Introduction to Cisco Catalyst Switches
| The Cisco Catalyst switch family represents one of the most popular LAN switches on the market today. The Catalyst range is designed to meet the needs of a wide range of customersfrom small to medium businesses, right up to large enterprise networks and service providers. Cisco Catalyst switches provide high performance, scalability, manageability, and many other intelligent features that ensure their success to date. I find that Cisco Catalyst switches present one of more difficult product sets to work with, simply because of the large range of switch families available, the vast differences in features between low-end and high-end platforms, and the different operating systems used. When you select a switch platform and model to use to build a LAN network, you must bear in mind that these differences exist; otherwise, you might purchase one or more switches that don't quite do the job you expected. Cisco Catalyst switches can physically described by one of two device types:
The fixed-configuration switch consists of a fixed number or ports contained within a fixed chassis that includes an internal switch processor. Some of these devices provide a limited degree of modularity in that they include modular slots that can be populated by variety of different modules. The major advantages of fixed-configuration switches are low cost and ease of deployment. The major disadvantages of a fixed-configuration switch are a lack of flexibility and the introduction of a multiple management points in the network when installing more than one switch. Scaling the network by introducing multiple fixed-configuration switches can also introduce bottlenecks between each switch. NOTE Some Catalyst switches support stacking¸ where a group of Catalyst switches can be managed as a single entity. Traditionally, the Catalyst 29xx and 35xx switches have supported stacking; however, inter-switch performance is limited for larger stacks and the ability to manage the stack as a single entity has had some restrictions. The recent Catalyst 3750 series of switches now include stacking technology that includes a high-speed 32 Gbps backplane and also allows the stack to be completely managed as a single switch. The chassis-based switch provides a chassis as a starting point, after which you can add the various components of the switch as you require. You can determine a particular type of switch processor and switching module, and then install these options. Chassis-based switches provide slots, which support various types of modules. The major advantages of chassis-based switches include high performance, flexibility, simplified management, and extended product lifetime. Chassis-based switches also commonly offer redundancy features to ensure the failure of a module, power supply, or other component does not cause a network outage. The major disadvantage of chassis-based switches is the high cost involved. Table 1-1 indicates the various models that comprise the Cisco Catalyst switch family.
In Table 1-1, each of the Catalyst product families are listed, with the form factor and current status of each switch indicated. Each of the product families in bold are considered current products and are recommended for deployment for new networks or for network upgrades. All other product families are either end of sale or considered legacy products that should be purchased only for existing networks where a common platform needs to be maintained. Each of the switches in Table 1-1 is targeted at a particular switching environment, based upon size, network traffic, and features required. One way of classifying the general role of a switch is to identify the hierarchical layer in which the switch is operating. Well-designed LAN networks can be divided into three key layers:
For many networks, a network switch can provide the functions of two layers or even the entire three. Only the very large networks typically have distinct core, distribution, and access layers; smaller networks typically have a combined core/distribution layer and an access layer. Following the core/distribution/access layer design provides a hierarchical network that can easily scale as the network grows. Figure 1-1 illustrates the various layers of a LAN network and which platforms fit into each of the layers. Figure 1-1. Core/Distribution/Access Layers
In Figure 1-1, notice that all of the Catalyst switches (bar the Catalyst 8500) can be used as an access layer switch. Most commonly, the access layer function is left to the switches up to the Catalyst 4000/4500 series; however, many larger networks use the Catalyst 5000/5500 and Catalyst 6000/6500 switch as a wiring closet switches, because they can provide very high port densities. When this happens, the high-end switch is normally providing distribution layer functionality as well. Cisco Catalyst Switch PlatformsAs described in Table 1-1, a number of Cisco Catalyst switch platforms are available, each of which are suitable for different switching environments depending on the size, complexity, features required and of course cost. In this section, each of the Cisco Catalyst switch platforms that are available for purchase and not considered legacy switches are described (i.e., the platforms highlighted bold in Table 1-1). This includes the following switch platforms:
NOTE The Catalyst 8500 switch is not discussed in this section because the Catalyst 6000/6500 switches now outperform this switch Catalyst 2950 FamilyThe Catalyst 2950 switches represent Cisco's entry-level switch product offering and are a fixed-configuration platform designed for access-layer/workgroup connectivity. Table 1-2 lists each of the Catalyst 2950 models and describes their hardware and software configurations. Each switch contains 8MB flash and 16MB memory.
