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rfc:rfc8368

Internet Engineering Task Force (IETF) T. Eckert, Ed. Request for Comments: 8368 Huawei Category: Informational M. Behringer ISSN: 2070-1721 May 2018

    Using an Autonomic Control Plane for Stable Connectivity of
     Network Operations, Administration, and Maintenance (OAM)

Abstract

 Operations, Administration, and Maintenance (OAM), as per BCP 161,
 for data networks is often subject to the problem of circular
 dependencies when relying on connectivity provided by the network to
 be managed for the OAM purposes.
 Provisioning while bringing up devices and networks tends to be more
 difficult to automate than service provisioning later on.  Changes in
 core network functions impacting reachability cannot be automated
 because of ongoing connectivity requirements for the OAM equipment
 itself, and widely used OAM protocols are not secure enough to be
 carried across the network without security concerns.
 This document describes how to integrate OAM processes with an
 autonomic control plane in order to provide stable and secure
 connectivity for those OAM processes.  This connectivity is not
 subject to the aforementioned circular dependencies.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It has been approved for publication by the Internet
 Engineering Steering Group (IESG).  Not all documents approved by the
 IESG are candidates for any level of Internet Standard; see Section 2
 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8368.

Eckert & Behringer Informational [Page 1] RFC 8368 AN Stable Connectivity OAM May 2018

Copyright Notice

 Copyright (c) 2018 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
 (https://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.  Self-Dependent OAM Connectivity . . . . . . . . . . . . .   3
   1.2.  Data Communication Networks (DCNs)  . . . . . . . . . . .   3
   1.3.  Leveraging a Generalized Autonomic Control Plane  . . . .   4
 2.  GACP Requirements . . . . . . . . . . . . . . . . . . . . . .   5
 3.  Solutions . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.1.  Stable Connectivity for Centralized OAM . . . . . . . . .   6
     3.1.1.  Simple Connectivity for Non-GACP-Capable
             NMS Hosts . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.2.  Challenges and Limitations of Simple Connectivity . .   8
     3.1.3.  Simultaneous GACP and Data-Plane Connectivity . . . .   9
     3.1.4.  IPv4-Only NMS Hosts . . . . . . . . . . . . . . . . .  10
     3.1.5.  Path Selection Policies . . . . . . . . . . . . . . .  12
     3.1.6.  Autonomic NOC Device/Applications . . . . . . . . . .  16
     3.1.7.  Encryption of Data-Plane Connections  . . . . . . . .  16
     3.1.8.  Long-Term Direction of the Solution . . . . . . . . .  17
   3.2.  Stable Connectivity for Distributed       Network/OAM . .  18
 4.  Architectural Considerations  . . . . . . . . . . . . . . . .  18
   4.1.  No IPv4 for GACP  . . . . . . . . . . . . . . . . . . . .  18
 5.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
 6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
 7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
   7.1.  Normative References  . . . . . . . . . . . . . . . . . .  21
   7.2.  Informative References  . . . . . . . . . . . . . . . . .  22
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  23
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

Eckert & Behringer Informational [Page 2] RFC 8368 AN Stable Connectivity OAM May 2018

1. Introduction

1.1. Self-Dependent OAM Connectivity

 Operations, Administration, and Maintenance (OAM), as per BCP 161
 [RFC6291], for data networks is often subject to the problem of
 circular dependencies when relying on the connectivity service
 provided by the network to be managed.  OAM can easily but
 unintentionally break the connectivity required for its own
 operations.  Avoiding these problems can lead to complexity in OAM.
 This document describes this problem and how to use an autonomic
 control plane to solve it without further OAM complexity.
 The ability to perform OAM on a network device requires first the
 execution of OAM necessary to create network connectivity to that
 device in all intervening devices.  This typically leads to
 sequential "expanding ring configuration" from a Network Operations
 Center (NOC).  It also leads to tight dependencies between
 provisioning tools and security enrollment of devices.  Any process
 that wants to enroll multiple devices along a newly deployed network
 topology needs to tightly interlock with the provisioning process
 that creates connectivity before the enrollment can move on to the
 next device.
 Likewise, when performing change operations on a network, it is
 necessary to understand at any step of that process that there is no
 interruption of connectivity that could lead to removal of
 connectivity to remote devices.  This includes especially change
 provisioning of routing, forwarding, security, and addressing
 policies in the network that often occur through mergers and
 acquisitions, the introduction of IPv6, or other major overhauls of
 the infrastructure design.  Examples include change of an IGP or
 area, change from Provider Aggregatable (PA) to Provider Independent
 (PI) addressing, or systematic topology changes (such as Layer 2 to
 Layer 3 changes).
 All these circular dependencies make OAM complex and potentially
 fragile.  When automation is being used (for example, through
 provisioning systems), this complexity extends into that automation
 software.

1.2. Data Communication Networks (DCNs)

 In the late 1990s and early 2000, IP networks became the method of
 choice to build separate OAM networks for the communications
 infrastructure within Network Providers.  This concept was
 standardized in ITU-T G.7712/Y.1703 [ITUT_G7712] and called "Data
 Communications Networks" (DCNs).  These were (and still are)

Eckert & Behringer Informational [Page 3] RFC 8368 AN Stable Connectivity OAM May 2018

 physically separate IP or IP/MPLS networks that provide access to OAM
 interfaces of all equipment that had to be managed, from Public
 Switched Telephone Network (PSTN) switches over optical equipment to
 nowadays Ethernet and IP/MPLS production network equipment.
 Such DCNs provide stable connectivity not subject to the
 aforementioned problems because they are a separate network entirely,
 so change configuration of the production IP network is done via the
 DCN but never affects the DCN configuration.  Of course, this
 approach comes at a cost of buying and operating a separate network,
 and this cost is not feasible for many providers -- most notably,
 smaller providers, most enterprises, and typical Internet of Things
 (IoT) networks.

