Shaun Hummel, CCNP, is a Senior Network Engineer with 11 years experience in enterprise network planning, design, and implementation. He has worked for various private and public companies in Canada and the United States improving infrastructure, security, and management. He has written Network Planning and Design Guide, Cisco Wireless Network Design Guide and Network Assessment Guide. www.networkjobsolutions.com
Overview
The network switch is the most common network device with most network infrastructure and as such selection of new switches or upgrading is a key part of most network design projects. Wireless designs will have switches interfacing with access points. That will in some cases have an affect on the switch such as increased utilization, assigned switch ports, access lists, trunking, Power over Ethernet (PoE) wattage draw or spanning tree protocol. The decision to buy new switches or upgrade will be determined after considering the network assessment and design features specified. The 5 network switch components include switch chassis, supervisor engine, switching modules, power supplies and IOS/Cat OS software.
Switch Chassis Features
The Switch Chassis features include - dimensions, number of slots, processor slot assignments, switching fabric, supervisor engines supported, supervisor engine diversity, power supplies, power supply failover, rack units.
Supervisor Engine Features
Switches are implemented with a Supervisor Engine (Switch Processor) for processing packets on a network segment. Routing is available with an onboard Multi Layer switch feature card (MSFC) or route processor running IOS code. The network switch Supervisor Engine running IOS code on the MSFC and the switch processor is in native mode, while those running Cat OS on the processor is in hybrid mode. Some engines won't support native and hybrid mode. The engine with no MSFC supports what is called Cat OS mode. Select the engine that matches design specifications. The MSFC module is integrated with the Supervisor Engine or upgradeable. You must implement a PFC module with any MSFC. Some Supervisor Engines have no MSFC module. The routing is integrated with the hardware and as such support native mode only.
The Supervisor Engine features include - supported switch chassis, uplink speed, processor memory, native IOS, Cat OS, PFC, MSFC, slot assignment, diversity.
- Supervisor Engine 720: 6500 series switches, 400 mpps, MSFC3, IOS, Cat OS
- Supervisor Engine 32: 6500 series switches, 15 mpps, MSFC2A, IOS, Cat OS
- Supervisor Engine 5: 4500 series switches, 72 mpps, Integrated Routing, IOS
- Supervisor Engine 4: 4500 series switches, 48 mpps, Integrated Routing, IOS
Switching Module Features
The Switching Module features include - supported switch chassis, interface speed, number of ports, media, cabling, connectors, throughput, Supervisor Engine supported, protocol features, Power over Ethernet, Cisco Prestandard or 802.3af.
- Media: Copper, Fiber
- Cabling: UTP Cat 5, CAT 5e, CAT 6, STP, MMF, SMF
- Connectors: RJ45, RJ21, SC, LC
- Transceivers: GBIC, SFP
Power Supply Features
The Power Supply features include - supported chassis, wattage ratings, Power over Ethernet, input/output amps, power cord type, IOS, Cat OS.
IOS/Cat OS Software
Cisco network switches can be deployed with IOS, IOS and Cat OS or exclusive Cat OS software. Design features will determine what mode and IOS or Cat OS version is selected. The software running on the Route Processor must be IOS while the Supervisor Engine switch processor will run IOS (native mode) or Cat OS (hybrid mode). Some Cisco equipment such as the 4507R deploy the Supervisor Engine IV with no MSFC onboard. The routing processor is integrated with the engine. With that design, the Supervisor Engine IV doesn't support Cat OS.
- Native IOS - deployed at the network edge where most routing occurs and needs some switching
- Hybrid - deployed at the network core where there is routing and high speed switching
- Cat OS - deployed at the network access layer where most switching and no routing occurs
Switch Selection Process
The following describes the 5 components of any network switch selection process.
1. Consider Network Assessment and Design
2. Select Switches with Design Features
3. Select Switches with Scalability
4. Balance Cost with Features
5. Select IOS and/or Cat OS Version
The network assessment and design specifications should be considered before selecting any specific network switches. The network assessment examines what is implemented and what environment the selected device will be deployed. The design specifications will determine performance, availability and scalability features needed. Selecting IOS and/or Cat OS versions occur after you have the feature set determined. Companies will specify a budget and that is a key consideration with any equipment selection. It isn't cost effective to select a Cisco 6509 for an office with 50 employees. It is important that you select equipment that meet the design specifications, has the scalability features needed while meeting budget guidelines.
Some typical switch features to consider:
1) Are there enough chassis slots?
2) What Supervisor Engines are supported?
3) Does the Supervisor Engine support failover?
4) Is Multi Layer Switching available?
5) What Switching Modules are available?
6) What Uplinks are available?
7) What Power Supply wattage is available?
8) Number of Rack Units?
Switch Selection Example:
The Network Assessment discovered the following equipment at the company office.
· Distribution office has 300 employees
· Fast Ethernet implemented at the Desktop
· 6509 Cisco Switches with Gigabit Ethernet Trunking
· 3800 Cisco Router with dual T1 circuits
· Power over Ethernet is implemented
· Multiple VLANS defined
· Local Unix and Windows Servers
· Some bandwidth intensive applications
· Voice over IP is implemented
· Wiring closets are 500 feet apart
· Several rack units are available
The design specifies an additional 180 people will be employed soon. The company will have employees working from a third floor where the wiring closet is 500 feet from the 6509. The company will implement some Wireless, IP Telephony and define VLANS with specified groups.
The following is a list of specific features needed:
1. 4 chassis slots with Switching Modules of 48 Port - 10/100BaseT
2. Gigabit Trunking between wiring closets
3. Supervisor Engines with failover
4. Multi Layer Switching
5. Power over Ethernet support
6. Dual Power Supplies with at least 2800W for IP Telephony
7. Quality of Service for VoIP
8. Performance switching for converged telephony network
Selected Switch: Cisco 4507R
The 7 slot switch such as the Cisco 4507R is a good selection with an additional 180 employees. The device will have 4 - 48 port Modules with a slot available for any additional employees. The dual Supervisor Engines IV will be assigned 2 slots with failover, Multi Layer Switching between VLANS and Gigabit uplinks connecting the 6509 devices. Each of the switching module are PoE capable with the new 802.3af standard. Dual power supplies provide enough wattage for implementing hundreds of Cisco IP phones and access points. The performance is 75 mpps with wire speed switching. The 4507R is more cost effective than the nearest 6509 Cisco device. Several Supervisor Engine models are available with additional performance features.
- 7 slot chassis with 2 Supervisor Engines and 4 Switching Modules with 48 Port - 10/100BaseT
- Supervisor Engine IV with integrated Multi Layer Switching, diversity, dual Gigabit uplinks
- Power over Ethernet (PoE) support with 802.3af standard
- Dual Power Supplies with 2800W or 4200W for Telephony, Wireless, Power over Ethernet
- Quality of Service features for voice traffic
- Fast performance with 75 mpps wire speed switching for converged networking
The 3750 series Cisco switch wasn't as expensive however there were not enough slots, stacking technology is expensive and switches at 38.7 mpps compared with the 4507R device at 75 mpps. The company would have to buy 5 separate switches with 48 ports for 180 employees. The 2950 Cisco switch doesn't have power supply failover and scalability. The 6509 switch was much more expensive, had 2 additional slots, more performance than was needed and the switching modules were expensive. Implementation is somewhat difficult with the 6500 Cisco devices.
Shaun Hummel is the author of Network Planning and Design Guide and has a web site focused on information technology job search solutions, web conferencing and online technical interviews.
http://www.networkjobsolutions.com
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