Chapter Description

This thing introduces network architecture concepts, principles, models, and also architectures. It covers the benefits the are acquired by using a systematic architecture approach.

From the Book


Connecting Networks Companion overview


Hierarchical Network style Overview (1.1)

The Cisco ordered (three-layer) internetworking version is an industry large adopted version for creating a reliable, scalable, and also cost-efficient internetwork. In this section, you will learn about the access, distribution, and core layers and also their role in the ordered network model.

You are watching: Which of the following benefits does a hierarchical network provide?

Enterprise Network Campus style (1.1.1)

An knowledge of network scale and knowledge of an excellent structured design principles is recommended when discussing network campus design.

Network requirements (

When mentioning network design, the is beneficial to categorize networks based upon the variety of devices serviced:

Small network: provides services for as much as 200 devices.Medium-size network: gives services for 200 to 1,000 devices.Large network: gives services for 1,000+ devices.

Network designs vary depending upon the size and requirements that the organizations. Because that example, the networking facilities needs that a tiny organization v fewer devices will it is in less complicated than the framework of a huge organization through a far-reaching number that devices and connections.

There are many variables to think about when making a network. For instance, consider the example in number 1-1. The sample high-level topology chart is for a huge enterprise network that consists of a main campus site connecting small, medium, and big sites.


Figure 1-1 huge Enterprise Network Design

Network architecture is an expanding area and requires a good deal that knowledge and also experience. The will of this ar is to introduce typically accepted network style concepts.


The Cisco Certified design Associate (CCDA®) is one industry-recognized certification because that network style engineers, technicians, and support designers who show the an abilities required to design basic campus, data center, security, voice, and wireless networks.

Structured design Principles (

Regardless that network dimension or requirements, a an important factor for the successful implementation of any kind of network style is to follow good structured engineering principles. These values include

Hierarchy: A ordered network design is a useful high-level device for creating a trusted network infrastructure. It breaks the complex problem that network design into smaller sized and more manageable areas.Modularity: by separating the various functions that exist on a network into modules, the network is much easier to design. Cisco has determined several modules, consisting of the companies campus, solutions block, data center, and also Internet edge.Resiliency: The network need to remain accessible for use under both normal and also abnormal conditions. Normal conditions include normal or expected traffic flows and traffic patterns, and scheduled events such as maintain windows. Abnormal conditions include hardware or software program failures, excessive traffic loads, unusual website traffic patterns, denial-of-service (DoS) events, even if it is intentional or unintentional, and other unplanned events.Flexibility: The ability to modify parts of the network, add new services, or boost capacity there is no going with a major forklift upgrade (i.e., replacing major hardware devices).

To satisfy these fundamental design goals, a network have to be constructed on a ordered network style that permits for both flexibility and growth.

Hierarchical Network architecture (1.1.2)

This subject discusses the three functional layers of the hierarchical network model: the access, distribution, and also core layers.

Network hierarchy (

Early networks were deployed in a flat topology as displayed in number 1-2.


Figure 1-2 flat Switched Network

Hubs and also switches were added as an ext devices required to be connected. A level network design detailed little opportunity to regulate broadcasts or to filter undesirable traffic. As an ext devices and also applications were added to a flat network, an answer times degraded, do the network unusable.

A better network design method was needed. For this reason, organizations now usage a ordered network architecture as shown in figure 1-3.


Figure 1-3 ordered Network

A hierarchical network style involves splitting the network into discrete layers. Every layer, or tier, in the power structure provides particular functions that define its role within the in its entirety network. This help the network designer and architect to optimize and select the best network hardware, software, and features to perform particular roles for the network layer. Hierarchical models apply to both LAN and WAN design.

The advantage of splitting a level network right into smaller, much more manageable block is that neighborhood traffic continues to be local. Just traffic that is destined for other networks is relocated to a higher layer. Because that example, in number 1-3 the flat network has actually now been divided into three different broadcast domains.