1.3. Leveraging a Generalized Autonomic Control Plane

 One of the goals of the IETF ANIMA (Autonomic Networking Integrated
 Model and Approach) Working Group is the specification of a secure
 and automatically built in-band management plane that provides stable
 connectivity similar to a DCN, but without having to build a separate
 DCN.  It is clear that such an "in-band" approach can never fully
 achieve the same level of separation, but the goal is to get as close
 to it as possible.
 This document discusses how such an in-band management plane can be
 used to support the DCN-like OAM use case, how to leverage its stable
 connectivity, and what the options are for deploying it incrementally
 in the short and long term.
 The ANIMA Working Group's evolving specification [ACP] calls this in-
 band management plane the "Autonomic Control Plane" (ACP).  The
 discussions in this document are not dependent on the specification
 of that ACP, but only on a set of high-level constraints listed
 below, which were decided upon early during the work on the ACP.
 Except when being specific about details of the ACP, this document
 uses the term "Generalized ACP" (GACP) and is applicable to any
 designs that meet the high-level constraints -- for example, the
 variations of the ACP protocol choices.

Eckert & Behringer Informational [Page 4] RFC 8368 AN Stable Connectivity OAM May 2018

2. GACP Requirements

 The high-level constraints of a GACP assumed and discussed in this
 document are as follows:
 VRF isolation:  The GACP is a virtual network (Virtual Routing and
    Forwarding (VRF)) across network devices; its routing and
    forwarding are separate from other routing and forwarding in the
    network devices.  Non-GACP routing/forwarding is called the "data
    plane".
 IPv6-only addressing:  The GACP provides only IPv6 reachability.  It
    uses Unique Local Addresses (ULAs) [RFC4193] that are routed in a
    location-independent fashion, for example, through a subnet prefix
    for each network device.  Therefore, automatic addressing in the
    GACP is simple and stable: it does not require allocation by
    address registries, addresses are identifiers, they do not change
    when devices move, and no engineering of the address space to the
    network topology is necessary.
 NOC connectivity:  NOC equipment (controlling OAM operations) either
    has access to the GACP directly or has an IP subnet connection to
    a GACP edge device.
 Closed Group Security:  GACP devices have cryptographic credentials
    to mutually authenticate each other as members of a GACP.  Traffic
    across the GACP is authenticated with these credentials and then
    encrypted.
 GACP connect (interface):  The only traffic permitted in and out of
    the GACP that is not authenticated by GACP cryptographic
    credentials is through explicit configuration for the traffic
    from/to the aforementioned non-GACP NOC equipment with subnet
    connections to a GACP edge device (as a transition method).
 The GACP must be built to be autonomic and its function must not be
 able to be disrupted by operator or automated configuration/
 provisioning actions (i.e., Network Management System (NMS) or
 Software-Defined Networking (SDN)).  Those actions are allowed to
 impact only the data plane.  This document does not cover those
 aspects; instead, it focuses on the impact of the above constraints:
 IPv6 only, dual connectivity, and security.

Eckert & Behringer Informational [Page 5] RFC 8368 AN Stable Connectivity OAM May 2018

3. Solutions

3.1. Stable Connectivity for Centralized OAM

 The ANI is the Autonomic Networking Infrastructure consisting of
 secure zero-touch bootstrap (BRSKI [BRSKI]), the GeneRic Autonomic
 Signaling Protocol (GRASP [GRASP]), and Autonomic Control Plane (ACP
 [ACP]).  Refer to the reference model [REF_MODEL] for an overview of
 the ANI and how its components interact and [RFC7575] for concepts
 and terminology of ANI and autonomic networks.
 This section describes stable connectivity for centralized OAM via
 the GACP, for example, via the ACP with or without a complete ANI,
 starting with the option that we expect to be the most easy to deploy
 in the short term.  It then describes limitations and challenges of
 that approach and the corresponding solutions and workarounds; it
 finishes with the preferred target option of autonomic NOC devices in
 Section 3.1.6.
 This order was chosen because it helps to explain how simple initial
 use of a GACP can be and how difficult workarounds can become (and
 therefore what to avoid).  Also, one very promising long-term
 solution is exactly like the most easy short-term solution, only
 virtualized and automated.
 In the most common case, OAM will be performed by one or more
 applications running on a variety of centralized NOC systems that
 communicate with network devices.  This document describes approaches
 to leverage a GACP for stable connectivity, from simple to complex,
 depending on the capabilities and limitations of the equipment used.
 Three stages can be considered:
 o  There are simple options described in Sections 3.1.1 through 3.1.3
    that we consider to be good starting points to operationalize the
    use of a GACP for stable connectivity today.  These options
    require only network and OAM/NOC device configuration.
 o  The are workarounds to connect a GACP to non-IPv6-capable NOC
    devices through the use of IPv4/IPv6 NAT (Network Address
    Translation) as described in Section 3.1.4.  These workarounds are
    not recommended; however, if non-IPv6-capable NOC devices need to
    be used longer term, then the workarounds are the only way to
    connect them to a GACP.

Eckert & Behringer Informational [Page 6] RFC 8368 AN Stable Connectivity OAM May 2018

 o  Options for the near to long term can provide all the desired
    operational, zero-touch, and security benefits of an autonomic
    network, but a range of details for this still have to be worked
    out, and development work on NOC/OAM equipment is necessary.
    These options are discussed in Sections 3.1.5 through 3.1.8.

