Network Working Group L. Dunbar Internet Draft A. Malis Intended status: Informational Huawei Expires: January 2018 C. Jacquenet Orange M. Toy Verizon March 5, 2018 Seamless Interconnect Underlay to Cloud Overlay Problem Statement draft-dm-net2cloud-problem-statement-01 Abstract This document describes common approaches deployed by enterprises for interconnection of workloads & applications hosted in Cloud DCs with on-premises DCs & branch offices. This document also describes some of the (network) problems that many enterprises face when they have workloads & applications & data split among hybrid data centers, especially for those enterprises with multiple sites that are already interconnected by VPNs (e.g. MPLS L2VPN/L3VPN) and leased lines. Current operational problems in the field are examined to determine whether there is a need for enhancements to existing protocols or whether a new protocol is necessary to solve them. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. This document may not be modified, and derivative works of it may not be created, except to publish it as an RFC and to translate it into languages other than English. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. xxx, et al. Expires September 5, 2018 [Page 1] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on September 5, 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 (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. Definition of terms............................................4 3. Current Practices in Interconnecting Enterprise Sites with Cloud DCs...............................................................5 3.1. Interconnect to Cloud DCs.................................5 3.2. Interconnect to Hybrid Cloud DCs..........................7 3.3. Connecting workloads among hybrid Cloud DCs...............7 4. Desired Properties for Networking that interconnects Hybrid Cloud DCs...............................................................8 5. Problems with MPLS-based VPNs extending to Hybrid Cloud DCs....8 6. Problem with using IPsec tunnels to Cloud DCs.................10 Dunbar, et al. Expires June 5, 2018 [Page 2] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 6.1. Complexity of multi-point any-to-any interconnection.....10 6.2. Poor performance over long distance......................11 6.3. Scaling Issues with IPsec Tunnels........................11 7. Problems of Using SD-WAN to connect to Cloud DCs..............12 7.1. SD-WAN among branch offices vs. interconnect to Cloud DCs12 8. End-to-End Security Concerns for Data Flows...................15 9. Requirements for Dynamic Cloud Data Center VPNs...............15 10. Security Considerations......................................16 11. IANA Considerations..........................................16 12. References...................................................16 12.1. Normative References....................................16 12.2. Informative References..................................16 13. Acknowledgments..............................................17 1. Introduction Cloud applications and services continue to change how businesses of all sizes work and share information. "Cloud applications & workloads" are those that are instantiated in third party DCs that also host services for other customers. With the advent of widely available third party cloud DCs in diverse geographic locations and the advancement of tools for monitoring and predicting application behaviors, it is technically feasible for enterprises to instantiate applications and workloads in locations that are geographically closest to their end users. This property aids in improving end-to-end latency and overall user experience. Conversely, an enterprise can easily shutdown applications and workloads when their end users' geographic base changes (therefore needing to change the networking connection to those relocated applications and workloads). In addition, an enterprise may wish to take advantage of more and more business applications offered by third party private cloud DCs, such as SAP HANA, Oracle Cloud, Salesforce Cloud, etc. However, typically, enterprise branch offices & on-premises data centers are connected via VPNs, such as MPLS based l2VPN/L3VPN, and therefore connecting to the cloud-based resources may not be straightforward if the provider of the VPN service does not have direct connections to the Cloud DCs. Under those circumstances, the enterprise can upgrade their