NETCONF Working Group Mohamad Badra
Internet Draft LIMOS Laboratory
Intended status: Standard Track January 1, 2008
Expires: July 2008
NETCONF over TLS
draft-ietf-netconf-tls-00.txt
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
The NETCONF configuration protocol provides mechanisms to install,
manipulate, and delete the configuration of network devices. This
document describes how to use TLS to secure NETCONF exchanges.
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Table of Contents
1. Introduction...................................................2
1.1. Conventions used in this document.........................2
2. NETCONF over TLS...............................................3
2.1. Connection Initiation.....................................3
2.2. Connection Closure........................................3
3. Endpoint Authentication and Identification.....................4
3.1. Public Key Based-Certificate Authentication...............4
3.1.1. Server Identity......................................4
3.1.2. Client Identity......................................5
3.2. Password-Based Authentication for the NETCONF manager (TLS
client)........................................................5
4. Security Considerations........................................6
5. IANA Considerations............................................6
6. Acknowledgments................................................6
7. References.....................................................7
7.1. Normative References......................................7
7.2. Informative References....................................7
Author's Addresses................................................8
Intellectual Property Statement...................................8
Disclaimer of Validity............................................8
1. Introduction
The NETCONF protocol [NETCONF] defines a simple mechanism through
which a network device can be managed. NETCONF is connection-
oriented, requiring a persistent connection between peers. This
connection must provide reliable, sequenced data delivery, integrity
and confidentiality and peers authentication. This document describes
how to use TLS [TLS] to secure NETCONF connections.
1.1. Conventions used in this document
This document uses the following terms:
manager
It refers to the end initiating the NETCONF connection. It issues
the NETCONF RPC commands.
agent
It refers to the end replying to the manager's commands during the
NETCONF connection.
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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 RFC-2119 [RFC2119].
2. 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 Transport Layer Security (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 IANA-to-be-assigned TCP port <TBC>. It
MUST therefore send the TLS ClientHello to begin the TLS handshake.
Once the TLS handshake has been finished, the manager and the agent
MAY then send their NETCONF exchanges. In particular, the manager
will send complete XML documents to the server containing <rpc>
elements, and the agent will respond with complete XML documents
containing <rpc-reply> elements. The client MAY indicate interest in
receiving event notifications from a NETCONF server by creating a
subscription to receive event notifications [NETNOT], in which the
NETCONF server replies to indicate whether the subscription request
was successful and, if it was successful, begins sending the event
notifications to the NETCONF client as the events occur within the
system. All these elements are encapsulated into TLS records of type
"application data". These records are protected using the TLS
material keys.
Current NETCONF messages don't include a message's length. This
document uses consequently the same delimiter sequence defined in
[NETSSH] and therefore the special character sequence, ]]>]]>, to
delimit XML documents.
2.2. Connection Closure
Either NETCONF peer MAY stop the NETCONF connection at any time and
therefore notify the other NETCONF peer that no more data on this
channel will be sent and that any data received after a closure
request will be ignored. This MAY happen when no data is received
from a connection for a long time, where the application decides what
"long" means.
TLS has the ability for secure connection closure using the Alert
protocol. When the NETCONF peer processes a closure request of the
NETCONF connection, it MUST send a TLS close_notify alert before
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closing the connection. Any data received after a closure alert is
ignored.
Unless some other fatal alert has been transmitted, each party is
required to send a close_notify alert before closing the write side
of the connection. The other party MUST respond with a close_notify
alert of its own and close down the connection immediately,
discarding any pending writes. It is not required for the initiator
of the close to wait for the responding close_notify alert before
closing the read side of the connection.
3. Endpoint Authentication and Identification
Usually, TLS uses public key based-certificates [TLS], Kerberos
[TLSKERB], or preshared keys [TLSPSK] for authentication.
3.1. Public Key Based-Certificate Authentication
When public key is used for authentication, TLS supports three
authentication modes: authentication of both parties, server
authentication with an unauthenticated client, and total anonymity.
For the last two modes, a profile to enable the password-based client
(manager) authentication is defined in section 3.2.
3.1.1. Server Identity
During the TLS negotiation, the client MUST carefully examine the
certificate presented by the server to determine if it meets their
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 these rules [RFC4642]:
- The client MUST use the server hostname it used to open the
connection (or the hostname specified in TLS "server_name"
extension [TLSEXT]) 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.
