One document matched: draft-ietf-netconf-call-home-02.txt
Differences from draft-ietf-netconf-call-home-01.txt
NETCONF Working Group K. Watsen
Internet-Draft Juniper Networks
Updates: 4253 (if approved) December 5, 2014
Intended status: Standards Track
Expires: June 8, 2015
NETCONF Call Home and RESTCONF Call Home
draft-ietf-netconf-call-home-02
Abstract
This document presents NETCONF Call Home and RESTCONF Call Home,
which respectively enable a NETCONF/RESTCONF server to initiate a
secure connection to a NETCONF/RESTCONF client.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 8, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Terminology . . . . . . . . . . . . . . . . 3
1.3. Applicability Statement . . . . . . . . . . . . . . . . . 3
1.4. Update to RFC 4253 . . . . . . . . . . . . . . . . . . . 4
2. The NETCONF Server or RESTCONF Server . . . . . . . . . . . . 4
2.1. Protocol Operation . . . . . . . . . . . . . . . . . . . 4
2.2. Configuration Data Model . . . . . . . . . . . . . . . . 5
3. The NETCONF Client or RESTCONF Client . . . . . . . . . . . . 5
3.1. Protocol Operation . . . . . . . . . . . . . . . . . . . 5
3.2. Server Identification and Verification . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 11
A.1. 00 to 01 . . . . . . . . . . . . . . . . . . . . . . . . 11
A.2. 01 to 02 . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
This document presents NETCONF Call Home and RESTCONF Call Home,
which respectively enable a NETCONF/RESTCONF server to initiate a
secure connection to a NETCONF/RESTCONF client. The NETCONF protocol
is described in [RFC6241] and the RESTCONF is described in
[draft-ietf-netconf-restconf].
Both NETCONF Call Home and RESTCONF Call Home preserve the SSH
[RFC4253] and TLS [RFC5246] transport roles, as when compared to
standard NETCONF and RESTCONF connections. Specifically, regardless
if call home is used or not, the NETCONF server is always the SSH or
TLS server, and the RESTCONF server is always the TLS server.
Ensuring consistency in the SSH and TLS roles is both necessary and
desirable. Ensuring consistency is necessary, for the SSH protocol,
as SSH channels and subsystems can only be opened on the SSH server,
as is needed to support NETCONF over SSH [RFC6242]. Ensuring
consistency is desirable, for both the SSH and TLS protocols, as it
conveniently leverages infrastructure that may be deployed for host-
key or certificate verification and user authentication.
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1.1. Motivation
Call home is generally useful for both the initial deployment and on-
going management of networking elements. Here are some scenarios
enabled by call home:
o The network element may proactively call home after being powered
on for the first time in order to register itself with its
management system.
o The network element may access the network in a way that
dynamically assigns it an IP address and it doesn't register its
assigned IP addressed to a mapping service.
o The network element may be configured in "stealth mode" and thus
doesn't have any open ports for the management system to connect
to.
o The network element may be deployed behind a firewall that doesn't
allow management access to the internal network.
o The network element may be deployed behind a firewall that
implements network address translation (NAT) for all internal
network IP addresses, thus complicating the ability for a
management system to connect to it.
o The operator may prefer to have network elements initiate
management connections, believing it is easier to secure one open-
port in the data center than to have an open port on each network
element in the network.
Having call home for the NETCONF protocol, and the RESTCONF protocol
by extension, is particularly useful as NETCONF is the recommended
protocol for configuration [iesg-statement], which is needed for
provisioning workflows.
1.2. Requirements Terminology
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].
1.3. Applicability Statement
The techniques described in this document are suitable for network
management scenarios such as the ones described in Section 1.1.
However, these techniques SHOULD only be used for NETCONF Call Home
and RESTCONF Call Home, as described in this document.
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The reason for this restriction is that different protocols have
different security assumptions. The NETCONF and RESTCONF protocols
require clients and servers to verify the identity of the other party
before starting the NETCONF/RESTCONF protocol (section 2.2 of
[RFC6241] and section FIXME of [draft-ietf-netconf-restconf]).
