NETCONF Call Home and RESTCONF Call Home
draft-ietf-netconf-call-home-03
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8071.
|
|
|---|---|---|---|
| Author | Kent Watsen | ||
| Last updated | 2015-01-13 | ||
| Replaces | draft-ietf-netconf-reverse-ssh | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 8071 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-netconf-call-home-03
NETCONF Working Group K. Watsen
Internet-Draft Juniper Networks
Updates: 4253 (if approved) January 13, 2015
Intended status: Standards Track
Expires: July 17, 2015
NETCONF Call Home and RESTCONF Call Home
draft-ietf-netconf-call-home-03
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.
Editorial Note (To be removed by RFC Editor)
This draft contains many placeholder values that need to be replaced
with finalized values at the time of publication. This note
summarizes all of the substitutions that are needed. Please note
that no other RFC Editor instructions are specified anywhere else in
this document.
Artwork in this document contains placeholder references for this
draft. Please apply the following replacement:
o "XXXX" --> the assigned RFC value for this draft
This document contains references to other drafts in progress, both
in the Normative References section, as well as in body text
throughout. Please update the following references to reflect their
final RFC assignments:
o draft-ietf-netconf-restconf
o draft-ietf-netconf-server-model
Artwork in this document contains placeholder values for ports
pending IANA assignment from "draft-ietf-netconf-call-home". Please
apply the following replacements:
o "PORT-X" --> the assigned port value for "netconf-ch-ssh"
o "PORT-Y" --> the assigned port value for "netconf-ch-tls"
o "PORT-Z" --> the assigned port value for "restconf-ch-tls"
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The following two Appendix sections are to be removed prior to
publication:
o Appendix A. Change Log
o Appendix B. Open Issues
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 17, 2015.
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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Terminology . . . . . . . . . . . . . . . . 4
1.3. Applicability Statement . . . . . . . . . . . . . . . . . 4
1.4. Update to RFC 4253 . . . . . . . . . . . . . . . . . . . 5
2. The NETCONF or RESTCONF Server . . . . . . . . . . . . . . . 5
2.1. Protocol Operation . . . . . . . . . . . . . . . . . . . 5
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2.2. Configuration Data Model . . . . . . . . . . . . . . . . 6
3. The NETCONF or RESTCONF Client . . . . . . . . . . . . . . . 6
3.1. Protocol Operation . . . . . . . . . . . . . . . . . . . 6
3.2. Server Identification and Verification . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 12
A.1. 00 to 01 . . . . . . . . . . . . . . . . . . . . . . . . 12
A.2. 01 to 02 . . . . . . . . . . . . . . . . . . . . . . . . 12
A.3. 02 to 03 . . . . . . . . . . . . . . . . . . . . . . . . 12
Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . 12
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 client/
server roles of underlying transport, as when compared to standard
NETCONF and RESTCONF connections. Specifically, regardless if call
home is used or not, the SSH and TLS client/server roles are the
same. The SSH protocol is defined in [RFC4253] and the TLS protocol
is defined in [RFC5246].
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,
which thus must always be the NETCONF server, in order 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.
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:
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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, thus complicating the
ability for a management system to connect to it.
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 network element may be deployed behind a firewall that doesn't
allow any management access to the internal network.
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 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.
As the NETCONF and RESTCONF protocols become increasingly popular for
programatic management of networking elements, having call home
support for these two protocols is particularly desirable.
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.
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 sections 2.4 and 2.5 of [draft-ietf-netconf-restconf]).
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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
in 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 NETCONF server would initiate in a
call home connection using the SSH protocol, even though it will not
take on the role of the SSH client. Security implications related to
this change are discussed in Security Considerations (Section 4).
2. The NETCONF or RESTCONF Server
2.1. Protocol Operation
o The NETCONF/RESTCONF server initiates a TCP connection request
(SYN) to the NETCONF/RESTCONF client. The server SHOULD default
to connecting to one of the IANA-assigned ports defined in section
Section 5, but MAY be configured to use a non-default port.
o The TCP connection request is accepted and a TCP connection is
established.
o Using this TCP connection, the NETCONF/RESTCONF server MUST
immediately start using either the SSH-server [RFC4253] or the
TLS-server [RFC5246] protocol, depending on how it is configured.
For example, assuming the use of the IANA-assigned ports, the SSH-
server protocol is used for PORT-X and the TLS-server protocol is
used for either port PORT-Y or PORT-Z.
o Once the SSH or TLS connection is established, the NETCONF/
RESTCONF server MUST immediately start using either the NETCONF-
server [RFC6241] or RESTCONF-server [draft-ietf-netconf-restconf]
protocol, depending on how it is configured. Assuming the use of
the IANA-assigned ports, the NETCONF-server protocol is used for
PORT-X or PORT-Y and the RESTCONF-server protocol is used for
PORT-Z.
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o The NETCONF protocol's binding to SSH and TLS is defined in
[RFC6242] and [RFC5539] respectively. The RESTCONF protocol's
binding to TLS is is defined in [RFC7230].
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 or RESTCONF Client
3.1. Protocol Operation
o The NETCONF/RESTCONF client listens for TCP connections from
NETCONF/RESTCONF servers. The client SHOULD default to listening
for connections on the IANA-assigned ports defined in section
Section 5, but MAY be configured to use a non-default port.
o The NETCONF/RESTCONF client accepts an incoming TCP connection
request and a TCP connection is established.
o Using this TCP connection, the NETCONF/RESTCONF client MUST
immediately start using either the SSH-client [RFC4253] or the
TLS-client [RFC5246] protocol, depending on how it is configured.
For example, assuming the use of the IANA-assigned ports, the SSH-
client protocol is used for PORT-X and the TLS-client protocol is
used for either port PORT-Y or PORT-Z.
o Once the SSH or TLS connection is established, the NETCONF/
RESTCONF client MUST immediately start using either the NETCONF-
client [RFC6241] or RESTCONF-client [draft-ietf-netconf-restconf]
protocol, depending on how it is configured. Assuming the use of
the IANA-assigned ports, the NETCONF-client protocol is used for
PORT-X or PORT-Y and the RESTCONF-client protocol is used for
PORT-Z.
o The NETCONF protocol's binding to SSH and TLS is defined in
[RFC6242] and [RFC5539] respectively. The RESTCONF protocol's
binding to TLS is is defined in [RFC7230].
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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 used 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
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
home 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,
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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
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
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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).
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
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Harrington, Jeffrey Hutzelman, Radek Krejci, Alan Luchuk, Mouse, Russ
Mundy, Tom Petch, Peter Saint-Andre, Joe Touch, Hannes Tschofenig,
Sean Turner, Bert Wijnen.
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.
[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.
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[RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Message Syntax and Routing", RFC 7230, June
2014.
[draft-ietf-netconf-restconf]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", draft-ieft-netconf-restconf-04 (work in
progress), 2014.
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>.
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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.
A.3. 02 to 03
o Tried to improve readability (issue #6)
o Removed "FIXME" in section 1.3 (issue #7)
o Added RFC Editor notes (issue #8)
o Removed "TCP session" term (issue #9)
o Improved language for usage of IANA-assigned ports (issue #10)
Appendix B. Open Issues
All issues with this draft are tracked using GitHub issues. Please
see: https://github.com/netconf-wg/call-home/issues to see currently
opened issues.
Author's Address
Kent Watsen
Juniper Networks
EMail: kwatsen@juniper.net
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