existing CPEs to utilize SD-WAN to reach cloud resources (without any assistance from the VPN service Dunbar, et al. Expires June 5, 2018 [Page 3] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 provider), or wait for their VPN service provider to make new agreements with data center providers to connect to the Cloud resources. Either way this is non-trivial and has additional infrastructure costs, and is slow to operationalize. In addition, it is an uptrend with more and more enterprises changing their Apps & workloads so that they can be split among hybrid DCs to maximize the benefits of geographical convenience & elasticity and special property of on-premises DCs. 2. Definition of terms Cloud DC: Off-Premise Data Centers that usually host applications and workload owned by different organizations or tenants. Controller: Used interchangeably with SD-WAN controller to manage SD-WAN overlay path creation/deletion and monitoring the path conditions between two or more sites. DMVPN: Dynamic Multipoint Virtual Private Network. DMVPN is a secure network that exchanges data between sites without needing to pass traffic through an organization's headquarter virtual private network (VPN) server or router. Heterogeneous Cloud: applications & workloads split among Cloud DCs owned & managed by different operators. Hybrid Cloud: applications & workloads split between on-premises Data centers and Cloud DCs. In this document Hybrid Cloud also include heterogeneous cloud as well. SD-WAN: Software Defined Wide Area Network, which can mean many different things. In this document, "SD-WAN" refers to the solutions specified by ONUG (Open Network User Group), https://www.onug.net/software-defined-wide-area- Dunbar, et al. Expires June 5, 2018 [Page 4] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 network-sd-wan/, which is about pooling WAN bandwidth from n service providers to get better WAN bandwidth management, visibility & control. VPC: Virtual Private Cloud. A service offered by many Cloud DC operators to allocate a logically isolated cloud resources, including compute, networking and storage. 3. Current Practices in Interconnecting Enterprise Sites with Cloud DCs 3.1. Interconnect to Cloud DCs Most Cloud operators offer some type of network gateway through which an enterprise can reach their workloads hosted in the Cloud DC. For example, AWS (Amazon Web Services) offers the following options to reach workloads in AWS Cloud DCs: - Internet gateway for any external entities to reach the workloads hosted in AWS Cloud DC via the internet. - virtual gateway (vGW) to which IPsec tunnels [RFC6071] are established between an enterprise's own gateways and AWS vGW, so that the communications between those gateways can be secured from the underlay (which might be the public internet). - Direct Connect, which allows enterprises to purchase direct connect from network service providers to get a private leased line interconnecting the enterprises gateway(s) and the AWS Direct Connect routers co-located with the network operators. Dunbar, et al. Expires June 5, 2018 [Page 5] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 +------------------------+ | ,---. ,---. | | (TN-1 ) ( TN-2)| | `-+-' +--+ `-+-' | | +----|vR|-----+ | | ++-+ | | | +-+----+ | | /Internet\ For External | +-------+ Gateway +---------------------- | \ / to reach via Internet | +-+----+ | | +------------------------+ +------------------------+ | ,---. ,---. | | (TN-1 ) ( TN-2)| | `-+-' +--+ `-+-' | | +----|vR|-----+ | | ++-+ | | | +-+----+ | | / virtual\ For IPsec Tunnel | +-------+ Gateway +---------------------- | \ / termination | +-+----+ | | +------------------------+ +------------------------+ | ,---. ,---. | | (TN-1 ) ( TN-2)| | `-+-' +--+ `-+-' | | +----|vR|-----+ | | ++-+ | | | +-+----+ +------+ | | / \ For Direct /customer\ | +-------+ Gateway +----------+ gateway | | \ / Connect \ / | +-+----+ +------+ | | +------------------------+ Figure 1: Examples of connecting to a Cloud DC Dunbar, et al. Expires June 5, 2018 [Page 6] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 3.2. Interconnect to Hybrid Cloud DCs According to Gartner, by 2020 "hybrid will be the most common usage of the cloud" as more enterprises see the benefits of integrating public and private cloud infrastructures. However, enabling the growth of hybrid cloud deployments in the enterprise requires fast and safe interconnection between public and private cloud services. The