This contrasts with the base SSH and TLS protocols, which do not
require programmatic verification of the other party (section 9.3.4
of [RFC4251], section 4 of [RFC4252], and section 7.3 of [RFC5246]).
In such circumstances, allowing the SSH/TLS server to contact the
SSH/TLS client would open new vulnerabilities. Any use of call home
with SSH/TLS for purposes other than NETCONF or RESTCONF will need a
thorough, contextual security analysis.
1.4. Update to RFC 4253
This document updates the SSH Transport Layer Protocol [RFC4253] only
by removing the "The client initiates the connection" statement made
in Section 4 (Connection Setup). This document assumes that the
reference to "connection" refers to the underlying transport
connection (e.g., TCP), which the server initiates in a call home
connection. Security implications related to this change are
discussed in Security Considerations (Section 4).
2. The NETCONF Server or RESTCONF Server
2.1. Protocol Operation
o The NETCONF/RESTCONF server initiates a TCP connection to the
NETCONF/RESTCONF client on one of the IANA-assigned ports for call
home (PORT-X for netconf-ch-ssh, PORT-Y for netconf-ch-tls, or
PORT-Z for restconf-ch-tls).
o The TCP connection is accepted and a TCP session is established.
o Using this TCP session, the NETCONF/RESTCONF server immediately
starts either the SSH-server or the TLS-server protocol, depending
on which port is connected. The server MUST start the SSH-server
protocol when port PORT-X is connected or the TLS-server protocol
when either port PORT-Y or PORT-Z is connected. The SSH-server
and TLS-server protocols are described by [RFC4253] and [RFC5246]
respectively.
o When port PORT-X or PORT-Y is connected, the NETCONF protocol
proceeds normally for SSH and TLS, as defined in [RFC6242] and
[RFC5539] respectively. When port PORT-Z is connected, the
RESTCONF protocol proceeds normally for TLS, as defined in
[draft-ietf-netconf-restconf].
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2.2. Configuration Data Model
How to configure a NETCONF or RESTCONF server to initiate a call home
connection is outside the scope of this document, as implementations
can support this protocol using proprietary configuration data
models. That said, a YANG [RFC6020] model for configuring both
NETCONF Call Home and RESTCONF Call Home is provided in
[draft-ietf-netconf-server-model].
3. The NETCONF Client or RESTCONF Client
3.1. Protocol Operation
o The NETCONF/RESTCONF client listens for TCP connections on one or
all of the IANA-assigned ports for NETCONF Call Home (PORT-X for
netconf-ch-ssh and PORT-Y for netconf-ch-tls) or RESTCONF Call
Home (PORT-Z for restconf-ch-tls).
o The NETCONF/RESTCONF client accepts an incoming TCP connection and
a TCP session is established.
o Using this TCP session, the NETCONF/RESTCONF client immediately
starts either the SSH-client or the TLS-client protocol, depending
on which port is connected. The client MUST start the SSH-client
protocol when port PORT-X is connected and the TLS-client protocol
when port PORT-Y or PORT-Z is connected. The SSH-client and TLS-
client protocols are described by [RFC4253] and [RFC5246]
respectively.
o When port PORT-X or PORT-Y is connected, the NETCONF protocol
proceeds normally for SSH and TLS, as defined in [RFC6242] and
[RFC5539] respectively. When port PORT-Z is connected, the
RESTCONF protocol proceeds normally for TLS, as defined in
[draft-ietf-netconf-restconf].
3.2. Server Identification and Verification
Under normal circumstances, a NETCONF/RESTCONF client initiates the
connection to the NETCONF/RESTCONF server. This action provides
essential input to verify the NETCONF/RESTCONF server's identity.
For instance, when using TLS, the input can be compared to the domain
names and IP addresses encoded in X.509 certificates. Similarly,
when using SSH, the input can be compared to information persisted
previously.
However, when receiving a call home connection, the NETCONF/RESTCONF
client does not have any context leading it to know the connection is
from a particular NETCONF/RESTCONF server. Thus the NETCONF/RESTCONF
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client must derive the NETCONF/RESTCONF server's identity using
information provided by the network and the NETCONF/RESTCONF server
itself. This section describes strategies a NETCONF/RESTCONF client
can use to identify a NETCONF/RESTCONF server.
