Wan Design01

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Semester 4 v. 2.1

WAN DesignWAN DesignWAN DesignWAN Design

Chapter 3Chapter 3

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WAN Design RequirementsWAN Design RequirementsWAN Design RequirementsWAN Design Requirements

WAN communication is often called a serviceWAN communication is often called a service

because the network provider often charges usersbecause the network provider often charges users

for the WAN services it provides.for the WAN services it provides.

All technologies and features used in WANs areAll technologies and features used in WANs are

developed to meet the following designdeveloped to meet the following design

requirements:requirements:

Optimize WAN bandwidth.Optimize WAN bandwidth.

Minimize cost.Minimize cost.

Maximize the effective service to the end users.Maximize the effective service to the end users.

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Traditional sharedTraditional shared--media networks are now beingmedia networks are now beingovertaxed because of the following:overtaxed because of the following:Network usage has increased.Network usage has increased.

Application software evolution is continually moreApplication software evolution is continually moredemanding.demanding.

Applications increasingly require distinct networkApplications increasingly require distinct networkqualities of service.qualities of service.

An unprecedented number of connections are beingAn unprecedented number of connections are being

established.established. The explosive growth of corporate intranets andThe explosive growth of corporate intranets and

extranets has created a greater demand for bandwidth.extranets has created a greater demand for bandwidth.

The increased use of enterprise servers continues toThe increased use of enterprise servers continues togrow to serve the business needs of organizations.grow to serve the business needs of organizations.

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New WAN infrastructures must be:New WAN infrastructures must be:

more complex.more complex.

based on new technologies.based on new technologies.

able to handle an everable to handle an ever--increasing (and rapidly changing)increasing (and rapidly changing)application mix with required and guaranteed serviceapplication mix with required and guaranteed service

levels.levels.

Within the next five years, theres an expectedWithin the next five years, theres an expected300% traffic increase.300% traffic increase.

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WAN Design GoalsWAN Design GoalsWAN Design GoalsWAN Design Goals

Two primary goals drive WAN design and implementation:Two primary goals drive WAN design and implementation:

Application availability:Application availability:

Networks carry application information between computers.Networks carry application information between computers.

If the applications are not available, the network is not doing its job.If the applications are not available, the network is not doing its job.

Total cost of ownership:Total cost of ownership: Information Systems (IS) department budgets often run in the millions ofInformation Systems (IS) department budgets often run in the millions of

dollars.dollars.

More businesses rely on electronic data, therefore the costs ofMore businesses rely on electronic data, therefore the costs of

computing resources will continue to rise.computing resources will continue to rise.

A wellA well--designed WAN can help to balance these objectives.designed WAN can help to balance these objectives.

When properly implemented, the WAN infrastructure can optimizeWhen properly implemented, the WAN infrastructure can optimize

application availability and allow the costapplication availability and allow the cost--effective use of existingeffective use of existing

network resources.network resources.

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WAN Design GoalsWAN Design GoalsWAN Design GoalsWAN Design Goals

In general, WAN design needs to take into accountIn general, WAN design needs to take into account

three general factors:three general factors:

Environmental variablesEnvironmental variables::

Includes the location of hosts, servers, terminals, and other endIncludes the location of hosts, servers, terminals, and other endnodes; the projected traffic for the environment; and the projectednodes; the projected traffic for the environment; and the projected

costs for delivering different service levels.costs for delivering different service levels.

Performance constraintsPerformance constraints::

Consist of network reliability, traffic throughput, and host/clientConsist of network reliability, traffic throughput, and host/client

computer speeds (for example, network interface cards and hardcomputer speeds (for example, network interface cards and harddrive access speeds).drive access speeds).

Networking variablesNetworking variables::

Includes the network topology, line capacities, and packet traffic.Includes the network topology, line capacities, and packet traffic.

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WAN Design ModelsWAN Design ModelsWAN Design ModelsWAN Design Models

Network designs tend to follow one of two generalNetwork designs tend to follow one of two generaldesign strategies:design strategies:Mesh:Mesh:

The network topology is flat.The network topology is flat.

All routers perform essentially the same functions, and there isAll routers perform essentially the same functions, and there isusually no clear definition of where specific functions areusually no clear definition of where specific functions areperformed.performed.

Expansion of the network tends to proceed in a haphazard,Expansion of the network tends to proceed in a haphazard,arbitrary manner.arbitrary manner.

Hierarchical:Hierarchical: The structure the network is organized in layers, each of whichThe structure the network is organized in layers, each of which

has one or more specific functions.has one or more specific functions.

Data traffic flows based on source / destination addressing.Data traffic flows based on source / destination addressing.

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Hierarchical WAN Design ModelHierarchical WAN Design ModelHierarchical WAN Design ModelHierarchical WAN Design Model

Benefits to using a hierarchical model include theBenefits to using a hierarchical model include the

following:following:

Easier to implement.Easier to implement.

Easier to manage.Easier to manage.Easier to troubleshoot.Easier to troubleshoot.

Improved scalability.Improved scalability.

Predictability.Predictability.

Protocol support.Protocol support.

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Semester 4 v. 2.1

Three Layer DesignThree Layer DesignThree Layer DesignThree Layer Design

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3Hierarchical WAN Design Layers3Hierarchical WAN Design Layers3Hierarchical WAN Design Layers3Hierarchical WAN Design Layers

A hierarchical network design includes the followingA hierarchical network design includes the following

three layers:three layers:

The CORE layer:The CORE layer:

Provides optimal transport between sites.Provides optimal transport between sites. The DISTRIBUTION layer:The DISTRIBUTION layer:

Provides policyProvides policy--based connectivity.based connectivity.

The ACCESS layer:The ACCESS layer:

Provides workgroup and user access to the network.Provides workgroup and user access to the network.