Hybrid Cloud scenario also includes heterogeneous Cloud DCs. For enterprises to connect to applications & workloads hosted in multiple Cloud DCs, enterprises can use IPsec tunnels or lease private lines to connect their own gateways to each of the Cloud DC's gateways or any other suitable design (including a combination thereof). Some users prefer to instantiate their own virtual CPEs inside the public Cloud DC to connect the workloads within the Cloud DC. Then an overlay path is established between customer gateways to the virtual CPEs for reaching the workloads inside the cloud DC. 3.3. Connecting workloads among hybrid Cloud DCs When workloads among different Cloud DCs need to communicate, one way is to hairpin all the traffic through the customer gateway, which creates additional transmission delay & incurs cost exiting Cloud DCs. Another way is to establish direct tunnels among different VPCs (Virtual Private Clouds), such as using DMVPN (Dynamic Multipoint Virtual Private Network) or DSVPN (Dynamic Smart VPN) to establish direct Multi-edge tunnels. DMVPN (and DSVPN) uses NHRP (Next Hop Resolution Protocol) [RFC2735] so that spoke nodes can register their IP addresses with the hub node. The IETF ION WG, Internetworking over NBMA (non-broadcast multiple access), standardized NHRP for connection-oriented NBMA network (such as ATM) network address resolution more than two decades ago. There are many differences between virtual routers in Public Cloud DCs and the nodes in an NBMA network. It would be useful for the IETF community to examine the effectiveness of NHRP as the registration protocol for registering virtual routers in Cloud DCs to gateways or entities that connect to enterprise private networks. Dunbar, et al. Expires June 5, 2018 [Page 7] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 As the result of this evaluation, enhancement or new registration protocols may result. 4. Desired Properties for Networking that interconnects Hybrid Cloud DCs The networks that interconnect hybrid Cloud DCs have to enable users to take advantage of Cloud DCs: - High availability, any time usage for any length of time. Many enterprises incorporate Cloud as their disaster recovery strategy, e.g. periodically backup data into the cloud, or running backup applications in the Cloud, etc. Therefore, the connection to the cloud DCs may not be permanent, but rather needs to be on-demand. - Global accessibility in different geographical zones, thereby facilitating the proximity of applications as a function of the end users' location, for improved latency. - Elasticity and mobility, to instantiate additional applications at Cloud DCs when end users' usages increase and shut down applications at locations with fewer end users. Some enterprises have front-end web portals running in Cloud DCs and Database servers in their on-premises DCs. Those Front- end web portals need to be reachable from the public Internet. The backend connection to the sensitive data in database servers hosted in the on-premises DCs might need secure connections. 5. Problems with MPLS-based VPNs extending to Hybrid Cloud DCs Traditional MPLS-based VPNs have been widely deployed as an effective way to support businesses and organizations that require network performance and reliability. MPLS shifted the burden of managing a VPN service from enterprises to service providers. The CPEs for MPLS VPN are also simpler and less expensive, since they do not need to manage how to send packets to remote sites; they simply pass all outbound traffic to the MPLS VPN PEs to which the CPE is attached (albeit multi-homing scenarios require more processing Dunbar, et al. Expires June 5, 2018 [Page 8] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 logic on CPEs). MPLS has addressed the problems of scale, availability, and fast recovery from network faults, and incorporated traffic-engineering capabilities. However, traditional MPLS-based VPN solutions are not optimized for connecting end-users to dynamic workloads/applications in cloud DCs because: - The Provider Edge (PE) nodes of the enterprise's VPNs might not have direct connection to the third party cloud DCs that are optimal for hosting workloads with the goal of easy access to enterprises' end users. - It takes a relatively long time to deploy provider edge (PE) routers at new locations. When enterprise's workloads are changed from one cloud DC to another (i.e., removed from one DC and re-instantiated to