In addition to identifying a NETCONF/RESTCONF server, a NETCONF/
RESTCONF client must also be able to verify the NETCONF/RESTCONF
server's credentials. Verifying a NETCONF/RESTCONF server's
credentials is necessary under normal circumstances but, due to call
home being commonly used for newly deployed NETCONF/RESTCONF servers,
how to verify its credentials the very first time becomes a prominent
concern. Therefore, this section also describes strategies a
NETCONF/RESTCONF client can use to verify a NETCONF/RESTCONF server's
credentials.
The first information a NETCONF/RESTCONF client learns from a call
rhHome connection is the IP address of the NETCONF/RESTCONF server,
as provided by the source address of the TCP connection. This IP
address could be used as an identifier directly, but doing so would
only work in networks that use known static addresses, in which case
a standard NETCONF/RESTCONF connection would have worked just as
well. Due to this limited use, it is not recommended to identify a
NETCONF/RESTCONF server based on its source IP address.
The next information a NETCONF/RESTCONF client learns is provided by
the NETCONF/RESTCONF server in the form of a host-key or a
certificate, for the SSH and TLS protocols respectively. Without
examining the contents of the host-key or certificate, it is possible
to form an identity for the NETCONF/RESTCONF server using it directly
(e.g., a fingerprint), since each NETCONF/RESTCONF server is assumed
to have a statistically unique public key, even in virtualized
environments. This strategy also provides a mechanism to verify the
NETCONF/RESTCONF server, in that a secure connection can only be
established with the NETCONF/RESTCONF server having the matching
private key. This strategy is commonly implemented by SSH clients,
and could be used equally well by TLS-based clients, such as may be
required when the NETCONF/RESTCONF servers have self-signed
certificates. This strategy is viable and useful when the NETCONF/
RESTCONF servers call home using either SSH with standard RSA/DSA
host-keys, or using TLS with self-signed certificates.
Yet another option for identifying a NETCONF/RESTCONF server is for
its host key or certificate to encode its identity directly (e.g.,
within the "Subject" field). However, in order to trust the content
encoded within a host-key or certificate, it must be signed by a
certificate authority trusted by the NETCONF/RESTCONF client. This
strategy's use of PKI enables a NETCONF/RESTCONF client to
transparently authenticate NETCONF/RESTCONF servers, thus eliminating
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the need for manual authentication, as required by the previously
discussed strategies. Elimination of manual steps is needed to
achieve scalable solutions, however one can claim that this merely
pushes equivalent work to provisioning the NETCONF/RESTCONF servers
with signed credentials. This assessment is accurate in general, but
not in the case where the manufacturer itself provisions the
credentials, such as is described by [Std-802.1AR-2009]. When
NETCONF/RESTCONF servers are pre-provisioned this way, NETCONF/
RESTCONF clients can transparently authenticate NETCONF/RESTCONF
servers using just the manufacturer's trust anchor and a list of
expected NETCONF/RESTCONF server identifiers, which could be provided
along with shipping information. This strategy is recommended for
all deployment scenarios.
In discussing the use of certificates, it is worth noting that TLS
uses X.509 certificates by default. However, to use X.509
certificates with SSH, both the NETCONF client and server must
support [RFC6187].
4. Security Considerations
The security considerations described throughout [RFC6242] and
[RFC5539], and by extension [RFC4253], [RFC5246], and
[draft-ietf-netconf-restconf] apply here as well.
This RFC deviates from standard SSH and TLS usage by having the SSH/
TLS server initiate the underlying TCP connection. For SSH,
[RFC4253] says "the client initiates the connection", whereas for
TLS, [RFC5246] says it is layered on top of "some reliable transport
protocol" without further attribution.
Not having the SSH/TLS client initiate the TCP connection means that
it does not have a preconceived notion of the SSH/TLS server's
identity, and therefore must dynamically derive one from information
provided by the network or the SSH/TLS server itself. Security
Considerations for strategies for this are described in Section 3.2.
