Operations Area Working Group                                    T. Tsou
Internet-Draft                                 Huawei Technologies (USA)
Intended status: Informational                     J. Schoenwaelder, Ed.
Expires: July 27, 2013                          Jacobs University Bremen
                                                                  Y. Shi
                                                               T. Taylor
                                                     Huawei Technologies
                                                                 G. Yang
                                                           China Telecom
                                                        January 23, 2013

  Survey of Possibilities for the Automated Configuration of Large IP


   This memo discusses the steps required to bring a large number of
   devices into service in IP networks in an automated fashion.  The
   goal of this document is to list known solutions where they exist, to
   point out approaches proven to be problematic, and to identify gaps
   that require further specifications.

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 July 27, 2013.

Copyright Notice

   Copyright (c) 2013 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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   (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
   2.  Intra-domain and Inter-domain Scenarios  . . . . . . . . . . .  5
   3.  Model of the Automated Configuration Process . . . . . . . . .  6
   4.  Phase 1: Pre-configuration . . . . . . . . . . . . . . . . . .  7
   5.  Phase 2: Bootstrapping . . . . . . . . . . . . . . . . . . . .  8
     5.1.  Establishment of Link Layer Connectivity . . . . . . . . .  8
     5.2.  Acquisition of IP Addresses and Basic Routing
           Information  . . . . . . . . . . . . . . . . . . . . . . .  8
     5.3.  Finding the Configuration Server . . . . . . . . . . . . .  9
     5.4.  Establishing a Secure Channel to the Configuration
           Server . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   6.  Phase 3: Initial Configuration . . . . . . . . . . . . . . . . 12
   7.  Phase 4: Configuration Auditing  . . . . . . . . . . . . . . . 15
   8.  Phase 5: Configuration Update  . . . . . . . . . . . . . . . . 16
   9.  Gap Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 16
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
   13. Informative References . . . . . . . . . . . . . . . . . . . . 18
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22

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1.  Introduction

   Many large IP networks are being deployed that entail the
   installation of tens of thousands of new network devices.  To keep
   costs down, it is desirable to automate the establishment of such
   networks to the maximum extent possible.  This naturally raises the
   question how new devices can pick up the configuration information
   they need to operate properly in an automated fashion.  The goal of
   this document is to list known solutions where they exist, to point
   out approaches proven to be problematic, and to identify gaps that
   require further specifications.

   The document primarily targets (a) network operators (in the generic
   sense) who are facing the challenge to roll out a large number of new
   devices and think about how to implement things properly, (b) network
   equipment vendors who like to add features to their products that
   make the roll out of lots of new devices simpler for their customers,
   and (c) people active in the IETF by identifying gaps where further
   standards may be useful to develop.  The aim of the document is to
   provide guidance to actors who have not already experienced success
   in this area by informing about the trade-offs of different

   A certain basic amount of configuration information must be pre-
   configured by the vendor or network operator before the devices are
   physically deployed.  This pre-provisioned configuration can either
   be stored directly on the device itself or it can be provided to the
   device during the deployment operation via pluggable memory cards or
   near field communication technologies.  Further device configuration
   information is best delivered after startup, to ensure that it is
   consistent with the physical deployment and the desired network

   One example where automated configuration is important are new
   service provider networks. 3GPP work in progress describes
   requirements [TS_32_500] and an architectural specification
   [TS_36_300] for the self-configuration of edge node entities called
   eNodeBs.  (The expansion of eNodeB is too unwieldy to spell out.)
   Specifically, procedures are specified for establishing transport
   connections to and for exchanging configuration data with control
   entities called MMEs (Mobility Management Entities) and with
   neighbouring eNodeBs.  [TS_36_300] currently assumes as a starting
   precondition that the eNodeB knows its own IP address and knows IP
   address endpoints for the target MMEs and neighbouring eNodeBs.

   The Broadband Forum has defined a CPE WAN Management Protocol
   (running over SOAP/HTTP/TLS) to manage customer premise equipment
   (CPE) terminating broadband access networks (typically DSL access

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   networks) [TR_069].  CPE devices locate and connect to an Auto-
   Configuration Server (ACS), which provides configuration data and
   software/firmware images and modules.  The ACS also performs status
   and performance monitoring and diagnostic functions.  CPE devices use
   DHCP to locate an ACS and since both peers, the ACS and CPE, can
   initiate connections, the protocol can work across network address
   translators (NATs).  The DHCP exchange uses vendor-specific options
   defined by the Broadband Forum (number 3561 in the IANA Enterprise
   Numbers registry).

   Next to service provider networks, many large enterprise networks
   face the same challenge to roll out a large number of network
   devices, which often connect to a 3rd party network provider.  The
   current development of IP-based home automation and utility
   monitoring technologies might carry the problem to roll out large
   numbers of devices that need to automatically configure themselves to
   private households.

