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
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
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
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
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
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
* 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
(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.
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
(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
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
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.
Appendix A. Changes from RFC 5539
This section summarizes major changes between this document and RFC
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
o Added a high-level description on how NETCONF usernames are
derived from certificates.
o Removed the reference to BEEP.
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.