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Chapter 2: Analyzing Small- to Medium-Sized Business NetworksThis chapter introduces the role that a Cisco Certified Design Associate (CCDA) will play in designing networks, and presents a framework for you to use in your designs.
Role of the Cisco Certified Design AssociateYour role as a Cisco Certified Design Associate is to be a network design consultant. You will act like an architect, building comprehensive designs that solve your customer's internetworking problems and provide the required functionality, performance, and scalability. In the same way that an architect designs a building or house for a client, you will develop blueprints for an overall internetwork design, as well as component plans for various pieces of the internetwork.
CiscoFusionCisco has developed an integrated network architecture, called CiscoFusion. With the CiscoFusion architecture, multiple networking technologies operating at different networking layers, can provide the best capabilities to handle different networking issues.
Many of your customers may already be aware of the recent internetworking trend toward an integrated view of networking technologies. As a Cisco Certified Design Associate, you will be uniquely positioned to produce network designs, based on CiscoFusion, that meet the needs of state-of-the-art networks that integrate Layer 2, Layer 3, and Asynchronous Transfer Mode (ATM) services. For example, the intelligent networking services associated with Layer 3 can be combined with the cost-effective, high-capacity services provided by Layer 2 in both local-area networks and wide-area networks.
Evolution of Layer 2 and Layer 3 ServicesLayer 2, also known as the data link layer, operates within a specific local-area network (LAN) or wide-area network (WAN) segment. In the last two years, LANs have been revolutionized by the exploding use of switching at Layer 2. Companies are replacing hubs with switches at a quick pace. LAN switches provide performance enhancements for new and existing data networking applications by increasing bandwidth and throughput for workgroups and local servers.
Layer 3, also known as the network layer, operates between and across segments. Protocols such as Internet Protocol (IP), Internetwork Packet Exchange (IPX), and AppleTalk's Datagram Delivery Protocol (DDP) operate at Layer 3. In WANs, Layer 3 networking allows businesses to build global data networks. As an example, the global Internet is based on Layer 3 IP technology.
Layer 3 networking, implemented with routing, interconnects the switched workgroups and provides services such as security, Quality of Service (QoS) options, and traffic management. Routing provides the control needed to build functional, scalable networks.
NOTE Traditionally, Layer 2 switching has been provided by LAN switches, and Layer 3 networking has been provided by routers. Increasingly, these two networking functions are being integrated into one common platform.
There will still be a wide range of platforms providing different performance and capacity ranges for each networking function, but users will gain fundamental benefits from integration of the layers. Users will be able to reduce the number of networking devices that need to be purchased, installed, supported, and serviced. In addition, users will be able to efficiently apply Layer 3 services, such as security and QoS capabilities, to specific individual users and applications.
Mirroring the integration of Layer 3 networking technology into LAN switching devices, WAN switching equipment likely will increasingly incorporate Layer 3 networking capabilities. As traditional Layer 3 routers gain support for higher capacity and bandwidth, the integration of Layer 2 technologies will enable routers to achieve optimum levels of performance, port density, and cost effectiveness.
Figure 2-1 shows how Layer 2 and Layer 3 switching can be used to facilitate communications between Client X and Server Y, with or without routing.
When To Use Layer 2 or Layer 3 FunctionalityThe decision to use Layer 2 or Layer 3 functionality in a network design depends on which problems you are trying to solve for your customer. These problems can be any of the following:
- Media problems
- Protocol problems
- The need to transport large payloads
Media ProblemsMedia problems occur when too many devices contend for access to a LAN segment, causing an excessive number of collisions on Ethernet networks and long waits for the token on Token Ring or FDDI networks. The level of contention can be estimated by examining network utilization and, in the case of Ethernet, the collision rate. Media contention problems are obvious from complaints from users about slow response time and difficulties accessing services.
Protocol ProblemsProblems are caused by protocols that do not scale well. For example, some protocols send too many broadcasts. The number of broadcasts becomes excessive when there are too many clients looking for services, too many servers announcing services, and too many bridge protocol data unit (BPDU) frames. Protocol problems occur when a protocol that was designed for small workgroups is being used for larger networks or for a network that has outgrown the capability of the protocol. The protocol no longer provides the scale required for the business.
Example scenarios of when protocol problems can result include the following:
- Network layer addressing issues, including running out of addresses.
- The requirement to use variable-length subnet masks.
- The need for physically discontiguous subnets.
- The need for a private address space.
The Need to Transport Large PayloadsThe need to transport large payloads, such as multicast video, can require much more bandwidth than is available on a customer's network or backbone. Multicast video will need more bandwidth than standard data. Multicast video may also require support for low and predictable latency.
A Framework for Solving Small- to Medium-Sized Business Network ProblemsTo help reduce the complexity associated with identifying and analyzing customer problems and designing solutions, Cisco developed a basic framework into which most customer problems fit. The small- to medium-sized business solutions framework is represented as a triangle, as shown in Figure 2-2.
As illustrated in Figure 2-2, use the following simple rules when designing solutions to customer problems:
- If the problems involve media contention, use LAN switching.
- If the problems are protocol related -- for example, resulting in an excessive number of broadcasts -- use routing.
- If the customer needs to transport payloads that require high bandwidth, use Fast Ethernet switching. In large networks where high bandwidth and predictable low latency are required, consider ATM switching.
SummaryNow that you have an understanding of the problems that customers may encounter on their networks and potential solutions available to you in a network, you are ready to start the network design process.
In the next part of the book, you will learn how to identify customer needs. While reading the chapter content and performing the chapter exercises, keep in mind the small- to medium-sized business solutions framework identified in this chapter to help you understand typical customer problems. At the end of Part III of this book, you will be able to determine whether the needs are related to media, protocols, or bandwidth.