   IETF work on automated configuration goes back to BOOTP [RFC0951],
   followed eight years later by DHCP ([RFC1541] and successors).  The
   years since have seen a steady growth in the number of DHCP options.
   The Simple Network Management Protocol (SNMP) [RFC3410] was designed
   to convey management information between SNMP entities such as
   managers and agents.  The number of SNMP MIB modules grew steadily,
   but SNMP has historically seen only limited use for configuration
   [RFC3535].  For a period, IETF configuration efforts were focussed on
   the distribution of policy information in the network.  [RFC3139]
   provides a good insight into this period.  More recently, the network
   configuration protocol NETCONF [RFC6241] was devised as an
   alternative to SNMP, but the development of standard NETCONF
   configuration data models is just beginning.

   Recent IETF work closest in spirit to the 3GPP self-organizing
   network effort cited above is embodied in CAPWAP [RFC5415].  Like the
   3GPP work, CAPWAP focusses on the configuration of edge nodes, in a
   Wi-Fi rather than cellular network.  The CAPWAP work goes beyond that
   of 3GPP by specifying the process of Access Controller (AC) discovery
   rather than leaving discovery out of scope.  A CAPWAP Wireless
   Termination Point (WTP) may use broadcasts and multicasts to discover
   local ACs, it may use CAPWAP DHCP options [RFC5417] to obtain IP
   addresses of ACs, or it may utilize CAPWAP DNS SRV records if a
   domain name is known.  With regard to the configuration process
   itself, CAPWAP provides for the download of new images to the WTP
   (Wireless Termination Point).  In contrast, [TS_32_500] assumes that
   this has already been completed for the eNodeB.

   As can seen, standards for the automated configuration of devices in
   IP networks have so far been primarily developed for specific network

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   access technologies (3GPP, Broadband, 802.11 WLANs) and the various
   solutions make different assumptions about the services that are
   available and they are designed to support a configuration protocol
   that is specific to a certain access technology.  The aim of this
   document is to analyse the various phases of an automated
   configuration process and to identify gaps that are currently not
   covered in standard and general purpose configuration management
   protocols of the IETF.

2.  Intra-domain and Inter-domain Scenarios

   There are two different scenarios to consider.  In the first
   scenario, called the Intra-domain Scenario, the new network device N
   is attached to the network operated by the service provider which is
   also operating the new device.  In the second scenario, called the
   Inter-domain Scenario, the new device N is attached to a third party
   network providing connectivity to the network of the service provider
   operating the new device.

        | CONF |
        +---+     +---+          |
        | N +-...-+ R +------+---+---+----...
        +---+     +---+      |       |
        +--+--+ +--+---+
        | DNS | | DHCP |
        +-----+ +------+

        |-- N's Service Provider --|

                      Figure 1: Intra-domain Scenario

   Figure 1 depicts the Intra-domain Scenario.  We assume that the new
   device N attaches to a link connected to router R. Furthermore, we
   assume that the service provider provides a Domain Name System (DNS)
   server, a reachable DHCP server, and a Configuration Server (CONF).
   Overall, this scenario does not differ much from conventional network

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       | CONF |
       +---+     +---+                       +---+         |
       | N +-...-+ R +-----+---+---+-----...-+ R +-----+---+---+-----...
       +---+     +---+     |       |         +---+     |       |
       +--+--+ +--+---+            +--+--+ +--+---+
       | DNS | | DHCP |            | DNS | | DHCP |
       +-----+ +------+            +-----+ +------+

       |-- Service Provider X ---| |-- N's Service Provider --|

                      Figure 2: Inter-domain Scenario

   Figure 2 depicts the Inter-domain Scenario where the new device N
   attaches to a router R owned by a different service provider X. The
   service provider X might offer its own DNS service and a reachable
   DHCP service.  We assume that the service provider X has connectivity
   to the service provider planning to operate the new device.

   It should be noted that handing out DHCP options specific to N's
   service provider via X's DHCP service requires some close
   coordination between the two parties involved.  This might be
   difficult in practice.  A more general alternative might be to have
   X's service provider establish a tunnel such that the new device
   logically appears to be part of N's service provider network.

   In both scenarios, the new device N is either directly reachable or
   it may be behind a middlebox such as a Network Address Translator
   (NAT) or a firewall.  Middleboxes may impose restrictions on which
   party is able to initiate communication.  As detailed in
   [I-D.kwatsen-reverse-ssh], it is often desirable to allow device-
   initiated connections.

3.  Model of the Automated Configuration Process

   We introduce a model of the configuration process in order to
   identify the parts that have well-known solutions.  The remainder may
   be worth studying to see if the industry can agree on a solution.

