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RFC 7589

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

Pages: 11
Proposed Standard
Obsoletes:  5539

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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/