Post on 02-Jan-2016
transcript
LAN Design
LAN Switching and Wireless – Chapter 1
Vilina Hutter, Instructor
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Hierarchical Network Design 3 layered model
• Access, Distribution, & Core Layers
• Each layer has specific functions
• Facilitates modularity
• Modularity facilitates scalability and enhanced performance
In small networks, the core and distribution layers can be combined—known as the collapsed core model
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Access Layer
End user devices
•PCs, phones, printers
Access to network for users
Can include any networking device
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Distribution Layer
Controls the flow of network traffic
•Policy implementation
•Broadcast containment
•VLAN connectivity
Switches and Routers
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Core Layer
High-speed backbone
Routers or switches
Redundant links
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Physical Layout of a Hierarchical Design
Less easy to see the hierarchical design layers in the physical layout!
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Benefits of a Hierarchical Design
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Four Design Principles
Network Diameter
Bandwidth Aggregation
Redundant Links
Start at the Access Layer!
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Network Diameter
How many devices a packet must cross to reach its destination
•Lower is better!
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Bandwidth Aggregation
Combining several parallel links between two switches to form one logical link
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Redundant Links
Used between devices at the core and distribution layer to ensure network availability
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Start at the Access Layer!
Business needs are met at the access layer
All network design is driven by the needs of the business and its users
U.S.A.F’s Network Centric Collaborative Targeting (NCCT) system
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Converged Networks
Networks that carry video, data, and voice•Convergence has been slowed by installed analog phone infrastructure
Advantages of convergence:•One network to manage
•One set of cabling
•One ring to rule them all
•Lower management costs
•New technology options• Softphones, webcams• Videoconferencing
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Selecting Network Devices Traffic Flow Analysis
•To select the right switches, network designers must accommodate present and projected network traffic requirements
•Traffic flow analysis tools are available to track, record, and analyze traffic patterns on a network
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User Communities Analysis Consider the number of devices that need to join the
network now and in the projected future•Switch port number planning
Consider any special traffic flow needs for particular applications used by a particular user community
• If a community uses a traffic-intensive application, they should be located physically close to their server to reduce network diameter for the workers
Smaller diameter for HR Dept.
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Data Stores and Data Servers Analysis
Examine traffic patterns between clients and their servers and between servers and data storage
•Potential bottlenecks between clients and servers can be reduced by aggregating bandwidth and by installing powerful switches
•High traffic volume between servers will have less impact on the entire network if the servers are physically close to each other
• Typically, all servers are located in a secure data center• Distribution layer switches are also located in the data center
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Topology Diagram Analysis
Careful examination of a detailed topology map will all identification of potential bottlenecks
•Traffic flow analysis can then be focused on those likely problem spots
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Switch Features Form Factor
•Fixed or modular hardware configuration
•Rack units (thickness)
•Stackable vs. non-stackable
Performance•Port density
•Forwarding rates
•Bandwidth aggregation
PoE (Power over Ethernet)
Layer 3 Functionality
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Match the Appropriate Cisco Switch to each Layer in the Hierarchical Network Design Model
Identify the considerations used to select a switch for a hierarchical network
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Form Factor—Fixed vs. Modular Fixed configuration switches cannot be modified or upgraded
Modular switches accept line cards
• Line cards contain the ports
• Line cards can be added or upgraded
• The larger the chassis, the more line cards can be supported
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Form Factor--Stackable Stackable switches can be connected by a backplane
cable
Allows a group of switches to effectively act as one switch
•Backplane cables use a special fast port to connect switches
Cross-connections allow for fast recovery if a single switch fails
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Match the Appropriate Cisco Switch to each Layer in the Hierarchical Network Design Model
Identify the switch features found in each level in a hierarchical network
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Performance—Port Density Number of ports available on a
single switch
Higher port density is more efficient• Space considerations
• Power outlets/consumption
Fixed switches support a maximum density of 48 ports
Modular switches support up to 1000+ ports
If many fixed switches are installed, they must all be uplinked, consuming ports for link aggregation
Modular switches support the line port aggregation via the backplane
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Performance—Forwarding Rates
How much total data the switch can forward per second
Especially at the distribution and core layers, the switch must support full speed on all port simultaneously
At the access layer, switches are limited by the uplink capability, so the forwarding rate is less crucial
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Switch Performance—Link Aggregation
All switches should support link aggregation to avoid uplink bottlenecks
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Switch Performance—PoE
PoE is the ability to provide electrical power to devices over the Ethernet ports
•Particularly useful for IP phones or access points which may need to be located away from electrical power lines
PoE is an expensive feature, which should not be ordered unless needed
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Switch Performance—Layer 3 Functionality
Known as multilayer switching
Supports routing function and security policy implementation
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Access Layer Switch Features
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Distribution Layer Switch Features
Distribution layer switches are typically implemented in pairs to ensure availability. It is also recommended that distribution layer switches support multiple, hot swappable power supplies
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Core Layer Switch Features
Because of the high workload carried by core layer switches, they tend to operate hotter than access or distribution layer switches, so they should have more sophisticated cooling options. Many true, core layer-capable switches have the ability to swap cooling fans without having to turn the switch off.
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Switch Model Selection
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Summary Hierarchical Design model addresses performance,
scalability, maintainability & manageability issues.
Traffic Analysis is used to monitor network performance.
Hierarchical Design Model is composed of 3 layers:•Access
•Distribution
•Core
Switches selected for each layer must meet the needs of each hierarchical layer as well as the needs of the business.
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