g native IOS). Each module is hot-swappable, with the only limitation being that some modules must be shut down before being removed. Also, because the modules communicate with each other over the backplane, they offer substantial increases in speed over their standalone counterparts. The FWSM, for example, is capable of more than 5.5 Gbps of throughput. Only recently, with the introduction of the ASA 5580-40, has a stand- alone appliance exceeded this throughput with a whopping 10 Gbps. The ASA 5580-20 is only capable of 2.5 Gbps. While this processing difference has a lot to do with the design of the FWSM and ASA firewalls, remember that standalone devices must com- municate through Ethernet interfaces, while service modules communicate directly over the backplane of the switch. This has become less of an issue with larger ASAs that support 10 Gb Ethernet. 6500-series switches are designed to be highly redundant. They support dual power supplies and dual supervisors. The supervisor MSFCs can run as individual routers or in single-router mode. The power supplies can be configured in a failover mode or a combined mode to allow more power for hungry modules. Combine this switch's features, scalability, and resilience with the additional fault tol- erance of a high-availability network design, and you've got a world-class architecture at your fingertips. Though the Nexus is becoming the switch of choice in the data center, it cannot yet match the versatility of the 6500. Architecture The 6500-series switches are an evolution of the 6000 series. The 6000-series switch contains only a 32 Gbps backplane bus, whereas the 6500 series contains an additional bus called the fabric bus or crossbar switching bus. This bus allows backplane speeds to be boosted up to 720 Gbps and beyond. The addition of the crossbar switching fabric in the 6500 series also provides an amazing amount of flexibility in the new chassis. Legacy modules from the 6000 chassis can still be used, as the 32 Gbps bus in the 6500 is identical to the one 