As you can see from Table 1-2, many different models exist, each with different hardware and software specifications. In terms of software image, it is important to understand the difference between the standard image and enhanced image:
NOTE It is important to understand that the Catalyst 2950 enhanced image does not provide Layer 3 routing capabilities, but rather the ability to understand the Layer 3 and Layer 4 properties of network traffic and apply security and/or QoS based upon those properties. Figure 1-2 shows an example of the Catalyst 2950 switch (a Catalyst 2950G-48). Figure 1-2. The Catalyst 2950G-48 Switch
In Figure 1-2, notice the two GBIC slots, which provide connectivity for any combination of the following GBICs:
NOTE All of the GBICs just described are supported on all gigabit-capable Cisco Catalyst switch platforms, with the exception of the GigaStack GBIC, which is only supported on Cisco Catalyst 29xx/35xx platforms. Support for the 1000BASE-T module on CatOS-based switches requires CatOS 7.2, and on the Catalyst 4000/4500 Supervisor 3/4 requires Cisco IOS 12.1(13)EW. NOTE Cisco also produces the Catalyst 2955 series of switches, which are 12-port switches with a variety of gigabit uplink options designed for industrial environments. The Catalyst 2955 ships with an industrial strength case, includes no moving parts, and ships with the enhanced software image. Catalyst 3550 FamilyThe Catalyst 3550 switches represent the entry-level platform from Cisco that provides the ability to perform Layer 3 switching. Layer 3 switching is a feature that allows a switch to route traffic between different LAN segments (VLANs), without impacting performance. This allows organizations to gain the benefits of implementing a hierarchical Layer 3 routing topology in the LAN without sacrificing performance. Cisco Catalyst 3550 switches still support traditional Layer 2 switching; in fact by default, a Catalyst 3550 operates as a Layer 2 switch. Layer 3 switching must be explicitly configured, and the features that you can configure for Layer 3 switching depend on the software image you have installed. Two software images are available when you purchase a Catalyst 3550 switch:
Table 1-3 provides a list of advanced features and describes there availability on the Catalyst 2950 SI and EI images, as well as the Catalyst 3550 SMI and EMI images.
As you can see from Table 1-3, the SI for the Catalyst 2950 provides hardly any advanced switching features at all. The Catalyst 3550 SMI possesses more features than the Catalyst 2950 EI, and the Catalyst 3550 EMI provides all features listed in Table 1-3. Table 1-4 lists each of the Catalyst 3550 models and describes there hardware and software configuration. Each switch contains 16 MB flash and 64 MB memory.
In Table 1-4, notice the Catalyst 3500-12T and Catalyst 3550-12G, which provide 12 gigabit Ethernet ports and only ship with an EMI. These switches have a different physical layout to the other Catalyst 3550 models. Figure 1-3 and Figure 1-4 show examples of the Catalyst 3550 switches (the Catalyst 3550-48 and Catalyst 3550-12T). Figure 1-3. The Catalyst 3550-48 Switch
Figure 1-4. The Catalyst 3550-12T Switch
The GBIC options for 1000BASE-X ports on the Catalyst 3550 switches are the same as for the Catalyst 2950. Catalyst 3750 FamilyIn April 2003, Cisco announced the Catalyst 3750 as a new product family. The Catalyst 3750 provides Cisco's first high density gigabit Ethernet over copper switch in a fixed chassis, providing up to 24 x 10/100/1000BASE-T ports + 4 x 1000BASE-X ports in a single 1.5RU chassis. The Catalyst 3750 is similar in many respects to the Catalyst 3550, with the same concept of SMI and EMI and full Layer 3 switching capabilities. It also provides several enhancements over the Catalyst 3550, which include the following:
Table 1-5 lists each of the Catalyst 3750 switches. Each switch contains 16 MB flash and 128 MB memory.