   Some basic terminology is needed for the discussion.  Depending on
   the implementation, let us agree that "configuration data" consist of
   software and sets of configured parameters in some combination.  This
   includes firmware, licenses, certificates, and other configuration
   data.  Also, the system that provides the configuration data is
   called the "configuration server".  Finally, the term "joining

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   device" is used to denote a network device that is in the process of
   being incorporated into the network.

   Broadly speaking, the configuration process can be broken into five

   1.  Pre-configuration: configuration carried out either by the vendor
       or by the service provider prior to physical installation.  One
       possible example is the pre-configuration of certificates or
       licenses or specific firmware.

   2.  Bootstrapping: the portion of the process from the time that
       physical installation is complete until a secure connection is
       established between the joining device and the configuration

   3.  Initial configuration: downloading of the configuration data that
       the joining device needs to carry out its function in the

   4.  Configuration auditing: tracking image versions and configuration
       parameters for each network device and verifying that the
       installed configuration data matches the physical installation,
       the network plan, and the records of what data was downloaded.
       It is possible that an initial audit of the physical installation
       is done before initial configuration, so that the validity of the
       intended download can be verified.

   5.  Configuration update: transferring configuration data to a fully
       configured and operating device from time to time as the need

4.  Phase 1: Pre-configuration

   This memo identifies a specific requirement for pre-configuration of
   an invariant device identity and authentication-related material in
   the form of pre-shared secrets or certificates.  There is, as one
   alternative, also a requirement for pre-configuration of information
   that permits the joining device to discover the address of the
   configuration server.

   Note that pre-configuration may be carried out on the joining device
   itself or it may be provided to the joining device during the
   deployment process via pluggable memory cards or nearfield

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5.  Phase 2: Bootstrapping

   [I-D.sarikaya-core-sbootstrapping] deals with the process of security
   bootstrapping, with particular emphasis on the requirements for
   highly resource-constrained devices.  The document makes a
   distinction between a data channel, which is used during network
   operation, and a control channel, which is used during bootstrapping.
   While both channels can be the same physical channel, they can also
   be different (e.g., a wireless access point using an infrared control
   channel to receive bootstrapping information).  The draft discusses a
   number of possible security bootstrapping protocols for resource
   constrained devices that can be executed in several bootstrapping
   rounds and can be adapted to the specific contexts in terms of the
   resources available within individual devices and for the network as
   a whole.

   For network devices in service provider networks or large enterprise
   networks, bootstrapping consists of several stages:

   1.  establishment of link layer connectivity with neighbouring nodes;

   2.  acquisition of IP addresses and basic routing information;

   3.  discovery of the configuration server;

   4.  establishment of a secure channel to the configuration server.

   Each of these stages is further discussed below.

5.1.  Establishment of Link Layer Connectivity

   The protocol aspects of this phase are out of scope, since it
   involves non-IETF protocols only.  While some link-layer technologies
   may provide authentication and access control, this cannot be assumed
   to be available in the general case.

5.2.  Acquisition of IP Addresses and Basic Routing Information

   For IPv4, DHCPv4 [RFC2131] is widely deployed and the usual way to
   obtain an IPv4 address, the IPv4 address of a link- local router and
   the IPv4 address of a DNS server.  For IPv6, a choice has to be made
   between stateful DHCPv6 [RFC3315] versus stateless DHCPv6 [RFC3736]
   combined with stateless address autoconfiguration [RFC4862].  In the
   latter case, DHCPv6 is needed to configure parameters such as DNS
   server addresses.  A routing advertisement option to configure the
   IPv6 address of a DNS server as part of the stateless address
   autoconfiguration is defined in [RFC6106].

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   Some security protection is provided in this stage by using DHCP
   authentication [RFC3118].  However, security of the configuration
   process as a whole has to be assured by other means.  This is
   discussed further below.

   Currently the lack of a stable identifier for use in DHCPv6 messaging
   is an impediment to authentication of the joining device.  [RFC6355]
   discusses the problems with the current DHCPv6 identifiers (DUIDs)
   and proposes a new form that could be a more stable alternative.

   A joining device can also choose to use a pre-configured IP address,
   a pre-configured link-local router address and a pre- configured DNS
   server address.  This pre-configuration may be hard wired into the
   device or provided by a pluggable memory card or nearfield
   communication.  However, a static pre-configuration hard- wires
   assumption about the network a devices operates in and is therefore
   brittle and not recommended.

5.3.  Finding the Configuration Server

   Four alternatives are available for finding the configuration server:

   o  pre-configuration;

   o  DHCP configuration;

   o  Service Location Protocol [RFC2608]; or

   o  DNS service discovery using DNS SRV records [RFC2782].

   Pre-configuration of an IP address is brittle and not recommended
   unless the IP address is used as an anycast address.  In the case of
   an IP anycast address, the routing system will select one out of an
   anycast cluster of configuration servers the devices connects to.
   For this to work well, all configuration servers in the anycast
   cluster should provide the same configuration data.

