Network Switch Selection – How to Select a Network Switch
Overview
The network switch is the most common network device implemented with company infrastructure and as such the selection of any new switches or upgrading is a key part of most network design projects. The Cisco network switch components include Switch Chassis, Supervisor Engine, Switching Modules, IOS/CatOS software and Power Supplies. The decision to buy new switches or upgrade equipment will be decided after considering the network assessment and design features specified. Wireless designs, as an example, will have network switches interfacing with access points. That will have an affect on the switch such as increased utilization, assigned switch ports, access control lists, Trunking, Spanning Tree Protocol and increased wattage draw from Power over Ethernet (PoE).
Switch Chassis Features
The Switch Chassis features include – chassis dimensions, number of slots, processor slot assignments, switching fabric, engines types supported, power supplies, rack units needed.
Cisco Supervisor Engine (SE) Features
Cisco switches are implemented with an Engine (Switch Processor) for processing packets on a network segment. Routing is accomplished with an on-board Multi Layer Switch Feature Card (MSFC) or Route Processor running IOS code. The switch Engine running IOS code on the MSFC and the switch processor is in native mode, while those running CatOS on the processor are in hybrid mode. Some engines won’t support native and hybrid mode. The engine with no MSFC supports what is called CatOS mode. Select the engine that matches your design specifications. The MSFC module is integrated with the Engine or upgradeable. You must implement a PFC module with any MSFC. Some Engines have no MSFC module – the routing is integrated with the hardware and as such support native mode only.
The Cisco Supervisor Engine features include – supported chassis, uplink speed, processor memory, native IOS, CatOS, PFC, MSFC, slot assignment, failover.
These are some of the popular Cisco engines and their switching features.
720 – Cisco 6500 switches, 400 mpps, MSFC3, IOS, CatOS
32 – Cisco 6500 switches, 15 mpps, MSFC2A, IOS, CatOS
V – Cisco 4500 switches, 72 mpps, Integrated Routing, IOS
IV – Cisco 4500 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 (mpps), supervisor engines 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, failover, input/output amps, power cord type, IOS, CatOS.
IOS/CatOS Software
Cisco network switches can be deployed with IOS, IOS and CatOS or exclusive CatOS software. Design features will determine what mode and IOS or CatOS version is selected. The software running on the Route Processor must be IOS while the Engine Switch Processor will run IOS (native mode) or CatOS (hybrid mode). Some Cisco equipment such as the 4507R deploy the Supervisor Engine IV with no MSFC onboard. The Route Processor is integrated with the engine. With that design, the Engine IV doesn’t support CatOS.
Native IOS – deployed at the network edge where most routing occurs and some switching is needed
Hybrid – deployed at the network core where there is both routing and high speed switching
CatOS – deployed at the network access layer where there is switching and no routing
Switch Selection Process:
The following describes the 5 components of any network switch selection process:
1. Consider the network assessment and design features specified
2. Select switches that include all the design features
3. Select switches with proper scalability
4. Balance cost and equipment features while meeting budget guidelines
5. Select IOS and/or CatOS software version
The Network Assessment and design specifications should be considered before selecting any network switches. The network assessment examines the design, configuration and equipment that is implemented at the office where the selected devices will be deployed. The design specifications will determine performance, availability and scalability features needed. Selecting the IOS and/or CatOS version occur after deciding on the feature set. 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 switch 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 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) How many Rack Units are needed?
Switch Selection Example:
The Network Assessment discovered the following at the company office.
· The Distribution Office has 300 employees
· Fast Ethernet (100BaseT) is 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
· IP Telephony is implemented at all offices
· Wiring closets are 500 feet apart
· Several Rack Units are available in the Rack Cabinet
The design specifies that an additional 180 people will be employed soon. The company will have those employees working from a third floor where the nearest wiring closet is 500 feet from the Cisco 6509. The company will implement some Wireless, IP Telephony and define VLANS with each specific company department.
The following is a list of specific switching features needed:
1. 4 Chassis slots with Switching Modules of 48 Port – 10/100BaseT
2. Gigabit Ethernet 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 Phones
7. Quality of Service for IP Telephony
8. Performance switching for converged telephony network
Selected Switch: Cisco 4507R
The Cisco 4507R switch has 7 slots and is a good selection with the additional 180 employees. The device will have 4 – 48 port modules with a slot available for any additional employees. The dual Engines IV will be assigned 2 slots with failover, Multi Layer Switching between VLANS and Gigabit Ethernet uplinks connecting the 6509 devices. Each of the switching modules are PoE capable with the new 802.3af standard. Dual power supplies provide enough wattage for implementing hundreds of Cisco IP Phones and Wireless Access Points. The engine performance is 75 mpps with wire speed switching. The Cisco 4507R is more cost effective than the nearest Cisco 6509 device. Several Engine models are available with additional performance features.
– 7 slot chassis with 2 Supervisor Engines and 4 Switching Modules with 48 Port – 10/100BaseT
– Engine IV with integrated Multi Layer Switching, failover, 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 Cisco 2950 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.
