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Network Design and Planning for
Enterprise networks
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Cisco 3 Layer hierarchical Model
◦ Core, Distribution and Access Layers
◦ Hub and spoke designs
◦ Mesh topologies
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Internetworking is the communication between two or more networks
◦ Requires many protocols and features to
 permit scalability
 manageability without constant manual intervention
Large internetworks can consist of the three distinct components:
1.
Campus networks, which consist of locally connected users in a building or group of buildings
2.
Wide-area networks (WANs), which connect campuses together
3.
Remote connections, which link branch offices and single users (mobile users and/or telecommuters) to a local campus or the Internet
Typical Enterprise Network
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High Level view of Enterprise
Network
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Why reference model for network design
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Large networks can be extremely complicated,
◦ with multiple protocols
 IPv4, IPv6, IPX, Appletalk
◦ detailed configurations, and
◦ diverse technologies
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 Frame Relay, FDDI, ATM, Ethernet, Token Ring
Hierarchy helps us summarize a complex collection of details into an understandable model
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Hierarchy, when used properly, makes network more predictable
The Cisco hierarchical model can help you design, implement, and maintain a scalable , reliable , cost-effective hierarchical internetwork
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A campus is a building or group of buildings all connected into one enterprise network that consists of many local area networks (LANs).
◦ A large campus with groups of buildings can also use WAN technology to connect the buildings
Campus network generally optimized for the fastest functional architecture that runs on existing physical wire.
Scalable to requirements of emerging applications
Campus Network
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Reduces workload on network devices
◦ Avoids devices having to communicate with too many other devices (reduces
“CPU adjacencies”)
Constrains broadcast domains
Enhances simplicity and understanding
Facilitates changes
Facilitates scaling to a larger size

Cisco’s Hierarchical Design Model
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Like OSI 7 layer model, Cisco hierarchical model is a three layered model.
The layers from below are:
◦ Layer 1: Access
◦ Layer 2: Distribution
◦ Layer 3: Core
A core layer of high-end routers and switches that are optimized for availability and speed
A distribution layer of routers and switches that implement policies and segment traffic
An access layer that connects users via hubs, switches, and other devices

Hierarchical Network Design
Campus A
Enterprise WAN
Backbone
Campus B
Core Layer
Campus C
Campus C Backbone
Distribution
Layer
Access Layer
Building C-1 Building C-2

Headquarters in Bedford
Headquarter in Bedford
Grimsby
Branch
Office
Kelmarsh
Branch
Office
Ashford
Branch
Office
Flat Loop Topology
Grimsby
Branch
Office
Kelmarsh
Branch Office
Ashford
Branch
Office
Whitby
Branch
Office
Hierarchical Redundant Topology

Full and partial mesh designs are used in network design to provide redundancy or high availability
Partial-Mesh Topology Full-Mesh Topology

A Partial-Mesh Hierarchical Design
Headquarters
(Core Layer)
Regional
Offices
(Distribution
Layer)
Branch Offices (Access Layer)

A Hub-and-Spoke Hierarchical Topology
Branch
Office
Home
Office
Corporate
Headquarters
Branch
Office
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Single hub node
◦ Common in enterprise networks
◦ Main location and satellite sites
◦ Simple design and trivial routing
Problems
◦ Single point of failure
◦ Bandwidth limitations
◦ High delay between sites
◦ Costs to backhaul to hub

Simple Alternatives to Hub-and-Spoke
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Dual hub-and-spoke
◦ Higher reliability
◦ Higher cost
◦ Good building block
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Levels of hierarchy
◦ Reduce backhaul cost
◦ Aggregate the bandwidth
◦ Shorter site-to-site delay
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Avoid Chains and Backdoors
Core Layer
Distribution Layer
Access Layer
Chain
Backdoor

How Do You Know When You Have a Good Design?
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When you already know how to add a new building, floor, WAN link, remote site, ecommerce service, and so on
When new additions cause only local change, to the directly-connected devices
When your network can double or triple in size without major design changes
When troubleshooting is easy because there are no complex protocol interactions to wrap your brain around

Cisco’s SAFE Security Reference
Architecture

Enterprise Composite Network
Model
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Grouping Devices into Networks and
Hierarchical Addressing
 Devices are grouped into sub-networks
 Based on geographical location
 Based on
Functionality
 Departments
 Communication requirements
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Network Designs: breaking into sub-networks
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Given a network requirement, find the optimum number of sub networks in the larger inter-network.
◦ Count on the basis of
 Departments
 Geographical locations..
Determine the total number of hosts in a network, accounting for present and future requirements
Hosts include
◦ PCs, printers, servers, special devices
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Use a hierarchical, modular approach
Minimize the size of bandwidth domains
Minimize the size of broadcast domains
Provide redundancy
◦ Mirrored servers
◦ Multiple ways for workstations to reach a router for off-net communications

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Revisit IP Addressing
Subnetting
Class B subnetting
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