- If a subjectAltName extension of type dNSName is present in the
certificate, it MUST be used as the source of the server's
identity.
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- Matching is case-insensitive.
- A "*" wildcard character MAY be used as the left-most name
component in the certificate. For example, *.example.com would
match a.example.com, foo.example.com, etc., but would not match
example.com.
- 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 in Section 6 of
[PKICERT] 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.
3.1.2. Client Identity
Typically, the server has no external knowledge of what the client's
identity ought to be and so checks (other than that the client has a
certificate chain rooted in an appropriate CA) are not possible. If a
server has such knowledge (typically from some source external to
NETCONF or TLS) it MUST check the identity as described above.
3.2. Password-Based Authentication for the NETCONF manager (TLS client)
RFC4279 supports authentication based on pre-shared keys (PSKs).
These pre-shared keys are symmetric keys, shared in advance among the
communicating parties.
The PSK can be generated in many ways and its length is variable.
Implementation of this document MAY rely on RFC4279 to enable
password based user authentication. In this case, the hashed version
of the password is stored is used to generate the PSK. It is
RECOMMENDED that implementations that allow the administrator to
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manually configure the password also provide functionality for
generating a new random password, taking RFC4086 into account.
This document generates the PSK from the password as follow:
PSK = SHA-1(SHA-1(stored-hash + "Key Pad for Netconf") +
psk_identity_hint)
Where + means concatenation.
The stored-hash is the hashed version of the password.
The label "Key Pad for Netconf" is an ASCII string.
The psk_identity_hint is initially defined in section 5.1 of RFC4279.
The psk_identity_hint can do double duty and also provide a form of
server authentication in the case where the user has the same
password on a number of NETCONF agents. If a hint is provided, the
psk_identity_hint is encoded in the same way as in [RFC4279] and
should be a string representation of the name of the server
recognizable to the administrator or his software. In the case where
the user types a server name to connect to, it should be that string.
If the string the user enters differs from the one returned as
psk_identity_hint, the software could display the server's name and
ask the user to confirm. For automated scripts, the names could be
expected to match. It is highly recommended that implementations set
the psk_identity_hint to the DNS name of the NETCONF agent (i.e., the
TLS server).
4. Security Considerations
The security considerations described throughout [TLS] and [TLSPSK]
apply here as well.
5. IANA Considerations
IANA is requested to assign a TCP port number that will be the
default port for NETCONF over TLS sessions as defined in this
document.
IANA has assigned port <TBD> for this purpose.
6. Acknowledgments
The author would like to acknowledge Eric Rescorla and Juergen
Schoenwaelder for their detailed reviews of the content of the
document. The author appreciates also David Harrington, Miao Fuyou
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and Dan Romascanu for their effort on issues resolving discussion,
and Charlie Kaufman for his contribution on the password-based
authentication.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[NETCONF] Enns, R., "NETCONF Configuration Protocol", RFC 4741,
December 2006.
[TLS] Dierks, T. and E. Rescorla, "The TLS Protocol Version 1.1",
RFC 4346, April 2005.
[TLSEXT] Blake-Wilson, S., et. al., "Transport Layer Security (TLS)
Extensions", RFC 4346, April 2006.
[TLSPSK] Eronen, P., et. al., "Pre-Shared Key Ciphersuites for
Transport Layer Security (TLS)", RFC 4279, December 2005.
[RFC4642] Murchison, K., Vinocur, J., Newman, C., "Using Transport
Layer Security (TLS) with Network News Transfer Protocol
(NNTP)", RFC 4642, October 2006
[PKICERT] 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.
[NETSSH] Wasserman, M. and T. Goddard, "Using the NETCONF
Configuration Protocol over Secure Shell (SSH)", RFC 4742,
December 2006.
[NETNOT] Chisholm, S. and H. Trevino, "NETCONF Event Notifications",
draft-ietf-netconf-notification-11.txt, (work in progress),
November 2007.
7.2. Informative References
[TLSKERB] Medvinsky, A. and M. Hur, "Addition of Kerberos Cipher
Suites to Transport Layer Security (TLS)", RFC 2712,
October 1999.
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Author's Addresses
Mohamad Badra
LIMOS Laboratory - UMR6158, CNRS
France
Email: badra@isima.fr
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Copyright Statement
Copyright (C) The IETF Trust (2008).
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Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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