3.1.1. Simple Connectivity for Non-GACP-Capable NMS Hosts

 In the most simple candidate deployment case, the GACP extends all
 the way into the NOC via one or more GACP edge devices.  See also
 Section 6.1 of [ACP].  These devices "leak" the (otherwise encrypted)
 GACP natively to NMS hosts.  They act as the default routers to those
 NMS hosts and provide them with IPv6 connectivity into the GACP.  NMS
 hosts with this setup need to support IPv6 (e.g., see [RFC6434]) but
 require no other modifications to leverage the GACP.
 Note that even though the GACP only uses IPv6, it can of course
 support OAM for any type of network deployment as long as the network
 devices support the GACP: The data plane can be IPv4 only, dual
 stack, or IPv6 only.  It is always separate from the GACP; therefore,
 there is no dependency between the GACP and the IP version(s) used in
 the data plane.
 This setup is sufficient for troubleshooting mechanisms such as SSH
 into network devices, NMS that performs SNMP read operations for
 status checking, software downloads onto autonomic devices,
 provisioning of devices via NETCONF, and so on.  In conjunction with
 otherwise unmodified OAM via separate NMS hosts, this setup can
 provide a good subset of the stable connectivity goals.  The
 limitations of this approach are discussed in the next section.
 Because the GACP provides "only" for IPv6 connectivity, and because
 addressing provided by the GACP does not include any topological
 addressing structure that a NOC often relies on to recognize where
 devices are on the network, it is likely highly desirable to set up
 the Domain Name System (DNS; see [RFC1034]) so that the GACP IPv6
 addresses of autonomic devices are known via domain names that
 include the desired structure.  For example, if DNS in the network
 were set up with names for network devices as
 devicename.noc.example.com, and if the well-known structure of the
 data-plane IPv4 address space were used by operators to infer the
 region where a device is located, then the GACP address of that
 device could be set up as devicename_<region>.acp.noc.example.com,
 and devicename.acp.noc.example.com could be a CNAME to
 devicename_<region>.acp.noc.example.com.  Note that many networks
 already use names for network equipment where topological information
 is included, even without a GACP.

Eckert & Behringer Informational [Page 7] RFC 8368 AN Stable Connectivity OAM May 2018

3.1.2. Challenges and Limitations of Simple Connectivity

 This simple connectivity of non-autonomic NMS hosts suffers from a
 range of challenges (that is, operators may not be able to do it this
 way) and limitations (that is, operators cannot achieve desired goals
 with this setup).  The following list summarizes these challenges and
 limitations, and the following sections describe additional
 mechanisms to overcome them.
 Note that these challenges and limitations exist because GACP is
 primarily designed to support distributed Autonomic Service Agent
 (ASA), a piece of autonomic software, in the most lightweight
 fashion.  GACP is not required to support the additional mechanisms
 needed for centralized NOC systems.  It is this document that
 describes additional (short-term) workarounds and (long-term)
 extensions.
 1.  (Limitation) NMS hosts cannot directly probe whether the desired
     so-called "data-plane" network connectivity works because they do
     not directly have access to it.  This problem is similar to
     probing connectivity for other services (such as VPN services)
     that they do not have direct access to, so the NOC may already
     employ appropriate mechanisms to deal with this issue (probing
     proxies).  See Section 3.1.3 for candidate solutions.
 2.  (Challenge) NMS hosts need to support IPv6, and this often is
     still not possible in enterprise networks.  See Section 3.1.4 for
     some workarounds.
 3.  (Limitation) Performance of the GACP may be limited versus normal
     "data-plane" connectivity.  The setup of the GACP will often
     support only forwarding that is not hardware accelerated.
     Running a large amount of traffic through the GACP, especially
     for tasks where it is not necessary, will reduce its performance
     and effectiveness for those operations where it is necessary or
     highly desirable.  See Section 3.1.5 for candidate solutions.
 4.  (Limitation) Security of the GACP is reduced by exposing the GACP
     natively (and unencrypted) in a subnet in the NOC where the NOC
     devices are attached to it.  See Section 3.1.7 for candidate
     solutions.
 These four problems can be tackled independently of each other by
 solution improvements.  Combining some of these improvements together
 can lead towards a candidate long-term solution.

Eckert & Behringer Informational [Page 8] RFC 8368 AN Stable Connectivity OAM May 2018

3.1.3. Simultaneous GACP and Data-Plane Connectivity

 Simultaneous connectivity to both the GACP and data plane can be
 achieved in a variety of ways.  If the data plane is IPv4 only, then
 any method for dual-stack attachment of the NOC device/application
 will suffice: IPv6 connectivity from the NOC provides access via the
 GACP; IPv4 provides access via the data plane.  If, as explained
 above in the simple case, an autonomic device supports native
 attachment to the GACP, and the existing NOC setup is IPv4 only, then
 it could be sufficient to attach the GACP device(s) as the IPv6
 default router to the NOC subnet and keep the existing IPv4 default
 router setup unchanged.
 If the data plane of the network is also supporting IPv6, then the
 most compatible setup for NOC devices is to have two IPv6 interfaces
 -- one virtual (e.g., via IEEE 802.1Q [IEEE.802.1Q]) or physical
 interface connecting to a data-plane subnet, and another connecting
 into a GACP connect subnet.  See Section 8.1 of [ACP] for more
 details.  That document also specifies how a NOC device can receive
 autoconfigured addressing and routes towards the ACP connect subnet
 if it supports default address selection as specified in [RFC6724]
 and default router preferences as specified in [RFC4191].
 Configuring a second interface on a NOC host may be impossible or
 seen as undesired complexity.  In that case, the GACP edge device
 needs to provide support for a "combined ACP and data-plane
 interface" as described in Section 8.1 of [ACP].  This setup may not
 work with autoconfiguration and all NOC host network stacks due to
 limitations in those network stacks.  They need to be able to perform
 Rule 5.5 of [RFC6724] regarding source address selection, including
 caching of next-hop information.
 For security reasons, it is not considered appropriate to connect a
 non-GACP router to a GACP connect interface.  The reason is that the
 GACP is a secured network domain, and all NOC devices connecting via
 GACP connect interfaces are also part of that secure domain.  The
 main difference is that the physical links between the GACP edge
 device and the NOC devices are not authenticated or encrypted and,
 therefore, need to be physically secured.  If the secure GACP was
 extendable via untrusted routers, then it would be a lot more
 difficult to verify the secure domain assertion.  Therefore, the GACP
 edge devices are not supposed to redistribute routes from non-GACP
 routers into the GACP.

