This document primarily compares the two software operating system models available for the Cisco® Catalyst® 6500 Series Switches:
• The Cisco Catalyst OS with optional Cisco IOS® Software running on the multilayer switch feature card (MSFC); this model is commonly referred to as "hybrid."
• Cisco IOS Software running on the supervisor and the MSFC, this model is commonly referred to as "native."
An overview of the software architecture, operation, and configuration for hybrid and native models is discussed along with primary feature and network deployment comparisons. Additionally, this paper is a resource for those planning a migration from a hybrid or Cisco Catalyst OS to a native Cisco IOS Software model.
It is important to note that the native software model can be implemented with either a modular software operating software image or with the monolithic software image. Both images run on the supervisor engine and the MSFC. The native software model, either modular or monolithic, provides a single configuration file and user interface. It is beyond the scope of this document to discuss the architectural differences between the modular and monolithic operating system images. Unless specifically noted, this paper will refer to both the modular and monolithic implementations as "native" software models.
Introduction
The Cisco Catalyst 6500 Series Switches are the industry-leading chassis-based switches. With their rich support of media types and intelligent network services, the Cisco Catalyst 6500 Series Switches are deployed in all parts on the network including the core, distribution, data center, WAN edge, and access layers. An integral part of the success of Cisco Catalyst 6500 Series Switches is their deployment flexibility.
The flexibility of the Cisco Catalyst 6500 Series Switches is in part because of the support of the two software operating models, hybrid and native. These operating system models were developed to use their respective strengths: the Cisco Catalyst OS for Layer 2/3/4 functionality and Cisco IOS Software for its rich Layer 3 routing protocols and services. This dual operating system model allowed customers to choose the right software model for their specific deployment scenarios while using the benefits of having a common hardware switching platform end to end in their network. This strategy has proven successful over the years, providing customers with scalability with superior investment protection.
Since the initial native Cisco IOS Software releases in early 2000, native releases have evolved to include the majority of Layer 2/3/4 access layer features originally available only in the Cisco Catalyst OS. As of August 2007, the following features previously unique in the Cisco Catalyst OS are now available in the native Cisco IOS Software Release 12.2(33)SXH software train:
• IEEE 802.1x user authentication in combination with important extensions
With the addition of these primary features, combined with the strengths of Cisco IOS Software, Cisco is now able to recommend native Cisco IOS Software deployments end to end in the network. Subsequently Cisco has announced the end-of-sale and end-of-life dates for the hybrid Cisco IOS Software Release 12.2SX software train.
• End of sale hybrid Cisco IOS Software 12.2SX is January 29, 2008.
• Last customer ship hybrid Cisco IOS Software Release 12.2SX April 28, 2008.
The Cisco Catalyst 6500 Series offers a high-performance blend of Layer 2/3/4+ technology. Independent of the software model chosen, the forwarding intelligence of the system is handled in the following hardware: the supervisor engine baseboard, the policy feature card (PFC) daughter card, and the MSFC (route processor) daughter card (Figure 1).
Figure 1. Cisco Catalyst 6500 Series Supervisor Engine 720 Components
The MSFC daughter card is composed of two CPU complexes: the switch processor and the route processor. The primary difference when deploying a hybrid software model versus a native software model is where the different software images reside. Figure 2 and Figure 3 illustrate this difference.
Figure 2. Hybrid Software Model
Figure 3. Native Software Model
• Cisco Catalyst OS with optional Cisco IOS Software on the MSFC provides Layer 2/3/4 functionality for the Cisco Catalyst 6500 by integrating two operating systems. A switch running the Cisco Catalyst OS only on the supervisor engine is a Layer 2 forwarding device with Layer 2/3/4 functionality for quality of service (QoS), security, multicast, and network management, but does not have any routing capabilities. Layer 3 routing functionality is provided by a Cisco IOS Software image on the MSFC routing engine (optional in the Cisco Catalyst 6500 Series Supervisor Engine 1A and Cisco Catalyst 6500 Series Supervisor Engine 2 and integrated within Cisco Catalyst 6500 Supervisor Engine 32 and Cisco Catalyst 6500 Series Supervisor Engine 720 models). The two operating systems work together to provide complete Layer 2/3/4 system functionality.
The hybrid model operates based on two operating images, two configurations, and two command lines; one each for Cisco Catalyst OS and Cisco IOS Software. The default operation of Cisco Catalyst OS is as a switch (all ports bridging in VLAN1). Additionally, the switch-running hybrid can be configured to operate as a router.
