WAN design

ผศ.ดร. อนั�นัต์ ผลเพิ่ �มAsst.Prof.Anan Phonphoem, Ph.D.

anan@cpe.ku.ac.thhttp://www.cpe.ku.ac.th/~anan

Computer Engineering DepartmentKasetsart University, Bangkok, Thailand

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Types of WAN Service

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WAN Technology

Technology Typical Uses

Leased Line PPP networks, hub and spoke, back-ups

ISDN Remote-access, voice, video, back-ups

Frame Relay Fast, efficient mesh between remote sites

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WAN requirements Optimise WAN bandwidth Minimise cost Maximise the effective service to

end users

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LAN/WAN integration LAN/WAN, previously logically

separated, must now be fully integrated for seamless performance

Both now must be able to handle... Voice traffic (VoIP) Bandwidth intensive multimedia applications

Video conferencing On-line training

Increased business critical data access

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Goals Availability Total cost of ownership

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Concerns Environmental variables Performance constraints Networking variables

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WAN Design strategies Mesh

Network is flat All routers perform same function Expansion proceeds haphazardly

Hierarchical Organized in layers Easier to implement/Troubleshooting Scalability Predictability

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Important of Layers Designing networks using the OSI model

designed in layers simplify the tasks required for internetworking Design elements can be replicated as grows

Therefore, networks should be designed using a hierarchical model. Unfortunately, most networks are thrown

together into a mesh (“a mess!”) with little or no vision of future needs.

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Benefit of Hierarchical Design

Scalability allows for future growth without sacrificing

control or functionality Ease of Implementation

logically constructed layers specify the functions of each layer

Ease of troubleshooting well-defined functions at each layer aid in

the isolation of problems

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Benefit of Hierarchical Design Predictability

behavior of functional layers can be estimated and planned for

Protocol support allows easier implementation of future

technologies because the network has been logically constructed

Manageability All the above aids net. admin. in overall

management of the network

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The Hierarchical Design ModelThe Three-Layer

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The Hierarchical Design ModelThe Three-Layer

Core layer--provides transport between remote sites

Distribution layer--provides policy-based connectivity

Access layer--provides workgroup/user access to network

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Core Layer

Fast WAN connections between remote sites

Core links are normally point-to-point with no host devices

Core services include: T1/T3 Frame Relay ATM SMDS

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Distribution Layer Provides WAN services to multiple LANs Usually the campus backbone Uses Fast Ethernet (or Gigabit

Ethernet) Used on large sites to interconnect

blgs.

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Access Layer Usually a LAN or group of LANs Gives access to specific users and

workgroups This layer is where all hosts (including

servers) are attached to the network

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WAN Layer Functions Core Layer Functions Distribution Layer Functions Access Layer Functions

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Core Layer Functions Optimize Transport Between Remote

Sites Redundant paths to guard against circuit

outages Provide load sharing and rapid

convergence when link states change Efficient use of bandwidth by...

Implementing scalable routing protocols and Blocking local traffic access to the core

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Distribution Layer Functions

Policy-Based Connectivity Boundary definition & packet manipulation Control access to services of the core layer and

other distribution layer routers VLAN routing Address aggregation (i.e., subnets) & route

optimization ACLs and other security measures

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Access LayerFunctions

Workgroup & User Access to the Network Isolation of Broadcast Traffic Shared and Switched Bandwidth MAC-layer filtering Microsegmentation

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Other Hierarchical Options One-Layer Design Two-Layer Design

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One-Layer Design Only a few remote sites need to be

connected Servers are placed in farms or in each

workgroup to reduce traffic on the backbone

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Two-Layer Design WAN link is used to interconnect separate

sites Link does not have to be dedicated. An

alternative would be ISDN.

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Hierarchical Design Advantages

Controlling data traffic patterns through source/destination network layer addressing A packet only needs to travel up the

hierarchy as far as it needs to find the destination.

With good design, most traffic would be contained in the access layer with users accessing their workgroup servers

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Hierarchical Design Advantages

Server Placement Enterprise Servers needed by all

workgroups should be placed in the Distribution Layer (e.g. email, DNS, etc.)

Workgroup Servers needed by a unique set of users should be placed in the Access Layer, preferably in the same broadcast domain as the users

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References Cisco course material Allan Johnson’s material (from cisco) user:dam0c00k’s material (from cisco)