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Characteristics of ScaleableInternetworks
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 - nohierarchy
Each router/ switch has essentially the same job
Network not divided into layers or modules and is easyto 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 beused here
Can operate over remote accesstechnologies such as POTS, ISDN, FrameRelay 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 servicesto the access layer
–Implements policies regarding security, trafficloading and routing etc.
In a campus network, the access layerprovides 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 thedirectly connected devices
When your network can double or triple in size withoutmajor design changes
When troubleshooting is easy because there are nocomplex 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 andpriorities
End users of the network notice responsivityat 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 anetwork – less important today
IP, IPX, SNA, APPLETALK etc.
Consideration must be paid to certain non-routable protocols such as SNA which maysuffer unless catered for
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Accessibility and Security
Accessibility is allowing access to thenetwork by users either on-site or remotely
Security is making sure that the users areauthenticated so that the users are thosewho should be allowed access
Technologies such as ACLs, PAP, CHAPcan be used here
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Small Enterprise Design Profile
The Enterprise Design Profile delivers the foundationalnetwork design that all enterprise services, applications, andsolutions use to interact and communicate with one another.
The Enterprise Design Profile is constructed in a fashion thatsupports all the applications and services that will ride on it.
Additionally, these profiles must be aware of the type of traffictraversing and treat each application or service with the correctpriority based on the needs and importance of that application.
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Summary
Three Layer Hierarchical Design Model isused to simplify the complex tasks of networkdesign
Basics of internetwork scaleability
–Reliability and Availability
–Responsivity
–Efficiency
–Adaptability
–Accessibility and Security
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References
Small Enterprise Design Profile Reference Guide, Cisco, 2010