Eckert & Behringer Informational [Page 9] RFC 8368 AN Stable Connectivity OAM May 2018

3.1.4. IPv4-Only NMS Hosts

 One architectural expectation for the GACP as described in
 Section 1.3 is that all devices that want to use the GACP (including
 NMS hosts) support IPv6.  Note that this expectation does not imply
 any requirements for the data plane, especially it does not imply
 that IPv6 must be supported in it.  The data plane could be IPv4
 only, IPv6 only, dual stack, or it may not need to have any IP host
 stack on the network devices.
 The implication of this architectural decision is the potential need
 for short-term workarounds when the operational practices in a
 network do not yet meet these target expectations.  This section
 explains when and why these workarounds may be operationally
 necessary and describes them.  However, the long-term goal is to
 upgrade all NMS hosts to native IPv6, so the workarounds described in
 this section should not be considered permanent.
 Most network equipment today supports IPv6, but it is very far from
 being ubiquitously supported in NOC backend solutions (hardware or
 software) or in the product space for enterprises.  Even when it is
 supported, there are often additional limitations or issues using it
 in a dual-stack setup, or the operator mandates (for simplicity)
 single stack for all operations.  For these reasons, an IPv4-only
 management plane is still required and common practice in many
 enterprises.  Without the desire to leverage the GACP, this required
 and common practice is not a problem for those enterprises even when
 they run dual stack in the network.  We discuss these workarounds
 here because it is a short-term deployment challenge specific to the
 operations of a GACP.
 To connect IPv4-only management-plane devices/applications with a
 GACP, some form of IP/ICMP translation of packets between IPv4 and
 IPv6 is necessary.  The basic mechanisms for this are in [RFC7915],
 which describes the Stateless IP/ICMP Translation Algorithm (SIIT).
 There are multiple solutions using this mechanism.  To understand the
 possible solutions, we consider the requirements:
 1.  NMS hosts need to be able to initiate connections to any GACP
     device for management purposes.  Examples include provisioning
     via NETCONF, SNMP poll operations, or just diagnostics via SSH
     connections from operators.  Every GACP device/function that
     needs to be reachable from NMS hosts needs to have a separate
     IPv4 address.

Eckert & Behringer Informational [Page 10] RFC 8368 AN Stable Connectivity OAM May 2018

 2.  GACP devices need to be able to initiate connections to NMS
     hosts, for example, to initiate NTP or RADIUS/Diameter
     connections, send syslog or SNMP trap, or initiate NETCONF Call
     Home connections after bootstrap.  Every NMS host needs to have a
     separate IPv6 address reachable from the GACP.  When a connection
     from a GACP device is made to an NMS host, the IPv4 source
     address of the connection (as seen by the NMS host) must be
     unique per GACP device and must be the same address as in (1) to
     maintain addressing simplicity similar to a native IPv4
     deployment.  For example in syslog, the source IP address of a
     logging device is used to identify it, and if the device shows
     problems, an operator might want to SSH into the device to
     diagnose it.
 Because of these requirements, the necessary and sufficient set of
 solutions are those that provide 1:1 mapping of IPv6 GACP addresses
 into IPv4 space and 1:1 mapping of IPv4 NMS host space into IPv6 (for
 use in the GACP).  This means that SIIT-based solutions are
 sufficient and preferred.
 Note that GACP devices may use multiple IPv6 addresses in the GACP.
 For example, Section 6.10 of [ACP] defines multiple useful addressing
 sub-schemes supporting this option.  All those addresses may then
 need to be reachable through IPv6/IPv4 address translation.
 The need to allocate for every GACP device one or multiple IPv4
 addresses should not be a problem if -- as we assume -- the NMS hosts
 can use private IPv4 address space ([RFC1918]).  Nevertheless, even
 with private IPv4 address space, it is important that the GACP IPv6
 addresses can be mapped efficiently into IPv4 address space without
 too much waste.
 Currently, the most flexible mapping scheme to achieve this is
 [RFC7757] because it allows configured IPv4 <-> IPv6 prefix mapping.
 Assume the GACP uses the ACP Zone Addressing Sub-Scheme and there are
 3 registrars.  In the ACP Zone Addressing Sub-Scheme, for each
 registrar, there is a constant /112 prefix for which an Explicit
 Address Mapping (EAM), as defined in RFC 7757, to a /16 prefix can be
 configured (e.g., in the private IPv4 address space described in
 [RFC1918]).  Within the registrar's /112 prefix, Device-Numbers for
 devices are sequentially assigned: with the V bit (Virtualization
 bit) effectively two numbers are assigned per GACP device.  This also
 means that if IPv4 address space is even more constrained, and it is
 known that a registrar will never need the full /15 extent of Device-
 Numbers, then a prefix longer than a /112 can be configured into the
 EAM in order to use less IPv4 space.

Eckert & Behringer Informational [Page 11] RFC 8368 AN Stable Connectivity OAM May 2018

