Only traffic that is destined for other networks is moved to a higher layer. The benefit of dividing a flat network into smaller, more manageable blocks is that local traffic remains local. Hierarchical models apply to both LAN and WAN design. This helps the network designer and architect to optimize and select the right network hardware, software, and features to perform specific roles for that network layer. Each layer, or tier, in the hierarchy provides specific functions that define its role within the overall network. Network Hierarchy (1.1.2.1)Įarly networks were deployed in a flat topology as shown in Figure 1-2.Ī hierarchical network design involves dividing the network into discrete layers. This topic discusses the three functional layers of the hierarchical network model: the access, distribution, and core layers. To meet these fundamental design goals, a network must be built on a hierarchical network architecture that allows for both flexibility and growth. Flexibility: The ability to modify portions of the network, add new services, or increase capacity without going through a major forklift upgrade (i.e., replacing major hardware devices).Abnormal conditions include hardware or software failures, extreme traffic loads, unusual traffic patterns, denial-of-service (DoS) events, whether intentional or unintentional, and other unplanned events. Normal conditions include normal or expected traffic flows and traffic patterns, as well as scheduled events such as maintenance windows. Resiliency: The network must remain available for use under both normal and abnormal conditions.Cisco has identified several modules, including the enterprise campus, services block, data center, and Internet edge. Modularity: By separating the various functions that exist on a network into modules, the network is easier to design.It breaks the complex problem of network design into smaller and more manageable areas. Hierarchy: A hierarchical network model is a useful high-level tool for designing a reliable network infrastructure.Regardless of network size or requirements, a critical factor for the successful implementation of any network design is to follow good structured engineering principles. Structured Engineering Principles (1.1.1.2) The Cisco Certified Design Associate (CCDA®) is an industry-recognized certification for network design engineers, technicians, and support engineers who demonstrate the skills required to design basic campus, data center, security, voice, and wireless networks. The sample high-level topology diagram is for a large enterprise network that consists of a main campus site connecting small, medium, and large sites. For instance, consider the example in Figure 1-1. There are many variables to consider when designing a network. For example, the networking infrastructure needs of a small organization with fewer devices will be less complex than the infrastructure of a large organization with a significant number of devices and connections. Network designs vary depending on the size and requirements of the organizations. Large network: Provides services for 1,000+ devices.Medium-size network: Provides services for 200 to 1,000 devices.Small network: Provides services for up to 200 devices.When discussing network design, it is useful to categorize networks based on the number of devices serviced: Enterprise Network Campus Design (1.1.1)Īn understanding of network scale and knowledge of good structured engineering principles is recommended when discussing network campus design. In this section, you will learn about the access, distribution, and core layers and their role in the hierarchical network model. The Cisco hierarchical (three-layer) internetworking model is an industry wide adopted model for designing a reliable, scalable, and cost-efficient internetwork. Hierarchical Network Design Overview (1.1)
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