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rfc:rfc4934

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

Hollenbeck Standards Track [Page 1] RFC 4934 EPP TCP Transport May 2007

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

Hollenbeck Standards Track [Page 2] RFC 4934 EPP TCP Transport May 2007

 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.

Hollenbeck Standards Track [Page 3] RFC 4934 EPP TCP Transport May 2007

                     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 Standards Track [Page 4] RFC 4934 EPP TCP Transport May 2007

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:
  1. 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.
  1. Sections 2 and 3 of this mapping describe how the stateful nature

of EPP is preserved through managed sessions and controlled

    message exchanges.

Hollenbeck Standards Track [Page 5] RFC 4934 EPP TCP Transport May 2007

  1. 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.
  1. 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

Hollenbeck Standards Track [Page 6] RFC 4934 EPP TCP Transport May 2007

 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.

Hollenbeck Standards Track [Page 7] RFC 4934 EPP TCP Transport May 2007

 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.

Hollenbeck Standards Track [Page 8] RFC 4934 EPP TCP Transport May 2007

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

Hollenbeck Standards Track [Page 9] RFC 4934 EPP TCP Transport May 2007

Full Copyright Statement

 Copyright (C) The IETF Trust (2007).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
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Acknowledgement

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

Hollenbeck Standards Track [Page 10]

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