another location when demand changes), the enterprise branch offices need to be connected to the new cloud DC, but the network service provider might not have PEs located at the new location. One of the main drivers for moving workloads into the cloud is the widely available cloud DCs at geographically diverse locations, where apps can be instantiated so that they can be as close to their end users as possible. When the user base changes, the applications may be moved to a new cloud DC location closest to the new user base. - Most of the cloud DCs do not expose their internal networks, so the provider MPLS based VPNs cannot reach the workloads natively. - Many cloud DCs use an overlay to connect their gateways to the workloads inside the DC. There has not been any standard to address the interworking between the Cloud Overlay and the enterprise' existing underlay networks. Another roadblock is the lack of a standard way to express and enforce consistent security policies to workloads that not only use virtual addresses, do not have a port number, but also have a high chance of placement in different locations within the Cloud DC Dunbar, et al. Expires June 5, 2018 [Page 9] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 [RFC8192]. The traditional VPN path computation and bandwidth allocation schemes may not be flexible enough to address the need for enterprises to rapidly connect to dynamically instantiated (or removed) workloads and applications regardless of their location/nature (i.e., third party cloud DCs). 6. Problem with using IPsec tunnels to Cloud DCs As described in the previous section, many Cloud operators expose their gateways for external entities (which can be enterprises themselves) to directly establish IPsec tunnels. If there is only one enterprise location that needs to reach the Cloud DC, an IPsec tunnel is a very convenient solution. However, many medium-to-large enterprises usually have multiple sites and multiple data centers. For workloads and apps hosted in Cloud DCs, multiple sites need to communicate securely with those Cloud workloads and apps. This section documents some of the issues associated with using IPsec tunnels to connect enterprise' sites with Cloud operator's Gateways. 6.1. Complexity of multi-point any-to-any interconnection The dynamic workload instantiated in cloud DC needs to communicate with multiple branch offices and on-premises data centers. Most enterprises need multi-point interconnection among multiple locations, as done by MPLS L2/L3 VPNs. Using IPsec overlay paths to connect all branches & on-premises data centers to cloud DCs require CPEs to manage routing among Cloud DCs gateways and the CPEs located at other branch locations, which can dramatically increase the complexity of the design, possibly at the cost of jeopardizing the CPE performance. The complexity of requiring CPEs to maintain routing among other CPEs is one of the reasons why enterprises migrated from Frame Relay based services to MPLS-based VPN services. MPLS-based VPNs have their PEs directly connected to the CPEs. Therefore, CPEs only need to forward all traffic to the directly attached PEs, which are therefore responsible for enforcing the routing policy within the corresponding VPNs. Even for multi-homed CPEs, the CPEs only need to forward traffic among the directly connected PEs (note: the complexity may vary for IPv6 network). Dunbar, et al. Expires June 5, 2018 [Page 10] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 However, when using IPsec tunnels between CPEs and Cloud DCs, the CPEs need to manage the routing for traffic to Cloud DCs, to remote CPEs via VPN, or directly. 6.2. Poor performance over long distance When enterprise CPEs or gateways are far away from Cloud DC gateways or across country/continent boundaries, performance of IPsec tunnels over the public Internet can be problematic and unpredictable. Even though there are many monitoring tools available to measure delay and various performance characteristics of the network, the measurement for paths over the Internet is passive and past measurements may not represent future performance. Many cloud providers can replicate workloads in different available zones. An App instantiated in a Cloud DC closest to clients may have to cooperate with another App (or its mirror image) in another region or the database server in the on-premises DC. This kind of coordination requires predicable networking behavior/performance among those locations. 