Catalyst 4000/4500 FamilyThe Catalyst 4000/4500 switch family represents the entry-level chassis-based switch offering from Cisco. The Catalyst 4000/4500 switches are made up of three basic components:
Each of these components are now discussed. Catalyst 4000/4500 ChassisThe chassis provided by the Catalyst 4000/4500 series switches vary across the Catalyst 4000 and Catalyst 4500 family. The major difference between the Catalyst 4000 series chassis and Catalyst 4500 series chassis is power; the Catalyst 4500 has an improved power distribution system that is capable of supporting inline power (i.e., the ability to power phones and wireless access points over Ethernet cabling) without requiring an external power shelf (as is required with the Catalyst 4000). The Catalyst 4500 series also provides a chassis that allows for redundant supervisor engines, whereas the Catalyst 4000 series chassis do not provide this. Within the Catalyst 4000 series, two chassis are provided:
Within the Catalyst 4500 series, three chassis are provided:
Figure 1-5 and Figure 1-6 shows examples of the Catalyst 4000 and 4500 chassis (the Catalyst 4006 and 4507R). Figure 1-5. The Catalyst 4006 Chassis
Figure 1-6. The Catalyst 4507R Chassis
It is important to note that the Catalyst 2948G and Catalyst 2980G switches are essentially fixed configuration Catalyst 4000 switches with a Supervisor engine, power supply and a fixed configuration of 48 * 10/100BASE-T + 2 * 1000BASE-X ports (2948G) or 80 * 10/100BASE-T + 2 * 1000BASE-X ports (2980G). Figure 1-7 shows the Catalyst 2980G switch. Figure 1-7. The Catalyst 2980G Switch
Supervisor EnginesThe Catalyst 4000/4500 switch family consists of four Supervisor engines, which each vary in internal architecture, functionality, and operating system used for switch management. Table 1-6 describes each of the Catalyst 4000/4500 supervisors
The Supervisor 1 and Supervisor 2 engines are Layer 2 switching only supervisors and are managed using the CatOS operating system. It is important to note that the Supervisor 2 contains a blocking architecture internally, meaning congestion is possible in certain configurations internally on the Supervisor. Figure 1-8 shows the internal blocking architecture of the Supervisor 2 switch. Figure 1-8. Internal Architecture of Supervisor 2 Switch
NOTE The Supervisor 1 is non-blocking, because it contains only a single 24-Gbps non-blocking switching engine that provides each of the 2-Gbps traces to module 2 and module 3 in the Catalyst 4003. In Figure 1-8, notice that three separate switching engines (SEs) exist (each provide 24-Gbps internal non-blocking forwarding bandwidth), with each providing a 2-Gbps full-duplex trace to each module in the chassis (providing a total of 3 * 2-Gbps or 6-Gbps full-duplex bandwidth to each module). Be careful of the "marketing terms" using by Cisco and other switch vendors to provide forwarding bandwidth performance figures. The quoted performance figures always refer to the total system bandwidth and not to the full-duplex bandwidth provided. For example, a 1-Gbps full-duplex connection is considered to provide a total of 2-Gbps bandwidth (1 Gbps in one direction, 1 Gbps in the other direction). In the case of SE1 and SE3 on a Catalyst 4000 Supervisor 2, each SE has 5 * 2-Gbps full-duplex connections to each line card, a single external 1-Gbps full-duplex 1000BASE-X connection on the supervisor and a 1-Gbps full-duplex connection to SE2. This provides a total of 12 Gbps full-duplex bandwidth (5 * 2 + 1 + 1), or a total forwarding bandwidth of 24 Gbps. Although each SE is non-blocking internally, a single 1-Gbps full-duplex connection interconnects the switching engines, which potentially causes blocking (congestion) on the interconnections between each SE if devices attached to one switching engine are communicating with devices attached to another switching engine. NOTE If you are not using the two external 1000BASE-X ports on the Supervisor 2 module, you can disable them by configuring switch acceleration and introduce a third 1-Gbps interconnection between SE1 and SE3, reducing the amount of potential blocking (see dashed connection between SE1 and SE3 in Figure 1-8). You can also purchase a backplane channel module for the Supervisor 2, which doubles the bandwidth between each switching engine from 1 Gbps to 2 Gbps. The Supervisor 3 and Supervisor 4 