 When using the ACP Vlong Addressing Sub-Scheme, it is unlikely that
 one wants or needs to translate the full /8 or /16 of addressing
 space per GACP device into IPv4.  In this case, the EAM rules of
 dropping trailing bits can be used to map only N bits of the V bits
 into IPv4.  However, this does imply that only addresses that differ
 in those high-order N V bits can be distinguished on the IPv4 side.
 Likewise, the IPv4 address space used for NMS hosts can easily be
 mapped into an address prefix assigned to a GACP connect interface.
 A full specification of a solution to perform SIIT in conjunction
 with GACP connect following the considerations below is outside the
 scope of this document.
 To be in compliance with security expectations, SIIT has to happen on
 the GACP edge device itself so that GACP security considerations can
 be taken into account.  For example, IPv4-only NMS hosts can be dealt
 with exactly like IPv6 hosts connected to a GACP connect interface.
 Note that prior solutions such as NAT64 ([RFC6146]) may equally be
 useable to translate between GACP IPv6 address space and NMS hosts'
 IPv4 address space.  As a workaround, this can also be done on non-
 GACP Edge Devices connected to a GACP connect interface.  The details
 vary depending on implementation because the options to configure
 address mappings vary widely.  Outside of EAM, there are no
 standardized solutions that allow for mapping of prefixes, so it will
 most likely be necessary to explicitly map every individual (/128)
 GACP device address to an IPv4 address.  Such an approach should use
 automation/scripting where these address translation entries are
 created dynamically whenever a GACP device is enrolled or first
 connected to the GACP network.
 The NAT methods described here are not specific to a GACP.  Instead,
 they are similar to what would be necessary when some parts of a
 network only support IPv6, but the NOC equipment does not support
 IPv6.  Whether it is more appropriate to wait until the NOC equipment
 supports IPv6 or to use NAT beforehand depends in large part on how
 long the former will take and how easy the latter will be when using
 products that support the NAT options described to operationalize the
 above recommendations.

3.1.5. Path Selection Policies

 As mentioned above, a GACP is not expected to have high performance
 because its primary goal is connectivity and security.  For existing
 network device platforms, this often means that it is a lot more
 effort to implement that additional connectivity with hardware

Eckert & Behringer Informational [Page 12] RFC 8368 AN Stable Connectivity OAM May 2018

 acceleration than without -- especially because of the desire to
 support full encryption across the GACP to achieve the desired
 security.
 Some of these issues may go away in the future with further adoption
 of a GACP and network device designs that better tend to the needs of
 a separate OAM plane, but it is wise to plan for long-term designs of
 the solution that do NOT depend on high performance of the GACP.
 This is the opposite of the expectations that future NMS hosts will
 have IPv6 and that any considerations for IPv4/NAT in this solution
 are temporary.
 To solve the expected performance limitations of the GACP, we do
 expect to have the above-described dual connectivity via both GACP
 and data plane between NOC application devices and devices with GACP.
 The GACP connectivity is expected to always be there (as soon as a
 device is enrolled), but the data-plane connectivity is only present
 under normal operations and will not be present during, e.g., early
 stages of device bootstrap, failures, provisioning mistakes, or
 network configuration changes.
 The desired policy is therefore as follows: In the absence of further
 security considerations (see below), traffic between NMS hosts and
 GACP devices should prefer data-plane connectivity and resort only to
 using the GACP when necessary.  The exception is an operation known
 to be covered by the use cases where the GACP is necessary, so that
 it makes no sense to try using the data plane.  An example is an SSH
 connection from the NOC to a network device to troubleshoot network
 connectivity.  This could easily always rely on the GACP.  Likewise,
 if an NMS host is known to transmit large amounts of data, and it
 uses the GACP, then its data rate needs to be controlled so that it
 will not overload the GACP path.  Typical examples of this are
 software downloads.
 There is a wide range of methods to build up these policies.  We
 describe a few below.
 Ideally, a NOC system would learn and keep track of all addresses of
 a device (GACP and the various data-plane addresses).  Every action
 of the NOC system would indicate via a "path-policy" what type of
 connection it needs (e.g., only data-plane, GACP only, default to
 data plane, fallback to GACP, etc.).  A connection policy manager
 would then build connection to the target using the right
 address(es).  Shorter term, a common practice is to identify
 different paths to a device via different names (e.g., loopback vs.
 interface addresses).  This approach can be expanded to GACP uses,
 whether it uses the DNS or names local to the NOC system.  Below, we
 describe example schemes using DNS.

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 DNS can be used to set up names for the same network devices but with
 different addresses assigned:
 o  One name (name.noc.example.com) with only the data-plane
    address(es) (IPv4 and/or IPv6) to be used for probing connectivity
    or performing routine software downloads that may stall/fail when
    there are connectivity issues.
 o  One name (name-acp.noc.example.com) with only the GACP reachable
    address of the device for troubleshooting and probing/discovery
    that is desired to always only use the GACP.
 o  One name (name-both.noc.example.com) with data-plane and GACP
    addresses.
 Traffic policing and/or shaping at the GACP edge in the NOC can be
 used to throttle applications such as software download into the
 GACP.
 Using different names that map to different addresses (or subsets of
 addresses) can be difficult to set up and maintain, especially
 because data-plane addresses may change due to reconfiguration or
 relocation of devices.  The name-based approach alone cannot strongly
 support policies for existing applications and long-lived flows to
 automatically switch between the ACP and data plane in the face of
 data-plane failure and recovery.  A solution would be host transport
 stacks on GACP nodes that support the following requirements:
 1.  Only the GACP addresses of the responder must be required by the
     initiator for the initial setup of a connection/flow across the
     GACP.
 2.  Responder and Initiator must be able to exchange their data-plane
     addresses through the GACP, and then -- if needed by policy --
     build an additional flow across the data plane.
 3.  For unmodified application, the following policies should be
     configurable on at least a per-application basis for its TCP
     connections with GACP peers:
     Fallback (to GACP):  An additional data-plane flow is built and
        used exclusively to send data whenever the data plane is
        operational.  When the additional flow cannot be built during
        connection setup or when it fails later, traffic is sent
        across the GACP flow.  This could be a default policy for most
        OAM applications using the GACP.

