What's the Purpose of the Network?

As a network designer, understanding the purpose and goal of the network is critical to properly designing it. This sample chapter from Cisco Certified Design Expert (CCDE 400-007) Official Cert Guide maps to the CCDE v3.0 Unified Exam Topics Section 4.0, "Service Design," and covers the service design topics—from business applications and service models, to the cloud and data management—you need to meet business objectives.

This chapter covers the following topics:

• Business Applications: This section covers business applications and the associated network design elements for them.

• Service Models: This section covers the different service models, how to leverage them, and what the network design characteristics are for each model.

• The Cloud: This section covers the cloud in all its forms and the associated network design elements.

• Data Management: This section covers data and the data management methodologies that will help every network designer make better design decisions.

What’s the purpose of the network? Why do we need a network? Why is a network there in the first place? These questions should always be at the top of your mind as network designer because understanding the purpose and goal of the network is critical to properly designing it.

As we answer these questions, a technical (and potentially a tactical) answer is that the network’s purpose is to get data from point A to point B in the right amount of time. This is a generally good answer to these questions, and usually network engineers, not network designers, can easily identify.

From a network design perspective, we need to take this answer a step further. Why is the network transferring data in the first place? To meet the business outcomes and objectives…to make the business successful!

Businesses have become so reliant on networks that the required availability of the network and its associated services has to be designed at an extremely high level. This is similar to what transpired with the plain old telephone service (POTS) network. It became so relied upon that the overall availability had to be designed at an extremely high level.

There is a shift in the network, as discussed in the previous chapters, toward a service-focused network. When we talk about services in this context, we are talking about applications, service models, the cloud in all its forms, and data.

This chapter covers the following “CCDE v3.0 Unified Exam Topics” section:

• 4.0 Service Design

“Do I Know This Already?” Quiz

The “Do I Know This Already?” quiz allows you to assess whether you should read this entire chapter thoroughly or jump to the “Exam Preparation Tasks” section. If you are in doubt about your answers to these questions or your own assessment of your knowledge of the topics, read the entire chapter. Table 3-1 lists the major headings in this chapter and their corresponding “Do I Know This Already?” quiz questions. You can find the answers in Appendix A, “Answers to the ‘Do I Know This Already?’ Quizzes.”

Table 3-1 “Do I Know This Already?” Section-to-Question Mapping

1. Which of the following options is the correct application model for the statement “This is the simplest application model and it is equivalent to running the application on a personal computer”?

1. 3-tier model

2. Single-server model

3. 2-tier model

4. SaaS

2. Which of the following application models is like the client/server architecture?

1. 3-tier model

2. Single-server model

3. 2-tier model

4. SaaS

3. Which of the following application models has web, application, and database layers?

1. 3-tier model

2. Single-server model

3. 2-tier model

4. SaaS

4. Which service model is best used when a business requires full control of all components within an application?

1. PaaS

2. IaaS

3. SaaS

4. On-premises

5. Which service model is best for application developers?

1. PaaS

2. IaaS

3. SaaS

4. On-premises

6. Which service model is best if a business wants complete control over its virtual infrastructure but also wants to operate on a pay-as-you-go basis?

1. PaaS

2. IaaS

3. SaaS

4. On-premises

7. Which service model is best if a business wants an application to run with ensured availability but doesn’t want the headache of managing the application in any form?

1. PaaS

2. IaaS

3. SaaS

4. On-premises

8. Which cloud type has the highest cost?

1. Hybrid cloud

2. Private cloud

3. Multi-cloud

4. Public cloud

9. Which cloud type is best if a business wants the most control possible?

1. Hybrid cloud

2. Private cloud

3. Multi-cloud

4. Public cloud

10. Which cloud type is best if a business wants to ease into a cloud computing environment over a long period of time?

1. Hybrid cloud

2. Private cloud

3. Multi-cloud

4. Public cloud

11. Which option is the proper data management pillar for the definition “The planning of all aspects of data management”?

1. Data quality

2. Data governance

3. Data architecture

4. Data security

Foundation Topics

Business Applications

The network is the information highway for the business applications of today, and for the business to be successful, these applications must be able to properly communicate as required between users, devices, data, databases, and other application components.

