NETCONF Working Group K. Watsen Internet-Draft Juniper Networks Updates: 4253 (if approved) February 2, 2015 Intended status: Standards Track Expires: August 6, 2015 NETCONF Call Home and RESTCONF Call Home draft-ietf-netconf-call-home-04 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" Watsen Expires August 6, 2015 [Page 1] Internet-Draft NETCONF Call Home and RESTCONF Call Home February 2015 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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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 August 6, 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 (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 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 Watsen Expires August 6, 2015 [Page 2] Internet-Draft NETCONF Call Home and RESTCONF Call Home February 2015 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 A.4. 03 to 04 . . . . . . . . . . . . . . . . . . . . . . . . 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: Watsen Expires August 6, 2015 [Page 3] Internet-Draft NETCONF Call Home and RESTCONF Call Home February 2015 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]). Watsen Expires August 6, 2015 [Page 4] Internet-Draft NETCONF Call Home and RESTCONF Call Home February 2015 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. Watsen Expires August 6, 2015 [Page 5] Internet-Draft NETCONF Call Home and RESTCONF Call Home February 2015 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]. Watsen Expires August 6, 2015 [Page 6] Internet-Draft NETCONF Call Home and RESTCONF Call Home February 2015 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 server's identity. Verifying a NETCONF/RESTCONF server's identity is necessary under normal circumstances but, due to call home being commonly used for newly deployed NETCONF/RESTCONF servers, how to verify its identity 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 identity. 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). This works because 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 identity of 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- Watsen Expires August 6, 2015 [Page 7] Internet-Draft NETCONF Call Home and RESTCONF Call Home February 2015 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 the NETCONF/RESTCONF server's certificate, 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 certificates. This assessment is accurate in general, but not in the case where the manufacturer itself provisions the certificates, 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 Watsen Expires August 6, 2015 [Page 8] Internet-Draft NETCONF Call Home and RESTCONF Call Home February 2015 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 Contact: IETF Chair Description: NETCONF Call Home (SSH) Reference: RFC XXXX Port Number: PORT-X Service Name: netconf-ch-tls Transport Protocol(s): TCP Assignee: IESG Contact: IETF Chair Description: NETCONF Call Home (TLS) Reference: RFC XXXX Port Number: PORT-Y Service Name: restconf-ch-tls Transport Protocol(s): TCP Assignee: IESG Contact: IETF Chair 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 Watsen Expires August 6, 2015 [Page 9] Internet-Draft NETCONF Call Home and RESTCONF Call Home February 2015 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. Watsen Expires August 6, 2015 [Page 10] Internet-Draft NETCONF Call Home and RESTCONF Call Home February 2015 [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, . [draft-ietf-netconf-server-model] Watsen, K. and J. Schoenwaelder, "NETCONF Server Configuration Model", 2014, . Watsen Expires August 6, 2015 [Page 11] Internet-Draft NETCONF Call Home and RESTCONF Call Home February 2015 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) A.4. 03 to 04 o Replaced "verify credentials" with "verify identity" (issue #11) 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. Watsen Expires August 6, 2015 [Page 12] Internet-Draft NETCONF Call Home and RESTCONF Call Home February 2015 Author's Address Kent Watsen Juniper Networks EMail: kwatsen@juniper.net Watsen Expires August 6, 2015 [Page 13]