   The pre-configuration of a Uniform Resource Identifier (URI) or fully
   qualified domain name (FQDN) is a slightly better approach than pre-
   configuring non-anycast IP addresses since this allows for a limited
   dynamic mapping of the name to an IP address.  One variant that has
   been suggested is to burn the URI of a vendor server into the
   device's firmware along with a device identifier, and have that
   server redirect to the URI of the service provider's configuration
   server based on the device identity.  Such an approach requires that
   the device vendor's redirection server is always reachable, that the
   device vendor offers such a redirection service for the lifetime of
   their devices and that service providers are able to update the URI

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   of the service provider's redirection server.  Furthermore, this
   approach can lead to problems if certificates are used to
   authenticate the involved parties if a service provider tries to
   prevent the usage of a vendor's redirection service.  Finally, this
   approach also requires a trust relationship between the vendor and
   the service provider and agreement on a protocol to update the
   redirect information on the vendor's server.  As a consequence of
   these considerations, using this approach is not recommended.

   DHCP configuration can use the usual DHCP options and is technically
   straightforward since DHCP is widely used by end user devices to
   obtain basic configuration information.  There is, however, no
   standardized DHCP option to communicate the address of a
   configuration server.

   The Service Location Protocol (SLP) has seen some usage to locate
   services such as printers or file system shares.  Usage of SLP to
   locate configuration servers requires to define a new service
   template [RFC2609].

   The use of DNS SRV records requires the joining device to obtain the
   correct domain suffix first, presumably from DHCP or via Routing
   Advertisements in the case of IPv6 or pre-configuration.  A service
   type for the desired configuration protocol would have to be defined
   in the DNS for the purpose.  See Section 3.3 of [RFC5415] for a
   discussion of the corresponding discovery process for CAPWAP.

   The Inter-domain Scenario requires that the DHCP server or the SLP
   server of service provider X's network is able to provide the correct
   information to the joining devices.  To accomplish this, the
   discovery servers need to be able to match a device identification
   against a list of possible configuration servers.  Furthermore, there
   needs to be a mechanism for the service provider operating the
   joining device to provision the configuration server's address, e.g.,
   by using an extension of the Extensible Provisioning Protocol (EPP)
   [RFC5730].  However, if the joining device has pre- configured
   information about the name of the service provider's network, DNS SRV
   records may be queried after obtaining IP connectivity, avoiding the
   need to provision information in service provider X's network.

5.4.  Establishing a Secure Channel to the Configuration Server

   It is essential that the configuration server and the joining device
   authenticate themselves to each other, since the steps leading up to
   this point in the process may not be fully secure.  This raises two
   issues: how the joining device identifies itself, and how
   authentication takes place.

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   It seems best if the device has an invariant identity built in and
   accessible to whatever operating system is running on it.  [RFC6355]
   provides such an identity in the form of a Universally Unique
   IDentifier (UUID).  The vendor should make that identity available in
   a form that can be read and transferred into a database accessible to
   the configuration server along with the associated configuration data
   in advance of the bootstrapping stage (e.g., in bar-coded format on
   the device packaging).

   Serial numbers may be used for identification purposes if UUIDs are
   not available.  However, serial numbers often encode information such
   as model-numbers or manufacturing dates.  Hence, it is not
   recommended to pass serial-numbers in the clear for security reasons.
   Similar precautions apply to Common Language Equipment Identifier
   (CLEI) codes that encode information about properties of the device.

   This leaves the mutual authentication process itself.  This has two
   aspects: the security protocol used to perform authentication, and
   initial keying methodology.  The security protocol is tied together
   with the choice of configuration data transport, but the basic
   choices are:

   o  IP Security (IPsec) [RFC4301];

   o  Transport Layer Security (TLS) [RFC5246];

   o  Datagram Transport Layer Security (DTLS) [RFC6347];

   o  Secure Shell (SSH) [RFC4251], [RFC4252], [RFC4253], and [RFC4254];

   o  SNMPv3's User-based Security Model (USM) [RFC3414].

   For initial keying methodology, the two basic choices are between
   pre-shared secrets and certificates.  All of the security protocols
   listed above except USM support both methods.  USM supports pre-
   shared secrets only.

   The usual concern with pre-shared secrets is scalability.  In the
   bootstrapping case, the scale of operation required is linear with
   the number of devices to be configured, so it would definitely be a
   feasible approach if connection to the configuration system were the
   only consideration.  The most likely procedure would be for the
   secret to be configured in the device during pre-configuration and
   also captured in a database along with the device identity, for use
   by the configuration server.