Application Models

Network designers need to understand how an application is built to properly design the network for that application. The following are the different application models being leveraged today and their associated design elements that you need to know as a network designer:

• Single-server model: This is the simplest application model and it is equivalent to running the application on a personal computer. All of the required components for an application to run are on a single application or server.

• 2-tier model: This application model is like the client/server architecture, where communication takes place between client and server. In this model, the presentation layer or user interface layer runs on the client side while the dataset layer gets executed and stored on the server side.

  There is no intermediate layer (aka application layer) in between client and server.

• 3-tier model: This application model is the most common at the time of writing. This model has three tiers or layers:

  • Presentation: This is the front end of the application that all end users access. This is how an end user sees and interacts with the application. This is often called the web tier or GUI tier of the application. The main function of this layer is to translate tasks and results to something the end user can understand.

  • Intermediate: This is the layer where all of the application’s functions and logic occur. This layer processes tasks, functions, and commands, makes decisions and evaluations, and performs calculations. It also is how data is moved between the presentation (web/GUI) and database layers. This is often referred to as the application or logic layer of the application.

  • Database: Here information is stored and retrieved from a database. The information is then passed back to the intermediate (application) layer and then eventually back to the end user.

Breaking elements of an application into different layers like the n-tier architectures allows network designers to properly design the network for each tier or layer individually. Each layer may need its own load balancing, applying source NAT, DNS, source routing, and traffic engineering design. This means more work from a network design perspective but a better purpose-built environment for each tier with all associated elements needed, which allows the different application layers to scale out as needed.

Table 3-2 shows the different network design elements for each layer of the 3-tier model and provides leading questions to ask to help elicit the information needed to make a proper design.

Table 3-2 3-Tier Application Model Network Design Elements

Application Constraints and Requirements

As a network designer, there are a number of common application constraints and requirements that you should be aware of. These are topics that a network designer should be asking about as a network is being designed to support an application. This is by no means an all-inclusive list.

• Multicast: Usually leveraged between a cluster of servers to keep data synchronized, such as a backend database replication architecture, or as a transport mechanism for data streaming applications like IPTV and real-time stock market updates for day traders. In these situations, not having multicast breaks the application in question.

• Layer 2 extension: Probably one of the most common network design requirements after an application has completed its development process. As the application is being deployed, it is quickly identified that the application servers, maybe in a 3-tier model, do not communicate outside of their Layer 2 segments. Now it’s the network designer’s job to provide Layer 2 extension options that allow the application to properly function. This leads to bad network designs with large Layer 2 fault domains that are generally unreliable. Even though these are bad network design options from a network design perspective, they do solve the application requirement and thus they make the business successful. If there is a requirement to extend Layer 2, some of these limitations can be mitigated with overlay technologies while still allowing for an expanded Layer 2 environment.

• Hardcoded items: Thankfully, we are seeing issues with hardcoded items in the code less frequently today. They do happen, and that’s why network designers need to know about them. These hardcoded items bring a security element into the mix with compliance controls and overall security requirements for the application in question. From a network design perspective, though, how do we handle hardcoded IP addresses in the code? The simplest answer is to not allow hardcoded items in the code, but what do you do as a network designer when it does happen? This is where solutions like Network Address Translation (NAT), traffic engineering, and source routing can be leveraged to help mitigate this issue.

• High availability: How an application is designed for high availability has a large impact on the network supporting that application. Is the application in multiple locations, such as geographically separated data centers? If so, how is the application data synchronized between these locations? How do end users access the applications in each location? Is one location preferred over the other at all times (active/standby), or can the application be accessed from either location at any time (active/active)? What about the load-balancing options for the application? Is it leveraging DNS load balancing or a physical load balancer? Does the application require the use of source NAT (SNAT) between its different application layers? There are so many network design–related questions that we have to ask and answer to properly facilitate the creation of a network design that makes the application successful.