• Cisco IOS Software for the supervisor engine on the Cisco Catalyst 6500 Series provides a single Cisco IOS Software image, configuration, and command line to support all Layer 2, 3, and 4 functionality on the switch. Cisco IOS Software has historically been a Layer 3 operating system on routing platforms, and when installed on the supervisor engine of a Cisco Catalyst 6500 has expanded these capabilities to include true Layer 2 functionality as well. Cisco IOS Software requires an MSFC daughter card be present on the supervisor engine (default on the Cisco Catalyst 6500 Supervisor Engine 32 and Cisco Catalyst 6500 Series Supervisor Engine 720).
The default operation of Cisco IOS Software is as a router (all ports are Layer 3 and in the shutdown state), but the interfaces can also be configured to operate as a switch.
The native Cisco IOS Software operating model was originally developed to target service provider and enterprise data center backbones and distribution layer services. However, with the SXF and SXH Cisco IOS Software trains, many wiring closet features have been added. Cisco IOS Software combines the switching features of the Cisco Catalyst 6500 Series with routing features of Cisco IOS Software to create a single, integrated operating system that performs all switching and routing functionality, providing operational ease of use. A Cisco IOS Software system has the capability to scale the throughput and bandwidth of a Cisco Catalyst 6500 Series to 400+ Mpps and 720 Gbps, respectively.
Switch Processor Functions
The switch processor controls all chassis-related operations such as the detection of online insertion and removal (OIR) events, power management, environmental management, and redundancy management. The switch processor also handles the download of the appropriate line card firmware to each line card, basic port management (setting of port configuration, detection of link state, and so on), and other Layer 2 functionality such as Spanning Tree Protocol, VLAN Trunking Protocol (VTP), Internet Group Management Protocol (IGMP) snooping, and Dynamic Trunking Protocol (DTP). Finally, the switch processor provides console connection for the Cisco Catalyst OS or Cisco IOS Software during initial system boot.
Route Processor Functions
The route processor provides Layer 3 functionality such as routing and Cisco Express Forwarding table creation. Cisco Express Forwarding is the default Layer 3 forwarding mechanism. The route processor is responsible for creating and maintaining Cisco Express Forwarding and adjacency tables while pushing this information down to the PFC for hardware forwarding, QoS, and security functionality. Other functions residing on the route processor include IP address resolution (ARP) and routing table maintenance.
Policy Feature Card (PFC)
The PFC is the application-specific integrated circuit (ASIC) forwarding complex for the system. The PFC performs the hardware-based features and services at a high performance level (tens of millions of packets per second). Features such as Layer 2 bridging, Layer 3 routing, access control, QoS marking and policing, NetFlow statistics, and multicast are implemented within the PFC.
Software Implementation
Native Cisco IOS Software model mandates that both CPUs (switch processor and route processor) run the full Cisco IOS Software operating system. There is no hidden Cisco Catalyst software running in the switch, and the executable images used by both CPUs run the complete Cisco IOS Software kernel. With both processors running Cisco IOS Software, overall system performance is enhanced.
In contrast, the Cisco Catalyst OS operates on the switch processor and the PFC to provide Layer 2 forwarding and Layer 3/4 services. Should the user require Layer 3 forwarding/routing capabilities, the MSFC daughter card must be present and runs Cisco IOS Software (as part of the hybrid OS) on the route processor.
Software Feature Support
The two software models-Cisco Catalyst OS, and Cisco IOS Software-on the Cisco Catalyst 6500 Series are not at complete feature parity. The following table presents the Cisco Catalyst OS and Cisco IOS Software support for some of the more commonly used protocols. Note that many features in Cisco IOS Software are not platform specific (for example, the Open Shortest Path First [OSPF], Border Gateway Protocol [BGP], or Protocol Independent Multicast [PIM] protocols). In these cases, the Cisco IOS Software features in the hybrid OS are identical to those in Cisco IOS Software.
Table 1 lists commonly used features available through the Cisco Catalyst OS Version 8.6 and Cisco IOS Software Release 12.2(33)SXH. Feature support is hardware dependent where noted.
Table 1. Software Comparison
Software Feature
Cisco Catalyst OS
Cisco IOS Software
VLAN ranges: up to 4096 VLAN SVIs (Layer 3 VLAN Interfaces)
