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Network Working Group                                           M. BadraRequest for Comments: 5539                         CNRS/LIMOS LaboratoryCategory: Standards Track                                       May 2009NETCONF over Transport Layer Security (TLS)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) 2009 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents in effect on the date of   publication of this document (http://trustee.ietf.org/license-info).   Please review these documents carefully, as they describe your rights   and restrictions with respect to this document.   This document may contain material from IETF Documents or IETF   Contributions published or made publicly available before November   10, 2008.  The person(s) controlling the copyright in some of this   material may not have granted the IETF Trust the right to allow   modifications of such material outside the IETF Standards Process.   Without obtaining an adequate license from the person(s) controlling   the copyright in such materials, this document may not be modified   outside the IETF Standards Process, and derivative works of it may   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.Abstract   The Network Configuration Protocol (NETCONF) provides mechanisms to   install, manipulate, and delete the configuration of network devices.   This document describes how to use the Transport Layer Security (TLS)   protocol to secure NETCONF exchanges.Badra                       Standards Track                     [Page 1]

RFC 5539                    NETCONF over TLS                    May 2009Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .21.1.  Conventions Used in This Document . . . . . . . . . . . . .22.  NETCONF over TLS  . . . . . . . . . . . . . . . . . . . . . . .32.1.  Connection Initiation . . . . . . . . . . . . . . . . . . .32.2.  Connection Closure  . . . . . . . . . . . . . . . . . . . .43.  Endpoint Authentication and Identification  . . . . . . . . . .43.1.  Server Identity . . . . . . . . . . . . . . . . . . . . . .43.2.  Client Identity . . . . . . . . . . . . . . . . . . . . . .54.  Security Considerations . . . . . . . . . . . . . . . . . . . .55.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .66.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . .67.  Contributor's Address . . . . . . . . . . . . . . . . . . . . .78.  References  . . . . . . . . . . . . . . . . . . . . . . . . . .78.1.  Normative References  . . . . . . . . . . . . . . . . . . .78.2.  Informative References  . . . . . . . . . . . . . . . . . .71.  Introduction   The NETCONF protocol [RFC4741] defines a mechanism through which a   network device can be managed.  NETCONF is connection-oriented,   requiring a persistent connection between peers.  This connection   must provide integrity, confidentiality, peer authentication, and   reliable, sequenced data delivery.   This document defines "NETCONF over TLS", which includes support for   certificate-based mutual authentication and key derivation, utilizing   the protected ciphersuite negotiation, mutual authentication, and key   management capabilities of the TLS (Transport Layer Security)   protocol, described in [RFC5246].   Throughout this document, the terms "client" and "server" are used to   refer to the two ends of the TLS connection.  The client actively   opens the TLS connection, and the server passively listens for the   incoming TLS connection.  The terms "manager" and "agent" are used to   refer to the two ends of the NETCONF protocol session.  The manager   issues NETCONF remote procedure call (RPC) commands, and the agent   replies to those commands.  When NETCONF is run over TLS using the   mapping defined in this document, the client is always the manager,   and the server is always the agent.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].Badra                       Standards Track                     [Page 2]

