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Characteristics of Scaleable Internetworks

M Clements

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Last Week

IP Addressing Crisis and Solutions CIDR vs. classful addressing Supernetting NAT/ PAT IPv6 primer

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This week………..

Characteristics of Scaleable Internetworks 3 Layer Design Model Reliability and Availability 24/7 access, transparency, routing failure plans Responsiveness

– QoS without latency– Efficiency in use of BW

Adaptability Accessibility and Security

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Three Layer Design Model

Used for planning a new network Hierarchical design now possible Caters for the operation of the network Design considerations

– User access– Traffic segmentation and efficiency– High speed inter-site delivery

OSI model would be no use here!

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Flat Versus Hierarchical Topologies

Flat network topology ok for very small networks - no hierarchy

Each router/ switch has essentially the same job Network not divided into layers or modules and is easy

to design and implement Easy to maintain, as long as it stays small Flat network undesirable as network grows Lack of hierarchy makes locating a fault difficult May need to inspect the entire network

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Top Two Layers

Core Layer– For high speed switching of traffic– Lowest latency required here

Distribution Layer– For separating Core traffic from the rest of the network– Uses policies for:

Routing updates Route summaries Address aggregation VLAN traffic

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Lower Layer - Access Layer

Allows traffic and users into the network Low capability routers or switches may be

used here Can operate over remote access

technologies such as POTS, ISDN, Frame Relay for remote site connectivity

Security policies should be implemented– ACLs, PAP, CHAP etc.

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Three Layer Design Model (Campus Network)

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Functions of the Layers

Core layer - optimal transport between sites Distribution layer connects network services

to the access layer– Implements policies regarding security, traffic

loading and routing etc. In a campus network, the access layer

provides switches for end-user access

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Your design is right ………

When you already know how to add a new building, floor, WAN link, remote site, e-commerce service etc.

When new additions cause only local changes 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 confuse matters

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Network Design Goals

Reliability Availability Responsivity Efficiency Adaptability Accessibility and Security

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Reliability and Availability

Scaleable Routing Protocols Alternate Paths to destinations where possible Load Balancing

– Per packet– Per destination

Protocol Tunnels Dial-Backup

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Responsivity

This brings in ideas such as queuing and priorities

End users of the network notice responsivity at the desktop.

1.First-in,first-out queuing (FIFO)2.Priority queuing3.Custom queuing4.Weighted fair queuing

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Efficiency (of bandwidth)

This is the attempt to conserve bandwidth (BW) over (costly) WAN links

Local proxy server to hold frequently requested files Reduce size and frequency of routing updates Use Access Control lists to filter traffic Snapshot Routing Compression over WAN Dial-on-demand routing Route summarisation Incremental routing updates.

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Adaptability

Allows several protocols to co-exist across a network – less important today

IP, IPX, SNA, APPLETALK etc. Consideration must be paid to certain non-

routable protocols such as SNA which may suffer unless catered for

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Accessibility and Security

Accessibility is allowing access to the network by users either on-site or remotely

Security is making sure that the users are authenticated so that the users are those who should be allowed access

Technologies such as ACLs, PAP, CHAP can be used here

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Small Enterprise Design Profile 

The Enterprise Design Profile delivers the foundational network design that all enterprise services, applications, and solutions use to interact and communicate with one another.

The Enterprise Design Profile is constructed in a fashion that supports all the applications and services that will ride on it.

Additionally, these profiles must be aware of the type of traffic traversing and treat each application or service with the correct priority based on the needs and importance of that application.

Read on…

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Summary

Three Layer Hierarchical Design Model is used to simplify the complex tasks of network design

Basics of internetwork scaleability– Reliability and Availability– Responsivity– Efficiency– Adaptability– Accessibility and Security

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References

http://www.edrawsoft.com/Hierarchical-Network-Design.php http://images.ientrymail.com/networknewz/020604figure2.jpg Small Enterprise Design Profile Reference Guide, Cisco, 2010