   The problem with the use of pre-shared secrets is that the device

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   needs to authenticate itself at an earlier stage, while it is
   establishing communications with its neighbours and acquiring IP
   addresses.  It seems undesirable to use the same secret that is used
   to authenticate the device to the configuration server for that
   purpose as well, on the basic principle of limiting the potential
   damage from disclosure of a particular key.

   This need for additional pre-shared secrets argues for consideration
   of certificates as an alternative.  One issue for certificates is
   where the trust anchor resides.  It seems logical that it should
   reside with the service provider rather than the vendor, to make it
   easy to install equipment from multiple vendors.  On that basis, pre-
   configuration requires service provider input.  On the other hand, if
   devices are drop-shipped to the destination from the vendor, having
   the trust anchor reside with the vendor might be acceptable as well.

   CAPWAP (Section of [RFC5415]) makes use of the Extended Key
   Usage (EKU) certificate extension [RFC5280] to distinguish
   certificates identifying the Access Controllers (i.e., the
   configuration servers in the CAPWAP case) from the Wireless Transfer
   Points (the configured devices in the CAPWAP case).  Thought should
   be given to whether such distinctions are required in the general
   case of network device configuration.

   CAPWAP (Section 12.8 of [RFC5415]) also discusses the use of the
   Common Name rather than SubjectAltName field of the certificate to
   carry device identity, due to lack of a Uniform Resource Name (URN)
   specification allowing the use of SubjectAltName to carry MAC
   addresses.  This encoding of device identifiers in certifications
   needs to be investigated further if a new form of device unique
   identity is used, as discussed above.

   Middleboxes such as NATs or firewalls may impose restriction on which
   party is able to initiate communication.  In the common case of NATs
   in IPv4 access networks, communication can only be established from
   the device to the configuration server.  Not all secure transports,
   in particular those where authentication is not symmetric, support
   this "call home" mode of operation.  A recent proposal to reverse the
   establishment of the TCP connection for SSH can be found in

6.  Phase 3: Initial Configuration

   As mentioned at the beginning, the configuration data being
   downloaded may be a combination of software/firmware and
   configuration parameters.  Some of the data will be vendor-specific
   and not subject to standardization.  It appears that there is a

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   continuing debate on whether the configuration data should be pushed
   to the joining device or whether the device should pull the
   configuration data from the configuration server.  In the latter
   case, the device needs to know about the existence of the data and
   the path to reach it before it can act.  One way to acquire this
   information is through DHCP.  DHCPv4 has provided the necessary
   options from its beginnings, inheriting them from BOOTP.  They have
   been recently added to DHCPv6 [RFC5970].

   Protocols that can transport configuration data can be classified as
   follows: The first class consists of generic file transfer protocols
   that can carry configuration data serialized into configuration
   files.  The second class consists of protocols that manipulate
   structured configuration data directly.  The structure of the
   configuration data is defined by some data model.

   In the first class, we find the following file transfer protocols:

   o  The File Transfer Protocol (FTP) [RFC0959] can be used to move
      files containing configuration data.  It can be secured by running
      FTP over TLS [RFC4217].

   o  The Trivial File Transfer Protocol (TFTP) [RFC1350] has been used
      extensively to load boot images over the network.  However, it
      does not provide security and the only option is to rely on IP
      layer security (IPsec).

   o  The Hypertext Transfer Protocol (HTTP) [RFC2616] can be used to
      transfer documents containing configuration data.  It is commonly
      secured by running HTTP over TLS [RFC2817], [RFC2818].

   o  The SSH File Transfer Protocol (SFTP) [I-D.ietf-secsh-filexfer]
      provides roughly the same services as FTP but runs over SSH and
      thus utilizes the security services provided by SSH.

   o  UNIX utilities to transfer files such as RCP and SCP provide
      limited flexibility and they differ in their degree of integration
      with SSH.

   o  The Control And Provisioning of Wireless Access Points (CAPWAP)
      protocol [RFC5415] can be used to control the download of images.
      CAPWAP can be secured by running CAPWAP over DTLS.

   In the second class, we find the following configuration protocols:

   o  Version 3 of the Simple Network Management Protocol (SNMPv3)
      [RFC3411] can be used to manipulate MIB objects and to carry event
      notifications.  SNMPv3 has its own security protocol (USM)

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      [RFC3414] but can also run over the secure transports SSH
      [RFC5592], TLS, or DTLS [RFC6353].

   o  The Common Open Policy Service for Policy Provisioning protocol
      (COPS-PR) [RFC3084] was designed to provision structured policy
      information from a Policy Decision Point (PDP) to a Policy
      Enforcement Point (PEP).  The COPS protocol [RFC2748] provides an
      integrity object that can achieve authentication, message
      integrity, and replay prevention.  Optionally, COPS and COPS-PR
      can run over TLS.

   o  The NETCONF protocol [RFC6241] provides mechanisms to install,
      manipulate, and delete the configuration of network devices.  A
      protocol extension provides an asynchronous event notification
      delivery mechanism [RFC5277].  NETCONF by default runs over SSH
      but can also run over transports secured by TLS.

   o  The Control And Provisioning of Wireless Access Points protocol
      (CAPWAP) [RFC5415] supports the discovery of so called Access
      Controller (AC) by Wireless Termination Points (WTPs) and the
      configuration of WTPs by an AC.  While CAPWAP can be extended to
      configure other devices, its main focus are WTPs.  The CAPWAP
      protocol is protected by using DTLS after the discovery phase.