A usual enterprise ordered LAN campus network architecture includes the following three layers:

Access layer: offers workgroup/user access to the networkDistribution layer: offers policy-based connectivity and controls the boundary in between the accessibility and core layersCore layer: Provides quick transport in between distribution switches in ~ the companies campus

Another sample three-layer ordered network architecture is shown in number 1-4. Notice that each structure is utilizing the same ordered network model that consists of the access, distribution, and core layers.


Figure 1-4 Multi building Enterprise Network Design


There room no pure rules for the method a campus network is physical built. While the is true that many campus networks are built using 3 physical tiers the switches, this is not a strictly requirement. In a smaller sized campus, the network could have two tiers of switches in i beg your pardon the core and also distribution elements are merged in one physical switch. This is referred to as a fell down core design.

The access Layer (

In a LAN environment, the access layer emphasize grants end devices accessibility to the network. In the WAN environment, that may provide teleworkers or far sites access to the that company network throughout WAN connections.

As displayed in number 1-5, the access layer because that a little business network generally incorporates layer 2 switches and accessibility points giving connectivity between workstations and servers.

The access layer offer a variety of functions, including

Layer 2 switchingHigh availabilityPort securityQoS classification and marking and trust boundariesAddress Resolution Protocol (ARP) inspectionVirtual accessibility control list (VACLs)Spanning treePower over Ethernet (PoE) and also auxiliary VLANs because that VoIPThe circulation Layer (

The distribution layer aggregates the data got from the accessibility layer switches prior to it istransfer come the main point layer because that routing come its final destination. In figure 1-6, the distribution layer is the boundary in between the great 2 domains and the layer 3 routed network.

The distribution layer maker is the focal suggest in the wiring closets. Either a router or a multilayer move is provided to segment workgroups and isolate network difficulties in a campus environment.

A distribution layer switch may carry out upstream solutions for many access layer switches.

The distribution layer deserve to provide

Aggregation the LAN or WAN links.Policy-based defense in the form of access control lists (ACLs) and also filtering.Routing services in between LANs and also VLANs and between routing domain names (e.g., EIGRP come OSPF).Redundancy and also load balancing.A border for path aggregation and summarization configured top top interfaces towards the main point layer.Broadcast domain control, since routers or multilayer switches carry out not front broadcasts. The machine acts together the demarcation allude between broadcast domains.The main point Layer (

The core layer is likewise referred to as the network backbone. The main point layer consists of high-speed network tools such as the Cisco Catalyst 6500 or 6800. These room designed to move packets as fast as feasible and interconnect multiple campus components, together as distribution modules, business modules, the data center, and also the WAN edge.

As shown in figure 1-7, the main point layer is vital for interconnectivity in between distribution layer gadgets (for example, interconnecting the circulation block come the WAN and Internet edge).

The core need to be highly available and redundant. The main point aggregates the website traffic from all the distribution layer devices, therefore it need to be qualified of forwarding large amounts of data quickly.

Considerations in ~ the main point layer include

Providing high-speed switching (i.e., rapid transport)Providing reliability and also fault toleranceScaling by making use of faster, and not more, equipmentAvoiding CPU-intensive packet manipulation led to by security, inspection, quality of organization (QoS) classification, or other processesTwo-Tier collapsed Core architecture (

The three-tier ordered design maximizes performance, network availability, and also the capability to scale the network design.

However, many little enterprise networks do not grow significantly larger over time. Therefore, a two-tier hierarchical design whereby the core and distribution layers are fell down into one layer is often more practical. A “collapsed core” is when the distribution layer and also core layer attributes are applied by a solitary device. The primary an inspiration for the fell down core architecture is to reduce network cost, while preserving most of the services of the three-tier hierarchical model.

The example in number 1-8 has fell down the distribution layer and also core great functionality right into multilayer move devices.

The ordered network model provides a modular frame that allows flexibility in network design and also facilitates ease of implementation and also troubleshooting.

Activity Identify hierarchical Network Characteristics


Go to the course virtual to carry out this practice activity.

5. Cisco Enterprise architecture (1.2) | following Section Previous section

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