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     Suspend/Fail:  Like the Fallback policy, except that traffic will
        not use the GACP flow; instead, it will be suspended until a
        data-plane flow is operational or until a policy-configurable
        timeout indicates a connection failure to the application.
        This policy would be appropriate for large-volume background
        or scavenger-class OAM applications such as firmware downloads
        or telemetry/diagnostic uploads -- applications that would
        otherwise easily overrun performance-limited GACP
        implementations.
     GACP (only):  No additional data-plane flow is built, traffic is
        only sent via the GACP flow.  This can just be a TCP
        connection.  This policy would be most appropriate for OAM
        operations known to change the data plane in a way that could
        impact connectivity through it (at least temporarily).
 4.  In the presence of responders or initiators not supporting these
     host stack functions, the Fallback and GACP policies must result
     in a TCP connection across the GACP.  For Suspend/Fail, presence
     of TCP-only peers should result in failure during connection
     setup.
 5.  In case of Fallback and Suspend/Fail, a failed data-plane
     connection should automatically be rebuilt when the data plane
     recovers, including when the data-plane address of one side or
     both sides may have changed -- for example, because of
     reconfiguration or device repositioning.
 6.  Additional data-plane flows created by these host transport stack
     functions must be end-to-end authenticated by these host
     transport stack functions with the GACP domain credentials and
     encrypted.  This maintains the expectation that connections from
     GACP addresses to GACP addresses are authenticated and encrypted.
     This may be skipped if the application already provides for end-
     to-end encryption.
 7.  For enhanced applications, the host stack may support application
     control to select the policy on a per-connection basis, or even
     more explicit control for building of the flows and which flow
     should pass traffic.
 Protocols like Multipath TCP (MPTCP; see [RFC6824]) and the Stream
 Control Transmission Protocol (SCTP; see [RFC4960]) can already
 support part of these requirements.  MPTCP, for example, supports
 signaling of addresses in a TCP backward-compatible fashion,
 establishing additional flows (called subflows in MPTCP), and having
 primary and fallback subflows via MP_PRIO signaling.  The details of
 how MPTCP, SCTP, and/or other approaches (potentially with extensions

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 and/or (shim) layers on top of them) can best provide a complete
 solution for the above requirements need further work and are outside
 the scope of this document.

3.1.6. Autonomic NOC Device/Applications

 Setting up connectivity between the NOC and autonomic devices when
 the NOC device itself is non-autonomic is a security issue, as
 mentioned at the beginning of this document.  It also results in a
 range of connectivity considerations (discussed in Section 3.1.5),
 some of which may be quite undesirable or complex to operationalize.
 Making NMS hosts autonomic and having them participate in the GACP is
 therefore not only a highly desirable solution to the security
 issues, but can also provide a likely easier operationalization of
 the GACP because it minimizes special edge considerations for the
 NOC.  The GACP is simply built all the way automatically, even inside
 the NOC, and it is only authorizes and authenticates NOC devices/
 applications that will have access to it.
 According to [ACP], supporting the ACP all the way into an
 application device requires implementing the following aspects in it:
 AN bootstrap/enrollment mechanisms, the secure channel for the ACP
 and at least the host side of IPv6 routing setup for the ACP.
 Minimally, this could all be implemented as an application and be
 made available to the host OS via, e.g., a TAP driver to make the ACP
 show up as another IPv6-enabled interface.
 Having said this: If the structure of NMS hosts is transformed
 through virtualization anyhow, then it may be considered equally
 secure and appropriate to construct a (physical) NMS host system by
 combining a virtual GACP-enabled router with non-GACP-enabled Virtual
 Machines (VMs) for NOC applications via a hypervisor.  This would
 leverage the configuration options described in the previous sections
 but just virtualize them.

3.1.7. Encryption of Data-Plane Connections

 When combining GACP and data-plane connectivity for availability and
 performance reasons, this too has an impact on security: When using
 the GACP, most traffic will be encryption protected, especially when
 considering the above-described use of application devices with GACP.
 If, instead, the data plane is used, then this is not the case
 anymore unless it is done by the application.
 The simplest solution for this problem exists when using GACP-capable
 NMS hosts, because in that case the communicating GACP-capable NMS
 host and the GACP network device have credentials they can mutually

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 trust (same GACP domain).  As a result, data-plane connectivity that
 does support this can simply leverage TLS [RFC5246] or DTLS [RFC6347]
 with those GACP credentials for mutual authentication -- and this
 does not incur new key management.
 If this automatic security benefit is seen as most important, but a
 "full" GACP stack into the NMS host is unfeasible, then it would
 still be possible to design a stripped-down version of GACP
 functionality for such NOC hosts that only provides enrollment of the
 NOC host with the GACP cryptographic credentials and does not
 directly participate in the GACP encryption method.  Instead, the
 host would just leverage TLS/DTLS using its GACP credentials via the
 data plane with GACP network devices as well as indirectly via the
 GACP connect interface with the above-mentioned GACP connect
 interface into the GACP.
 When using the GACP itself, TLS/DTLS for the transport layer between
 NMS hosts and network device is somewhat of a double price to pay
 (GACP also encrypts) and could potentially be optimized away;
 however, given the assumed lower performance of the GACP, it seems
 that this is an unnecessary optimization.

3.1.8. Long-Term Direction of the Solution

 If we consider what potentially could be the most lightweight and
 autonomic long-term solution based on the technologies described
 above, we see the following direction:
 1.  NMS hosts should at least support IPv6.  IPv4/IPv6 NAT in the
     network to enable use of a GACP is undesirable in the long term.
     Having IPv4-only applications automatically leverage IPv6
     connectivity via host-stack translation may be an option, but
     this has not been investigated yet.
 2.  Build the GACP as a lightweight application for NMS hosts so GACP
     extends all the way into the actual NMS hosts.
 3.  Leverage and (as necessary) enhance host transport stacks with
     automatic GACP with multipath connectivity and data plane as
     outlined in Section 3.1.5.
 4.  Consider how to best map NMS host desires to underlying transport
     mechanisms: The three points above do not cover all options.
     Depending on the OAM, one may still want only GACP, want only
     data plane, automatically prefer one over the other, and/or want
     to use the GACP with low performance or high performance (for
     emergency OAM such as countering DDoS).  As of today, it is not
     clear what the simplest set of tools is to explicitly enable the

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     choice of desired behavior of each OAM.  The use of the above-
     mentioned DNS and multipath mechanisms is a start, but this will
     require additional work.  This is likely a specific case of the
     more generic scope of TAPS.