An attacker could DoS the NETCONF/RESTCONF client by having it
perform computationally expensive operations, before deducing that
the attacker doesn't posses a valid key. This is no different than
any secured service and all common precautions apply (e.g.,
blacklisting the source address after a set number of unsuccessful
login attempts).
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5. IANA Considerations
This document requests that IANA assigns three TCP port numbers in
the "Registered Port Numbers" range with the service names "netconf-
ch-ssh", "netconf-ch-tls", and "restconf-ch-tls". These ports will
be the default ports for NETCONF Call Home and RESTCONF Call Home
protocols. Below is the registration template following the rules in
[RFC6335].
Service Name: netconf-ch-ssh
Transport Protocol(s): TCP
Assignee: IESG <iesg@ietf.org>
Contact: IETF Chair <chair@ietf.org>
Description: NETCONF Call Home (SSH)
Reference: RFC XXXX
Port Number: PORT-X
Service Name: netconf-ch-tls
Transport Protocol(s): TCP
Assignee: IESG <iesg@ietf.org>
Contact: IETF Chair <chair@ietf.org>
Description: NETCONF Call Home (TLS)
Reference: RFC XXXX
Port Number: PORT-Y
Service Name: restconf-ch-tls
Transport Protocol(s): TCP
Assignee: IESG <iesg@ietf.org>
Contact: IETF Chair <chair@ietf.org>
Description: RESTCONF Call Home (TLS)
Reference: RFC XXXX
Port Number: PORT-Z
6. Acknowledgements
The author would like to thank for following for lively discussions
on list and in the halls (ordered by last name): Andy Bierman, Martin
Bjorklund, Mehmet Ersue, Wes Hardaker, Stephen Hanna, David
Harrington, Jeffrey Hutzelman, Radek Krejci, Alan Luchuk, Mouse, Russ
Mundy, Tom Petch, Peter Saint-Andre, Joe Touch, Sean Turner, Bert
Wijnen.
7. References
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7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4251] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Protocol Architecture", RFC 4251, January 2006.
[RFC4252] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Authentication Protocol", RFC 4252, January 2006.
[RFC4253] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Transport Layer Protocol", RFC 4253, January 2006.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5539] Badra, M., "NETCONF over Transport Layer Security (TLS)",
RFC 5539, May 2009.
[RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the
Network Configuration Protocol (NETCONF)", RFC 6020,
October 2010.
[RFC6187] Igoe, K. and D. Stebila, "X.509v3 Certificates for Secure
Shell Authentication", RFC 6187, March 2011.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
Bierman, "Network Configuration Protocol (NETCONF)", RFC
6241, June 2011.
[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, June 2011.
[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, August 2011.
[draft-ietf-netconf-restconf]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", draft-ieft-netconf-restconf-04 (work in
progress), 2014.
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7.2. Informative References
[Std-802.1AR-2009]
IEEE SA-Standards Board, "IEEE Standard for Local and
metropolitan area networks - Secure Device Identity",
December 2009, <http://standards.ieee.org/findstds/
standard/802.1AR-2009.html>.
[draft-ietf-netconf-server-model]
Watsen, K. and J. Schoenwaelder, "NETCONF Server
Configuration Model", 2014, <http://tools.ietf.org/html/
draft-ietf-netconf-server-model>.
[iesg-statement]
"Writable MIB Module IESG Statement", March 2014,
<https://www.ietf.org/iesg/statement/writable-mib-
module.html>.
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Appendix A. Change Log
A.1. 00 to 01
o The term "TCP connection" is now used throughout.
o The terms "network element" and "management system" are now only
used in the Motivation section.
o Restructured doc a little to create an Introduction section.
o Fixed reference in Applicability Statement so it would work
equally well for SSH and TLS.
o Fixed reported odd wording and three references.
A.2. 01 to 02
o Added call home support for the RESTCONF protocol.
o Fixed paragraph 3 of Security Considerations to equally apply to
the TLS protocol.
Author's Address
Kent Watsen
Juniper Networks
EMail: kwatsen@juniper.net
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