When creating a network design that’s goal is to make an application successful, it really comes down to the applications, services, and so forth being created incorrectly. Network designers have been forced to provide band-aid solutions like Layer 2 extension options because of these problems. This is most definitely not solving the true issue of proper application development. We simply extend Layer 2 as a short-term solution that ends up becoming a permanent one. This is similar to hardcoding IP addresses and hostnames in an application’s code. Network designers always have to provide bad network design options because of these application issues.

To solve these issues, a network designer and a security specialist should be part of the team that builds and reviews an application, to ensure network design and security controls are being properly considered in the application. It’s not fair to expect an application developer to know and understand the details of network design or security; network designers have to help them, teach them, and show them.

If we want to change these situations with the plan to limit them from happening, we need to be a part of the creation process so we can explain the reasons to the business at those critical steps. The business doesn’t know what a network designer knows. A network designer can tell the business why they shouldn’t rely on a Layer 2 extension for the application, why they shouldn’t hardcode IP addresses, hostnames, usernames, and passwords in code, and why they should ensure security controls are implemented during the creation process.

In the end, it all comes back to business decisions and the respective trade-offs.

Service Models

We highlighted the different application models for how an application can be created earlier. This section takes that discussion a step further by covering the different service models that can be leveraged for the application. These service models determine where the application is located and what elements of the application are owned and managed by the business. The following are the most common service models:

• On-premises: On-premises is the service model where a business owns and manages an application. A business will procure all of the infrastructure required to run the service and then fully manage, maintain, and operate it. In some situations, the management is outsourced but the infrastructure is procured and owned by the business.

• Software as a Service (SaaS): SaaS is where a vendor makes its software available to users, usually for a monthly or annual subscription service fee.

• Platform as a Service (PaaS): PaaS is where a vendor provides hardware and software tools, and people use these tools to develop applications. PaaS users tend to be application developers.

• Infrastructure as a Service (IaaS): IaaS is a pay-as-you-go service model for storage, networking, and virtualization—all of a business’s infrastructure needs. IaaS gives users cloud-based alternatives to on-premises infrastructure, so businesses can avoid investing in expensive onsite resources.

Table 3-3 shows the comparison between these service models.

Table 3-3 Service Model Comparison

The Cloud

When a business starts planning to leverage cloud in any form, there are three use cases that network designers should consider throughout the design process:

• Securely extending a private network to a single or multiple public cloud environments: Includes multiple clouds (for example, multiple Amazon Web Services [AWS] and Azure), multiple regions in a cloud, or multiple VPCs in a cloud; VPN; multi-cloud and multi-VPC connectivity; scaling; and performance optimization of transit VPC. Also supports extending data centers into the cloud and enabling direct branch-to-cloud connectivity.

• Optimizing data center and branch connectivity performance to cloud IaaS and SaaS: Includes best path to a destination, cloud segmentation, monitoring to assure the best performance, visibility into traffic going to applications, and traffic shaping/Quality of Service (QoS). Also supports extending data centers into the cloud and enabling direct branch-to-cloud connectivity.

• Securing access to the Internet and SaaS from the branch: Includes connecting and protecting branch office users directly to the multi-cloud environment using Direct Internet Access (DIA) and properly securing them.

Cloud Connectivity Models

When businesses start to leverage cloud in any form, be it public, private, hybrid, or multi-cloud, how the business is going to connect to cloud environments is a topic for a network designer to address. There are multiple options, each with its own pros and cons.

Direct Cloud Access

Direct cloud access (DCA) allows a remote site to access SaaS applications directly from the Internet and through dedicated private connections. The cloud permits only the designated application traffic to use the directly connected Internet transport securely, while all other Internet-bound traffic takes the usual path, which could be through a regional hub, a data center, or a carrier-neutral facility (CNF). This feature allows the remote site to bypass the latency of tunneling Internet-bound traffic to a central site, subsequently improving the connectivity to the prioritized SaaS application; this feature is commonly referred to as Direct Internet Access (DIA). The edge router chooses the most optimal Internet path for access to these SaaS applications. Different applications could traverse different paths because the path selection is calculated on a per-application basis.