3.2. Stable Connectivity for Distributed Network/OAM

 Today, many distributed protocols implement their own unique security
 mechanisms.
 Keying and Authentication for Routing Protocols (KARP; see [RFC6518])
 has tried to start to provide common directions and therefore reduce
 the reinvention of at least some of the security aspects, but it only
 covers routing protocols and it is unclear how applicable it is to a
 wider range of network distributed agents such as those performing
 distributed OAM.  The common security of a GACP can help in those
 cases.
 Furthermore, a GRASP instance ([GRASP]) can run on top of a GACP as a
 security and transport substrate and provide common local and remote
 neighbor discovery and peer negotiation mechanisms; this would allow
 unifying and reusing future protocol designs.

4. Architectural Considerations

4.1. No IPv4 for GACP

 The GACP is intended to be IPv6 only, and the prior explanations in
 this document show that this can lead to some complexity when having
 to connect IPv4-only NOC solutions, and that it will be impossible to
 leverage the GACP when the OAM agents on a GACP network device do not
 support IPv6.  Therefore, the question was raised whether the GACP
 should optionally also support IPv4.
 The decision not to include IPv4 for GACP in the use cases in this
 document was made for the following reasons:
 In service provider networks that have started to support IPv6, often
 the next planned step is to consider moving IPv4 from a native
 transport to just a service on the edge.  There is no benefit or need
 for multiple parallel transport families within the network, and
 standardizing on one reduces operating expenses and improves
 reliability.  This evolution in the data plane makes it highly
 unlikely that investing development cycles into IPv4 support for GACP
 will have a longer term benefit or enough critical short-term use
 cases.  Support for IPv6-only for GACP is purely a strategic choice
 to focus on the known important long-term goals.

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 In other types of networks as well, we think that efforts to support
 autonomic networking are better spent in ensuring that one address
 family will be supported so all use cases will work with it in the
 long term, instead of duplicating effort with IPv4.  Also, auto-
 addressing for the GACP with IPv4 would be more complex than in IPv6
 due to the IPv4 addressing space.

5. Security Considerations

 In this section, we discuss only security considerations not covered
 in the appropriate subsections of the solutions described.
 Even though GACPs are meant to be isolated, explicit operator
 misconfiguration to connect to insecure OAM equipment and/or bugs in
 GACP devices may cause leakage into places where it is not expected.
 Mergers and acquisitions and other complex network reconfigurations
 affecting the NOC are typical examples.
 GACP addresses are ULAs.  Using these addresses also for NOC devices,
 as proposed in this document, is not only necessary for the simple
 routing functionality explained above, but it is also more secure
 than global IPv6 addresses.  ULAs are not routed in the global
 Internet and will therefore be subject to more filtering even in
 places where specific ULAs are being used.  Packets are therefore
 less likely to leak and less likely to be successfully injected into
 the isolated GACP environment.
 The random nature of a ULA prefix provides strong protection against
 address collision even though there is no central assignment
 authority.  This is helped by the expectation that GACPs will never
 connect all together, and that only a few GACPs may ever need to
 connect together, e.g., when mergers and acquisitions occur.
 Note that the GACP constraints demand that only packets from
 connected subnet prefixes are permitted from GACP connect interfaces,
 limiting the scope of non-cryptographically secured transport to a
 subnet within a NOC that instead has to rely on physical security
 (i.e., only connect trusted NOC devices to it).
 To help diagnose packets that unexpectedly leaked, for example, from
 another GACP (that was meant to be deployed separately), it can be
 useful to voluntarily list your own ULA GACP prefixes on some sites
 on the Internet and hope that other users of GACPs do the same so
 that you can look up unknown ULA prefix packets seen in your network.
 Note that this does not constitute registration.
 <https://www.sixxs.net/tools/grh/ula/> was a site to list ULA

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 prefixes, but it has not been open for new listings since mid-2017.
 The authors are not aware of other active Internet sites to list ULA
 use.
 Note that there is a provision in [RFC4193] for address space that is
 not locally assigned (L bit = 0), but there is no existing
 standardization for this, so these ULA prefixes must not be used.
 According to Section 4.4 of [RFC4193], PTR records for ULA addresses
 should not be installed into the global DNS (no guaranteed
 ownership).  Hence, there is also the need to rely on voluntary lists
 (as mentioned above) to make the use of an ULA prefix globally known.
 Nevertheless, some legacy OAM applications running across the GACP
 may rely on reverse DNS lookup for authentication of requests (e.g.,
 TFTP for download of network firmware, configuration, or software).
 Therefore, operators may need to use a private DNS setup for the GACP
 ULAs.  This is the same setup that would be necessary for using RFC
 1918 addresses in DNS.  For example, see the last paragraph of
 Section 5 of [RFC1918].  In Section 4 of [RFC6950], these setups are
 discussed in more detail.
 Any current and future protocols must rely on secure end-to-end
 communications (TLS/DTLS) and identification and authentication via
 the certificates assigned to both ends.  This is enabled by the
 cryptographic credential mechanisms of the GACP.
 If DNS and especially reverse DNS are set up, then they should be set
 up in an automated fashion when the GACP address for devices are
 assigned.  In the case of the ACP, DNS resource record creation can
 be linked to the autonomic registrar backend so that the DNS and
 reverse DNS records are actually derived from the subject name
 elements of the ACP device certificates in the same way as the
 autonomic devices themselves will derive their ULAs from their
 certificates to ensure correct and consistent DNS entries.
 If an operator feels that reverse DNS records are beneficial to its
 own operations, but that they should not be made available publicly
 for "security" by concealment reasons, then GACP DNS entries are
 probably one of the least problematic use cases for split DNS: The
 GACP DNS names are only needed for the NMS hosts intending to use the
 GACP -- but not network wide across the enterprise.

6. IANA Considerations

 This document has no IANA actions.