   Table 1 lists the protocols plus their basic properties while Table 2
   lists the security options available for each protocol.

   | Transport | Data Transfer Model                                   |
   | FTP       | Push or pull of (configuration) files                 |
   | TFTP      | Push or pull of (configuration) files                 |
   | HTTP      | Push or pull of (configuration) files                 |
   | SFTP      | Push or pull of (configuration) files                 |
   | RCP       | Push or pull of (configuration) files                 |
   | SCP       | Push or pull of (configuration) files                 |
   | CAPWAP    | AC pushes configuration parameters, WTP pulls         |
   |           | software                                              |
   | SNMPv3    | Push of structured configuration parameters, event    |
   |           | notifications                                         |
   | COPS-PR   | Push of structured policy information                 |
   | NETCONF   | Push of structured configuration data, event          |
   |           | notifications                                         |

          Table 1: Protocols for transporting configuration data

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             | Transport | IPsec | TLS | DTLS | SSH | Other |
             | FTP       |   +   |  +  |      |     |       |
             | TFTP      |   +   |     |      |     |       |
             | HTTP      |   +   |  +  |      |     |       |
             | SFTP      |   +   |     |      |  +  |       |
             | RCP       |   +   |     |      |     |       |
             | SCP       |   +   |     |      |  +  |       |
             | CAPWAP    |   +   |     |   +  |     |       |
             | SNMPv3    |   +   |  +  |   +  |  +  |  USM  |
             | COPS-PR   |   +   |  +  |      |     |       |
             | NETCONF   |   +   |  +  |      |  +  |       |

      Table 2: Security options for configuration transport protocols

   SNMPv3, NETCONF, and COPS-PR carry structured data specified in pre-
   defined data models.  SNMPv3 and COPS-PR have size limitations on the
   data objects and thus make the transport of larger software images
   difficult.  NETCONF does not suffer from hard size restrictions and
   can in principle carry software images inline.  However, there is
   currently no work in progress to standardize the transfer of software
   images over NETCONF.  CAPWAP combines the functions of configuration
   parameter transport and software download.  The parameter transport
   aspect lacks the generality offered by SNMP, NETCONF, and COPS-PR,
   since the parameters are specified within the protocol specification
   itself.  The remaining transports are independent of the nature of
   the information being transferred.

7.  Phase 4: Configuration Auditing

   To complete the process, it must be possible to audit the
   configuration status of the device in some detail.  This is likely to
   begin even before all the configuration data has been downloaded.
   For instance, configuration management may wish to collect basic
   information such as the MAC addresses of the device's interfaces, the
   link-local addresses assigned to them, and similar information for
   the neighbours of the joining device.

   SNMP and SNMP MIB modules are obviously one way to collect this
   information.  NETCONF [RFC6241] is an alternative, but the necessary
   data models have to be defined.  YANG modules for NETCONF [RFC6020]
   can be generated from existing SNMP MIB modules by translating the
   SNMP modules into YANG modules [RFC6643].

   Another important auditing activity is the analysis of system events.

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   The SYSLOG protocol [RFC5424] is widely used for this purpose but
   SNMPv3 and NETCONF can ship event notifications as well.
   Translations of SNMP notifications into structured SYSLOG messages
   and vice versa do exist [RFC5675], [RFC5676].  NETCONF can carry
   SYSLOG content as well [RFC5277].

   NETCONF provides generic notifications that help with tracking
   configuration changes [RFC6470].  Similar standardized configuration
   change notifications do not exist for SNMP or SYSLOG.

8.  Phase 5: Configuration Update

   Configuration updates can in principle be handled with the same
   protocol that delivered the initial configuration.  However, in some
   deployments, the mechanism used for initial configuration might be

   An advantage of NETCONF over SNMPv3 and CAPWAP in the context of
   configuration updates is the support of concurrent updates through
   explicit locking mechanisms and the support of network wide
   configuration change transactions through the confirmed commit

9.  Gap Analysis

   This document discussed the automated configuration of devices in
   large IP networks.  Several gaps were identified requiring further

   G1:  Definition of a DHCP option to provide the IPv4/IPv6 address of
      a configuration server.  Such an option allows a joining device to
      pickup the configuration server's address as part of the DHCP
      exchange.  This is particularly interesting for Intra-domain

   G2:  Definition of DNS SRV records for locating configuration
      servers.  Using SRV records, a joining device can lookup the
      configuration server's address in the DNS.  This is particularly
      useful in an Inter-domain Scenario.