engines are Layer 2 and Layer 3 switching capable and are managed using the Cisco IOS operating system. These supervisors are completely non-blocking internally, unlike the Supervisor 1 and Supervisor 2, consisting essentially of one large non-blocking switching engine to which each module trace connects to. Just as for the Catalyst 3550/3750 switches, a basic image provides Layer 3 switching using static and RIP routing, whilst a separate enhanced image provides full Layer 3 switching using static, RIP, IGRP, EIGRP, OSPF, and BGP routing. NOTE The differences between the Supervisor 3 and Supervisor 4 include memory (128 MB in Supervisor 3, 256 MB in Supervisor 4); support for redundant supervisors (Supervisor 4); and the ability to add a NetFlow feature daughter card (Supervisor 4). Switching ModulesThe Catalyst 4000/4500 switch family provides for a wide variety of switching modules, allowing for high-density 10/100BASE-T, 10/100/1000BASE-T, and 1000BASE-X deployments. Other modules supported include a Layer 3 routing module (for Supervisor 1/2 deployment, not supported in Supervisor 3/4) and an access gateway module (provides voice gateway functionality). Table 1-7 lists some of the switching modules available for the Catalyst 4000/4500.
Catalyst 6000/6500 FamilyThe Catalyst 6000/6500 family represents the flagship of the Cisco Catalyst switching product range. The switch is aimed at the enterprise network and also at service provider networks. The Catalyst 6000/6500 is chassis-based, which means that it consists of the same fundamental components as a Catalyst 4000/4500 switch (i.e., chassis, supervisor engine, and switching modules), which are now discussed in more detail. Catalyst 6000/6500 ChassisThe chassis provided by the Catalyst 6000/6500 series switches vary across the Catalyst 6000 and Catalyst 6500 family. The differences between the Catalyst 6000 series chassis and Catalyst 6500 series are listed below:
Figure 1-9 and Figure 1-10 shows examples of the Catalyst 6000 and 6500 chassis (the Catalyst 6006 and 6509). Figure 1-9. The Catalyst 6006 Chassis
Figure 1-10. The Catalyst 6509 Chassis
Supervisor EnginesThe Catalyst 6000/6500 switch family consists of three Supervisor engines, which each vary in terms of functionality and performance:
All supervisors can be installed in redundant pairs, ensuring maximum availability in the event of an active supervisor failure. Any additional add-on modules that extend system performance or functionality (e.g., SFM, PFC daughter card, and MSFC daughter card) can also be installed in a redundant configuration, ensuring the highest levels of availability You have learned that the Supervisor 2 engine supports the SFM; each Supervisor also supports two types of add-on modules onboard the Supervisor itself (i.e., daughter cards), which extend the functionality and performance of the supervisor engine to provide the features and performance described above. These daughter cards are described as follows:
NOTE Without a MSFC, the Catalyst 6000/6500 Supervisor engines operate the CatOS operating system. When you add a MSFC, by default, the Supervisor still runs CatOS and the MSFC runs Cisco IOS (this configuration is known as referred to as hybrid IOS). You can then configure the switch to operate in native IOS mode, where the Supervisor and MSFC are managed by the same Cisco IOS management interface, as long as the switch has an MSFC installed. There are three generations of PFC and MSFC modules, with various combinations of Supervisor engines and different versions of PFC and MSFC modules making it a reasonably complex task to understand which features are supported in each configuration. Chapter 6, "Layer 3 Switching," discusses the features of the various Supervisor, PFC, and MSFC configurations in more detail. Switching ModulesOn the Catalyst 6000/6500, you can purchase three types of line cards:
Even though there are three types of modules, all modules can communicate with each other, even if they are attached to different switching backplanes (e.g., classic and fabric-only cards are not connected to the same bus). In this situation, an interconnection between the crossbar switching matrix is interconnected with the shared bus backplane allows classic cards and fabric-only cards to communicate. Table 1-8 lists some of the LAN switching modules available for the Catalyst 6000/6500.
