Download Campus Networks - Department of Computing & Immersive

Cisco Hierarchical Network
Model
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Outline
Network Design and Planning for
Enterprise networks
 Cisco 3 Layer hierarchical Model
◦ Core, Distribution and Access Layers
◦ Hub and spoke designs
◦ Mesh topologies
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Internetworking

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

Large networks can be extremely complicated,
◦ with multiple protocols
 IPv4, IPv6, IPX, Appletalk
◦ detailed configurations, and
◦ diverse technologies
 Frame Relay, FDDI, ATM, Ethernet, Token Ring
 Hierarchy helps us summarize a complex collection of
details into an understandable model
 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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Campus Networks

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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Why Use a Hierarchical Model?

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

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
Enterprise WAN
Backbone
Campus A
Core Layer
Campus B
Campus C
Campus C Backbone
Access Layer
Building C-1
Building C-2
Distribution
Layer
Flat Versus Hierarchy
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
Mesh Designs
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

Corporate
Headquarters
◦ Common in enterprise
networks
◦ Main location and
satellite sites
◦ Simple design and trivial
routing

Branch
Office
Home
Office
Branch
Office
Single hub node
Problems
◦
◦
◦
◦
Single point of failure
Bandwidth limitations
High delay between sites
Costs to backhaul to
hub
Simple Alternatives to Hub-and-Spoke

Dual hub-and-spoke
◦ Higher reliability
◦ Higher cost
◦ Good building block

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
Backdoor
Chain
How Do You Know When You Have
a Good Design?




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

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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Campus Topology Design
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
Next Week
Revisit IP Addressing
 Subnetting
 Class B subnetting

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