RFC 5539                    NETCONF over TLS                    May 20092.  NETCONF over TLS   Since TLS is application-protocol-independent, NETCONF can operate on   top of the TLS protocol transparently.  This document defines how   NETCONF can be used within a TLS session.2.1.  Connection Initiation   The peer acting as the NETCONF manager MUST also act as the TLS   client.  It MUST connect to the server that passively listens for the   incoming TLS connection on the TCP port 6513.  It MUST therefore send   the TLS ClientHello message to begin the TLS handshake.  Once the TLS   handshake has finished, the client and the server MAY begin to   exchange NETCONF data.  In particular, the client will send complete   XML documents to the server containing <rpc> elements, and the server   will respond with complete XML documents containing <rpc-reply>   elements.  The client MAY indicate interest in receiving event   notifications from a server by creating a subscription to receive   event notifications [RFC5277].  In this case, the server replies to   indicate whether the subscription request was successful and, if it   was successful, the server begins sending the event notifications to   the client as the events occur within the system.   All NETCONF messages MUST be sent as TLS "application data".  It is   possible that multiple NETCONF messages be contained in one TLS   record, or that a NETCONF message be transferred in multiple TLS   records.   This document uses the same delimiter sequence ("]]>]]>") defined in   [RFC4742], which MUST be sent by both the client and the server after   each XML document in the NETCONF exchange.  Since this character   sequence can legally appear in plain XML in attribute values,   comments, and processing instructions, implementations of this   document MUST ensure that this character sequence is never part of a   NETCONF message.   Implementation of the protocol specified in this document MAY   implement any TLS cipher suite that provides certificate-based mutual   authentication [RFC5246].  The server MUST support certificate-based   client authentication.   Implementations MUST support TLS 1.2 [RFC5246] and are REQUIRED to   support the mandatory-to-implement cipher suite, which is   TLS_RSA_WITH_AES_128_CBC_SHA.  This document is assumed to apply to   future versions of TLS; in which case, the mandatory-to-implement   cipher suite for the implemented version MUST be supported.Badra                       Standards Track                     [Page 3]

RFC 5539                    NETCONF over TLS                    May 20092.2.  Connection Closure   A TLS client (NETCONF manager) MUST close the associated TLS   connection if the connection is not expected to issue any NETCONF RPC   commands later.  It MUST send a TLS close_notify alert before closing   the connection.  The TLS client MAY choose to not wait for the TLS   server (NETCONF agent) close_notify alert and simply close the   connection, thus generating an incomplete close on the TLS server   side.  Once the TLS server gets a close_notify from the TLS client,   it MUST reply with a close_notify unless it becomes aware that the   connection has already been closed by the TLS client (e.g., the   closure was indicated by TCP).   When no data is received from a connection for a long time (where the   application decides what "long" means), a NETCONF peer MAY close the   connection.  The NETCONF peer MUST attempt to initiate an exchange of   close_notify alerts with the other NETCONF peer before closing the   connection.  The close_notify's sender that is unprepared to receive   any more data MAY close the connection after sending the close_notify   alert, thus generating an incomplete close on the close_notify's   receiver side.3.  Endpoint Authentication and Identification3.1.  Server Identity   During the TLS negotiation, the client MUST carefully examine the   certificate presented by the server to determine if it meets the   client's expectations.  Particularly, the client MUST check its   understanding of the server hostname against the server's identity as   presented in the server Certificate message, in order to prevent man-   in-the-middle attacks.   Matching is performed according to the rules below (following the   example of [RFC4642]):   o  The client MUST use the server hostname it used to open the      connection (or the hostname specified in the TLS "server_name"      extension [RFC5246]) as the value to compare against the server      name as expressed in the server certificate.  The client MUST NOT      use any form of the server hostname derived from an insecure      remote source (e.g., insecure DNS lookup).  CNAME canonicalization      is not done.   o  If a subjectAltName extension of type dNSName is present in the      certificate, it MUST be used as the source of the server's      identity.Badra                       Standards Track                     [Page 4]

RFC 5539                    NETCONF over TLS                    May 2009   o  Matching is case-insensitive.   o  A "*" wildcard character MAY be used as the leftmost name      component in the certificate.  For example, *.example.com would      match a.example.com, foo.example.com, etc., but would not match      example.com.   o  If the certificate contains multiple names (e.g., more than one      dNSName field), then a match with any one of the fields is      considered acceptable.   If the match fails, the client MUST either ask for explicit user   confirmation or terminate the connection and indicate the server's   identity is suspect.   Additionally, clients MUST verify the binding between the identity of   the servers to which they connect and the public keys presented by   those servers.  Clients SHOULD implement the algorithm inSection 6   of [RFC5280] for general certificate validation, but MAY supplement   that algorithm with other validation methods that achieve equivalent   levels of verification (such as comparing the server certificate   against a local store of already-verified certificates and identity   bindings).   If the client has external information as to the expected identity of   the server, the hostname check MAY be omitted.3.2.  Client Identity   The server MUST verify the identity of the client with certificate-   based authentication according to local policy to ensure that the   incoming client request is legitimate before any configuration or   state data is sent to or received from the client.4.  Security Considerations   The security considerations described throughout [RFC5246] and   [RFC4741] apply here as well.   This document in its current version does not support third-party   authentication (e.g., backend Authentication, Authorization, and   Accounting (AAA) servers) due to the fact that TLS does not specify   this way of authentication and that NETCONF depends on the transport   protocol for the authentication service.  If third-party   authentication is needed, BEEP or SSH transport can be used.Badra                       Standards Track                     [Page 5]

