RFC 3734 PROPOSED STANDARD DNS · DOMAIN NAMES · TRANSPORT · TLS
Extensible Provisioning Protocol (EPP) Transport Over TCP
Carrying domain registry messages over TCP with security.
RFC EDITOR
Hollenbeck, S., "Extensible Provisioning Protocol (EPP) Transport Over TCP", RFC 3734, DOI 10.17487/RFC3734, March 2004, <https://www.rfc-editor.org/info/rfc3734>.
BIBTEX
@misc{rfc3734,
series = {Request for Comments},
number = 3734,
howpublished = {RFC 3734},
publisher = {RFC Editor},
doi = {10.17487/RFC3734},
url = {https://www.rfc-editor.org/info/rfc3734},
author = {S. Hollenbeck},
title = {{Extensible Provisioning Protocol (EPP) Transport Over TCP}},
pagetotal = 9,
year = 2004,
month = mar,
} LINEAGE · FROM THE RFC INDEXOpen full graph →
RFC text
Contents
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 (C) 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
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
[RFC3730]. TCP is described in [RFC793].
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
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.
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 [RFC3730]. 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 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 [RFC3730]
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
[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 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.
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.
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
[RFC793] 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.
[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.
[RFC3730] 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
12. Full Copyright Statement
Copyright (C) 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
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
AI ELI5
On this page
PROBLEMThe Extensible Provisioning Protocol (EPP) needed a standard way to be transmitted between domain registries and registrars over reliable internet connections.
MECHANISMRFC 3734 maps EPP messages onto TCP connections protected by TLS to provide secure, reliable transport. Messages are framed with a 32-bit length field preceding the XML payload.
STATUS TODAYEPP TCP transport became the standard for domain registry communication. RFC 4934 superseded this specification in 2007 with refinements.
§1Introduction to EPP over TCP
EPP (Extensible Provisioning Protocol) is a framework for provisioning objects, such as domain names, within the Domain Name System. This RFC describes how to carry EPP messages over a TCP connection protected by TLS (Transport Layer Security).
A registrar client connects to a registry server on a TCP port, typically port 700. After the TCP connection is established, both sides perform a TLS handshake to authenticate each other and establish encrypted communication. Only after successful TLS authentication does the server send an EPP greeting, and the client may then send EPP commands.
A registrar is like a postal clerk; a registry is like the post office. The clerk needs a secure, locked phone line to the post office to send commands like "register this domain name."
§2Session Management
The EPP session is mapped directly onto the TCP connection. The client initiates a TCP connection to the server, which listens on a configured TCP port. After the connection is established and TLS handshake completes, the server sends an EPP greeting message.
The client can then send EPP commands. An EPP session normally ends when the client sends a logout command, which causes the server to close the TCP connection. A server may also timeout inactive sessions or impose limits on how long an EPP session may remain open. If a server receives and processes a command but the connection closes before the response is sent, the server may attempt to undo the command to maintain consistency.
One EPP session uses one phone call. When the call ends, the session ends. The registry server can hang up if nobody is talking for too long.
§3Sending Commands and Responses
Except for the server greeting, all EPP messages are initiated by the client as commands. The server returns a response to each command on the same TCP connection. A client may send multiple commands before receiving responses to previous ones (command pipelining), though the server should not require this.
Each EPP command is processed independently and in the order sent. Commands are idempotent, meaning that processing a command more than once produces the same net effect on the registry as processing it once. A server may limit the time a client has to send a well-formed command and may close the connection if this limit is exceeded.
The registrar asks a question; the registry answers. The registrar can ask more questions without waiting for all answers, like leaving multiple voicemails. Each question always gets the same answer, no matter how many times you ask.
Registrar (Client)Registry (Server)
- TCP ConnectClient initiates TCP connection to port 700
- TLS HandshakeMutual authentication and encryption setup
- EPP GreetingServer welcomes client after TLS succeeds
- Login
- Login Response
- Command (e.g., register domain)
- Response
- Logout
- Logout Response & TCP Close
§4Data Unit Format
Each EPP data unit transported by TCP consists of two parts: a 32-bit header field describing the total length of the data unit (measured in octets in network byte order), followed by the EPP XML instance. The length field includes itself in the total count, so the minimum value is 4 bytes (the header alone).
This framing allows the TCP receiver to know exactly how many octets comprise each EPP message, even though TCP itself does not preserve message boundaries.
Before sending each command, write down how many bytes are about to arrive, like labeling a package with its weight. This helps the other side know when a message ends.
§5Security Requirements
EPP alone provides only weak authentication: a username and password in plain text. The TLS layer MUST protect EPP sessions against eavesdropping, tampering, and command forgery. Both the client and server must authenticate each other using the TLS Handshake Protocol. Signatures on the complete certificate chains for both machines MUST be validated, including verifying certificate validity periods and machine names.
EPP service MUST NOT be granted until after a successful TLS handshake and certificate validation. EPP uses an additional user identifier and password (beyond the machine authentication from TLS) to identify the specific user. Servers should protect against TCP denial of service attacks using firewall filters and other defenses.
The locked line is the TLS connection. Both sides show ID cards (certificates) and check them before talking. Even with a locked line, the registrar still sends a username and password to prove who they are.
§6References
[RFC793]RFC 793Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981.September 1981[RFC2119]RFC 2119Bradner, S., "Key Words for Use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.March 1997[RFC2246]RFC 2246Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999.January 1999[RFC2581]RFC 2581Allman, M., Paxson, V. and W. Stevens, "TCP Congestion Control", RFC 2581, April 1999.April 1999[RFC3730]RFC 3730Hollenbeck, S., "Extensible Provisioning Protocol (EPP)", RFC 3730, March 2004.March 2004