Cisco Catalyst

In most cases, the technology for the Catalyst Switch was developed separately from Cisco's router technology. The Catalyst switches originally ran software called CatOS rather than the more widely known Cisco IOS software used by routers. However, this has changed as the product lines have merged closer together. In some cases, particularly in the modular chassis switches, a configuration called 'Hybrid' has emerged - this is where the layer 2 functions are configured using CatOS, and the layer 3 elements are configured using IOS. Native IOS can also be found with newer software versions that have eliminated CatOS entirely in favor of IOS, even on hardware that originally required CatOS.[3]

Some newer Catalyst switch models (with recent versions of the Cisco IOS) also allow web-based management using a graphical interface (GUI) module which is hosted on a HTTP server located on the switch. The Catalyst 2960-L SM Series of switches is an example of a Cisco Catalyst switch that allows this style of GUI via HTTP.

As Catalyst devices are primarily Ethernet switches, all modern Catalyst models have Ethernet interfaces ranging from 10 Mbit/s to 100 Gbit/s depending on the model. Other models can support T1, E1, and ISDN PRI interfaces to provide connections to the PSTN. Legacy models supported a variety of interfaces, such as Token Ring, FDDI, Asynchronous Transfer Mode and 100BaseVG, but are no longer sold by Cisco Systems.

The front of a Catalyst 3750G switch, with 48 interfaces for Ethernet over twisted pair and four interfaces for small form-factor pluggable transceivers.

All models have basic layer 2 functions and are capable of switching Ethernet frames between ports. Commonly found additional features are VLANs, trunking and QoS. The switches, whether IOS or IOS XE, are fully manageable.

Many Catalyst switches that run IOS or IOS XE are also capable of functioning as a router, making them layer 3 devices; when coupled with TCP and UDP filtering, these switches are capable of layer 2-4 operation. Depending on the exact software image, a Catalyst switch that runs IOS or IOS XE may be able to tackle large-scale enterprise routing tasks, using router technologies like OSPF or BGP.

Modular chassis-based Catalyst switching models, like the Catalyst 9400 and 9600 Series, have the concept of field-replaceable supervisor, line cards, power supplies and fans. Mirroring most Cisco router designs, these work by separating the line cards, chassis, and supervisor engine. The chassis provides power and a high-speed backplane, the line cards provide interfaces to the network, and the supervisor engine moves packets, participates in routing protocols, etc. This gives several advantages:

• If a failure occurs, only the failed component needs to be replaced (typically a power supply, fan, line card or supervisor). This means faster turnaround than replacing an entire switch.
• A redundant component may be installed to rapidly recover from component failures.
• A supervisor engine may be upgraded after purchase, increasing performance and adding features without losing any investment in the rest of the switch.

Catalyst switches offer advanced customization and manageability. The switches can be configured using a serial console, telnet or Secure Shell. Simple Network Management Protocol (SNMP) allows monitoring of many states, and measurement of traffic flows. Many devices can also run an HTTP server.

Configuration of the switch is done in plain text and is thus easy to audit. No special tools are required to generate a useful configuration. For sites with more than a few devices, it is useful to set up a Trivial File Transfer Protocol (TFTP) server for storing the configuration files and any IOS images for updating. Complex configurations are best created using a text editor (using a site standard template), putting the file on the TFTP server and copying it to the Cisco device. However, it can be noted that a TFTP server can present its own security problems.

StackWise and Stackwise Virtual are technologies offered by Cisco Systems that allows some models of Catalyst switches to operate as though they were one switch. One switch from the stack will act as the master switch. The master switch will maintain the stack and allow you to configure and monitor the whole stack as though one via a single console. This allows for more efficient management and typically provides more bandwidth between individual switches than other uplink technology.

If one switch fails, the remaining switches will continue to operate by bypassing it. If the master switch fails, another switch in the stack will automatically take over as master. This feature means greater redundancy, as one switch's failure will not bring about a failure of the entire stack.

As each switch contains the entire configuration for the stack, one of the benefits of this technology is the ability to replace a faulty switch (any—including master) with a new switch. The stack will configure the new switch on-the-fly to accommodate minimal downtime and reduce maintenance effort and errors.

Stackwise physically connects the switch stack using special stack interconnect cables, typically up to eight switches per stack. StackWise Virtual allows the virtual clustering of two chassis together into a single, logical entity without physical interconnect cables.

There are two general types of Catalyst switches: fixed configuration models that are usually one or two rack units in size, with 12 to 80 ports; and modular switches in which virtually every component, from the CPU card to power supplies to switch cards, are individually installed in a chassis.

In general, switch model designations start with WS-C or C, followed by the model line (e.g. C9600). A letter at the end of this number signifies a special feature, followed by the number of ports (usually 24 or 48) and additional nomenclature indicating other features like UPOE (e.g. C9300-48U). Catalyst 9000 switches also include software subscription license indicators (e.g. C9200-48T-P, E for Essentials, A for Advantage and P for Premier)