Using the NETCONF Protocol over Transport Layer Security (TLS) with Mutual X.509 Authentication
RFC 7589

Internet Engineering Task Force (IETF)                          M. Badra
Request for Comments: 7589                              Zayed University
Obsoletes: 5539                                                A. Luchuk
Category: Standards Track                            SNMP Research, Inc.
ISSN: 2070-1721                                         J. Schoenwaelder
                                                Jacobs University Bremen
                                                               June 2015

     Using the NETCONF Protocol over Transport Layer Security (TLS)
                    with Mutual X.509 Authentication

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 with mutual X.509 authentication to secure the exchange of
   NETCONF messages.  This revision of RFC 5539 documents the new
   message framing used by NETCONF 1.1 and it obsoletes RFC 5539.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7589.

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Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Connection Initiation . . . . . . . . . . . . . . . . . . . .   3
   3.  Message Framing . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Connection Closure  . . . . . . . . . . . . . . . . . . . . .   4
   5.  Certificate Validation  . . . . . . . . . . . . . . . . . . .   4
   6.  Server Identity . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Client Identity . . . . . . . . . . . . . . . . . . . . . . .   4
   8.  Cipher Suites . . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     11.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Appendix A.  Changes from RFC 5539  . . . . . . . . . . . . . . .  10
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

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1.  Introduction

   The NETCONF protocol [RFC6241] 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 how NETCONF messages can be exchanged over
   Transport Layer Security (TLS) [RFC5246].  Implementations MUST
   support mutual TLS certificate-based authentication [RFC5246].  This
   assures the NETCONF server of the identity of the principal who
   wishes to manipulate the management information.  It also assures the
   NETCONF client of the identity of the server for which it wishes to
   manipulate the management information.

   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.  Connection Initiation

   The peer acting as the NETCONF client MUST act as the TLS client.
   The TLS client actively opens the TLS connection and the TLS server
   passively listens for the incoming TLS connections.  The well-known
   TCP port number 6513 is used by NETCONF servers to listen for TCP
   connections established by NETCONF over TLS clients.  The TLS client
   MUST send the TLS ClientHello message to begin the TLS handshake.
   The TLS server MUST send a CertificateRequest in order to request a
   certificate from the TLS client.  Once the TLS handshake has
   finished, the client and the server MAY begin to exchange NETCONF
   messages.  Client and server identity verification is done before the
   NETCONF <hello> message is sent.  This means that the identity
   verification is completed before the NETCONF session is started.

3.  Message Framing

   All NETCONF messages MUST be sent as TLS "application data".  It is
   possible for multiple NETCONF messages to be contained in one TLS
   record, or for a NETCONF message to be transferred in multiple TLS
   records.

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   The previous version of this specification [RFC5539] used the framing
   sequence defined in [RFC4742].  This version aligns with [RFC6242]
   and adopts the framing protocol defined in [RFC6242] as follows:

   The NETCONF <hello> message MUST be followed by the character
   sequence ]]>]]>.  Upon reception of the <hello> message, the peers
   inspect the announced capabilities.  If the :base:1.1 capability is
   advertised by both peers, the chunked framing mechanism defined in
   Section 4.2 of [RFC6242] is used for the remainder of the NETCONF
   session.  Otherwise, the old end-of-message-based mechanism (see
   Section 4.3 of [RFC6242]) is used.

4.  Connection Closure

   A NETCONF server will process NETCONF messages from the NETCONF
   client in the order in which they are received.  A NETCONF session is
   closed using the <close-session> operation.  When the NETCONF server
   processes a <close-session> operation, the NETCONF server SHALL
   respond and close the TLS session as described in Section 7.2.1 of
   [RFC5246].

5.  Certificate Validation

   Both peers MUST use X.509 certificate path validation [RFC5280] to
   verify the integrity of the certificate presented by the peer.  The
   presented X.509 certificate may also be considered valid if it
   matches one obtained by another trusted mechanism, such as using a
   locally configured certificate fingerprint.  If X.509 certificate
   path validation fails and the presented X.509 certificate does not
   match a certificate obtained by a trusted mechanism, the connection
   MUST be terminated as defined in [RFC5246].

6.  Server Identity

   The NETCONF client MUST check the identity of the server according to
   Section 6 of [RFC6125].

7.  Client Identity

   The NETCONF server MUST verify the identity of the NETCONF client to
   ensure that the incoming request to establish a NETCONF session is
   legitimate before the NETCONF session is started.

   The NETCONF protocol [RFC6241] requires that the transport protocol's
   authentication process results in an authenticated NETCONF client
   identity whose permissions are known to the server.  The
   authenticated identity of a client is commonly referred to as the
   NETCONF username.  The following algorithm is used by the NETCONF

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   server to derive a NETCONF username from a certificate.  (Note that
   the algorithm below is the same as the one described in the
   SNMP-TLS-TM-MIB MIB module defined in [RFC6353] and in the
   ietf-x509-cert-to-name YANG module defined in [RFC7407].)

