





Network Working Group                                      S. Hollenbeck
Request for Comments: 4934                                VeriSign, Inc.
Obsoletes: 3734                                                 May 2007
Category: Standards Track


       Extensible Provisioning Protocol (EPP) Transport over TCP

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   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.  This document obsoletes RFC 3734.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
     1.1.  Conventions Used in This Document . . . . . . . . . . . . . 2
   2.  Session Management  . . . . . . . . . . . . . . . . . . . . . . 2
   3.  Message Exchange  . . . . . . . . . . . . . . . . . . . . . . . 2
   4.  Data Unit Format  . . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Transport Considerations  . . . . . . . . . . . . . . . . . . . 5
   6.  Internationalization Considerations . . . . . . . . . . . . . . 6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     10.1. Normative References  . . . . . . . . . . . . . . . . . . . 8
     10.2. Informative References  . . . . . . . . . . . . . . . . . . 8
   Appendix A.  Changes from RFC 3734  . . . . . . . . . . . . . . . . 9

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
   [RFC4930].  TCP is described in [RFC0793].  This document obsoletes
   RFC 3734 [RFC3734].

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Session Management

   Mapping EPP session management facilities onto the TCP service is
   straightforward.  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 EPP server MUST return an EPP <greeting> to the client after the
   TCP session has been established.

   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 with a CLOSE call.
   A client MAY end an EPP session by issuing a 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 a CLOSE call.  A server MAY also
   close TCP connections that have been open and active for longer than
   a server-defined period.

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 MUST NOT distribute commands from a single
   EPP session over multiple TCP connections.  A client MAY establish
   multiple TCP connections to support multiple EPP sessions with each
   session mapped to a single connection.  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.

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

   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 [RFC4930].  General client-server message exchange using TCP
   transport is illustrated in Figure 1.

                       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

4.  Data Unit Format

   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.  The
   length of the EPP XML instance is determined by subtracting four
   octets from the total length of the data unit.  A receiver must
   successfully read that many octets to retrieve the complete EPP XML
   instance before processing the EPP message.

   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.

5.  Transport Considerations

   Section 2.1 of the EPP core protocol specification [RFC4930]
   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 follows:

   -  TCP includes features to provide reliability, flow control,
      ordered delivery, and congestion control.  Section 1.5 of RFC 793
      [RFC0793] 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 exchanges.

   -  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 unit.

6.  Internationalization Considerations

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

7.  IANA Considerations

   System port number 700 has been assigned by the IANA for mapping EPP
   onto TCP.

   User port number 3121 (which was used for development and test
   purposes) has been reclaimed by the IANA.

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.

   When layered over TCP, the Transport Layer Security (TLS) Protocol
   version 1.0 [RFC2246] or its successors (such as TLS 1.1 [RFC4346]),
   using the latest version supported by both parties, MUST be used to
   provide integrity, confidentiality, and mutual strong client-server
   authentication.  Implementations of TLS often contain a weak
   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 certification path
   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.  A complete description of the issues associated with
   certification path validation can be found in RFC 3280 [RFC3280].
   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.  Acceptable certificate identities MUST be
   negotiated between client operators and server operators using an
   out-of-band mechanism.  Presented certificate identities MUST match
   negotiated identities before EPP service is granted.

   There is a risk of login credential compromise if a client does not
   properly identify a server before attempting to establish an EPP
   session.  Before sending login credentials to the server, a client
   needs to confirm that the server certificate received in the TLS
   handshake is an expected certificate for the server.  A client also
   needs to confirm that the greeting received from the server contains
   expected identification information.  After establishing a TLS
   session and receiving an EPP greeting on a protected TCP connection,
   clients MUST compare the certificate subject and/or subjectAltName to
   expected server identification information and abort processing if a
   mismatch is detected.  If certificate validation is successful, the
   client then needs to ensure that the information contained in the
   received certificate and greeting is consistent and appropriate.  As
   described above, both checks typically require an out-of-band
   exchange of information between client and server to identify
   expected values before in-band connections are attempted.

   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.

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

10.1.  Normative References

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, September 1981.

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

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

   [RFC4930]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
              RFC 4930, May 2007.

10.2.  Informative References

   [RFC2581]  Allman, M., Paxson, V., and W. Stevens, "TCP Congestion
              Control", RFC 2581, April 1999.

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

   [RFC3280]  Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
              X.509 Public Key Infrastructure Certificate and
              Certificate Revocation List (CRL) Profile", RFC 3280,
              April 2002.

   [RFC3734]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
              Transport Over TCP", RFC 3734, March 2004.

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346, April 2006.

Appendix A.  Changes from RFC 3734

   1.  Minor reformatting as a result of converting I-D source format
       from nroff to XML.

   2.  Updated Security Considerations to include strong authentication
       among the list of needed security services.  Removed paragraph
       describing replay attacks because it's not specific to TCP.  New
       text has been added to RFC 4930 to describe this issue.

   3.  Modified description of TCP operation as a result of IESG
       evaluation.

   4.  Moved RFCs 2581 and 2914 from the normative reference section to
       the informative reference section.

   5.  Added informative references to RFCs 3280 and 4346 and
       descriptive text for each as a result of IESG evaluation.

   6.  Revised security considerations as a result of IESG evaluation.

   7.  Updated EPP references.

Author's Address

   Scott Hollenbeck
   VeriSign, Inc.
   21345 Ridgetop Circle
   Dulles, VA  20166-6503
   US

   EMail: shollenbeck@verisign.com

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