 2003                 [Page 13]