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7. References

7.1. Normative References

 [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
            and E. Lear, "Address Allocation for Private Internets",
            BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
            <https://www.rfc-editor.org/info/rfc1918>.
 [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
            More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
            November 2005, <https://www.rfc-editor.org/info/rfc4191>.
 [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
            Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
            <https://www.rfc-editor.org/info/rfc4193>.
 [RFC6724]  Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
            "Default Address Selection for Internet Protocol Version 6
            (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
            <https://www.rfc-editor.org/info/rfc6724>.
 [RFC6824]  Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
            "TCP Extensions for Multipath Operation with Multiple
            Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
            <https://www.rfc-editor.org/info/rfc6824>.
 [RFC7575]  Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
            Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
            Networking: Definitions and Design Goals", RFC 7575,
            DOI 10.17487/RFC7575, June 2015,
            <https://www.rfc-editor.org/info/rfc7575>.
 [RFC7757]  Anderson, T. and A. Leiva Popper, "Explicit Address
            Mappings for Stateless IP/ICMP Translation", RFC 7757,
            DOI 10.17487/RFC7757, February 2016,
            <https://www.rfc-editor.org/info/rfc7757>.
 [RFC7915]  Bao, C., Li, X., Baker, F., Anderson, T., and F. Gont,
            "IP/ICMP Translation Algorithm", RFC 7915,
            DOI 10.17487/RFC7915, June 2016,
            <https://www.rfc-editor.org/info/rfc7915>.

Eckert & Behringer Informational [Page 21] RFC 8368 AN Stable Connectivity OAM May 2018

7.2. Informative References

 [ACP]      Eckert, T., Behringer, M., and S. Bjarnason, "An Autonomic
            Control Plane (ACP)", Work in Progress,
            draft-ietf-anima-autonomic-control-plane-13,
            December 2017.
 [BRSKI]    Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
            S., and K. Watsen, "Bootstrapping Remote Secure Key
            Infrastructures (BRSKI)", Work in Progress,
            draft-ietf-anima-bootstrapping-keyinfra-15, April 2018.
 [GRASP]    Bormann, C., Carpenter, B., and B. Liu, "A Generic
            Autonomic Signaling Protocol (GRASP)", Work in Progress,
            draft-ietf-anima-grasp-15, July 2017.
 [IEEE.802.1Q]
            IEEE, "IEEE Standard for Local and metropolitan area
            networks -- Bridges and Bridged Networks",
            IEEE 802.1Q-2014, DOI 10.1109/ieeestd.2014.6991462,
            December 2014, <http://ieeexplore.ieee.org/servlet/
            opac?punumber=6991460>.
 [ITUT_G7712]
            ITU, "Architecture and specification of data communication
            network", ITU-T Recommendation G.7712/Y.1703, November
            2001, <https://www.itu.int/rec/T-REC-G.7712/en>.
 [REF_MODEL]
            Behringer, M., Carpenter, B., Eckert, T., Ciavaglia, L.,
            and J. Nobre, "A Reference Model for Autonomic
            Networking", Work in Progress,
            draft-ietf-anima-reference-model-06, February 2018.
 [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
            STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
            <https://www.rfc-editor.org/info/rfc1034>.
 [RFC4960]  Stewart, R., Ed., "Stream Control Transmission Protocol",
            RFC 4960, DOI 10.17487/RFC4960, September 2007,
            <https://www.rfc-editor.org/info/rfc4960>.
 [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.2", RFC 5246,
            DOI 10.17487/RFC5246, August 2008,
            <https://www.rfc-editor.org/info/rfc5246>.

Eckert & Behringer Informational [Page 22] RFC 8368 AN Stable Connectivity OAM May 2018

 [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
            NAT64: Network Address and Protocol Translation from IPv6
            Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
            April 2011, <https://www.rfc-editor.org/info/rfc6146>.
 [RFC6291]  Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
            D., and S. Mansfield, "Guidelines for the Use of the "OAM"
            Acronym in the IETF", BCP 161, RFC 6291,
            DOI 10.17487/RFC6291, June 2011,
            <https://www.rfc-editor.org/info/rfc6291>.
 [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
            Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
            January 2012, <https://www.rfc-editor.org/info/rfc6347>.
 [RFC6434]  Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
            Requirements", RFC 6434, DOI 10.17487/RFC6434, December
            2011, <https://www.rfc-editor.org/info/rfc6434>.
 [RFC6518]  Lebovitz, G. and M. Bhatia, "Keying and Authentication for
            Routing Protocols (KARP) Design Guidelines", RFC 6518,
            DOI 10.17487/RFC6518, February 2012,
            <https://www.rfc-editor.org/info/rfc6518>.
 [RFC6950]  Peterson, J., Kolkman, O., Tschofenig, H., and B. Aboba,
            "Architectural Considerations on Application Features in
            the DNS", RFC 6950, DOI 10.17487/RFC6950, October 2013,
            <https://www.rfc-editor.org/info/rfc6950>.

Acknowledgements

 This work originated from an Autonomic Networking project at Cisco
 Systems, which started in early 2010, with customers involved in the
 design and early testing.  Many people contributed to the aspects
 described in this document, including in alphabetical order: BL
 Balaji, Steinthor Bjarnason, Yves Herthoghs, Sebastian Meissner, and
 Ravi Kumar Vadapalli.  The authors would also like to thank Michael
 Richardson, James Woodyatt, and Brian Carpenter for their review and
 comments.  Special thanks to Sheng Jiang and Mohamed Boucadair for
 their thorough reviews.

Eckert & Behringer Informational [Page 23] RFC 8368 AN Stable Connectivity OAM May 2018

Authors' Addresses

 Toerless Eckert (editor)
 Huawei USA
 2330 Central Expy
 Santa Clara  95050
 United States of America
 Email: tte+ietf@cs.fau.de, toerless.eckert@huawei.com
 Michael H. Behringer
 Email: michael.h.behringer@gmail.com

Eckert & Behringer Informational [Page 24]

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