Could also be called the 3 levels of a router hierarchy.Could also be called the 3 levels of a router hierarchy.

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Core LayerCore LayerCore LayerCore Layer

Provides fast WAN area connections between remote sites,Provides fast WAN area connections between remote sites,

tying a campus networks together in a corporate ortying a campus networks together in a corporate or

enterprise WAN.enterprise WAN.

Is usually implemented as a WAN.Is usually implemented as a WAN.

Needs redundant paths.Needs redundant paths. Can withstand individual circuit outages and continue to function.Can withstand individual circuit outages and continue to function.

Links are pointLinks are point--toto--point.point.

There are rarely any hosts in the core layer.There are rarely any hosts in the core layer.

Should not perform any filteringShould not perform any filtering slows down performance.slows down performance.

Core services (for example, T1/T3, Frame Relay, SMDS)Core services (for example, T1/T3, Frame Relay, SMDS)

typically are leased from a telecom service provider.typically are leased from a telecom service provider.

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Distribution LayerDistribution LayerDistribution LayerDistribution Layer

Provides network services to multiple LANs within aProvides network services to multiple LANs within a

WAN environment.WAN environment.

This is where the WAN backbone network is found, and itThis is where the WAN backbone network is found, and it

is typically based on Fast Ethernet.is typically based on Fast Ethernet. This is implemented on large sites and is used toThis is implemented on large sites and is used to

interconnect buildings.interconnect buildings.

Provides boundary definition, and it is the layer at whichProvides boundary definition, and it is the layer at which

packet manipulation occurs.packet manipulation occurs.

Can be summarized as the layer that provides policyCan be summarized as the layer that provides policy--

based connectivity.based connectivity.

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Distribution LayerDistribution LayerDistribution LayerDistribution Layer

Can include several functions, such as the following:Can include several functions, such as the following:

Address or area aggregation.Address or area aggregation.

Departmental or workgroup access to the core layer.Departmental or workgroup access to the core layer.

Broadcast/multicast domain definition.Broadcast/multicast domain definition.

Virtual LAN (VLAN) routing.Virtual LAN (VLAN) routing.

Any media transitions that need to occur.Any media transitions that need to occur.

Security.Security.

Provides policyProvides policy--based connectivity.based connectivity.

Not putting end stations on the backbone frees up the backbone toNot putting end stations on the backbone frees up the backbone to

act strictly as a transit path for traffic between workgroups oract strictly as a transit path for traffic between workgroups or

campuscampus--wide servers.wide servers.

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Access LayerAccess LayerAccess LayerAccess Layer

The access layer is usually a LAN or a group of LANs,The access layer is usually a LAN or a group of LANs,

typically Ethernet orToken Ring, that provide users withtypically Ethernet orToken Ring, that provide users with

frontline access to network services.frontline access to network services.

Almost all hosts are attached to the network, including servers of allAlmost all hosts are attached to the network, including servers of all

kinds and user workstations.kinds and user workstations. Allows logical segmentation of the network and grouping of usersAllows logical segmentation of the network and grouping of users

based on their function.based on their function.

Can also use access control lists or filters to further optimize theCan also use access control lists or filters to further optimize the

needs of a particular set of users.needs of a particular set of users.

Workgroup servers should be located here.Workgroup servers should be located here.

The main goal of the Access layer is to isolate the broadcastThe main goal of the Access layer is to isolate the broadcast

traffic between the individual workgroups, segments, ortraffic between the individual workgroups, segments, or

LAN

s.LAN

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Access LayerAccess LayerAccess LayerAccess Layer

In the campus environment, accessIn the campus environment, access--layer functionslayer functions

can include the following:can include the following:

Shared bandwidth.Shared bandwidth.

Switched bandwidth.Switched bandwidth.MACMAC--layer filtering.layer filtering.

Microsegmentation.Microsegmentation.

The access layer connects users into LANs, andThe access layer connects users into LANs, andLANs into WAN backbones orWAN links.LANs into WAN backbones orWAN links.

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Semester 4 v. 2.1

Other DesignsOther DesignsOther DesignsOther Designs

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Other DesignsOther DesignsOther DesignsOther Designs

A threeA three--layer model can meet the needs of mostlayer model can meet the needs of most

enterprise networks.enterprise networks.

However, a twoHowever, a two--layer design may be adequate orlayer design may be adequate oreven a single layer flat network.even a single layer flat network.

A hierarchical structure should still be planned orA hierarchical structure should still be planned or

maintained to allow these network designs tomaintained to allow these network designs to

expand to three layers as the need arises.expand to three layers as the need arises.

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One Layer DesignOne Layer DesignOne Layer DesignOne Layer Design

In a 1 layer design, the key design decisionIn a 1 layer design, the key design decisionbecomes the placement of servers:becomes the placement of servers: They can be distributed across multiple LANsThey can be distributed across multiple LANs

Or concentrated in a central server farm location.Or concentrated in a central server farm location.

A oneA one--layer design is typically implemented if therelayer design is typically implemented if thereare only a few remote locations in the company,are only a few remote locations in the company,and access to applications is mainly done via theand access to applications is mainly done via the

local LAN to the site file server.local LAN to the site file server.

Each site is its own broadcast domain.Each site is its own broadcast domain.

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Two Layer DesignTwo Layer DesignTwo Layer DesignTwo Layer Design

In a twoIn a two--layer design, a WAN link is used tolayer design, a WAN link is used to

interconnect separate sites.interconnect separate sites.

Inside the site, multiple LANs may be implemented,Inside the site, multiple LANs may be implemented,with each LAN segment being its own broadcastwith each LAN segment being its own broadcast

domain.domain.

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Wan Design01

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