   G3:  Definition of a SLP template for discovering configuration
      servers.  Such a template is useful only in environments where SLP
      is used also for other purposes.

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   G4:  Definition of NETCONF data models to support the download
      /update of software images through NETCONF.

   G5:  Definition of NETCONF data models for collecting basic system
      information and integrity information (e.g., checksums of software

   G6:  Some management protocols lack a mechanisms for devices to
      initiate a secure communication channel with a management system
      ("call home").

10.  Security Considerations

   The security of a configuration management solution is of crucial
   importance.  Section 6 discusses the security options of several
   protocols that might be used.  The relevant protocol definitions
   should be consulted to learn more about the specific security aspects
   of the various protocols.

   It should be noted that some steps in the described process, in
   particular the bootstrapping phase, may not be secure and it is thus
   important to verify the identity of the device and the identity of
   the configuration server when a secure connection to a configuration
   server is established.  Usage of IPsec, which focuses on securing the
   IP layer, may not be sufficient for this.

   During the choice of protocols, the available security mechanisms and
   the required key management infrastructures may play a major role in
   the selection of protocols.  Easy integration into existing
   Authentication, Authorization and Accounting (AAA) infrastructures
   can significantly reduce the operational costs associated with the
   security management of the configuration system.

   While [I-D.sarikaya-core-sbootstrapping] discusses security
   bootstrapping mechanisms in the context of constrained devices, many
   of the mechanisms are also applicable for bootstrapping security in
   normal devices.

   Finally, [RFC6092] discusses security capabilities for customer
   premises equipment providing residential IPv6 Internet service.

11.  IANA Considerations

   This memo includes no request to IANA.

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12.  Acknowledgements

   Thanks to Ronald Bonica, Mehmet Ersue, Wesley George, Yiu Lee,
   Christopher Liljenstolpe, Kent Watsen, and Cathy Zhou for their
   comments during the preparation of this memo.

13.  Informative References

              Galbraith, J. and O. Saarenmaa, ""SSH File Transfer
              Protocol", draft-ietf-secsh-filexfer-13 (work in
              progress)", July 2006.

              Watsen, K., ""Reverse Secure Shell (Reverse SSH)",
              draft-kwatsen-reverse-ssh-01 (work in progress)",
              June 2011.

              Sarikaya, B., Ohba, Y., Moskowitz, R., Cao, Z., and R.
              Cragie, "Security Bootstrapping Solution for Resource-
              Constrained Devices" draft-sarikaya-core-sbootstrapping-05
              (work in progress)", July 2012.

   [RFC0951]  Croft, B. and J. Gilmore, "Bootstrap Protocol", RFC 951,
              September 1985.

   [RFC0959]  Postel, J. and J. Reynolds, "File Transfer Protocol",
              STD 9, RFC 959, October 1985.

   [RFC1350]  Sollins, K., "The TFTP Protocol (Revision 2)", STD 33,
              RFC 1350, July 1992.

   [RFC1541]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 1541, October 1993.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.

   [RFC2608]  Guttman, E., Perkins, C., Veizades, J., and M. Day,
              "Service Location Protocol, Version 2", RFC 2608,
              June 1999.

   [RFC2609]  Guttman, E., Perkins, C., and J. Kempf, "Service Templates
              and Service: Schemes", RFC 2609, June 1999.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,

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              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2748]  Durham, D., Boyle, J., Cohen, R., Herzog, S., Rajan, R.,
              and A. Sastry, "The COPS (Common Open Policy Service)
              Protocol", RFC 2748, January 2000.

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              February 2000.

   [RFC2817]  Khare, R. and S. Lawrence, "Upgrading to TLS Within
              HTTP/1.1", RFC 2817, May 2000.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC3084]  Chan, K., Seligson, J., Durham, D., Gai, S., McCloghrie,
              K., Herzog, S., Reichmeyer, F., Yavatkar, R., and A.
              Smith, "COPS Usage for Policy Provisioning (COPS-PR)",
              RFC 3084, March 2001.

   [RFC3118]  Droms, R. and W. Arbaugh, "Authentication for DHCP
              Messages", RFC 3118, June 2001.

   [RFC3139]  Sanchez, L., McCloghrie, K., and J. Saperia, "Requirements
              for Configuration Management of IP-based Networks",
              RFC 3139, June 2001.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3410]  Case, J., Mundy, R., Partain, D., and B. Stewart,
              "Introduction and Applicability Statements for Internet-
              Standard Management Framework", RFC 3410, December 2002.

   [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
              Architecture for Describing Simple Network Management
              Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
              December 2002.

