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).
AbstractThis 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. 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
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
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. 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.
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. [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. [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.
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.
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