Transcript WAN Design

Year 2 - Chapter 10/Cisco 4 - Module 3
WAN Design
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WAN Options
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WAN Design Requirements
• Optimize WAN Bandwidth
• Minimize Costs
• Maximize the Effective Service to the End
Users
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Pressures on Existing
Networks
• Increased use of client/server and multimedia
applications.
• Increased use of enterprise servers.
• Applications increasingly require distinct
network qualities of service.
• Increased network connections for remote
users, mobile users, international sites,
customers/suppliers, and the Internet.
• Growth of corporate intranets and extranets.
• Internet and "push" technologies.
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WAN Design Goals
• Application availability
– If the applications are not available to network
users, the network is not doing its job.
• Total cost of ownership
– To properly implement the WAN infrastructure to
optimize application availability and allow the costeffective use of existing network resources.
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Secondary Design Goals
• Functionality
Does the network work? Can the users do their job? The
network must provide acceptable and reliable connectivity to
the organizational resources that user needs.
• Manageability
Can the network be monitored and managed conveniently
and efficiently by network professionals? If routine monitoring
and maintenance is not convenient, it tends to be skipped.
• Scalability
Can the network expand and contract with changes within the
organization? The original design should be able to adjust
without having to be redesigned.
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Steps in Designing a WAN
• Gathering Requirements
• Analyzing Requirements
• Sensitivity Testing
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Types of Requirements
• Business requirements
• Organizational requirements
• Technical requirements
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Performance requirements
Application requirements
Network management requirements
Security requirements
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Business Requirements
• Looks only at the organization’s business
model
– Does the design benefit or hinder their way of
doing business?
– Does the design provide a competitive
advantage?
• If so, which costs are reduced and by how much?
– Is the organization an industry leader or industry
follower?
– Does the design scale consistent with the
organization’s expected growth?
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Organization Requirements
• Who has bought into this project?
– Is it supported high enough in the organization to
make sure that resources and attention will be
committed?
• Is there an existing budget?
– Is it reasonable for what needs to be done?
– Who must approve any changes or budget
increases?
• Is there an existing timeline for the project?
– Is the timeline reasonable?
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Technical Requirements
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Performance Requirements
Application Requirements
Network Management Requirements
Security Requirements
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Performance Requirements
• Defining Acceptable levels of performance
measured in:
– Response Time
– Bandwidth utilization
• How to ensure that those levels can be
preserved through both network growth and
increased utilization.
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Application Requirements
• Which centralized applications are currently used
on the network?
• Who needs access to these applications and where
are they located?
• What new applications are being added in the new
design?
• What are peak loads?
– Per day, per week, per month, per year?
– Can any high bandwidth applications be rescheduled to
run outside of normal business hours?
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Network Management
Requirements
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How much traffic to capture
How much statistics to gather
Where to measure network utilization
Remote configuration
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Security Requirements
• How is network security currently handled?
– Does the organization understand the need for security?
• Will there be additional exposure as a result of the
new design?
• How will the additional security and related training
be handled?
• Defining the level of security that the customer
could realistically pay for and live with.
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Methods to Obtain This
Information
• To determine user community profiles
– What different user groups require
• Interviews
– Least formal approach
• Focus groups
• Surveys
– Gathering statistically valid input
• Human factors tests (lab environment)
– Most expensive, time-consuming, and possibly revealing
method
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Analyzing Requirements
• How can the new design meet each of the
following:
– Business requirements
– Organizational requirements
– Technical requirements
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Performance requirements
Application requirements
Network management requirements
Security requirements
Cisco Press: CCNA Instructor’s Manual
www.ciscopress.com
WAN Sensitivity Testing
• Pilot—Small-scale test network (lab)
– Generally proving the technology works
– Often includes borrowed resources
• Prototype—Larger scale test network
– Proves all aspects of the entire design
– Purchasing enough resources to outfit a test branch or test
location (one classroom in a school upgrade)
• Computer design modeling programs
– Cisco’s Netsys Baseliner, a simulation-based planning and
problem-solving tool for network managers, analysts, and
designers
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Three-Layer Hierarchical
Model
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Benefits of a Hierarchical
WAN Design
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Scalability
Ease of Implementation
Ease of Troubleshooting
Predictability
Protocol Support
Manageability
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Functions of Hierarchical
Layers
• Core layer
– Provides optimal transport between sites
• Distribution layer
– Provides policy-based connectivity
• Access layer
– Provides workgroup and user access to the
network
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Core-Layer Functions
• If there is a failure in core every single user
can be affected.
• Speed and latency are driving concerns here.
• Things that we know we do not want to do:
– Do not do anything to slow down traffic (VLANs,
ACLs, Packet Filtering)
– Do not support workgroup access here
– Avoid expanding the core when the internet work
grows: Give preference to upgrade over
expansion.
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Core-Layer Functions
• Things we know we want to do:
– Design the core for high reliability
– Consider data link technologies that facilitate both
speed and redundancy (ATM, FDDI)
– Design with speed in mind. The core should have
very little latency.
– Select routing protocol with lower convergence
time (OSPF)
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Distribution Layer
• The distribution layer is where much of the action is
• The emphasis here is control.
• Items that should be done at the distribution layer:
– Implement tools such as access lists, packet filtering, and
queuing.
– Implement security, and network policies, including address
translation and firewalls.
– Redistribution between routing protocols
– Routing between VLANs.
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Access Layer
• Controls user and workgroup access to
internetwork resources.
• Some of the functions to be included at this
layer include:
– Continued (from distribution layer) access control
and policies.
– Creation of separate collision domains
– Workgroup connectivity into distribution layer.
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Three categories of customer
Problems
• Media Problems: Problem relating to contention for use of the
media itself. Examples include collision rates and utilization
rates.
– The recommended solution is to use LAN switching to separate
collision domains.
• Protocol Problems: Protocol problems result when protocols
designed for workgroup environment are used in significantly
larger environment.
– The recommended solution is to use routing to separate broadcast
domains.
• Transport Problems: Result when extreme transport problems
are placed on the network. For example many IS departments
are required to implement video conferencing and video
streaming solutions.
– Using ATM solves transport problems.
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Connectivity in a Three-Layer
Model
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Server Placement
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