   (a)  The server maintains an ordered list of mappings of certificates
        to NETCONF usernames.  Each list entry contains

        *  a certificate fingerprint (used for matching the presented
           certificate),

        *  a map type (indicates how the NETCONF username is derived
           from the certificate), and

        *  optional auxiliary data (used to carry a NETCONF username if
           the map type indicates the username is explicitly
           configured).

   (b)  The NETCONF username is derived by considering each list entry
        in order.  The fingerprint member of the current list entry
        determines whether the current list entry is a match:

        1.  If the list entry's fingerprint value matches the
            fingerprint of the presented certificate, then consider the
            list entry as a successful match.

        2.  If the list entry's fingerprint value matches that of a
            locally held copy of a trusted certification authority (CA)
            certificate, and that CA certificate was part of the CA
            certificate chain to the presented certificate, then
            consider the list entry as a successful match.

   (c)  Once a matching list entry has been found, the map type of the
        current list entry is used to determine how the username
        associated with the certificate should be determined.  Possible
        mapping options are:

        A.  The username is taken from the auxiliary data of the current
            list entry.  This means the username is explicitly
            configured (map type 'specified').

        B.  The subjectAltName's rfc822Name field is mapped to the
            username (map type 'san-rfc822-name').  The local part of
            the rfc822Name is used unaltered, but the host-part of the
            name must be converted to lowercase.

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        C.  The subjectAltName's dNSName is mapped to the username (map
            type 'san-dns-name').  The characters of the dNSName are
            converted to lowercase.

        D.  The subjectAltName's iPAddress is mapped to the username
            (map type 'san-ip-address').  IPv4 addresses are converted
            into decimal-dotted quad notation (e.g., '192.0.2.1').  IPv6
            addresses are converted into a 32-character all lowercase
            hexadecimal string without any colon separators.

        E.  The rfc822Name, dNSName, or iPAddress of the subjectAltName
            is mapped to the username (map type 'san-any').  The first
            matching subjectAltName value found in the certificate of
            the above types MUST be used when deriving the name.

        F.  The certificate's CommonName is mapped to the username (map
            type 'common-name').  The CommonName is converted to UTF-8
            encoding.  The usage of CommonNames is deprecated and users
            are encouraged to use subjectAltName mapping methods
            instead.

   (d)  If it is impossible to determine a username from the list
        entry's data combined with the data presented in the
        certificate, then additional list entries MUST be searched to
        look for another potential match.  Similarly, if the username
        does not comply to the NETCONF requirements on usernames
        [RFC6241], then additional list entries MUST be searched to look
        for another potential match.  If there are no further list
        entries, the TLS session MUST be terminated.

   The username provided by the NETCONF over TLS implementation will be
   made available to the NETCONF message layer as the NETCONF username
   without modification.

   The NETCONF server configuration data model [NETCONF-RESTCONF] covers
   NETCONF over TLS and provides further details such as certificate
   fingerprint formats exposed to network configuration systems.

8.  Cipher Suites

   Implementations MUST support TLS 1.2 [RFC5246] and are REQUIRED to
   support the mandatory-to-implement cipher suite.  Implementations MAY
   implement additional TLS cipher suites that provide mutual
   authentication [RFC5246] and confidentiality as required by NETCONF
   [RFC6241].  Implementations SHOULD follow the recommendations given
   in [RFC7525].

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9.  Security Considerations

   NETCONF is used to access configuration and state information and to
   modify configuration information, so the ability to access this
   protocol should be limited to users and systems that are authorized
   to view the NETCONF server's configuration and state or to modify the
   NETCONF server's configuration.

   Configuration or state data may include sensitive information, such
   as usernames or security keys.  So, NETCONF requires communications
   channels that provide strong encryption for data privacy.  This
   document defines a NETCONF over TLS mapping that provides for support
   of strong encryption and authentication.  The security considerations
   for TLS [RFC5246] and NETCONF [RFC6241] apply here as well.

   NETCONF over TLS requires mutual authentication.  Neither side should
   establish a NETCONF over TLS connection with an unknown, unexpected,
   or incorrect identity on the opposite side.  Note that the decision
   whether a certificate presented by the client is accepted can depend
   on whether a trusted CA certificate is white listed (see Section 7).
   If deployments make use of this option, it is recommended that the
   white-listed CA certificate is used only to issue certificates that
   are used for accessing NETCONF servers.  Should the CA certificate be
   used to issue certificates for other purposes, then all certificates
   created for other purposes will be accepted by a NETCONF server as
   well, which is likely not suitable.

   This document 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, the
   Secure Shell (SSH) transport [RFC6242] can be used.