If any SaaS application path becomes unreachable or its performance score falls below an unacceptable level, the path is removed as a candidate path option. If all paths cannot be path candidates because of reachability or performance, then traffic to the SaaS application follows the normal, routed path. Figure 3-1 illustrates a remote site using DIA to access SaaS applications

Cloud Access Through a Gateway (Cloud Access Point)

Many businesses do not use DIA at the branch office, because either their sites are connected only by private providers (MPLS, VPLS, etc.) or centralized policy or security requirements do not permit it. They may use data centers, regional hubs, or even CNFs to enable Internet connectivity. In this case, SaaS traffic is tunneled to the best-performing gateway site, where it is subsequently routed to the Internet to reach the requested SaaS application service.

Figure 3-2 shows how cloud access can be achieved through a gateway in a data center or a cloud access point (CAP). A branch office tunnels SaaS traffic to a gateway location and then uses the Internet at the gateway location to access the SaaS application.

Hybrid Approach

It is possible to have a combination of DIA and client/gateway sites. When defining both DIA and gateway sites, SaaS applications can use either the DIA exits of the remote site or the gateway sites for any given application, depending on which path provides the best performance. DIA sites are, technically, a special case of a client site, but the Internet exits are local instead of remote.

Cloud Types

When selecting a cloud solution, there are a number of different types to choose from, each with its own associated benefits and limitations:

• Private cloud: A private cloud consists of cloud computing resources used by one business. This cloud environment can be located within the business’s data center footprint, or it can be hosted by a cloud service provider (CSP). In a private cloud, the resources, applications, services, data, and infrastructure are always maintained on a private network and all devices are dedicated to the business.

• Public cloud: A public cloud is the most common type of cloud computing. The cloud computing resources are owned and operated by a CSP. All infrastructure components are owned and maintained by the CSP. In a public cloud environment, a business shares the same hardware, storage, virtualization, and network devices with other businesses.

• Hybrid cloud: A hybrid cloud is the use of both private and public clouds together to allow for a business to receive the benefits of both cloud environments while limiting their negative impacts on the business.

• Multi-cloud: Multi-cloud is the use of two or more CSPs, with the ability to move workloads between the different cloud computing environments in real time as needed by the business.

Table 3-4 compares the different cloud types in relation to each other based on various characteristics.

Table 3-4 Cloud Types Detailed Comparison

Cloud-Agnostic Architecture

A cloud-agnostic architecture is when there are no vendor specific features and functionality that are proprietary. It is focused on leveraging the same cloud capabilities across the different cloud providers no matter what vendor it is. When looking at cloud service providers and migrating applications to the cloud, there are three primary focus points that should be leveraged within a cloud-agnostic architecture:

• Portability: Moving to the cloud inherently provides a level of portability, but if not carefully architected, applications and services can lose their portability as they get locked into specific CSP services. Portability here specifically allows mobility between different CSPs with a proper abstraction layer.

• Abstraction: Leveraging an abstraction layer within the cloud architecture allows for a decoupling from the underlying cloud-specific platform functionality, which provides a direct cost reduction and an increase in flexibility. For example, using this abstraction layer to seamlessly invoke the same cloud capability between cloud provider one and cloud provider two, when there are different mechanisms and processes to do so. In addition, this same capability could be proprietary, but using this abstraction layer mitigates a potential hardcoded proprietary service call.

• Interoperability: Developing applications and services with cloud interoperability as a key priority will not be tied to a specific cloud feature set. This allows for these applications and services to leverage different cloud platforms without major redevelopment or changes. This specifically allows for a cloud-agnostic approach.

To achieve a cloud-agnostic architecture, network designers should consider adopting the following practices.

Decoupling

There are two perspectives to think about for decoupling. First, all applications should be designed to be inherently decoupled from the underlying cloud platform they are on. This can be accomplished by leveraging service-oriented architecture (SOA), which is discussed in detail a bit later in this chapter. Second, all cloud components should be decoupled from the applications that leverage them.

