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IETF RFC 3734
Extensible Provisioning Protocol (EPP) Transport Over TCP
Last modified on Tuesday, March 23rd, 2004
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Network Working Group S. Hollenbeck
Request for Comments: 3734 VeriSign, Inc.
Category: Standards Track March 2004
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 © The Internet Society (2004). All Rights Reserved.
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions Used In This Document. . . . . . . . . . . . 2
2. Session Management . . . . . . . . . . . . . . . . . . . . . . 2
3. Message Exchange . . . . . . . . . . . . . . . . . . . . . . . 3
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 . . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References. . . . . . . . . . . . . . . . . . 7
10.2. Informative References. . . . . . . . . . . . . . . . . 8
11. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 8
12. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 9
Hollenbeck Standards Track PAGE 1 
RFC 3734 EPP TCP Transport March 2004
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 [RFC 2246]. EPP is described in
[RFC 3730]. TCP is described in [RFC 793].
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 [RFC 2119].
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
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 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 Standards Track PAGE 2
RFC 3734 EPP TCP Transport March 2004
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 size.
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 [RFC 3730]. General client-server message exchange using TCP
transport is illustrated in Figure 1.
Hollenbeck Standards Track PAGE 3
RFC 3734 EPP TCP Transport March 2004
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
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RFC 3734 EPP TCP Transport March 2004
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.
5. Transport Considerations
Section 2.1 of the EPP core protocol specification [RFC 3730]
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
[RFC 793] describes these features in detail; congestion control
principles are described further in RFC 2581 [RFC 2581] and RFC
2914 [RFC 2914]. 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.
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RFC 3734 EPP TCP Transport March 2004
- 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.
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 [RFC 2246] 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
Hollenbeck Standards Track PAGE 6
RFC 3734 EPP TCP Transport March 2004
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.
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
[RFC 793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981.
[RFC 2119] Bradner, S., "Key Words for Use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[RFC 2581] Allman, M., Paxson, V. and W. Stevens, "TCP Congestion
Control", RFC 2581, April 1999.
Hollenbeck Standards Track PAGE 7
RFC 3734 EPP TCP Transport March 2004
[RFC 2914] Floyd, S., "Congestion Control Principles", BCP 41, RFC
2914, September 2000.
[RFC 3730] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
RFC 3730, March 2004.
10.2. Informative References
None
11. Author's Address
Scott Hollenbeck
VeriSign Global Registry Services
21345 Ridgetop Circle
Dulles, VA 20166-6503
USA
EMail: shollenbeck@verisign.com
Hollenbeck Standards Track PAGE 8
RFC 3734 EPP TCP Transport March 2004
12. Full Copyright Statement
Copyright © The Internet Society (2004). 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.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
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pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
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on the procedures with respect to rights in RFC documents can be
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Copies of IPR disclosures made to the IETF Secretariat and any
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The IETF invites any interested party to bring to its attention any
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Hollenbeck Standards Track PAGE 9
Extensible Provisioning Protocol (EPP) Transport Over TCP
RFC TOTAL SIZE: 19550 bytes
PUBLICATION DATE: Tuesday, March 23rd, 2004
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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