   RFC 5539 assumes that the end-of-message (EOM) sequence, ]]>]]>,
   cannot appear in any well-formed XML document, which turned out to be
   mistaken.  The EOM sequence can cause operational problems and open
   space for attacks if sent deliberately in NETCONF messages.  It is
   however believed that the associated threat is not very high.  This
   document still uses the EOM sequence for the initial <hello> message
   to avoid incompatibility with existing implementations.  When both
   peers implement the :base:1.1 capability, a proper framing protocol
   (chunked framing mechanism; see Section 3) is used for the rest of
   the NETCONF session, to avoid injection attacks.

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10.  IANA Considerations

   Per RFC 5539, IANA assigned TCP port number (6513) in the "Registered
   Port Numbers" range with the service name "netconf-tls".  This port
   is the default port for NETCONF over TLS, as defined in Section 2.
   Below is the registration template following the rules in [RFC6335].

      Service Name:           netconf-tls
      Transport Protocol(s):  TCP
      Assignee:               IESG <iesg@ietf.org>
      Contact:                IETF Chair <chair@ietf.org>
      Description:            NETCONF over TLS
      Reference:              RFC 7589
      Port Number:            6513

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

   [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, DOI 10.17487/RFC5280, May 2008,
              <http://www.rfc-editor.org/info/rfc5280>.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <http://www.rfc-editor.org/info/rfc6125>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <http://www.rfc-editor.org/info/rfc6241>.

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   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <http://www.rfc-editor.org/info/rfc6242>.

   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165,
              RFC 6335, DOI 10.17487/RFC6335, August 2011,
              <http://www.rfc-editor.org/info/rfc6335>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <http://www.rfc-editor.org/info/rfc7525>.

11.2.  Informative References

   [NETCONF-RESTCONF]
              Watsen, K. and J. Schoenwaelder, "NETCONF Server and
              RESTCONF Server Configuration Models", Work in Progress,
              draft-ietf-netconf-server-model-06, February 2015.

   [RFC4742]  Wasserman, M. and T. Goddard, "Using the NETCONF
              Configuration Protocol over Secure SHell (SSH)", RFC 4742,
              DOI 10.17487/RFC4742, December 2006,
              <http://www.rfc-editor.org/info/rfc4742>.

   [RFC5539]  Badra, M., "NETCONF over Transport Layer Security (TLS)",
              RFC 5539, DOI 10.17487/RFC5539, May 2009,
              <http://www.rfc-editor.org/info/rfc5539>.

   [RFC6353]  Hardaker, W., "Transport Layer Security (TLS) Transport
              Model for the Simple Network Management Protocol (SNMP)",
              STD 78, RFC 6353, DOI 10.17487/RFC6353, July 2011,
              <http://www.rfc-editor.org/info/rfc6353>.

   [RFC7407]  Bjorklund, M. and J. Schoenwaelder, "A YANG Data Model for
              SNMP Configuration", RFC 7407, DOI 10.17487/RFC7407,
              December 2014, <http://www.rfc-editor.org/info/rfc7407>.

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Appendix A.  Changes from RFC 5539

   This section summarizes major changes between this document and RFC
   5539.

   o  Documented that NETCONF over TLS uses the new message framing if
      both peers support the :base:1.1 capability.

   o  Removed redundant text that can be found in the TLS and NETCONF
      specifications and restructured the text.  Alignment with
      [RFC6125].

   o  Added a high-level description on how NETCONF usernames are
      derived from certificates.

   o  Removed the reference to BEEP.

Acknowledgements

   The authors like to acknowledge Martin Bjorklund, Olivier Coupelon,
   Pasi Eronen, Mehmet Ersue, Stephen Farrell, Miao Fuyou, Ibrahim
   Hajjeh, David Harrington, Sam Hartman, Alfred Hoenes, Simon
   Josefsson, Charlie Kaufman, Barry Leiba, Tom Petch, Tim Polk, Eric
   Rescorla, Dan Romascanu, Kent Watsen, Bert Wijnen, Stefan Winter, and
   the NETCONF mailing list members for their comments on this document.

   Juergen Schoenwaelder was partly funded by Flamingo, a Network of
   Excellence project (ICT-318488) supported by the European Commission
   under its Seventh Framework Programme.

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Authors' Addresses

   Mohamad Badra
   Zayed University
   P.O. Box 19282
   Dubai, United Arab Emirates

   Phone: +971 4 4021879
   EMail: mohamad.badra@zu.ac.ae
   URI:   http://www.zu.ac.ae

   Alan Luchuk
   SNMP Research, Inc.
   3001 Kimberlin Heights Road
   Knoxville, TN  37920
   United States

   Phone: +1 865 573 1434
   EMail: luchuk@snmp.com
   URI:   http://www.snmp.com/

   Juergen Schoenwaelder
   Jacobs University Bremen
   Campus Ring 1
   28759 Bremen
   Germany

   Phone: +49 421 200 3587
   EMail: j.schoenwaelder@jacobs-university.de
   URI:   http://www.jacobs-university.de/

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