Containerization

All applications should follow a containerized architecture. This is critical for cloud applications as well as on-premises data center applications. Ensuring all applications are developed with containerization in mind allows for real cloud adoption and portability. Container technology helps decouple applications from the cloud-specific environment, which provides an abstraction layer away from any of the CSP dependencies. The goal is to ensure that it is relatively easy to migrate applications between different cloud vendors if the mission requires it. Cloud containerized architectures is a topic that is covered in detail in an upcoming section.

Agnostic Versus Proprietary Cloud Services

Each cloud service provider is different and has unique services, with its own avenues to provision them to customers. There is a need to provide a mechanism to differentiate where these specific services interact with applications while also allowing for the standardization of agnostic services. Figure 3-3 shows how to delineate from an architecture perspective between cloud-agnostic services and cloud-proprietary services. This is how you should plan to migrate applications to a CSP.

Service-Oriented Architecture

To ensure a successful cloud-agnostic architecture, incorporating the software design service-oriented architecture (SOA) is hyper-critical. SOA is a style of software design where services are provided to other parts of an application component themselves. This is accomplished through network communication protocols. The underlying principles are vendor and technology agnostic. In SOA, services communicate with other services in two ways. The first way is to simply pass data between the different services. The second way is to logistically coordinate an activity event between two or more services. There are many benefits to SOA:

• Code can be created so that it is reusable, which cuts down on time spent in the development process.

• Developers can leverage multiple coding languages with SOA because it uses a central interface, which allows for flexibility and scalability within the software development cycle.

• With SOA, a standard communication process is created that allows systems to function on their own and communicate effectively between them.

• SOA is much more scalable, limiting client-server interaction, which allows for a direct increase in efficiency.

Cloud Containerized Architecture

Containerization is a large part of a cloud-agnostic architecture. Figure 3-4 shows the progression from a traditional on-premises deployment to a containerized cloud deployment.

Traditional Deployment Architecture

Traditionally, organizations and companies ran applications on physical servers. You could deploy multiple applications on the same physical server, but there was no way to properly restrict resources or set up controls to govern application guidelines. Because of these issues, there were a number of allocation and performance issues. Most of the time, each physical server was dedicated to a single application because of these limitations. This increased cost and resources and limited overall scalability.

Virtualization Deployment Architecture

Virtualization allows for multiple virtual machines (VMs) to be deployed on a single physical server. Each VM is isolated from other applications with its own resources and security controls allocated to it individually. Virtualization allows for better utilization of resources on a physical server and scales better because applications (VMs) can be added and removed as needed depending on the needed resources. Each VM runs all components that a physical server would run, such as the application and the operating system.

Container Deployment Architecture

Containers are similar to VMs but have less stringent isolation controls that allows them to share the operating system among other applications. Because of this, containers are lightweight. A container has its own file system, shares CPU time, memory, process space, and more. Because containers are decoupled from the underlying infrastructure, they are moveable between different fabrics as needed by the underlying business requirements.

Containers provide a number of benefits:

• Agile application creation and deployment (CI/CD)

• Separation of responsibilities between development and operational tasks

• Real-time application-level health analytics

• Standardization and consistency across all environments and enclaves

• Real-time distribution with the capability to port into other operating systems and locations as required

• Increased overall predictability of application performance and requirements

• Increased resource efficiency

Cloud Application Strategy

As a business readies its business lines of efforts and their respective applications for migration to the cloud, it is highly recommended that the business incorporate an application assessment process. As part of this process an application assessment team should be created with the following roles and purposes:

• Line of business owner: The business stakeholder for this application. They understand the application’s business role and impact. They also understand the implications of this application and can appropriate business resources and priorities to this effort.

• Security specialist, compliance auditor: The security team member in charge of the security controls, compliance regulations, and auditing of code. These are all critical roles that will direct decisions and actions from a risk management perspective for this application.

• Application owner, application developer: The software engineering member responsible for this application. Creates code, modifies current code, and drives associated technical requirements for the application.

• Network engineer, network designer, network architect: Facilitates the network resources to properly service the application based on the different requirements from the line of business owner, security specialist, and application owner.

Each application will have different requirements as it’s being reviewed in this process. The team will need to properly identify what the application is dependent on and make appropriate decisions to ensure the application is ready for the migration to the cloud environment.

