e port should another switch be connected. This is an important thing to understand, as the BPDU Guard cannot be disabled on a FEX. Fabric ports A fabric port's sole purpose is to connect to a 5000 or 7000. It is not directly con- figurable, but is instead utilized when the connected port on the 5000 is placed into fabric mode. This will be detailed in a later section. Fabric ports are 10 Gbps only and cannot be used for hosts. Nexus Hardware Figure 18-7. A 2148 FEX mounted in a cabinet with an airflow barrier above it FEXs come in three varieties as of this writing. They are: Nexus 2148T GE Fabric Extender Nexus 2232PP 10 GE Fabric Extender Nexus 2248TP GE Fabric Extender As listed previously, all of the Nexus devices are designed with data-center needs in mind. To that end, they all have dual hot-swappable power supplies and fan trays. Figure 18-8 shows the front of a 2148T FEX with the dual power supplies and single fan tray removed. Nexus 1000 Series The Nexus 1000 series resides at or near the server level. There are two main models: the 1000V virtual switch for use with VMware and the 1010V appliance. The Nexus 1000V switch is a software switch for use with VMware, especially in sup- port of cloud computing architectures. The 1010 Virtual Services Appliance (VSA) is essentially a VSM that controls the VMware virtual switches within Unified Computing System (UCS) or other vendors' servers. Figure 18-9 shows a Cisco Nexus 1010 VSA. These devices are not covered further in this chapter. Chapter 18: Cisco Nexus Figure 18-8. Nexus 2148 FEX with power supplies and fan tray removed 00000 Cisco Nexus 1010 Figure 18-9. Cisco Nexus 1010 VSA; courtesy of Cisco Systems, Inc.; unauthorized use not permitted NX-OS NX-OS is the operating system for Nexus switches. NX-OS was written from the ground up to be a modular, scalable, and resilient operating system for the next generation of data center switches. NX-OS looks like IOS. It's similar enough to make you feel comfortable but just dif- ferent enough to be interesting a