LAN Switching and Wireless
Chapter 1. Resume. LAN design.
Hierarchical network design involves dividing the network into discrete layers. Each layer provides specific functions that define its role within the overall network. By separating the various functions that exist on a network, the network design becomes modular, which facilitates scalability ( масштабируемость) and performance ( производительность). The typical hierarchical design model is broken up in to three layers: access, distribution, and core.
The access layer can include routers, switches, bridges, hubs, and wireless access points (AP), PCs, printers, and IP phones.
Purpose - provide a means of connecting devices to the network
- controle which devices are allowed to communicate on the network.
The distribution layer aggregates the data received from the access layer switches before it is transmitted to the core layer for routing to its final destination.
Purpose - controls the flow of network traffic using policies
- delineates broadcast domains by performing routing functions between (VLANs)
- VLANs allow to segment the traffic on a switch into separate subnetworks.
The core layer is critical for interconnectivity between distribution layer devices, so it is important for the core to be highly available and redundant. The core area can also connect to Internet resources.
Benefits of a Hierarchical Network
Scalability. Масштабируемость
The modularity of the design allows you to replicate design elements as the network grows. Because each instance of the module is consistent, expansion is easy to plan and implement.
Redundancy.Наличие запасных путей для уровней Core и Distribution.
We can dramatically increase availability through easy redundant implementations with hierarchical networks.
Performance. Производительность, информация передается наиболее быстрым путем.
Communication performance is enhanced by avoiding the transmission of data through low-performing, intermediary switches. Data is sent through aggregated switch port links from the access layer to the distribution layer at near wire speed in most cases.
Security. Настройка различных параметров безопасности портов на access layer, управление доступом на Distribution layer.
Manageability. Управляемость
Each layer of the hierarchical design performs specific functions that are consistent throughout that layer. Therefore, if you need to change the functionality of an access layer switch, you could repeat that change across all access layer switches in the network because they presumably perform the same functions at their layer.
Maintainability. Обслуживание, ремонт. Можно сэкономить деньги на оборудовании access уровня, и эффективно повысить производительность купив более дорогое оборудование высших уровней.
Because hierarchical networks are modular in nature and scale very easily, they are easy to maintain.
Network diameter is the number of devices that a packet has to cross before it reaches its destination. Keeping the network diameter low ensures low and predictable latency between devices.
Network device latency (задержка) is the time spent by a device as it processes a packet or frame.
Bandwidth Aggregation.
After bandwidth requirements of the network are known, links between specific switches can be aggregated, which is called link aggregation. Link aggregation allows multiple switch port links to be combined so as to achieve higher throughput between switches.
Redundancy. Резервность путей доступа.
Redundancy is one part of creating a highly available network.
Small and medium-sized businesses are embracing the idea of running voice and video services on their data networks.
Legacy Equipment. Convergence is the process of combining voice and video communications on a data network.
Advanced Technology. Another benefit is lower implementation and management costs. It is less expensive to implement a single network infrastructure than three distinct network infrastructures. Managing a single network is also less expensive.
User community analysis is the process of identifying various groupings of users and their impact on network performance. The way users are grouped affects issues related to port density and traffic flow, which, in turn, influences the selection of network switches.
Client-server traffic is the traffic generated when a client device accesses data from data stores or servers. Client-server traffic typically traverses multiple switches to reach its destination. Bandwidth aggregation and switch forwarding rates are important factors to consider when attempting to eliminate bottlenecks for this type of traffic.
Server-server traffic is the traffic generated between data storage devices on the network. Some server applications generate very high volumes of traffic between data stores and other servers. To optimize server-server traffic, servers needing frequent access to certain resources should be located in close proximity to each other so that the traffic they generate does not affect the performance of the rest of the network.
Switch Form Factors
Switch Form Factors
- Fixed Configuration Switches
- Modular Switches
- Stackable Switches. Stackable switches can be interconnected using a special backplane cable that provides high-bandwidth throughput between the switches.
Switch features
- Performance
- Port Density
- Forwarding Rates
- Link Aggregation
- Power over Ethernet (PoE) allows the switch to deliver power to a device over the existing Ethernet cabling.
- Layer 3 functionality offers advanced functionality. Layer 3 switches = multilayer switches.
Access Layer
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Distribution Layer
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Core Layer
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Switch Features
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· port security
· port speed
· VLANs
· Fast Ethernet/Gigabit Ethernet
· PoE
· link aggregation
· QoS
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· Layer 3 support
· High forwarding rate
· Gigabit /10 gigabit Ethernet
· Redundant components
· Security Policies /Access lists
· link aggregation
· QoS
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· Layer 3 support
· Very high forwarding rate
· Gigabit /10 gigabit Ethernet
· Redundant components
· link aggregation
· QoS
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