Perhaps one of the best features of the Catalyst 6000/6500 switch is the capability to extend switch functionality well outside the bounds of pure LAN switching and Layer 3 switching. The Catalyst 6000/6500 not only provides LAN switching modules, which allow for high-density 10/100BASE-T, 10/100/1000BASE-T, and 1000BASE-X deployments, but also provides a wide range of other modules called services modules that extend and enhance the functionality of the Catalyst 6000/6500. The following lists some examples of the services modules available for the Catalyst 6000/6500 switch:
As you can see from the preceding, the Catalyst 6000/6500 is not just a LAN switch; it is a platform that can integrate LAN switching features with advanced security, application, and network management features. Catalyst Operating SystemsToday there are two main operating systems that are used on Cisco Catalyst switches:
You are most likely familiar with Cisco IOS; Cisco IOS is the popular operating system installed on nearly all Cisco routers and is a very mature, feature-rich, and extensible operating system that offers Cisco customers significant value-add and return on investment. Historically, Cisco acquired a few major switch vendors in the early- to mid-1990s, which resulted in the introduction of what is now known as CatOS. CatOS is used to operate the following platforms:
CatOS has a very easy to use command-line interface and has traditionally supported bulk administration tasks much more effectively than Cisco IOS. These are important features when configuring a device that potentially has more than 500 ports. NOTE The ability to perform bulk administration tasks has been addressed in later releases of Cisco IOS. Unlike Cisco IOS, which has many configuration modes and different commands, CatOS provides three basic types of commands:
Other commands are used for system management, such as copy and write; however, for configuration tasks, you will only ever use the set and clear commands and then use show commands to verify your configuration. NOTE Many chassis-based CatOS switches support optional Layer 3 routing modules (e.g., Catalyst 5000/5500 RSM, Catalyst 6000/6500 MSFC), which include their own Cisco IOS. This means that the module essentially just uses the switch chassis for power and network connectivity, with management of the module performed separately from the Supervisor that runs the switch. When CatOS is used to manage the Layer 2 switching component, and Cisco IOS is used to manage the Layer 3 routing component, the switch is said to be managed using hybrid IOS, because two different operating systems (CatOS and Cisco IOS) are used to manage the switch. Cisco plans to eventually phase out CatOS, moving all switching platforms to Cisco IOS, which will allow for a uniform management interface across all Cisco switches and routers, as well as better integration of Cisco switching and routing features. Today, the following platforms are based upon Cisco IOS:
As you can see from the preceding list, the Catalyst 4000/4500 and Catalyst 6000/6500 switches can either run CatOS or Cisco IOS, which leads to the question: Which operating system should I run? On the Catalyst 4000/4500, the operating system is tied to the type of Supervisor engine, and normally the much higher performance capabilities and integrated Layer 3 switching capabilities of the Cisco IOS-based Supervisor 3/4 engines make them the obvious choice. It should be noted, however, that many features are still present in CatOS that are not present in Cisco IOS and that many new features are first released into CatOS code before Cisco IOS. This applies also to the Catalyst 6000/6500, where you can use either CatOS or Cisco IOS regardless of the Supervisor engine installed. NOTE Although CatOS still leads the development efforts in terms of new features over comparative Cisco IOS features, Cisco has indicated that this is short lived, with a goal of introducing feature parity and then focusing on the development of new features on Cisco IOS. Although Cisco IOS might be the way of the future, for now and many years to come, there still exists a large deployment of CatOS-based switches. This means you must ideally be proficient in both Cisco IOS and CatOS if you want to design, implement, and support Cisco switched networks. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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