6.3. Scaling Issues with IPsec Tunnels IPsec can achieve secure overlay connections between two locations over any underlay networks, e.g., between CPEs and Cloud DC Gateways. If there is only one enterprise location connected to the Cloud gateway, a small number of IPsec tunnels can be configured on-demand between the on-premises DC and the Cloud DC, which is an easy and flexible solution. However, for multiple enterprise locations to reach workloads hosted in cloud DCs, the Cloud DC gateway needs to maintain multiple IPsec tunnels to all those locations (e.g. hub & spoke topology). For a company with hundreds or thousands of locations, there could be hundreds (or even thousands) of IPsec tunnels terminating at the Cloud DC gateway, which is not only very expensive (because Cloud Operators charge based on connections), but can be very processing intensive for the gateway. Many cloud operators only allow a limited number of IPsec tunnels to each customer. Alternatively, you could use a solution like group encryption where a single IPSec SA is necessary at the GW but the drawback here is key distribution and maintenance of a key server etc. Dunbar, et al. Expires June 5, 2018 [Page 11] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 7. Problems of Using SD-WAN to connect to Cloud DCs SD-WAN enables multiple parallel paths between two locations, for example, two CPEs interconnected by a traditional MPLS VPN ([RFC4364] or [RFC4664]) as well as overlay tunnels. The overlay, possibly secured by IPsec tunnels [RFC6071], can traverse over the public Internet using fiber, cable, DSL-based Internet access, Wi- Fi, or 4G/Long Term Evolution (LTE). SD-WAN lets enterprises augment their current VPN network with cost- effective, readily available Broadband Internet connectivity, enabling some traffic offloaded to overlay paths based on traffic forwarding policy (application-based or otherwise), or when the MPLS VPN connection between the two locations is congested, or otherwise undesirable or unavailable. 7.1. SD-WAN among branch offices vs. interconnect to Cloud DCs SD-WAN interconnection of branch offices is not as simple as it appears. For an enterprise with multiple sites, using SD-WAN overlay paths among sites requires each CPE to manage all the addresses that local hosts have the potential to reach, i.e. map internal VPN addresses to appropriate SD-WAN paths. This is similar to the complexity of Frame Relay based VPNs, where each CPE needed to maintain mesh routing for all destinations if they were to avoid an extra hop through a hub router. Even though SD-WAN CPEs can get assistance from a central controller (instead of running a routing protocol) to resolve the mapping between destinations and SD-WAN paths, SD-WAN CPEs are still responsible for routing table maintenance as remote destinations change their attachments, e.g., the dynamic workload in other DCs are de-commissioned or added. Even though originally envisioned for interconnecting branch offices, SD-WAN offers a very attractive way for enterprises to connect to Cloud DCs. The SD-WAN for interconnecting branch offices and the SD-WAN for interconnecting to Cloud DCs have some differences: - SD-WAN for interconnecting branch offices usually have two end- points (e.g. CPEs) controlled by one entity (e.g., a controller or management system operated by the enterprise). Dunbar, et al. Expires June 5, 2018 [Page 12] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 - SD-WAN for interconnecting to Cloud DCs may have CPEs owned or managed by the enterprise and remote end-points being managed or controlled by Cloud DCs (For the ease of description, let's call it asymmetrically managed CPEs). Dunbar, et al. Expires June 5, 2018 [Page 13] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 - Cloud DCs may have different entering points (or devices) with one terminating private direct connect (such as MPLS, or direct line) and other points being the device terminating the IPsec tunnels, as shown in the following diagram. Therefore, the SD-WAN becomes asymmetric. +------------------------+ | ,---. ,---. | | (TN-1 ) ( TN-2)| | `-+-' +---+ `-+-' | | +----|vR1|----+ | | ++--+ | | | +-+----+ | | /Internet\ One path via | +-------+ Gateway +---------------------+ | \ / Internet \ | +-+----+ \ +------------------------+ \ \ +------------------------+ \ | ,---. ,---. | | | (TN-3 ) ( TN-4)| | | `-+-' +--+ `-+-' | | +------+ | +----|vR|-----+ | +------+ CPE | | ++-+ | | +------+ | | +-+----+ | | | / virtual\ One path via IPsec Tunnel | | +-------+ Gateway +-------------------------- + | \ / | | +-+----+ | +------------------------+ | | +------------------------+ | | ,---. ,---. | | | (TN-5 ) ( TN-6)| | | `-+-' +--+ `-+-' | | | +----|vR|-----+ | | | ++-+ | | | | +-+----+ +------+ | | | / \ Via Direct /customer\ | | +-------+ Gateway +----------+ gateway |-----+ | \ / Connect \ / | +-+----+ +------+ +------------------------+ Figure 2: Asymmetric Paths SD-WAN Dunbar, et al. Expires June 5, 2018 [Page 14] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 8. End-to-End Security Concerns for Data Flows When IPsec tunnels from enterprise on-premises CPEs are terminated at the Cloud DC gateway where the workloads or applications are hosted, some enterprises have concerns regarding traffic to/from their workload being exposed to others behind the data center gateway (e.g., exposed to other organizations that have workloads in the same data center). To ensure that traffic to/from workloads is not exposed to unwanted entities, it is necessary to have the IPsec tunnels go all the way to the workload (servers, or VMs) within the DC. 9. Requirements for Dynamic Cloud Data Center VPNs [Editor's note: this section is only a place holder. The requirement listed here are only to stimulate more discussions] In order to address the aforementioned issues, any solution for enterprise VPNs that includes connectivity to dynamic workloads or applications in cloud data centers should satisfy a set of requirements: - The solution should allow enterprises to take advantage of the current state-of-the-art in VPN technology, in both traditional MPLS-based VPNs and IPsec-based VPNs (or any combination thereof) that run over-the-top of the public Internet. - The solution should not require an enterprise to upgrade all their existing CPEs. - The solution should not require either CPEs or routers to support a large number of IPsec tunnels simultaneously. - The solution needs to support easy and fast VPN connections to dynamic workloads and applications in third party data centers, and easily allow these workloads to migrate both within a data center and between data centers. - Allow VPNs to provide bandwidth and other performance guarantees. Dunbar, et al. Expires June 5, 2018 [Page 15] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 - Be a cost-effective solution for enterprises to incorporate dynamic cloud-based applications and workloads into their existing VPN environment. 10. Security Considerations For the most part, we introduce no new security concerns beyond those of existing MPLS based VPNs, which are widely deployed. The one addition to MPLS VPNs is selective use of SD-WAN, which uses IPsec tunnels for the privacy and separation of VPN traffic. Also see Section 8 for a discussion of end-to-end security for data flows. 11. IANA Considerations This document requires no IANA actions. RFC Editor: Please remove this section before publication. 12. References 12.1. Normative References 12.2. Informative References [RFC2735] B. Fox, et al "NHRP Support for Virtual Private networks". Dec. 1999. [RFC8192] S. Hares, et al "Interface to Network Security Functions (I2NSF) Problem Statement and Use Cases", July 2017 [ITU-T-X1036] ITU-T Recommendation X.1036, "Framework for creation, storage, distribution and enforcement of policies for network security", Nov 2007. [RFC6071] S. Frankel and S. Krishnan, "IP Security (IPsec) and Internet Key Exchange (IKE) Document Roadmap", Feb 2011. Dunbar, et al. Expires June 5, 2018 [Page 16] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 [RFC4364] E. Rosen and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks (VPNs)", Feb 2006 [RFC4664] L. Andersson and E. Rosen, "Framework for Layer 2 Virtual Private Networks (L2VPNs)", Sept 2006. 13. Acknowledgments Many thanks to Ignas Bagdonas, Mehmet Toy, Michael Huang, Liu Yuan Jiao, Katherine Zhao, and Jim Guichard for the discussion and contributions. Dunbar, et al. Expires June 5, 2018 [Page 17] Internet-Draft Underlay to Cloud Overlay Stitching March 2018 Authors' Addresses Linda Dunbar Huawei Email: Linda.Dunbar@huawei.com Andrew G. Malis Huawei Email: agmalis@gmail.com Christian Jacquenet France Telecom Rennes, 35000 France Email: Christian.jacquenet@orange.com Mehmet Toy Verizon One Verizon Way Basking Ridge, NJ 07920 Email: mehmet.toy@verizon.com Dunbar, et al. Expires June 5, 2018 [Page 18]