RFC 5539                    NETCONF over TLS                    May 2009   An attacker might be able to inject arbitrary NETCONF messages via   some application that does not carefully check exchanged messages or   deliberately insert the delimiter sequence in a NETCONF message to   create a DoS attack.  Hence, applications and NETCONF APIs MUST   ensure that the delimiter sequence defined inSection 2.1 never   appears in NETCONF messages; otherwise, those messages can be   dropped, garbled, or misinterpreted.  If the delimiter sequence is   found in a NETCONF message by the sender side, a robust   implementation of this document should warn the user that illegal   characters have been discovered.  If the delimiter sequence is found   in a NETCONF message by the receiver side (including any XML   attribute values, XML comments, or processing instructions), a robust   implementation of this document must silently discard the message   without further processing and then stop the NETCONF session.   Finally, this document does not introduce any new security   considerations compared to [RFC4742].5.  IANA Considerations   IANA has assigned a TCP port number (6513) in the "Registered Port   Numbers" range with the name "netconf-tls".  This port will be the   default port for NETCONF over TLS, as defined in this document.      Registration Contact:  Mohamad Badra, badra@isima.fr.      Transport Protocol:  TCP.      Port Number:  6513      Broadcast, Multicast or Anycast: No.      Port Name:  netconf-tls.      Service Name: netconf.      Reference:RFC 55396.  Acknowledgements   A significant amount of the text inSection 3 was lifted from   [RFC4642].   The author would like to acknowledge David Harrington, Miao Fuyou,   Eric Rescorla, Juergen Schoenwaelder, Simon Josefsson, Olivier   Coupelon, Alfred Hoenes, and the NETCONF mailing list members for   their comments on the document.  The author also appreciates Bert   Wijnen, Mehmet Ersue, and Dan Romascanu for their efforts on issues   resolving discussion; and Charlie Kaufman, Pasi Eronen, and Tim Polk   for the thorough review of this document.Badra                       Standards Track                     [Page 6]

RFC 5539                    NETCONF over TLS                    May 20097.  Contributor's Address   Ibrahim Hajjeh   Ineovation   France   EMail: ibrahim.hajjeh@ineovation.fr8.  References8.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC4741]  Enns, R., "NETCONF Configuration Protocol",RFC 4741,              December 2006.   [RFC4742]  Wasserman, M. and T. Goddard, "Using the NETCONF              Configuration Protocol over Secure SHell (SSH)",RFC 4742,              December 2006.   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security              (TLS) Protocol Version 1.2",RFC 5246, August 2008.   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,              Housley, R., and W. Polk, "Internet X.509 Public Key              Infrastructure Certificate and Certificate Revocation List              (CRL) Profile",RFC 5280, May 2008.8.2.  Informative References   [RFC4642]  Murchison, K., Vinocur, J., and C. Newman, "Using              Transport Layer Security (TLS) with Network News Transfer              Protocol (NNTP)",RFC 4642, October 2006.   [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event              Notifications",RFC 5277, July 2008.Author's Address   Mohamad Badra   CNRS/LIMOS Laboratory   Campus de cezeaux, Bat. ISIMA   Aubiere  63170   France   EMail: badra@isima.frBadra                       Standards Track                     [Page 7]