This chapter discusses the next generation operation system relied upon in many data centers worldwide. The operating system is called NX-OS; it is used in Cisco Nexus switches. NX-OS is similar to Cisco IOS, but different enough to frustrate regular users of Cisco IOS. Some of the commands are the same but others are entirely different. This chapter covers these differences and many of the concepts already covered for IOS, including VLANs, VTP, EIGRP, OSPF, BGP, port channels, port profiles, Fabric Extenders (FEX), Hot Standby Redundancy Protocols (HSRP), virtual device context (VDC), virtual port channels (vPC), and VRF-lite (virtual routing and forwarding).