The application assessment team will document in an application binder (or run book) everything that is discovered, decided on, and implemented for this application. The application binder should include all requirements and where they originated from; all security controls and regulatory standards that this application must comply with; and where the application is in the migration process and what is needed for it to be successful.

Data Management

Data is the most critical resource that all other resources will be leveraging. We have to manage all data effectively, accurately, and securely so that these additional resources can properly leverage that data with ensured integrity, availability, and confidentiality. Data management in essence lays the foundation for data analytics. Without good data management, there will be no data analytics. Data management can be broken down into 11 pillars:

1. Data governance: The planning of all aspects of data management. This includes availability, usability, consistency, integrity, and security of all data within the organization.

2. Data architecture: The overall structure of an enterprise’s data and how it fits into the enterprise architecture.

3. Data modeling and design: The data analytics and the corresponding analytics systems. This includes the designing, building, testing, and ongoing maintenance of these analytics systems.

4. Data storage and operations: The physical hardware used to store and manage the data within the enterprise.

5. Data security: Encompasses all security requirements, controls, and components to ensure the data is protected and accessed only by authorized users.

6. Data integration and interoperability: The transformation of data into a structured form to be leveraged by other systems and resources.

7. Documents and content: All forms of unstructured data and the work necessary to make it accessible to the structured databases.

8. Reference and master data: The process of managing data in a way that allows it to be redundant, and if there are any errors or mistakes that can be normalized by standard values.

9. Data warehousing and business intelligence: Involves the management and application of data for analytics and business decision making.

10. Metadata: Involves all elements of creating, collecting, organizing, and managing metadata (i.e., data that references other data).

11. Data quality: Involves the practices of data monitoring to ensure the integrity of the data being delivered is maintained.

For a true data management model, all of these pillars need to be included. Without one of these pillars, there is an area of data management that is not being addressed. For example, if there isn’t a solution for metadata management, the business loses the ability to easily categorize data. Without data quality being ensured, all data is at risk and the analytics of that data becomes useless.

Summary

What is the purpose of the network? To ensure business success! This chapter went into great detail on how a network designer can accomplish this.

This chapter covered how businesses rely heavily on the network and the corresponding services and applications riding on it. This chapter also covered application and service models, showing how the location and architecture of the application or service directly affect the required network design elements. In addition, this chapter highlighted the multitude of cloud options and the associated advantages of each option. This chapter highlighted the preference for agnostic cloud services over proprietary cloud services, to ensure a business doesn’t lock itself into a specific cloud service provider, and how adopting a service-oriented architecture can be beneficial to the business. Last but not least, this chapter gave a quick overview of the importance of data and data management by highlighting the 11 data management pillars. Ensuring the confidentiality, integrity, and availability of a business’s data is paramount to the business’s success. If a business’s data is compromised, it can no longer make valid decisions on that data, which handicaps the business until the data is fixed.

Reference

Al-shawi, Marwan, CCDE Study Guide (Cisco Press, 2015)

Exam Preparation Tasks

As mentioned in the section “How to Use This Book” in the Introduction, you have a couple of choices for exam preparation: the exercises here, Chapter 18, “Final Preparation,” and the exam simulation questions in the Pearson Test Prep Software Online.

Review All Key Topics

Review the most important topics in this chapter, noted with the Key Topic icon in the outer margin of the page. Table 3-5 lists a reference of these key topics and the page numbers on which each is found.

Table 3-5 Key Topics for Chapter 3

Complete Tables and Lists from Memory

Print a copy of Appendix D, “Memory Tables” (found on the companion website), or at least the section for this chapter, and complete the tables and lists from memory. Appendix E, “Memory Tables Answer Key,” also on the companion website, includes completed tables and lists to check your work.

Define Key Terms

Define the following key terms from this chapter and check your answers in the glossary:

single-server model

2-tier model

3-tier model

web tier

application tier

database tier

on-premises

Software as a Service (SaaS)

Platform as a Service (PaaS)

Infrastructure as a Service (IaaS)

carrier-neutral facility (CNF)

cloud access point (CAP)

private cloud

public cloud

hybrid cloud

multi-cloud