Network Switch Selection – How to Select a Network Switch
The network switch is the most common network device deployed with the company’s infrastructure, and as such, the selection of any new or upgrade switches is a key part of most network design projects. The components of the Cisco network switch include the switch chassis, supervisor engine, switch modules, IOS / CatOS software, and power supplies. The decision to purchase new switches or upgrade equipment will be made after considering the evaluation of the network and the specified design characteristics. Wireless designs, for example, will have network switches interconnected with access points. That will have an effect on the switch, such as increased utilization, assigned switch ports, access control lists, trunks, spanning tree protocol, and increased Power over Ethernet (PoE) power consumption.
Switch Chassis Features
The switch chassis features include: chassis dimensions, number of slots, processor slot assignments, switch fabric, supported motor types, power supplies, required rack units.
Cisco Supervisor Engine (SE) Features
Cisco switches are implemented with an engine (switch processor) to process packets on a network segment. Routing is accomplished with a multilayer switch function card (MSFC) or a route processor running IOS code. The switch engine running the 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 do not support native and hybrid mode. The non-MSFC engine supports what is called CatOS mode. Select the motor that matches your design specifications. The MSFC module is integrated with the engine or can be upgraded. You must implement a PFC module with any MSFC. Some engines do not have an MSFC module – routing is integrated with the hardware and as such only supports native mode.
Cisco Supervisor Engine features include: supported chassis, uplink speed, processor memory, native IOS, CatOS, PFC, MSFC, slot mapping, failover.
Here are some of the most 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
Switch module features
Switch module features include: supported switch chassis, interface speed, number of ports, media, cabling, connectors, throughput (mpps), supported supervisor engines, protocol features, power over ethernet (Cisco pre-standard 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 characteristics
Power supply characteristics include: compatible chassis, power rating, failover, input / output amps, power cord type, IOS, CatOS.
IOS / CatOS software
Cisco network switches can be implemented with IOS, IOS, and CatOS or with exclusive CatOS software. The design features will determine which mode and which version of IOS or CatOS 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, implement Supervisor Engine IV without an MSFC on board. The Route Processor is integrated with the engine. With that design, Engine IV is not compatible with CatOS.
Native IOS – Deployed at the edge of the network where most of the routing occurs and some switching is needed
Hybrid – Implemented in the core of the network where there is high-speed routing and switching
CatOS – Implemented at the network access layer where there is switching and no routing
Switch selection process:
The 5 components of any network switch selection process are described below:
1. Consider the network evaluation and the specified design features.
2. Select switches that include all design features.
3. Select switches with appropriate scalability
4. Balance cost and equipment features while still meeting budget guidelines.
5. Select the IOS and / or CatOS software version
Network evaluation and design specifications should be considered before selecting any network switch. The network assessment examines the design, configuration, and equipment that is deployed in the office where the selected devices will be deployed. The design specifications will determine the required performance, availability, and scalability characteristics. Selection of the IOS and / or CatOS version occurs after deciding on the feature set. Companies will specify a budget and that is a key consideration with any equipment selection. It is not cost effective to select a Cisco 6509 switch for an office with 50 employees. It is important that you select equipment that meets design specifications, has the necessary scalability features, and meets budget guidelines.
Some typical switch features to consider:
1) Are there enough chassis slots?
2) Which Supervisor Engines are supported?
3) Does the engine support failover?
4) Is multilayer switching available?
5) What switch modules are available?
6) What uplinks are available?
7) What power of the power supply is available?
8) How many rack units do you need?
Switch selection example:
The Network Assessment found the following at the company office.
The Distribution Office has 300 employees
Fast Ethernet (100BaseT) is implemented on the desktop
6509 Cisco Switches with Gigabit Ethernet Trunking
Cisco 3800 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 in all offices.
Wiring closets are 500 feet apart
Multiple rack units are available in the rack cabinet
The design specifies that 180 more people will soon be employed. The company will have those employees working from a third floor where the closest wiring closet is 500 feet from the Cisco 6509. The company will implement some wireless IP telephony and define VLANS with each specific department in the company.
The following is a list of specific switch functions required:
1.4 Chassis slots with 48-port switch modules – 10 / 100BaseT
2. Gigabit Ethernet trunking between wiring closets
3. Failover Supervisor Engines
4. Multi-layer switching
5. Power over Ethernet support
6. Dual power supplies with at least 2800 W for IP phones
7. IP telephony quality of service
8. Performance switching for converged telephony networks
Selected switch: Cisco 4507R
The Cisco 4507R switch has 7 slots and is a good pick with the additional 180 employees. The device will have modules from 4 to 48 ports with one slot available for any additional employees. Dual IV engines will be assigned 2 slots with failover, multi-layer switching between VLANS and Gigabit Ethernet uplinks connecting 6509 devices. Each of the switch modules is PoE compliant with the new 802.3af standard. Dual power supplies provide enough power to deploy hundreds of Cisco IP phones and wireless access points. Engine performance is 75 mpps with cable speed change. The Cisco 4507R is more cost effective than the closest Cisco 6509 device. There are several engine models available with additional performance features.
– 7-slot chassis with 2 supervisor engines and 4 switch modules with 48 ports – 10 / 100BaseT
– Engine IV with integrated multilayer 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
– QoS features for voice traffic
– Fast performance with 75 mpps wire speed switching for converged networks
The Cisco 3750 series switch was not that expensive; however, there weren’t enough slots, stacking technology is expensive, and switches at 38.7 mpps compared to 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 does not have power supply failover or scalability. The 6509 switch was much more expensive, it had 2 additional slots, more performance than necessary, and the switch modules were expensive. Implementation is somewhat difficult with Cisco 6500 devices.