   [RFC3414]  Blumenthal, U. and B. Wijnen, "User-based Security Model
              (USM) for version 3 of the Simple Network Management
              Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.

   [RFC3535]  Schoenwaelder, J., "Overview of the 2002 IAB Network
              Management Workshop", RFC 3535, May 2003.

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   [RFC3736]  Droms, R., "Stateless Dynamic Host Configuration Protocol
              (DHCP) Service for IPv6", RFC 3736, April 2004.

   [RFC4217]  Ford-Hutchinson, P., "Securing FTP with TLS", RFC 4217,
              October 2005.

   [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.

   [RFC4254]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Connection Protocol", RFC 4254, January 2006.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event
              Notifications", RFC 5277, July 2008.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5415]  Calhoun, P., Montemurro, M., and D. Stanley, "Control And
              Provisioning of Wireless Access Points (CAPWAP) Protocol
              Specification", RFC 5415, March 2009.

   [RFC5417]  Calhoun, P., "Control And Provisioning of Wireless Access
              Points (CAPWAP) Access Controller DHCP Option", RFC 5417,
              March 2009.

   [RFC5424]  Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009.

   [RFC5592]  Harrington, D., Salowey, J., and W. Hardaker, "Secure
              Shell Transport Model for the Simple Network Management
              Protocol (SNMP)", RFC 5592, June 2009.

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   [RFC5675]  Marinov, V. and J. Schoenwaelder, "Mapping Simple Network
              Management Protocol (SNMP) Notifications to SYSLOG
              Messages", RFC 5675, October 2009.

   [RFC5676]  Schoenwaelder, J., Clemm, A., and A. Karmakar,
              "Definitions of Managed Objects for Mapping SYSLOG
              Messages to Simple Network Management Protocol (SNMP)
              Notifications", RFC 5676, October 2009.

   [RFC5730]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
              STD 69, RFC 5730, August 2009.

   [RFC5970]  Huth, T., Freimann, J., Zimmer, V., and D. Thaler, "DHCPv6
              Options for Network Boot", RFC 5970, September 2010.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

   [RFC6092]  Woodyatt, J., "Recommended Simple Security Capabilities in
              Customer Premises Equipment (CPE) for Providing
              Residential IPv6 Internet Service", RFC 6092,
              January 2011.

   [RFC6106]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
              "IPv6 Router Advertisement Options for DNS Configuration",
              RFC 6106, November 2010.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)",
              RFC 6241, June 2011.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

   [RFC6353]  Hardaker, W., "Transport Layer Security (TLS) Transport
              Model for the Simple Network Management Protocol (SNMP)",
              RFC 6353, July 2011.

   [RFC6355]  Narten, T. and J. Johnson, "Definition of the UUID-Based
              DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355,
              August 2011.

   [RFC6470]  Bierman, A., "Network Configuration Protocol (NETCONF)
              Base Notifications", RFC 6470, February 2012.

   [RFC6643]  Schoenwaelder, J., "Translation of Structure of Management
              Information Version 2 (SMIv2) MIB Modules to YANG

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              Modules", RFC 6643, July 2012.

   [TR_069]   Blackford, J., Ed., Kirksey, H., Ed., and W. Lupton, Ed.,
              ""CPE WAN Management Protocol", Broadband Forum TR-069",
              November 2010.

              3GPP, ""3rd Generation Partnership Project; Technical
              Specification Group Services and System Aspects;
              Telecommunication Management; Self-Organizing Networks
              (SON); Concepts and requirements (Release 9)", 3GPP TS
              32.500", 2010.

              3GPP, ""3rd Generation Partnership Project; Technical
              Specification Group Radio Access Network; Evolved
              Universal Terrestrial Radio Access (E-UTRA)  and Evolved
              Universal Terrestrial Radio Access Network  (E-UTRAN);
              Overall description; Stage 2 (Release 9)", 3GPP TS
              36.300", 2010.

Authors' Addresses

   Tina Tsou
   Huawei Technologies (USA)
   2330 Central Expressway
   Santa Clara, CA  95050

   Email: tina.tsou.zouting@huawei.com

   Juergen Schoenwaelder (editor)
   Jacobs University Bremen
   Campus Ring 1
   Bremen  28759

   Email: j.schoenwaelder@jacobs-university.de

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   Yang Shi
   Huawei Technologies
   156, Beiqing Road, Zhongguancun, Haidian District
   P.R. China

   Phone: +86 10 60614043
   Email: shiyang1@huawei.com

   Tom Taylor
   Huawei Technologies
   Ottawa, Ontario

   Email: tom.taylor.stds@gmail.com

   Guoliang Yang
   China Telecom
   No. 109 Zhongshan Ave. (West), Tianhe District
   P.R. China

   Phone: +86 020 38639615
   Email: iamyanggl@gmail.com

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